I recently acquired a dx7,as expected when I powered up the internal battery was dead so I changed it,then other problems started popping up ,I new I would have to re install the voices as they were corrupt.the first problem was that when I tried to select function 8 to change midi channel it was stuck on no 7 and I can’t change this value either with date slider or ± keys.
Further reading pointed me to the psu. I first changed the rifa capacitor so it didn’t burn my house down,I then re capped the psu board ,I then checked the voltages from the psu, have ± 15 ish volts,then I have 5 ish volts on all the green wires but I only have 1.7v on the white wire.
When I power up now I still can’t get midi to change, keys are intermittent and there’s also a dodgy leaf spring on the keyboard .apart from all this it looks in good condition.im just after some pointers to fix the problems.many thanks ian
I have acquired another working dx7 so I swapped my Psu into the working one and it works fine ,as soon as I put the known working into my dx7 it’s exactly the same .it seems bricked and only randomly lets me select options.would it be worth re capping the main board or is this a waste of time.
Since you have a fully working board you could isolate the issue further by swapping other boards in addition to the psu. If you say, isolate it to the main board, then you can then further refine it by swapping easily removable chips and cables and whatnot and gradually isolate it. You might find just the act of taking it apart and reassembling resolves it. I’ve had so many 80s synths that were buggy as hell and just popping every socketed chip and cable and spraying deoxit resolved it.
1.7V is an unusual number though. Does the known good psu board show that value on that same rail?
Thanks for the reply I have ordered some deoxit so in the mean time I have been checking things . I noticed on the rail with the odd 1.7v that it fluctuates between 1.5-3.5v . I now also have no functioning buttons since pulling out the main board .
In all these years, I’m yet to see a single keyboard that has issues because if the PSU caps. Like none nada zip zero. Not even the Ensoniqs which everyone talks about. Mind that I’m checking the voltages with/without load using oscilloscope. Could be pure luck 
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I Suggest to look for the below if haven’t already
Bad connectors
Incorrectly plugged connectors
Damaged open/shorted lines
Pull the schematics and probe the input matrix and see if the voltages are correct. Most likely you’ll need an oscilloscope for better diagnostics.
All the work above requires the unit to be POWERED ON . HIGH VOLTAGE will be present so do it at your own risk and only if you feel comfortable.
Good luck
I have isolated the problem to the keyboard ,when I unplugged the ribbon cable the dx7 came alive and all buttons worked.i backtracked checking the cable only to find a short on one of the diodes on the key bed.
Would any one know what type I need to get,I think it’s a germanium diode.
There would be no germanium diodes in a DX7. Well done finding that fault though. If it’s in the keybed it would be run of the mill small signal diode. Replace with the most common 1N4148
Thanks I ordered the correct diode and everything is working much appreciated for the advice.ian
Congrats on the repair !