DX7 strange behavior


I wonder if any of you could help me with this DX7 mk1 problem.

It har the grey matter E! card installed.

The problem
When I turn the DX7 on it works fine fro 5 to 10 minutes. All of a sudden it stops making sound and behaves like I was moving the data slider fast ut and down. If I reboot the synth it still has the error, but if I let it cool down before I start it it works for a couple of minutes again.

Tried Solution
Both slider are bad. Volume maskes a lot og noise and the data slider is a bit unreliable . I will change them out. I thought the the problem was caused by bad connections in the data slider, so I desoldered the slider and use the + and - buttons to navigate. But, the problem persists.

It might be a temperature issue, but I don’t know where to look to find errors like this.

Any hints and tips are mush appreciated.


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Acts like overheating problem. My guess is that thermal paste (typically white lithium grease) on heat sinks has dried out. I would (with power unplugged of course) remove each heat sink (hopefilly attached with a screw), wipe off old dry residue (alcohol swab may help), apply new heat sink compound, just enough to coat matching surfaces of components and heat sinks (avoid excess paste oozing out), and reattach sinks. Start looking in the power supply board section on voltage regulators. Also power amplification components. The heat sinks are typically black or bare metal colors and may have heat dissipation fins or grooves (like in power amp curcuitry).

Sorry I don’t have images or schematics to circle the heat sinks for reference. In any case, no component should be too hot to touch. So finger touching top of each component should identify any overheating. Good luck.

Thanks for replying! I actually thought it had to be something on the main board. Reading your suggestions I touched the heat sink on the transistor closest to the main board on the power supply.
There was a small spark on one of the legs of the transistor and the error appeared immediately.

It might only need at resolder. I’ll come back with a report when it is done.

I resoldered the transistors on the power PCB. Its been on for many hours and still works!!! HURRAH!

Thanks for the suggestion @MultiMuse

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