Originally Posted by rb20
This thread got me to a solution and I wish to share it as with the MC12B ageing, a failing power supply may well happen more and more often.
I tried to find the original power supply but it's been discontinued, so I contacted the local agent for Lexicon. They will not sell the power supply, but want the unit to be shipped in. Costs are anything upward from Euro 550 ($620) excl. shipping as they insist on doing a full check of the unit and will not just replace the power supply... So, considering my previous experience with them, the actual costs will be higher for sure.
This caused me to search for a replacement power supply with the same spec. It is the: Mean Well PQ-100C which cost me Euro 45 ($50) including DHL shipping. Exchanging it for the old power supply was simple.
I was pleasantly surprised that the sound was immediately noticeably much better as well. I guess the old power supply had been degrading slowly over a longer period of time.
I have the same problem with the power supply of my Lexicon MC-12B. The preamplifier works fine for a long time if I use just the standby button to "turn off", but when I turn off in the switch in back, and then turn on the switch again, the device starts performing the diagnostics and the tests fortunately are successful, but there is not sound in the outputs, just one low noise output on the analog channel.
If I want to turn it on again and make the Lexicon work, I have to unplug the cable on the back and connect again. I openned the MC-12 to look at the electrolytic capacitors of the power supply and so I realized that none of them seemed to be leaked or stuffed.
I read in this forum that there is the problem in the original power supply. You said that you were successful in replacing the old power supply with the new PS Mean Well PQ-100C. I know there is the option for the EOS LFVLT110-4302 power supply, but I already have the Mean Well. I have doubts about how connecting the cables to the pins. I read the datasheet from Mean Well PQ-100C and I saw that it was apparently equivalent with the Shindengen FYX 900 / 73P-BEbe (the old one).
So I took the schematic drawing of Mean Well PS PQ-100C from the manufacturer's data sheet and marked the wires with their corresponding colors of the MC-12 cables. Maybe you can help me to understand if the colors of the drawing that I posted matches the connections you made on your device.