IC290A- A practical repair and fix - other examples follow.
At ham radio flea markets and swap lists you can often pick up radios with problems at a real good price. I paid $25 each for these two ICOM IC290A 2 meter all
mode transceivers. The fellow who sold me the first one was honest and said that the radio worked fine but the encoder for frequency adjustment did not
function well at all. He was true to his word. The second IC290A had not too much wrong with it. The power plug had been changed and the speaker leads and
connections were broken but otherwise worked ok when I connected these things up.
This radio has no interna l battery for memory back up. You need to keep the power on or connect up a wall wart power supply or perhaps a battery to the
accessory jack. Every time you lose or shut the power off..you lose the memories (there are only 5 memory positions) and you lose your dial settings as well. The
rig reverts to 146.000 and you have to tune.. 1Khz at a time to the low end of the band..if you are on the SSB/CW portion. So for me..backup power to save the
settings will be a good idea. I am actually thinking of putting one of these rigs in the truck for mobile use. There are certain high hills around town here and I could
even try running it in a vhf contest with a yagi parked mobile shooting across Lake Huron into the USA and southern ontario.
mode transceivers. The fellow who sold me the first one was honest and said that the radio worked fine but the encoder for frequency adjustment did not
function well at all. He was true to his word. The second IC290A had not too much wrong with it. The power plug had been changed and the speaker leads and
connections were broken but otherwise worked ok when I connected these things up.
This radio has no interna l battery for memory back up. You need to keep the power on or connect up a wall wart power supply or perhaps a battery to the
accessory jack. Every time you lose or shut the power off..you lose the memories (there are only 5 memory positions) and you lose your dial settings as well. The
rig reverts to 146.000 and you have to tune.. 1Khz at a time to the low end of the band..if you are on the SSB/CW portion. So for me..backup power to save the
settings will be a good idea. I am actually thinking of putting one of these rigs in the truck for mobile use. There are certain high hills around town here and I could
even try running it in a vhf contest with a yagi parked mobile shooting across Lake Huron into the USA and southern ontario.
It wasn't all that difficult to take the front panel off the IC290A and
remove the probable cause of the problem. ..that being the Rotary
encoder. I use the words..probable cause..because it could also be that
the logic circuitry was causing the fault.
I removed the 3 wires from the encoder. I looked for a part number on
the item but I saw only 155X which did not seem to be a complete part
number.
I went to a site on the internet called DK MODs where I downloaded a
free copy of the service manual for this radio. DK mods allows a free
download every 4 days.
I had an old DDS vfo that I bought about 7 years ago. The dds vfo was
not working but I still kept it and the old rotary encoder was still with it.
The rotary encoder was square and smaller than this unit. It had 4
terminals but two connections were bridged together so..it might work. I
connected it in place and it did not work properly. The radio tuned only
in one direction. I then switched the two outer connections and the
radio now tuned fine. It works! -- So sometimes you luck out. I dont know
all that much about encoders but I intend to learn more.
remove the probable cause of the problem. ..that being the Rotary
encoder. I use the words..probable cause..because it could also be that
the logic circuitry was causing the fault.
I removed the 3 wires from the encoder. I looked for a part number on
the item but I saw only 155X which did not seem to be a complete part
number.
I went to a site on the internet called DK MODs where I downloaded a
free copy of the service manual for this radio. DK mods allows a free
download every 4 days.
I had an old DDS vfo that I bought about 7 years ago. The dds vfo was
not working but I still kept it and the old rotary encoder was still with it.
The rotary encoder was square and smaller than this unit. It had 4
terminals but two connections were bridged together so..it might work. I
connected it in place and it did not work properly. The radio tuned only
in one direction. I then switched the two outer connections and the
radio now tuned fine. It works! -- So sometimes you luck out. I dont know
all that much about encoders but I intend to learn more.
Symptom: VFO tuning is erratic, sometimes skips frequencies in a certain area if VFO knob travel.
Least significant digit in frequency display sometimes "flutters" back and forth instead of changing
incrementally when the VFO knob is turned slowly.
Probable Cause: Bad rotary encoder.
Cure: Substitute rotary encoder with a known good one. It is recommended that the rotary encoder
be replaced as a complete assembly if it is bad.
Remarks: If the unit tunes in only one direction, i.e. either up or down, there may be a problem on
the logic unit. Mine tuned only one way but changing the rotary encoder cleared it up.
My NOTE: the IC290A only did tune in one direction..down in frequency. I substituted in the rotary
encoder from my junkbox..as per photos and the IC290A does tune properly now..although ..it does
have a few quirks. Sometimes it tends to stall out or start turning the opposite direction. I can get it
going again correctly and it functions but not without these backlash type issues.
