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

Pulling out your hair? Don't know what to do or where to go? Ask in here.
Forum rules
READ: VSE Board-Wide Rules and Guidelines

If your Help request has been solved, please edit your first post in order to select the Image Topic Icon to let others know your topic has been solved.
rjd2
Active Member
Active Member
Posts: 301
Joined: Mon Jul 03, 2006 2:23 am

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

Post by rjd2 » Thu Oct 29, 2009 1:33 am

hi folks, so i have been tackling a pretty beat korg polysix, and im almost done. the specs:

KLM367 board:
---------------------------
-new battery-of course
-i have verified that every pin of IC's 30 and 31 of the KLM367 have continuity with the upper trace image i have.
-R91 is now a 1418 diode, C40 removed

now here's the problem: all functions and controls are working properly, except ONE problem: the LFO is modulating the VCO regardless of the MG LEVEL pot. the pot works, and if i switch it to VCF, the throw of the pot will mod the VCF from 0-10. but even at 0, and even set to VCF or VCA, it still modulates the VCO.

the schems in the service manual denote "C11" as the connector for the LFO from the 369 board to the 367 board, but i can't actually tell from the schems which IC on the 367 board would be the culprit i should focus my energies on.

any help? thanks. here's links to service manual, page 3 is the KLM367 board.

http://www.korganalogue.net/korgother/index.html


http://www.korganalogue.net/korgothe...e%20Manual.pdf

http://www.korganalogue.net/korgother/Polysixmanual/

EDIT:
i am getting some funny impedance measurements across D6 and D7 at the output of the MG MOD 3 way switch. i want to try swapping them out. however, the schems dont show what value diode is used. i have 1n4148's and 4004's here, but i hate guessing. any geniuses know what i can use there?
Last edited by rjd2 on Sun Nov 15, 2009 8:12 pm, edited 2 times in total.

cutoffres
Junior Member
Junior Member
Posts: 153
Joined: Fri May 15, 2009 2:24 pm
Location: Europe

Re: just repaired Polysix. 1 problem still left. schem help?

Post by cutoffres » Thu Oct 29, 2009 3:47 pm

Hello rjd2 !
Are you sure that the MG Wheel is completly down ? Cause MG wheel affect the sound even if the MG LEVEL pot is set to "0" .
Let us know

rjd2
Active Member
Active Member
Posts: 301
Joined: Mon Jul 03, 2006 2:23 am

Re: just repaired Polysix. 1 problem still left. schem help?

Post by rjd2 » Thu Oct 29, 2009 4:14 pm

yes, the MG wheel is completely down. it also exhibits this issue if the wheel assembly harness is unplugged.

i figure its got to be related to the encoding of either the VCO/VCF/VCA mod switch, or the MG LEVEL pot. i can see where harnesses C06 and C11 come into the KLM367 board on the schem, but from there, im not so clear on which IC is responsible for encoding this function.

cutoffres
Junior Member
Junior Member
Posts: 153
Joined: Fri May 15, 2009 2:24 pm
Location: Europe

Re: just repaired Polysix. 1 problem still left. schem help?

Post by cutoffres » Thu Oct 29, 2009 7:21 pm

Search for this topic in this help section :
Polysix MG Frequencie
I'm sure it will help you :D
Look around IC21 on board 367 specially look at Q1 close to IC21

rjd2
Active Member
Active Member
Posts: 301
Joined: Mon Jul 03, 2006 2:23 am

Re: just repaired Polysix. 1 problem still left. schem help?

Post by rjd2 » Thu Oct 29, 2009 8:29 pm

thanks, cutoffres.

i swapped IC21 for an LM13700; no change in behavior. q4 looks clean as a whistle.

trying to diagnose logic problems with your eyes is the dumbest idea in the world; with that said, IC25 had a bit of corrosion on the legs, and it is one IC i didnt replace/socket. if this IC is responsible for any MG or LFO functions, this is a good candidate, but guessing by eyeball is too much "shot in the dark" for me to go thru the trouble.

is that possible? again, schems just not clear to me....

EDIT: one more thing i realized: the VCO/VCF/VCA switch for the MG only works on VCF or VCO. when set to VCA, it does nothing. ive checked impedance of the actual switch, and its working fine, so wherever it is getting encoded, there is a problem. but where....

cutoffres
Junior Member
Junior Member
Posts: 153
Joined: Fri May 15, 2009 2:24 pm
Location: Europe

Re: just repaired Polysix. 1 problem still left. schem help?

