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Circuitbenders Forum => BENDING TIPS => Circuitbending discussion => Repair advice & questions. => Topic started by: mmoore5553 on January 11, 2019, 01:27:21 AM

Title: korg poly 800 - no power
Post by: mmoore5553 on January 11, 2019, 01:27:21 AM
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.
Title: Re: korg poly 800 - no power
Post by: mmoore5553 on January 12, 2019, 09:37:03 PM
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 ?
Title: Re: korg poly 800 - no power
Post by: mikekvan on June 14, 2019, 05:30:24 PM
I would check all the ribbon cables and make sure they are seated and not damaged. Also make sure all the chips are solidly in their holders. It just takes one pin not making contact!

Capacitors are always a problem on gear this old I would put all new ones in starting with the power supply. Check for a blown fuse.

If everything is working but the sound is aweful you may need to reset the programs with the tape function and a wav file.