Perhaps if/when I get the real McCoy rotary encoder as per ICOM original ..the tuning will smooth
out. For now..however..I am happy that I can use the IC290A to some degree. It is an older radio and
I'm not going to spend too much money on it.
Least significant digit in frequency display sometimes "flutters" back and forth instead of changing
incrementally when the VFO knob is turned slowly.
Probable Cause: Bad rotary encoder.
Cure: Substitute rotary encoder with a known good one. It is recommended that the rotary encoder
be replaced as a complete assembly if it is bad.
Remarks: If the unit tunes in only one direction, i.e. either up or down, there may be a problem on
the logic unit. Mine tuned only one way but changing the rotary encoder cleared it up.
My NOTE: the IC290A only did tune in one direction..down in frequency. I substituted in the rotary
encoder from my junkbox..as per photos and the IC290A does tune properly now..although ..it does
have a few quirks. Sometimes it tends to stall out or start turning the opposite direction. I can get it
going again correctly and it functions but not without these backlash type issues.
Perhaps if/when I get the real McCoy rotary encoder as per ICOM original ..the tuning will smooth
out. For now..however..I am happy that I can use the IC290A to some degree. It is an older radio and
I'm not going to spend too much money on it.
Searching the web I found this note about the IC-761 (Icom transceiver with similar symptoms to my
IC290A
IC290A
My IC706 suffered damage in travel. The control labeled S1FR, or SW159
Rotary Encoder, was broken. It is a part that looks like a variable
potentiometer that is connected directly the main frequency control
knob on the transceiver.
I was informed by ICOM Technical Support that it is part number
2250000290 but their Parts Department informed that I could not order
the part because it has been discontinued. My only alternative is to
mail in the IC706 to have is repaired. I have already removed the
defective rotary controller and it looks like a simple job to replace
it.
Does anyone know where I can get a commercial equivalent
replacement
for the rotary encoder?
Rotary Encoder, was broken. It is a part that looks like a variable
potentiometer that is connected directly the main frequency control
knob on the transceiver.
I was informed by ICOM Technical Support that it is part number
2250000290 but their Parts Department informed that I could not order
the part because it has been discontinued. My only alternative is to
mail in the IC706 to have is repaired. I have already removed the
defective rotary controller and it looks like a simple job to replace
it.
Does anyone know where I can get a commercial equivalent
replacement
for the rotary encoder?
MORE research on ICOM encoders for ICOM transceivers led me to an
interesting article (the url is indicated below). This is for an OPTICAL
encoder. What the IC290A uses is a more simple mechanical encoder.
The optical encoder has electronic parts such as IR LEDs,
phototransistors, switching transistors, resistors all mounted on a PCB.
There is a careful alignment to these devices and theer is a rotary mask
assembly to generate the pulses for tuning. I know very little about these
devices..but I presume..they might be expensive to replace and/or the
parts may be in short supply.
http://highfields-arc.6te.net/repairs/ic735opcenc.htm
interesting article (the url is indicated below). This is for an OPTICAL
encoder. What the IC290A uses is a more simple mechanical encoder.
The optical encoder has electronic parts such as IR LEDs,
phototransistors, switching transistors, resistors all mounted on a PCB.
There is a careful alignment to these devices and theer is a rotary mask
assembly to generate the pulses for tuning. I know very little about these
devices..but I presume..they might be expensive to replace and/or the
parts may be in short supply.
http://highfields-arc.6te.net/repairs/ic735opcenc.htm
IN SUMMARY: We as amateur radio people are experimenters by nature and inquisitive as well. I didn't do much research on this part substitution...I
just did it. I had no data sheets to look at or spec sheets. The parts had no part numbers on them. So..sometimes..you just go for it. What is the
worst that could happen? Smoke??? Sometimes with certain circuits and components.
I don't know much at all really about digital encoders. I did not study them in College (1980). I can only assume that the mechanical encoders
generate a pulse or perhaps a glitch waveform which is amplified and squared up by logic circuitry and then that causes a counter to increment or
decrement and the radio changes frequency either up or down.
Waveforms are waveforms are waveforms. If we cannot buy a replacement encoder or repair the existing one..perhaps we as amateurs can build
one or modify an existing commercial encoder in production.
I took a look on ebay, and there are all kinds of listings for mechanical encoders like this one I used in this circuit. Im sure digikey and mouser and
other suppliers sell them.
I intend to learn more and I welcome emails from the readers out there to correct me or set me straight. I may publish a part 2 to this article in the
near future with more SPECIFIC DETAILS and technical details.
