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korg poly 800

Posted: Fri Jan 11, 2019 2:20 am
by mmoore5553
I received a korg poly 800 and happy to get it back working. I am unable to power it on via the cord or battery. I did find the schematic and just started to look at it. I am needing help on getting it back to life.

I did check the voltage on the jack and have 11.7 volts. I then went and checked the diode -d2- as it had 11.7 volts coming out. I did unplug the unit and check the diode with continuity check and it looked good - infinite one direction and 576 in another. They were not the same so i went on to troubleshooting. I have limited skills on what to check but if you give me directions i can do whatever. I then looked at q1. I used the ground with the resistor and then measure the pins. I have 11.7 on one pin , 11.7 on the other pin , and then no volts. I thought that was odd.

I am not sure what to check next . I do not know how to check if the transistor is good or not. Any help would be appreciated. I hate to throw this away.

Also i noticed d1 was hooked to two double A batteries. I measured and got 3.17 volts. i thought it was odd there was not a diode present.

Re: korg poly 800

Posted: Fri Jan 11, 2019 4:20 pm
by meatballfulton
The AA batteries are some sort of modification. Perhaps someone trying to use it as memory backup instead of a button cell. Sounds like osomebody has been playing around with it.

Re: korg poly 800

Posted: Fri Jan 11, 2019 9:05 pm
by mmoore5553
I talked to the owner and he said he did not modify it. He just said he used it for years and then all of a sudden it stopped working. He just kept it all these years. I said i would look at it and try to fix it and he gave it to me.

I am hoping to get it working

Re: korg poly 800

Posted: Sat Jan 12, 2019 10:38 pm
by mmoore5553
I took another look and it appears I am not getting five volts out of q1. I did check r5 and r6 for 5 volts and nothing. I did check d4 with meter on continuity and it showed almost the same when switching leads -756, I would think that is bad. Would you say that is bad ? I did check voltage and had 11 volts in on one side and nothing on the other.

any one have any ideas ?

Re: korg poly 800

Posted: Sat Jan 12, 2019 11:01 pm
by Mooger5
this old thread should help. viewtopic.php?f=5&t=102594&hilit=poly+800+power

iirc it turned out to be oxidized contacts in the power connector switch

good luck