I’m working on a Korg PolySix synth that has at least one dead SSM-2044.
Going through the Adjustment Procedure from the service manual, I got to step 4 (2) 2) where I’m supposed to confirm a sawtooth wave coming out of each voices. However, of my 5 remaining working SSM-2044, 3 give me a sort of double peak sawtooth, and 2 only give me the top half of a sawtooth (sharks!). Pin 5 looks especially different on the group of 2 vs the group of 3.
The differences follow the chips when I swap them around from voice to voice, so I’m pretty sure that the SSM-2044 are the root cause.
All 5 of these chips still produce sound, but the group of 2 sounds noticeably different from the group of 3, so it’s not a good setup for a synth.
I’m assuming that the group of 2, which don’t produce as much of a sawtooth wave, are the “more defective” ones, and that the group of 3 are probably good. But that's an assumption, and it would suck to order some replacements only to get different sounding ones. I'd also want to make sure the group of 2 is actually defective and not just different. I wouldn’t resell defective ones, but if they are just different I will. If they have failed, they have failed in identical fashion, the half sawtooth is the same on both.
The batch numbers don’t all match on all my chips, but that doesn’t seem to be a factor in how they sound.
Is there a way to test these chips for defects, or partial failures? (voltage drop specs across pins? test jigs?)
A good way to tell if they are actually defective, and to tell fully functional ones?
Is my assumption correct that the 2 half-sawtooth ones are defective (the PolySix is, in itself, a test jig after all)?
Thanks for any insights!
Going through the Adjustment Procedure from the service manual, I got to step 4 (2) 2) where I’m supposed to confirm a sawtooth wave coming out of each voices. However, of my 5 remaining working SSM-2044, 3 give me a sort of double peak sawtooth, and 2 only give me the top half of a sawtooth (sharks!). Pin 5 looks especially different on the group of 2 vs the group of 3.
The differences follow the chips when I swap them around from voice to voice, so I’m pretty sure that the SSM-2044 are the root cause.
All 5 of these chips still produce sound, but the group of 2 sounds noticeably different from the group of 3, so it’s not a good setup for a synth.
I’m assuming that the group of 2, which don’t produce as much of a sawtooth wave, are the “more defective” ones, and that the group of 3 are probably good. But that's an assumption, and it would suck to order some replacements only to get different sounding ones. I'd also want to make sure the group of 2 is actually defective and not just different. I wouldn’t resell defective ones, but if they are just different I will. If they have failed, they have failed in identical fashion, the half sawtooth is the same on both.
The batch numbers don’t all match on all my chips, but that doesn’t seem to be a factor in how they sound.
Is there a way to test these chips for defects, or partial failures? (voltage drop specs across pins? test jigs?)
A good way to tell if they are actually defective, and to tell fully functional ones?
Is my assumption correct that the 2 half-sawtooth ones are defective (the PolySix is, in itself, a test jig after all)?
Thanks for any insights!
I do not think that you are going to get to many responses since it relates to a old eol chip and you do not provide a schematic for the application nor device data sheet. I had a quick look at the part. One could wire up a test circuit as shown in the data sheet to test the device for specifications. If you say the unit can act as the test jig then either the ic meets specs or it does not based on test conditions in the data sheet
I don't know much about the SSM-2044 chip other than what I have read in my experiments with DIY music synthesizer circuits including the current production SSI2144 chip. The SSI2144 from Sound Semiconductor Incorporated "Uses the same internal circuit as the SSM2044." It is however NOT pin or footprint compatible with the SSM2044, as it is a SMD device with an "optimized" pinout.
There is some information on the old chips and their use in various old synth in this web page. It appears that the PolySix is an odd case that runs the chips on +/- 5 volts where most other applications use +/- 12 or 15 volts. Your chips may have degraded just enough over the years that they all behave differently in a low voltage application.
https://electricdruid.net/ssm2044-lp-filter-designs/
It is possible to replace the SSM-2044 chip with the SSI2144 using an adapter board. One is available here, though I have not tried it.
https://synthcube.com/cart/ssm2044-drop-in-replacement-pcb-adapter-for-ssi2144-smt-ic
There is some information on the old chips and their use in various old synth in this web page. It appears that the PolySix is an odd case that runs the chips on +/- 5 volts where most other applications use +/- 12 or 15 volts. Your chips may have degraded just enough over the years that they all behave differently in a low voltage application.
https://electricdruid.net/ssm2044-lp-filter-designs/
It is possible to replace the SSM-2044 chip with the SSI2144 using an adapter board. One is available here, though I have not tried it.
https://synthcube.com/cart/ssm2044-drop-in-replacement-pcb-adapter-for-ssi2144-smt-ic
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Thanks!
My apologies for not including the datasheets @rsavas. The SSM-2044 can be found here. And the schematics for the Korg PolySix can be found in the service manual, here. Rigging the typical connection from the service manual is a good idea, though I'm not sure the charts give enough info to compare against real life measurements. I guess if I assume linear scale axis on the unmarked charts and refer to the min/max/typical measurements for quantities, it might work. It might all be in there if I look closely with my smart cap on.
@Tubelab_com I'm aware of the SSI2144 and the adapter board, but as you know the PolySix is one of those "legendary" vintage synths where the parts are best kept as original as possible. And I would have to replace all 6 of them for the unit to sound "together". I realize this may be the only financially practical option, and I may end up going that way in the end. But even if I do that, I'll need to some way of testing the ones I have before selling them. That page at Electric Druid is very interesting, and it's the first time I see it. Will take a good long look at that today.
I appreciate the help, cheers!
My apologies for not including the datasheets @rsavas. The SSM-2044 can be found here. And the schematics for the Korg PolySix can be found in the service manual, here. Rigging the typical connection from the service manual is a good idea, though I'm not sure the charts give enough info to compare against real life measurements. I guess if I assume linear scale axis on the unmarked charts and refer to the min/max/typical measurements for quantities, it might work. It might all be in there if I look closely with my smart cap on.
@Tubelab_com I'm aware of the SSI2144 and the adapter board, but as you know the PolySix is one of those "legendary" vintage synths where the parts are best kept as original as possible. And I would have to replace all 6 of them for the unit to sound "together". I realize this may be the only financially practical option, and I may end up going that way in the end. But even if I do that, I'll need to some way of testing the ones I have before selling them. That page at Electric Druid is very interesting, and it's the first time I see it. Will take a good long look at that today.
I appreciate the help, cheers!