73 Earl VE3AB (hamelectronicsmagazine.com)
just did it. I had no data sheets to look at or spec sheets. The parts had no part numbers on them. So..sometimes..you just go for it. What is the
worst that could happen? Smoke??? Sometimes with certain circuits and components.
I don't know much at all really about digital encoders. I did not study them in College (1980). I can only assume that the mechanical encoders
generate a pulse or perhaps a glitch waveform which is amplified and squared up by logic circuitry and then that causes a counter to increment or
decrement and the radio changes frequency either up or down.
Waveforms are waveforms are waveforms. If we cannot buy a replacement encoder or repair the existing one..perhaps we as amateurs can build
one or modify an existing commercial encoder in production.
I took a look on ebay, and there are all kinds of listings for mechanical encoders like this one I used in this circuit. Im sure digikey and mouser and
other suppliers sell them.
I intend to learn more and I welcome emails from the readers out there to correct me or set me straight. I may publish a part 2 to this article in the
near future with more SPECIFIC DETAILS and technical details.
73 Earl VE3AB (hamelectronicsmagazine.com)
"I could not order the part because it has been discontinued" as per the above with the IC706. The IC706 is a more recent
production than the IC290a and I have not approached ICOM (yet) about a replacement encoder, but I have doubts whether they
would support this product anymore.
production than the IC290a and I have not approached ICOM (yet) about a replacement encoder, but I have doubts whether they
would support this product anymore.
click here to go back to INDEX of (hamelectronicsmagazine.com)
Rotary Encoder Idea from the AM Qrp Club
This is very similar to the one I used in my IC290A. This one was used by the AM qrp club
in one of their dds projects/kits and is supposed to be a fairly good one.
Here are some of the specs
Smooth, detentless, inexpensive encoders for use with microcontroller-based homebrew
projects:
2-phase output signals (A and B) as contact closures to a common pin
SPST momentary pushbutton on shaft
48 pulses-per-revolution (each phase has 24 pulses)
These are the same rotary encoders as used in the Micro908 Kit
Noble (a supplier of these types of devices) P/N 100-1166-101
(REB162(9X5)PVBS18.5FINB1224)
Dimensions: 0.6" x 0.7" base, 1.1" from pcb to top of shaft
in one of their dds projects/kits and is supposed to be a fairly good one.
Here are some of the specs
Smooth, detentless, inexpensive encoders for use with microcontroller-based homebrew
projects:
2-phase output signals (A and B) as contact closures to a common pin
SPST momentary pushbutton on shaft
48 pulses-per-revolution (each phase has 24 pulses)
These are the same rotary encoders as used in the Micro908 Kit
Noble (a supplier of these types of devices) P/N 100-1166-101
(REB162(9X5)PVBS18.5FINB1224)
Dimensions: 0.6" x 0.7" base, 1.1" from pcb to top of shaft
I cannot provide details like the ones above concerning the encoder I used because mine was a junkbox item. Mine had 4
terminals on the back. Two were bridged together (COM) and there was an A and B line as well. Mine had a plastic shaft vs
the metal one here but looked very similar. Before I put the encoder in the radio I wrapped it up a bit in electrical tape in
order to keep dust particles from getting inside the unit. I forgot to take pictures of it before I mounted it in the radio.
terminals on the back. Two were bridged together (COM) and there was an A and B line as well. Mine had a plastic shaft vs
the metal one here but looked very similar. Before I put the encoder in the radio I wrapped it up a bit in electrical tape in
order to keep dust particles from getting inside the unit. I forgot to take pictures of it before I mounted it in the radio.
I received excellent audio report from the IC290a when I had a couple of qsos on a local FM repeater. I checked eham reviews and the
radio was a 3.9 out of 5. The memory backup problem is a problem. NO INTERNAL battery to provide memory backup. One fellow uses/used
a 9 volt battery to move the radio from the shack to the auto. Necessary because the memory is total volatile with this radio. When the
power is removed you lose any saved memory locations and your dial reads 146.000 mid band. YOU then have to dial the frequency 1kc at
a time.
radio was a 3.9 out of 5. The memory backup problem is a problem. NO INTERNAL battery to provide memory backup. One fellow uses/used
a 9 volt battery to move the radio from the shack to the auto. Necessary because the memory is total volatile with this radio. When the
power is removed you lose any saved memory locations and your dial reads 146.000 mid band. YOU then have to dial the frequency 1kc at
a time.
| BASIC KINDS OF REPAIRS to Ham Radio Equipment..examples with an emphasis on component interchangeability and discussion of generic parts such as TTL chips. |
hamelectronicsmagazine.com
by Earl Andrews VE3AB
FREE ON LINE Hands On kind of HAM
RADIO MAGAZINE.
