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Re: EDIT: polysix problem: 74LS08's, or 8048?

Posted: Mon Nov 16, 2009 3:18 pm
by rjd2
UPDATE:

i found a few 74LS08's in another carcass. pulled them, and swapped around for IC's 30/31, and also tried IC25. basically same problem.

i have a few 8048's on order. however, is it a programmed IC? anywhere else would you focus your energies on a possible culprit?

Re: EDIT: polysix problem: 74LS08's, or 8048?

Posted: Mon Nov 16, 2009 4:50 pm
by radek tymecki
check if there are no missing connections. i doubt that cpu is damaged

Re: EDIT: polysix problem: 74LS08's, or 8048?

Posted: Mon May 09, 2016 12:40 pm
by polysixer
Reviving this thread to see if anyone has a clue about VCA mod fix. Same symptoms as OP, namely:

- Mod wheel makes no effect (just very slightly interference).
- VCO Mod is always on, regardless of wheel position and intensity knob. I'd say intensity is full on.
- VCF Mod works ok, responds to intensity knob.
- VCA Mod doesn't work, no effect whatsoever.

Haven't yet replaced Q1 but I'll surely investigate that.

Re: EDIT: polysix problem: 74LS08's, or 8048?

Posted: Mon May 09, 2016 9:03 pm
by sam
you can discount the cpu... over 100 polysix repairs i never replaced one.

you need to look for damaged traces......clean the board with isopropl alcohol.

check out those 4558 op amps.

i will check out the service notes...also check the green cable..

Re: EDIT: polysix problem: 74LS08's, or 8048?

Posted: Tue May 10, 2016 9:39 am
by polysixer
sam wrote:you can discount the cpu... over 100 polysix repairs i never replaced one.

you need to look for damaged traces......clean the board with isopropl alcohol.

check out those 4558 op amps.

i will check out the service notes...also check the green cable..
Did you ever repair a broken VCA Mod? I see it comes from the KLM368 board into KLM367 via the orange connector in CN03, I think it's the 5th one, but I'd take advice on other testing points, thanks. I just picked up this Polysix a couple of days ago, the bottom screws are so oxidized I haven't been able to pull them out yet. I did lift a bit the upper case, enough to see the battery fix was done but no way to tell yet if traces where affected or bypassed. Lots of debris inside, mole on the wood (stored in a humid basement for at lest two years) but PCBs are surprisingly clean. I'm letting it dry up with a dehumidifier in a room (it's been there for 4 days). Cleaned the outside and it looks pretty good, all knobs work. I'l try to pry bottom screws today to take a deeper look. Symptoms so far:
  • All keys trigger fine, but circuits sound very cold with tons of noise, I'll be letting it warm up right later for about 4 or 5 hours, as every time it's plugged the rough noise seems to be improving.
  • Aforementioned constant VCO Modulation. Wheel does not shut it, neither does the MG Level.
  • Programmer buttons all work and LEDs light up, very hard to press though (replacement recommended or just blow some air?
  • No VCA Mod whatsoever as I said earlier.
  • Some different keys trigger the same note (miscalibration? Dirty contacts? Will probably have to fully disassemble the keybed for cleaning.
Do you recommend a full cleaning before warming it up?

My other problem is I don't have an oscilloscope to do calibrations if I can fix everything. I do have measurement equipment and someone who can help with soldering. Thanks for the help in advance.