|A-110-1 standard VCO|
Maybe you followed this blog for a while and wondered why I didn't write more about the Doepfer A-110-1 Standard VCO that is shown on some photographs.
Or maybe you don't care.
This module is the first module I bought new It's also the first I fried : I plugged the connector in reverse during one of my trials, before I have a case.
The module began to act odd. Plugging its output to Rings input halted the later. It became very hot.
I stopped everything and began to investigate.
-12V pin of the module connected to an unconnected pin of the bus board, presumably close to ground voltage. Gnd pin was at 12V and 12V pin at 0V. I headed to the A-110 service manual from Doepfer to find out which parts could have been stressed.
I spotted two components that would certainly suffer to be powered in reverse (inversion of the 12V and gnd pins) : the CA3046 transistor array (IC3) and the 78L10 10V regulator (IC5).
|The two components I changed.|
I reckoned the two TL074 op-amps wouldn't have been stressed as they were powered between 0V and a floating voltage that would most certainly be close to 0V. I removed them and tested them on a breadboard : they were OK.
I also checked the TL431 Reference Voltage and it gave me the proper 3V it should. So it was OK as well.
Maybe other transistors were stressed but I have no idea how to verify without desoldering them. The plan is to change the CA3046 and 78L10 first and test the module.
|Calibrating the module.|
Et voila. A quick check at the oscilloscope showed all outputs seemed fine. Maybe only these two components were affected after all.
Finally, I re-calibrated the module, following the service manual, skipping step 1 though (too complex).
I can finally use my VCO. End of the story.