(This article under construction..(as is
this entire ""NEW"" web site 73 Earl
by Earl Andrews VE3AB
FREE ON LINE Hands On kind of HAM
RADIO MAGAZINE.
(This article under construction..(as is
this entire ""NEW"" web site 73 Earl
MECHANICAL vs OPTICAL encoders
I have not yet gotten around to reading up on how
encoders work, the codes, ie grayhilll codes and stuff
like that.
Most of my older gear like FT301s, FT221, HW7, HR10B,
Galaxy R530, Ten Tec Argonauts 505, 509, 515 -- they are
all manufactured with very little if no digital circuitry in
them. They use either variable capacitors and a coil or
fixed capacitors and a variable coil (slug tuned coil) PMO
(Permeablility Tuned Oscillators, as with the Argonauts.
By the way, I read on my QRP-L list the other day where a
fellow picked up a Drake PMO 5 to 5.5 mhz and he said it
was dead stable and nice to use in a vfo circuit!
Anyways..I did read about IC 735 transceivers and
problems with the Optical encoder. The fellow has a web
site and he said he spent quite a few hours trying to
repair and align his. He said in his article..that IF the
radio tunes OK but sometimes acts up with a backlash
kind of situation..he would just leave it be rather than
struggle trying to repair it. (Apparently ..with optical
encoders..it is not as simple to find a fit form function
replacement.
This example I give with the IC290A..I just found a
junkbox part ecoder..no part number or markings that
could trace it to a specification sheet. I did have a
schematic of the next higher assembly..the (old) DDS
vfo..which gave a basic pin out of the encoder. I wired it
in and it worked. Maybe I just was lucky..or with mechical
encoders ..maybe they all pretty well work and are
interchangeable electrically. who knows??
I have not yet gotten around to reading up on how
encoders work, the codes, ie grayhilll codes and stuff
like that.
Most of my older gear like FT301s, FT221, HW7, HR10B,
Galaxy R530, Ten Tec Argonauts 505, 509, 515 -- they are
all manufactured with very little if no digital circuitry in
them. They use either variable capacitors and a coil or
fixed capacitors and a variable coil (slug tuned coil) PMO
(Permeablility Tuned Oscillators, as with the Argonauts.
By the way, I read on my QRP-L list the other day where a
fellow picked up a Drake PMO 5 to 5.5 mhz and he said it
was dead stable and nice to use in a vfo circuit!
Anyways..I did read about IC 735 transceivers and
problems with the Optical encoder. The fellow has a web
site and he said he spent quite a few hours trying to
repair and align his. He said in his article..that IF the
radio tunes OK but sometimes acts up with a backlash
kind of situation..he would just leave it be rather than
struggle trying to repair it. (Apparently ..with optical
encoders..it is not as simple to find a fit form function
replacement.
This example I give with the IC290A..I just found a
junkbox part ecoder..no part number or markings that
could trace it to a specification sheet. I did have a
schematic of the next higher assembly..the (old) DDS
vfo..which gave a basic pin out of the encoder. I wired it
in and it worked. Maybe I just was lucky..or with mechical
encoders ..maybe they all pretty well work and are
interchangeable electrically. who knows??
| More on Parts Subsitution and Interchangeabilty..it is actually a big topic. |
Small discrete components are manufactured to standards and are fairly standardized. Just like bolts, screws and nuts that sort of thing.
I don't know all the up to date details of the agencies responsible for standardization, but one of them is JEDEC Joint Engineering Device
something or other council.
Logic Gates such as NAND gates, NOR gates, JK flip flops are all manufactured to specifications and there are families of items such as RTL
(resistor transistor logic, TTL Transistor to Transistor Logic and so on. TTL logic circuits have different sub families such as Low Power
ie 74L00, standard logic, ie 7400, Schottky 74S00, low power schottky 74LS00.
Where I used to work (Nato Cataloguing of Microcircuits or ICs) we followed a convention and it made alot of sense. Often..we did not fully
understand the circuits but we followed the rules and the items were catalogued properly and we tried not to create unnecessary duplications in
the system and tried to get all items that were very close to being the same (a standardized approach). It worked for the most part.
So..if you have a circuit with a 7400 nand gate that needs replacing, you find another 7400 nand gate chip to replace it with. The parts SN7400N
(Texas Instruments) and F7400P (Fairchild) should be FIT FORM AND FUNCTION..DROP IN REPLACEMENT PARTS. These are logic gates. One of the
key characteristic of these NAND gates is propagation delay time. It is fairly standardized (probably totally standardized I would imagine). It would
have to be if you want your computers and timing circuits to all perform without glitches.
