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I have read the whole string from this post --- https://music-electronics-forum.com/...ection-circuit
I had a yamaha 512sc come in. No power up. repaired the SMPS. New R440 IC 402 and another resistor. Power supply will power up and +15/-15 good.
Now the dreaded 2-3 second power off protection circuit problem. Have removed the DC pin 11connection. unit runs fine. There is a 10 volt dc voltage on the DC pin11 after 2-3 seconds which set the protection circuit protocol and shuts the unit down.
I have tried with the temp jumpers for the grounding regimen with GA and GB and ribbon cables etc connected still same problem. I have measured resistance at all the ground locations. Front panel, back panel, fan case, metal straps, Grnd pin 2 of mixer ands PA ribbon cable both ends and The PA pins 5 and 9 and Mixer cable pins 5 and 7 and i get 1.1 to .6 ohms resistance between all the grounds. have completely assembled the unit with all screws and grounds in place.
PA +15 and -15 not shorted to ground. all the matching transistors on the PA have the same BE and BC forward and reverse bias resistance measurements on board.
Need some guidance on what might be the culprit and how to diagnose since it will only stay up for 23-3 seconds.
Though about making a temp ribbon cable with DC pin eleven omitted and bench powering the SMPS powersupply and PA board to measure voltages/waveforms
I had a yamaha 512sc come in. No power up. repaired the SMPS. New R440 IC 402 and another resistor. Power supply will power up and +15/-15 good.
Now the dreaded 2-3 second power off protection circuit problem. Have removed the DC pin 11connection. unit runs fine. There is a 10 volt dc voltage on the DC pin11 after 2-3 seconds which set the protection circuit protocol and shuts the unit down.
I have tried with the temp jumpers for the grounding regimen with GA and GB and ribbon cables etc connected still same problem. I have measured resistance at all the ground locations. Front panel, back panel, fan case, metal straps, Grnd pin 2 of mixer ands PA ribbon cable both ends and The PA pins 5 and 9 and Mixer cable pins 5 and 7 and i get 1.1 to .6 ohms resistance between all the grounds. have completely assembled the unit with all screws and grounds in place.
PA +15 and -15 not shorted to ground. all the matching transistors on the PA have the same BE and BC forward and reverse bias resistance measurements on board.
Need some guidance on what might be the culprit and how to diagnose since it will only stay up for 23-3 seconds.
Though about making a temp ribbon cable with DC pin eleven omitted and bench powering the SMPS powersupply and PA board to measure voltages/waveforms