[SOLVED] Stuck on a dead end trying to fix a Roland D50 keyboard

[poot36]

If all the input pins to the DAC have data going to them that is a good sign.  It looks like the longer pulses are for the sound and the shorter ones are data between the chorus and reverb IC.  I wonder if the sound is coming from the circuit attached to pin 20 of the DAC.  Try disconnecting R6 and see if that changes the sound.

[gkmaia]

FINALLY!!! After months I could finally get my hands on a mother board!

Thing is, no one knows if it works... so lets see. If it works I will be able to compare signals coming and going from my old board and confirm if the chorus is really dead!

[gkmaia]

The outcome is... the chorus IC was faulty. Replaced the IC and it is working perfectly now.

The D50 EPROM throws a start up routine where the CPU checks if the Gate array, Synth & dyna board INTs are present. Then the Gate array also checks if reverb and chorus are present. If they are all present the CPU boots up.

As the chorus was still sending I/O data the CPU (even if corrupted) the boot routine could not detect it's fault. And that made the whole diagnosis very tricky. I think there is no worse thing than an IC that only fails partially.

[shakalnokturn]

Happy ending... congratulations for being so stubborn at this!
I just noticed the Panasonic logo on the PCB, I didn't know Roland and Panasonic has anything to do with each other. Do you know any history behind this? Maybe a rebranded Technics synth or a co-designed model?

[gkmaia]

Happy ending... congratulations for being so stubborn at this!
I just noticed the Panasonic logo on the PCB, I didn't know Roland and Panasonic has anything to do with each other. Do you know any history behind this? Maybe a rebranded Technics synth or a co-designed model?

It was a nice ride. Learned heaps about this PCB. Great that now I managed to source 4 working CPUs and a bunch of working ASICs plus a few extra gate arrays.