Post by cutoffres » Fri Oct 30, 2009 4:50 pm

When i say "look" it's not only with your eyes , but it means parts to focus on

rjd2
Active Member
Active Member
Posts: 301
Joined: Mon Jul 03, 2006 2:23 am

Re: EDIT: what diodes are in a polysix?

Post by rjd2 » Fri Nov 06, 2009 12:17 am

EDIT:
i am getting some funny impedance measurements across D6 and D7 at the output of the MG MOD 3 way switch. i want to try swapping them out. however, the schems dont show what value diode is used. i have 1n4148's and 4004's here, but i hate guessing. any geniuses know what i can use there? the reason im assuming they are a uniform diode in the machine is that none of them are shown w/ value on the schems, AFAIK.

cutoffres
Junior Member
Junior Member
Posts: 153
Joined: Fri May 15, 2009 2:24 pm
Location: Europe

Re: EDIT: what diodes are in a polysix?

Post by cutoffres » Fri Nov 06, 2009 3:43 pm

Do you try with manual mode or with the presets sounds ?
Try with manual mode

Take the problem by the other side :
Start from IC21 and check continuity at every traces around . Replace Q1 and check continuity around (sometimes the part is good but not the connexions around , so problem is the same when replacing by a new part ) . Olso Check Q5 ; and olso try to find if you didn't moove VR2 ?

I don't think MG pot is the problem cause even if MG POT is faulty , MG wheel fully down should turn "off" the MG level .

IC21 is the part who run MG LEVEL .


However if you still believe it's the MG POt , gives us your measures and i will compare , cause your chance is that i've got actually a multimeter and an opened Polysix . :wink:
Hope it will help you

rjd2
Active Member
Active Member
Posts: 301
Joined: Mon Jul 03, 2006 2:23 am

Re: EDIT: what diodes are in a polysix?

Post by rjd2 » Fri Nov 06, 2009 3:54 pm

thanks, cutoffres.

i dont think its the pot. i measured its impedance, its fine. i think it might be the DIODES that are south of the MG MOD switch. they arent giving me the same measurements across them at all. one reads .8M one way, OL the other. the other 1.8M one way, OL the other. they perform identical functions, so i cant see why they shouldnt be behaving identically.

i can check continuity in IC21, but it looks as pristine as any other part of the circuits that were not battery damaged. i've also swapped it for an LM13700, and no difference. i havent checked Q5, but i can look for a sub; im sure i have a tranny here that would work. checking its actual function w/ machine on would be tough because of its locatin.

unfortunately, the programmer portion has now gone backwards. after working properly for days, i must have mistakenly done something. so, i am going to take one step backwards to fix that, and then come back to this VCO MOD issue.

as an aside, the wierd thing is that after i touched up some of the solder joints of R17 and IC22, the problem got BETTER, but not fully solved. but i have checked continuity on EVERY pin of IC"S 30,31,21, 25, and R17, as well as all traces surrounding. the only IC i cant swap out is IC22, so i will now order and cross my fingers....

cutoffres
Junior Member
Junior Member
Posts: 153
Joined: Fri May 15, 2009 2:24 pm
Location: Europe

Re: EDIT: what diodes are in a polysix?

Post by cutoffres » Fri Nov 06, 2009 7:45 pm

i can check continuity in IC21, but it looks as pristine as any other part of the circuits that were not battery damaged
Sometimes the part looks ok but inside it don't works .

but i have checked continuity on EVERY pin of IC"S 30,31,21, 25, and R17, as well as all traces surrounding.
Before replacing IC22 , Don"t forget to replace Q1 , i think Q1 is the transistor who "bypass" the MG .It really could be the source of the problem .
unfortunately, the programmer portion has now gone backwards. after working properly for days, i must have mistakenly done something
Maybe you've accidently cut a trace , be carefull when solder an de-solder IC (place sockets) . When i've repair my first Polysix , i 've add faulty parts when trying to reapirs others :?

Sorry for my bad english , i hope you'll be successfull in your repairs :D

User avatar
cornutt
Moderator
Moderator
Posts: 2117
Joined: Sun Dec 02, 2007 6:03 am
Gear: 6th
Location: Rocket City USA
Contact:

Re: EDIT: what diodes are in a polysix?

