During the last year I bought some Synth modules from E-bay, but I didn't have time to test them yet. One of them was this LFO module. I hooked it up to my newly build power supply and was a bit surprised that the led on the front panel didn't work. I hookup the output to my oscilloscope and there was signal coming from it, but it looked very strange. Like a 50 Hz hum added to all the outputs. When I studied the module closer I found it to be a MFOS VC-LFO (Music From Outer Space) with an Oakley front panel. I found the schematics quite quickly online. Isn't the Internet great for that? :) You can find almost anything on there in just a few second. I love that :) I can remember the old days where this would take weeks or even months.
The first thing I did after that was hook one of the power distribution boards that I got from MOTM to my lab power supply. Measuring on a live circuit always gives the risk of accidentally short circuiting something and this power supply is protected for that. You can also limit the current that can flow so nothing will burn out in case of a problem. The first thing I focused on what why the led didn't work. I put power on the led directly and it lid up, so it wasn't the led itself. One side of the led was connected to the PCB and the other side to the ground. Well I thought it was. Because after some tracing of the front panel wiring I found out that all the grounds were interconnected but there was no actual ground connection to the PCB.
So in the end I just soldered a wire from the front panel ground loop to the PCB and that didn't only solve the led problem but also the other problems I saw with the signal. After that I had a very stable output signal on all connections. In the documentation was also a calibrating procedure so I did that as well. It cost me a good part of the afternoon to solve this, but it always feels very satisfying when it works in the end :) Here you see another picture of the VC-LFO module hooked this time to the new dual power supply I build this morning. On to the next project :)
During the last year I bought some Synth modules from E-bay, but I didn't have time to test them yet. One of them was this LFO module. I hooked it up to my newly build power supply and was a bit surprised that the led on the front panel didn't work. I hookup the output to my oscilloscope and there was signal coming from it, but it looked very strange. Like a 50 Hz hum added to all the outputs. When I studied the module closer I found it to be a MFOS VC-LFO (Music From Outer Space) with an Oakley front panel. I found the schematics quite quickly online. Isn't the Internet great for that? :) You can find almost anything on there in just a few second. I love that :) I can remember the old days where this would take weeks or even months.
The first thing I did after that was hook one of the power distribution boards that I got from MOTM to my lab power supply. Measuring on a live circuit always gives the risk of accidentally short circuiting something and this power supply is protected for that. You can also limit the current that can flow so nothing will burn out in case of a problem. The first thing I focused on what why the led didn't work. I put power on the led directly and it lid up, so it wasn't the led itself. One side of the led was connected to the PCB and the other side to the ground. Well I thought it was. Because after some tracing of the front panel wiring I found out that all the grounds were interconnected but there was no actual ground connection to the PCB.
So in the end I just soldered a wire from the front panel ground loop to the PCB and that didn't only solve the led problem but also the other problems I saw with the signal. After that I had a very stable output signal on all connections. In the documentation was also a calibrating procedure so I did that as well. It cost me a good part of the afternoon to solve this, but it always feels very satisfying when it works in the end :) Here you see another picture of the VC-LFO module hooked this time to the new dual power supply I build this morning. On to the next project :)
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