I wont get into a whole lot of thick theory but I will just say: don't mix different logic familiies and you will be far better off and will get predictable
results without glitches and lock ups. I use the web site www dot datasheetarchive.com. A great free site. Once you start using it..you will return
again and again. You just ignore alot of the added advertising banners and dig in to find the data sheets in PDF format.
Also, it will have substitute items listed as well. For transistors this is great. The NTE semiconductor cross reference is another great free site.
I well remember the QST article in the mid to late 70s called the ACCU KEYER. A very popular homebrew keyer. I think you could probably order the
circuit boards from ARRL and/or FAR circuits. Anyways..I remember reading a follow up from the author a bit later in QST. Seems people were
having problems with the keyer. Things like "lock up" and sending errors ect. I had an accukeyer I monkeyed around with and it seemed to have a
problem as well. Its been a long time..but I think it would only send out one dit instead of a stream of dits when I held the keyer paddle in dit
position. Anyways..the problem was mainly due to PART SUBSTITUTIONS. For sake of this example, I have included a partial schematic and parts list
for the ACCU KEYER below. Just click on it to expand and hit your browser back buttom to return to normal screen. The author speaks of parts
substitutions in terms of different manufacturers of chips having slightly different part numbers. IE MC7400P (MOTOROLA) chip is the same as a
Texas Instruments chip ie SN7400N. The prefix letters indicate the company SN is Texas Instrument. MC Motorola. MC might stand for Motorola
Communications (Im not sure about this). LM is another prefix. National uses this one and the letters stand for Linear Monolithic. Monolithic refers
to the fact that the chip die is mounted on a single piece of ceramic substrate. How do I know these things you might ask?? Well I did work in the
Nato Cataloguing and Material Management for Microciruits (ICs) for a number of years and I picked up a great deal of little tid bits of information
and I made mental notes which stay with me to this day. I seem to have a keen mind for details when it comes to technical items because I was
really working hard to memorize these details and they came up so frequently in my day to day work. Also, I had was an electronics builder myself
and I am a graduate of the 2 year Electronics Engineering Technician Program. So Ive worked with these chips in Labs quite a bit. The think about
memory is strange. When it comes to more mundane things..I tend to have a short memory..such as ..where I parked my car at the mall??
Anyways..back to the ACCU KEYER CIRCUIT AND THE CASE OF THE PROBLEMS being reported by the hams who built this keyer up. Many problems
were a result of substituting ICs which were very similar but not quite the same. ICs in the accu keyer were STANDARD TTL ICS. Parts such as 7400
Nand gates (maybe the most common TTL chip), 7474 flip flops and 7410. Some builders might have tried using 74LS00 chips instead of the
standard 7400. LS is the Low Power Schottky family of the quad 2 input NAND gate. Other families of the same basic device were 74S00 (Schottky)
and Fairchilds F Fast. There were developments in the IC world occurring all the time. Advancements: speed and lower power consumption as
well as reliability were key attributes being worked on. The speed varies with each family and if you subtitute one family of chips for another in a
circuit that was not specifically designed for that family; you may well have glitches, odd lockups where the circuit will not "toggle" (toggle in logic
means change state ie from high to low or visa versa. Your keyer may just lock up and send out a steady tone. Something like a car alarm going off
and not shutting down (only not as noisy).
AFTER-Market Semiconductors.
NTE is an aftermarket supplier of replacement parts. If you look up 7400 or 74LS00 on the NTE crossreference web site...it will cross reference to a
device with an NTE number. Example a 7400 chip..ie SN7400N cross references to an NTE7400. 74LS00 ie SN7400N texas instrument chip crosses to
an NTE74LS00 . Actually..when I punched in 7400 into the NTE data base I got 50 hits returned. That is 50 different permutations of the same exact
item (standard item) only with different prefixes and suffixes. In the Nato Cataloguing world we tried to do a similar type of process. I found
though, there were alot more complications because of the coding systems that were used and sometimes misinterpreted. Some called it too
complex and they brought in some new systems when I chose to retire. The Nato system could be used to draw cross references to these
standardized parts but I would not try to use the system because it is difficult to interpret at the best of times. NTE on the other hand is easy to
use. I use the NTE system here with my parts bins. The NTE system is so powerful that it may even be illegal to reverse engineer it in order to
create a master data base (very powerful) of all parts. Of course, NTE is limited. They dont have all the part numbers you might encounter listed.
