Yamaha DX7 Has one sound, but the displays are crazy


I have a DX7 MK1 and it was working sometime ago. Now, when I power UP, the led display shows 88 for a while and then 2. The lcd shows a small shaddow on the firs line. Clicking the keys to change sound, seems on LCD that something is happening, but the display only show the number 2. Checked and changed power regulators on power supply. The voltages are ok 5V, +15V and -15V. Battery is OK. Checked and the tensions/signals are arriving from buttons board to main board.

Any other tip?



Most likely memory battery is flat. You need to change it, reload the factory sounds via sysex or cartridge and then reset the global parameters.

All Yamaha DX’s have time expired capacitors. i.e. the electrolyte of that generation is corrosive and eats the capacitor internals making them unreliable. This causes high currents and brown outs.

as synzoneau said, replace the 3 volt battery. If you have to unsolder the Panasonic coin cells, Digikey and Mouser still carry them (when I last looked last year)

if you have a modded unit using regular coin cells, replace it and reset the system as synzoneau said.

If your unit has not replaced at least the power supply capacitors, plan for it.

The Rifa safety caps in the AC input section should be split open and expanded by now. They must be changed so the unit doesn’t electrocute you. If your unit is turned off, and you plug it in, and it turns on, that how you know the Rifa caps are shorted. Then its an electrocution AND fire hazard.

The tantalum capacitors are notorious for failing. many times they fail internally with no external signs, or else they explode in flames. Have a real good look for any signs of capacitor failure.

Chips fail because of static shock, or power supply instability from failing caps. If its a failed memory chip, lets hope not.


Thank you guys for the answers, but I could manage to work it out.

I started checking the diagram and since it can play one sound, I realized that the Main CPU and Sub CPU where working fine (Oscillators and processing). Checked all tensions on main chips and they are ok.

When I bought the keyboar it was on a very bad condition and there was a lot of bad contacts on the connectors (main board). Just associated the problem started just before I ressolder all the conectors and I find out two pins from LCD accidentally soldered together. I have removed the “jumpers” and it come back to live.

So, at the End, the problem was caused by myself…

Thank you again guys.


Adailton / Brazil