Recovering a Failed EPROM
I purchased a non-working Ensoniq KS-32 MIDI keyboard earlier this year. My plan was to steal the keybed for another project, but it seemed to show faint signs of life, and has a nice hammer-action keybed, so I decided to have a go at repairing it. When I pressed front panel buttons, the LCD would identify them, as if it was stuck in some sort of test mode. This unit has a front panel/LCD PC board, in addition to the main PC bd with the 68000 CPU, sound chips, etc. I determined that the main board was not working, and was sending nothing to the LCD board. When stand-alone, the LCD board enters a factory test mode so that the LCD and buttons can be tested. I had no schematic for the main board and was not sure what to do next, but I noticed that the upper and lower code EPROMs had checksums on their labels, so I decided to read them and verify the checksums. The first EPROM checksum matched the label but the second one did not. Aha! I tried to find an image on the web for these EPROMs, with no luck. I had heard that EPROMs can lose their data after 15-20 years, and knew that running them at different voltages can sometimes affect how they read, so I decided to try an experiment. I bent out the power pin on an IC socket that was the same size as the bad EPROM, so that it could be connected separately. Then I plugged the EPROM into the socket and the socket into my EPROM programmer. I connected the power pin of the socket to a bench power supply, and set it to 5V. I read the EPROM data and noted that the checksum was still incorrect. Then I set the power supply to 4.5V and read the EPROM data again. The data and checksum were different, but still didn't match. I lowered the power supply to 4.0 volts and re-read the EPROM. This time the checksum matched what was on the label. I programmed a fresh EPROM with this data, re-installed the EPROMs, and powered on the KS-32. It came right up and has worked fine ever since. This is the first time I have ever tried using this technique to read flaky EPROMs.
Here is an archive containing upper and lower EPROM images for an Ensoniq KS-32 MIDI Music Keyboard, code V3.00, in Intel Hex format, and also in binary format.
Here is an archive containing upper and lower EPROM images for an Ensoniq KS-32 MIDI Music Keyboard, code V3.01, in Intel Hex format, and also in binary format.
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