Trust me..I have gone there done that. Same goes for datasheetarchive.com. They are good sites though and for the most part, I use them all the
time when researching parts. I sell parts by the way. I research parts for free for people when they are searching for a few parts to fix something
or build something. My email address is ve3ab(at sign)personainternet.com. My web page www.hamelectronicsmagazine.com has a link to my
parts listing page.
The NTEweb site is easy to use. YOU punch in the part number (or even part of a part number if you are reading it off a part..ie with TRANSISTOR
2SC1969 ..often the part has the 2S prefix missing off the part on the transistor itself. This "truncating" of part numbers is common with small wee
transistors and perhaps some resistors because of the limited space on the part surface to print the part number. If you go to the NTE cross
reference (you can google it) and punch in either 2SC1969 or C1969 you will get a cross reference to NTE236 along with a PDF data sheet. -- You
could go to an electronics store and buy a replacement NTE236 and replace your transistor (it is an RF output transistor) about 6 watts or so..or
you could do what I do and start looking for replacement transistors that I might have in my radio shack. I would start looking for 2N (the standard)
generic part numbers for bipolar transistors ie NPN and PNP types. As it turns out..I dont thing there are many direct drop in replacements in the
2N series for the 2SC1969. There could be a down grade type transistor that might work..OK in the circuit and has the same pin configurations..I
did not research it that deeply.
Some transistors such as 2N2222 type is very common and there are lots of suitable replacements. A bit of detective work might be necessary.
I use the computer quite a bit but books are very helpful. YOu can scan a book quickly by sight and find like items much quicker than a computer
(sometimes).
Just one more thing about NTE parts. NTE and ECG are the same parts. I think they were sister companies or something like that. So if you have or
look up an ECG222 it will have the same counterpart NTE number NTE222. They are interchangeable. Im not sure if ECG is still active or not..but
you will find their parts are still very much common.
I don't know all the up to date details of the agencies responsible for standardization, but one of them is JEDEC Joint Engineering Device
something or other council.
Logic Gates such as NAND gates, NOR gates, JK flip flops are all manufactured to specifications and there are families of items such as RTL
(resistor transistor logic, TTL Transistor to Transistor Logic and so on. TTL logic circuits have different sub families such as Low Power
ie 74L00, standard logic, ie 7400, Schottky 74S00, low power schottky 74LS00.
Where I used to work (Nato Cataloguing of Microcircuits or ICs) we followed a convention and it made alot of sense. Often..we did not fully
understand the circuits but we followed the rules and the items were catalogued properly and we tried not to create unnecessary duplications in
the system and tried to get all items that were very close to being the same (a standardized approach). It worked for the most part.
So..if you have a circuit with a 7400 nand gate that needs replacing, you find another 7400 nand gate chip to replace it with. The parts SN7400N
(Texas Instruments) and F7400P (Fairchild) should be FIT FORM AND FUNCTION..DROP IN REPLACEMENT PARTS. These are logic gates. One of the
key characteristic of these NAND gates is propagation delay time. It is fairly standardized (probably totally standardized I would imagine). It would
have to be if you want your computers and timing circuits to all perform without glitches.
I wont get into a whole lot of thick theory but I will just say: don't mix different logic familiies and you will be far better off and will get predictable
results without glitches and lock ups. I use the web site www dot datasheetarchive.com. A great free site. Once you start using it..you will return
again and again. You just ignore alot of the added advertising banners and dig in to find the data sheets in PDF format.
Also, it will have substitute items listed as well. For transistors this is great. The NTE semiconductor cross reference is another great free site.
I well remember the QST article in the mid to late 70s called the ACCU KEYER. A very popular homebrew keyer. I think you could probably order the
circuit boards from ARRL and/or FAR circuits. Anyways..I remember reading a follow up from the author a bit later in QST. Seems people were
having problems with the keyer. Things like "lock up" and sending errors ect. I had an accukeyer I monkeyed around with and it seemed to have a
problem as well. Its been a long time..but I think it would only send out one dit instead of a stream of dits when I held the keyer paddle in dit
position. Anyways..the problem was mainly due to PART SUBSTITUTIONS. For sake of this example, I have included a partial schematic and parts list
for the ACCU KEYER below. Just click on it to expand and hit your browser back buttom to return to normal screen. The author speaks of parts
substitutions in terms of different manufacturers of chips having slightly different part numbers. IE MC7400P (MOTOROLA) chip is the same as a
Texas Instruments chip ie SN7400N. The prefix letters indicate the company SN is Texas Instrument. MC Motorola. MC might stand for Motorola
Communications (Im not sure about this). LM is another prefix. National uses this one and the letters stand for Linear Monolithic. Monolithic refers
to the fact that the chip die is mounted on a single piece of ceramic substrate. How do I know these things you might ask?? Well I did work in the
Nato Cataloguing and Material Management for Microciruits (ICs) for a number of years and I picked up a great deal of little tid bits of information
and I made mental notes which stay with me to this day. I seem to have a keen mind for details when it comes to technical items because I was
really working hard to memorize these details and they came up so frequently in my day to day work. Also, I had was an electronics builder myself
and I am a graduate of the 2 year Electronics Engineering Technician Program. So Ive worked with these chips in Labs quite a bit. The think about
memory is strange. When it comes to more mundane things..I tend to have a short memory..such as ..where I parked my car at the mall??
