Yamaha DX7 s 88 in led display and squares in lcd

I have a Yamaha DX7 s that can not boot.

It lights up but it freezes with 88 in led display and squares in lcd.

I have investigated a bit. There is some treads on the internet that suggests that it is caused by a bad 9.4265 MHz Crystal.
I have checked the crystal with my oscilloscope and it is working.
I tried to pull out the EPROM and start the dx7s without it. It reacted å bit different. It had other numbers in the display. I have not checked all the pins on the EPROM.

Can the EPROM go bad?
Has anyone encountered similar problems?



You may want to check the power supply voltages and make sure they’re ok. The power supply provides +5 VDC, +15 VDC and -15 VDC. The unit very old and the power supply caps may have leaked or dried out and may need to be changed. The service manual and schematic is available for download.


Thanks you for replying, Pat.

I forgot to mention that I have checked the power supply. It has the correct values. I guess the next step is to look for bad connections and solder joints


Roms can definitely go bad… Do you have a reader/programmer to see if you can read them? I would think that’s unlikely, but it is possible. Reseating the ROMs didn’t help? I have an original DX7 (non-S) and could copy the roms, but I doubt the S would be compatible. Also, EPROMs would probably have a slightly different pinout than the original mask ROMS (just guessing here) so an interface socket would have to be devised. Hopefully you could at least verify the roms before going down any of that route. Maybe use your scope to see if the address and data lines are at least pulsing on the roms? That would at least tell you if you have a line stuck, and/or that the CPU is really trying to read from the ROMs and may give you some hints.

Thank you!

I have not have time, but I will check with the scope. The S ROM is not compatible with the MKi ones. I think I might find one on ebay though.

I will report back