Roland SH-101 analog synth repair

[beatnik]

in my case the transformer was damaged but in your case it might be something else

first of all you need to make sure the external power adapter is working properly and giving enough current

then you should isolate the power supply section from the rest of the circuit and determine what causes the voltage to drop

if i remember correctly the power supply voltage rails have jumper wires that can allow you to disconnect sections without having to cut the traces

you might find that a specific section of the synthesizer is causing excessive load to the power supply

good luck

 

[MRatton]

Thank you for the reply.
Sure. That´s what I did, and so I found diode D8 in short! (wonder what they did with this synth)
But the voltages are not ok. IC2 is hot, and its ouput voltages seem to be wrong (+6V  instead of +5V; -2V instead of -5V). And IC1 is providing 5.8V instead of 4.5V (to the CPU). I will try to find this IC and replace them.

Also, the CPU does not show activity, but the Reset pin is at 3.2V (seems lower than normal). I will check more things (I hope it still can run again!)

In case of damaged CPU, there is a company in Germany that sells an upgrade kit to replace the original CPU (a bit expensive): https://tubbutec.de

Anyway, thank you for your support. I will post the news.

All the best!