Post by cornutt » Sat Nov 07, 2009 1:05 am

rjd2 wrote:thanks, cutoffres.

i dont think its the pot. i measured its impedance, its fine. i think it might be the DIODES that are south of the MG MOD switch. they arent giving me the same measurements across them at all. one reads .8M one way, OL the other. the other 1.8M one way, OL the other. they perform identical functions, so i cant see why they shouldnt be behaving identically.
Are you using a digital voltmeter? If you are, it probably doesn't read diodes accurately because it doesn't apply enough voltage to overcome the diode drop. If your DVM has a "beep if it's conducting" setting, try that; sometimes these settings apply more voltage and will read diodes accurately. Diodes rarely fail "weird"; usually they fail either completely open or completely shorted. If you still have doubts, put your DVM on a voltage setting, get a 9V battery, and put the DVM, the battery, and the diode under test all in series. The diode should read about 8.3V in the forward direction, and of course zero in the reverse direction.

Ordinary silicon diodes are not that different from one another, other than in power dissipation and reverse breakdown voltage, neither of which is important in a typical synth circuit. So if you have a failed one, put in whichever type you have on hand.
Switches, knobs, buttons, LEDs, LCD screens, monitors, keys, mice, jacks, sockets. Now two joysticks!

rjd2
Active Member
Active Member
Posts: 301
Joined: Mon Jul 03, 2006 2:23 am

Re: EDIT: what diodes are in a polysix?

Post by rjd2 » Sat Nov 07, 2009 1:47 am

ok, time to eat some crow:

Q1 on KLM367 board swap seems to have BASICALLY solved it. i never would have guessed in a million years. this is the first time i've seen a transistor fail in the part of a circuit that basically looks brand new. cutoffres, you were totally right; thanks. the wierd part is that its still just FAINTLY modulating VCO; about 5%. barely noticeable. enough that i can live with.

however, the VCA setting of MG MOD still doesnt work. while measuring impedance of a diode that's in circuit is nowhere near a proper means, the huge discrepancy still doesnt seem right.

i have ordered a new 8048 IC; hope that fixes my programmer problem. i couldnt have broken a trace, as i have not been anywhere near the pcb with anything besides my fingers since it was repaired and traces verified.

cutoffres
Junior Member
Junior Member
Posts: 153
Joined: Fri May 15, 2009 2:24 pm
Location: Europe

Re: EDIT: what diodes are in a polysix?

Post by cutoffres » Sat Nov 07, 2009 4:17 pm

Q1 on KLM367 board swap seems to have BASICALLY solved it
You've told Swap , you should replace it by a new one .
the wierd part is that its still just FAINTLY modulating VCO; about 5%. barely noticeable. enough that i can live with.
It's not normal , maybe there's bad trace who goes to Q1 (only 3 trace to check of course )

You're close to fully repair your polysix . :)

Let us know

rjd2
Active Member
Active Member
Posts: 301
Joined: Mon Jul 03, 2006 2:23 am

Re: EDIT: what diodes are in a polysix?

Post by rjd2 » Sat Nov 07, 2009 7:48 pm

for Q1, by swapped, i meant replaced. it was a K30A; by bending the legs i was able to use an mp102. pinouts are different.

yes, getting close! i think the constant reseating of the 8048 might have taken a toll on it. here's hoping, cause every single trace on its socket verifies.

also, is there a transistor that would be responsible for the MG MOD being routed to the VCA? i might want to try to replace it. IC's 21 and 22 are now both new LM13700's, fyi.

rjd2
Active Member
Active Member
Posts: 301
Joined: Mon Jul 03, 2006 2:23 am

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

Post by rjd2 » Sun Nov 15, 2009 8:21 pm

so here's where i am at with this polysix(beside being a TOTAL glutton for punishment):

-all of the manual functions work properly, save for the bleed issue at VCO MG MOD, which i am saving for last issue.

-the programmer portion has some problems:

1-if a preset button is pushed, it "defaults" back to the MANUAL setting, and also i get a very loud, very bad sound at output when it performs this default. (on rare occasions, it will access a preset, but only on certain presets; it also doesnt seem to access the actual settings of the preset, but will remain at the preset's location).

2-if i hold the MANUAL button, and push a preset, i seem to be able to "unlock" the presets; it will then let me push a preset, and it will remain at the setting. i still have the problem of preset's actual sounds not being accessed. furthermore, once i hold the MANUAL button and access a preset, the WRITE button stays flashing until i disable the write function.

3-i can't write to a preset location at all.

i really just am hoping to know this: should i be focused on IC's 30 and 31, the 8048, or elsewhere? the only 2 74LS08's have are in the machine; if i swap 30 for 31, i get no change in results. i have tried swapping IC 25, the 4011 CMOS, but this doesnt change anything either. thanks for the help.

Post Reply