Anyways..back to the ACCU KEYER CIRCUIT AND THE CASE OF THE PROBLEMS being reported by the hams who built this keyer up. Many problems
were a result of substituting ICs which were very similar but not quite the same. ICs in the accu keyer were STANDARD TTL ICS. Parts such as 7400
Nand gates (maybe the most common TTL chip), 7474 flip flops and 7410. Some builders might have tried using 74LS00 chips instead of the
standard 7400. LS is the Low Power Schottky family of the quad 2 input NAND gate. Other families of the same basic device were 74S00 (Schottky)
and Fairchilds F Fast. There were developments in the IC world occurring all the time. Advancements: speed and lower power consumption as
well as reliability were key attributes being worked on. The speed varies with each family and if you subtitute one family of chips for another in a
circuit that was not specifically designed for that family; you may well have glitches, odd lockups where the circuit will not "toggle" (toggle in logic
means change state ie from high to low or visa versa. Your keyer may just lock up and send out a steady tone. Something like a car alarm going off
and not shutting down (only not as noisy).
AFTER-Market Semiconductors.
NTE is an aftermarket supplier of replacement parts. If you look up 7400 or 74LS00 on the NTE crossreference web site...it will cross reference to a
device with an NTE number. Example a 7400 chip..ie SN7400N cross references to an NTE7400. 74LS00 ie SN7400N texas instrument chip crosses to
an NTE74LS00 . Actually..when I punched in 7400 into the NTE data base I got 50 hits returned. That is 50 different permutations of the same exact
item (standard item) only with different prefixes and suffixes. In the Nato Cataloguing world we tried to do a similar type of process. I found
though, there were alot more complications because of the coding systems that were used and sometimes misinterpreted. Some called it too
complex and they brought in some new systems when I chose to retire. The Nato system could be used to draw cross references to these
standardized parts but I would not try to use the system because it is difficult to interpret at the best of times. NTE on the other hand is easy to
use. I use the NTE system here with my parts bins. The NTE system is so powerful that it may even be illegal to reverse engineer it in order to
create a master data base (very powerful) of all parts. Of course, NTE is limited. They dont have all the part numbers you might encounter listed.
Trust me..I have gone there done that. Same goes for datasheetarchive.com. They are good sites though and for the most part, I use them all the
time when researching parts. I sell parts by the way. I research parts for free for people when they are searching for a few parts to fix something
or build something. My email address is ve3ab(at sign)personainternet.com. My web page www.hamelectronicsmagazine.com has a link to my
parts listing page.
The NTEweb site is easy to use. YOU punch in the part number (or even part of a part number if you are reading it off a part..ie with TRANSISTOR
2SC1969 ..often the part has the 2S prefix missing off the part on the transistor itself. This "truncating" of part numbers is common with small wee
transistors and perhaps some resistors because of the limited space on the part surface to print the part number. If you go to the NTE cross
reference (you can google it) and punch in either 2SC1969 or C1969 you will get a cross reference to NTE236 along with a PDF data sheet. -- You
could go to an electronics store and buy a replacement NTE236 and replace your transistor (it is an RF output transistor) about 6 watts or so..or
you could do what I do and start looking for replacement transistors that I might have in my radio shack. I would start looking for 2N (the standard)
generic part numbers for bipolar transistors ie NPN and PNP types. As it turns out..I dont thing there are many direct drop in replacements in the
2N series for the 2SC1969. There could be a down grade type transistor that might work..OK in the circuit and has the same pin configurations..I
did not research it that deeply.
Some transistors such as 2N2222 type is very common and there are lots of suitable replacements. A bit of detective work might be necessary.
I use the computer quite a bit but books are very helpful. YOu can scan a book quickly by sight and find like items much quicker than a computer
(sometimes).
Just one more thing about NTE parts. NTE and ECG are the same parts. I think they were sister companies or something like that. So if you have or
look up an ECG222 it will have the same counterpart NTE number NTE222. They are interchangeable. Im not sure if ECG is still active or not..but
you will find their parts are still very much common.
