I doubt very much that it's the EPROM. They rarely get corrupted. EPROM's are very stable devices. Much more stable than flash.
Get the schematics from the file section and by checking some of the basics.
/mike
From: "lifeisaforeigncountry@... [korgpolyex]" <korgpolyex@yahoogroups.com>
To: korgpolyex@yahoogroups.com
Sent: Wednesday, October 19, 2016 12:25 PM
Subject: [korgpolyex] Dead? Poly 800 mkii
To: korgpolyex@yahoogroups.com
Sent: Wednesday, October 19, 2016 12:25 PM
Subject: [korgpolyex] Dead? Poly 800 mkii
Hello fellow Poly800 users!
I have been talking to Mike via email about my poly 800 mkii issue, but I figured I'd post to the group as well to see if there is any input on the matter.
I picked up an "as is" poly800 mkII on ebay a few weeks ago. The synth wouldn't turn on at all. I opened it up and noticed many parts damaged by poor soldering/repair work in the power supply, namely Q1, which had several damaged traces. I repaired the traces, pulled another 774B from a partially working poly800 I had in my garage as well as a couple diodes and replaced those. The poly800 would power on, but the display reads "9.9.9." in the first 3, 7 segment displays to the left. It makes no sound and generates no midi data. I have tested the power supply and the +5 v calibrates fine, but the -5 volt sits at about -4.7v on boot, and then slowly decays over a couple minutes down to -4.6 and so on. Q1 gets extremely hot as well. I noticed pulling the eeprom on the digital delay board does not change the state of the synth, could it be a bad eeprom?
thanks! any help is appreciated!!
n8