Hi guys, I’m hoping that someone can assist me with getting my recently acquired D-10 back working as it should?
This unit has some dead buttons typical tact switch failure which I will address when replacements arrive. Dead keys on main keyboard have been fixed after it proved to be a failed trace which I have jumpered around.
For testing I have several multimeters, a 8ch USB logic analyser and the service manual. Unfortunately no oscilloscope, though I’ve a couple of Arduino’s that could do something rudimentary if necessary.
The main problem is distorted output on line out and headphones.
I would describe the distortion as digital sounding - affecting different patches to varying degrees - the more HF harmonic content the more pronounced and interestingly with louder sounds the distortion is less pronounced. When sounds decay and fades away there’s a lot of noise, which I wondered if was the reverb gone bad - disabling reverb on the patch had little effect. Creating a basic SQU or SAW patch then at lower frequencies the distortion is not terrible, as you go up the keys the character of it changes.
I’ve some audio recordings here if that helps (onboard reverb is off)
SynBass
EchoBells
This main board has soldered v1.10 ROMS so I assume a later rev than earlier ones with socketed ROMS
Voltages seem ok from the PSU at +12.02v, -12.08v and +4.96v. Theres also IC34 79L005 that is outputting -5.03v for the IC37 74HC401
CPU was pulled from socket and pins checked and cleaned.
All connectors cleaned and re-seated.
On-board battery changed - synth initialised and factory banks uploaded over MIDI
Electrolytic caps visibly inspected, none bulging etc.
If I listen at TP5 to the PCM54HP DAC output the distortion is present there (though TP5 is after an M5238FP op amp so I suppose that could be bad) and this is before the IC37 74HC4051 which is used as S/H de-glitcher / multiplexer. That makes me feel its an issue before the analog audio output stage
Investigation on the ’net has brought up several possibilities:
PCM54HP DAC gone bad (I have a replacement on hand)
uPD41416 DRAM known to fail - though this ram appears to be used for the reverb chip. I’ve got some MN4264-12 replacements on the way just in case.
I have connected the logic probe to the DAC inputs and there is data getting to it suggesting pcb traces ok. I’ve also confirmed that there’s activity on the RAS/CAS/WE and DATA pins of the DRAM.
Looking at the system block diagram I imagine the IC32 reverb chip grabs passing data from the IC25 synth chip when it sends to the DAC, which it then processes. I assume the data arriving at the DAC is alternated between the synth chip and reverb chip, and the output of the DAC is switched to the amps via
Should I change the DAC (add a socket first?)
How likely is the distortion to be a bad M5238FP op-amp ?
Should I change the reverb DRAM (and socket them also) ?
Any thoughts and suggestions gratefully received!
Nick