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So I brought a dx7 at auction, I wasn’t too worried if it didn’t work as I was sure it would have an internal battery error,which I have mended before. When it came I changed the battery and also the psu cap before it burnt my house down. I also recapped the psu board as the caps were leaking. When I powered up I had very little button functionality some worked some didn’t so I removed and cleaned but still not working and synth seems to brick and nothing works. I have checked the voltages and are getting +15.27 and -15.09. 5.27v on all the greens then fluctuating voltage on the white cable from 1.5-3.5v . I’m a little stuck now to what to check next. I do have a loan working dx7 and have tried the psu which no difference so was thinking it’s not that . Does anyone have any thoughts of what I should look at next. I was going to try the working main board in the non working to see what happens.
Many thanks for reading
Posted : 13/04/2025 3:08 pm
You don't know how many times I re-read your message up until "burnt my house down". I initially thought the result of your purchase burned down your house and now, homeless, you're working on repairing the keyboard. I'm happy to now, I think, have the correct interpretation that you were proactively fixing the keyboard to prevent the keyboard from failing catastrophically.
Whew - ok.
I imagine the PSU doesn't fluctuate when it's disconnected (i.e. not under load). And that the voltages are within spec under this condition. Use a multimeter to check the current drawn under load for each rail. Check to see if these are in spec. If you don't have the spec - infer what you think is reasonable. Max current for the input voltage could be used as a sort of guide even if you don't have the per-rail breakdown.
On the bench without the keyboard plugged in, you may want to look at the impedance (resistance) between each rail and ground. This is a way to see if the whole rail itself is "shorted" (or near short). If the impedance is relatively high, then there's nothing necessarily static that's the issue.
Then depending on the rail(s) that are having to source too much current - trace through the downstream loads that are tied to these rails and find what's causing the overcurrent. You can do this by lifting pins, isolating chokes/filters (inductors), etc.
To consolidate decades of experience into a single message would be difficult.
Once you tackle the power issues move on to resets. Then move on to clocks. I'm assuming you have the service manual.
Current Yamaha Synthesizers: Montage Classic 7, Motif XF6, S90XS, MO6, EX5R
Posted : 15/04/2025 9:46 pm
