I have a Yamaha MX-600U stuck in protect mode.
I've tested the output transistors, rail voltage, capacitors, ect... and all tests good. So I believe I've narrowed the problem down to the protection circuit itself. I'm not getting any power to the relay. Zener diodes Q31, Q32 and Q33 test good. Would greatly appreciate any help diagnosing the circuit.
I've tested the output transistors, rail voltage, capacitors, ect... and all tests good. So I believe I've narrowed the problem down to the protection circuit itself. I'm not getting any power to the relay. Zener diodes Q31, Q32 and Q33 test good. Would greatly appreciate any help diagnosing the circuit.
Hi Chopperbuilder,
I've copied a post from the other thread. Much of the post deals with exercising the protection circuit.
Just to confirm, both channels show only a few mV offset error at amp outputs and both amps show nominal bias currents adjusted via VR3 and VR4--- right? If so, good reason to believe amps are OK and problem is within protection circuit.
A few simple tests to localize the trouble spot within the protection section; please advise when behavior departs from what's projected, and we'll evolve test.
I assume the Protection LED is lit?
Make sure there are no speakers load or dummy loads connected.
Connect a jumper across Q40 collector to emitter. Relay RY1 should energize and the Protect LED should go dark. If this test is successful, remove Q40 jumper.
Short Q37 base to ground. After a few seconds, relay should energize and Protect LED should go dark. If this happens, the issue is likely associated with Q31 through Q36. To further localize, please measure voltages across R99 and R100. If more than a few mV are present, the problem is with the associated Q31 or Q32. Otherwise, with the other transistors and we'll troubleshoot further.
I've copied a post from the other thread. Much of the post deals with exercising the protection circuit.
Just to confirm, both channels show only a few mV offset error at amp outputs and both amps show nominal bias currents adjusted via VR3 and VR4--- right? If so, good reason to believe amps are OK and problem is within protection circuit.
I'm not understanding what's being said here. There needs to be +64V present at the protection circuit, and -63V available to the MAIN(6) board. If you have trouble establishing that or if there's something about power switch, please clarify.
A few simple tests to localize the trouble spot within the protection section; please advise when behavior departs from what's projected, and we'll evolve test.
I assume the Protection LED is lit?
Make sure there are no speakers load or dummy loads connected.
Connect a jumper across Q40 collector to emitter. Relay RY1 should energize and the Protect LED should go dark. If this test is successful, remove Q40 jumper.
Short Q37 base to ground. After a few seconds, relay should energize and Protect LED should go dark. If this happens, the issue is likely associated with Q31 through Q36. To further localize, please measure voltages across R99 and R100. If more than a few mV are present, the problem is with the associated Q31 or Q32. Otherwise, with the other transistors and we'll troubleshoot further.