I will close this topic off for now..Wed April 27 2011. I will be writing a bit more about some practical examples of parts being substituted in
ham radio equipment. QST magazine..often encouraged builders to try different parts. Sometimes there is no problem. You dont have to
be right on with resistors and capacitors. With resistors and capacitors...there is the value that they say they are: ie a one kilohm resistor
with a tolerance of 5 percent. That means..off the shelf ..the value of this resistor will be between 950 ohms and 1050 ohms for a 5 percent
tolerance. I think this is called the selection tolerance. When the item is in a circuit and is subjected to heat it will change value with its
temperature coefficient. With resisistors if you go to substitute ..say you ran out of 1 kilohm resistors..I would maybe try a 1,100 ohm
resistor as a substitute if I had some of those on hand. With resistors, you always substitute up in value. You add (maybe) a bit more
resistance into the circuit because the most harm that you will likely do is to cause less current to flow in the circuit (slightly). Less
current is better than causing more current to flow (which would perhaps cause more heat-- in term more temperature drift due to
heating (temperature coefficient).
There are some more basic kinds of tips and rules of thumb that are good to know. I will be writing more on this shortly.
The entire hamelectronicsmagazine.com is in its infancy and I am working to develop its structure and as well write up some articles.
If you have an article to contribute ..I would be pleased to look it over and publish it for you. Another thing I do is create temporary spots
on the web for your ham event or ham advertisements or flea market , basement sale...whatever. I do it very economically. A big page for
a month with lots of photos and descriptions I can do for $15 a month which includes periodic ammendments of description what -ever.
And I keep all the information and your private email ect..just that..PRIVATE....73 earl ve3ab
ham radio equipment. QST magazine..often encouraged builders to try different parts. Sometimes there is no problem. You dont have to
be right on with resistors and capacitors. With resistors and capacitors...there is the value that they say they are: ie a one kilohm resistor
with a tolerance of 5 percent. That means..off the shelf ..the value of this resistor will be between 950 ohms and 1050 ohms for a 5 percent
tolerance. I think this is called the selection tolerance. When the item is in a circuit and is subjected to heat it will change value with its
temperature coefficient. With resisistors if you go to substitute ..say you ran out of 1 kilohm resistors..I would maybe try a 1,100 ohm
resistor as a substitute if I had some of those on hand. With resistors, you always substitute up in value. You add (maybe) a bit more
resistance into the circuit because the most harm that you will likely do is to cause less current to flow in the circuit (slightly). Less
current is better than causing more current to flow (which would perhaps cause more heat-- in term more temperature drift due to
heating (temperature coefficient).
There are some more basic kinds of tips and rules of thumb that are good to know. I will be writing more on this shortly.
The entire hamelectronicsmagazine.com is in its infancy and I am working to develop its structure and as well write up some articles.
If you have an article to contribute ..I would be pleased to look it over and publish it for you. Another thing I do is create temporary spots
on the web for your ham event or ham advertisements or flea market , basement sale...whatever. I do it very economically. A big page for
a month with lots of photos and descriptions I can do for $15 a month which includes periodic ammendments of description what -ever.
And I keep all the information and your private email ect..just that..PRIVATE....73 earl ve3ab
IC 706 example from the web I found. I (think) the IC706 encoder would likely be more
sophisticated than the one I replaced in my IC290A.
sophisticated than the one I replaced in my IC290A.
NAVIGATION LINK TO MY START PAGE: www.hamelectronicsmagazine.com
A free on line publication by Earl Andrews VE3AB
It is a commercial magazine but with limited advertising and very low budget.
I am chief cook and bottle washer.. (and I sell the odd part here and there and
do some repairs (by mail order)..fixes to gear at only $10 per hour bench rate.
A free on line publication by Earl Andrews VE3AB
It is a commercial magazine but with limited advertising and very low budget.
I am chief cook and bottle washer.. (and I sell the odd part here and there and
do some repairs (by mail order)..fixes to gear at only $10 per hour bench rate.
Here is a link to my PARTS PAGEs (2 PAGES of parts I sell in limited quantities to experimenters,
hams and future hams and swl people)..older solid state parts from 70s and 80s mainly. I also
sell some good used pulled parts from broken transcievers such as Atlas 210x, HW7/8, FT301
(my specialty) and HW16 among others.
hams and future hams and swl people)..older solid state parts from 70s and 80s mainly. I also
sell some good used pulled parts from broken transcievers such as Atlas 210x, HW7/8, FT301
(my specialty) and HW16 among others.
HERE is a link to my trouble shooting page index..new Sept 25 2011.
I am writing more concrete examples up every day now....
I am writing more concrete examples up every day now....