Marantz PM5000 DC offset voltage > protect mode

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#42
Wow! Some of the worst advice I have ever seen for diagnosing a defective power amp.

#1 is test EVERY device in-circuit with power OFF. Back in the 70s I used an $10 RS analog multimeter for screening. Look for short/open/leakage. Using a DVM in Ohmmeter/diode mode, BJT measure approx 0.5 volt B-C and B-E. C-E should be open. I prefer an Octopus/ component tester or a REAL curve tracer.

#2 Remove any device your in-circuit testing was unable to screen due to surrounding devices and do a REAL test. Todays Digital Component testers are hit or miss. Most are garbage. None will find a "leaky" or failing power BJT or MOSFET. You can make a test jig or a curve tracer. They cost nothing next to your wasted time.

#3 NEVER turn on power until your fairly sure you found EVERY bad device or your replacements will just go up in smoke...
 
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#43
We have different troubleshooting styes. I prefer powered diagnostic testing.

My observation is that blindly removing each component for out-of-circuit testing often causes damage in the process and is exceedingly laborious. Owner has already had power on his amp, so defect is relatively minor. Does your mechanic remove each engine part for on-bench-testing before he restarts the engine? How about your doctor and surgeon?
 
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#44
Where do I say remove every component? I can check the vast majority of semiconductors in-circuit using a DVM but I much rather use a curve tracer in I/V mode. Measuring voltages in defective power amps with multiple feedback paths and high open-loop gain generally won't point to all the bad devices. Does the original poster even know how semiconductors work and how they are biased? Will he know where to buy parts that aren't counterfeit?

Turning power on after you replace output components but BEFORE confirming you found every bad device is almost guaranteed to blow up what you replaced. This is a simple amp. Try doing it to a complicated amp.

If a mechanic only replaces some of the bad components in a transmission or engine a lot of time and money was wasted because he has to start all over...
 
#46

busaboy seriously ?​

if you are really here to help me for this repair please go ahead to details (though first read what was posted, because reading your comments seems you have not or don't care)
BUT
if you are just here to be disrespectful to BSST or other personn who is kind to try helping me effectively in this repair > go along your path !

to conclude, my words are not open to debate in this subject which is about succeeding this repair not about being rude nor giving lessons to others on supposed best repair technics...
thanks in advance to end of the argument
 
#47
this is the Q6028 and Q6027 tests and we have a suspect !

i swapped Q6027 and Q6028 and guess what ?

High DC is now on right chanel with Q6027 ! confirmation Q6027 culprit 👍

time to find some replacement for this 2SA1266 and change all (need 4) for peace of mind and maybe their pair 2SC3198 ?

thanks again for your kind help BSST :worship:
 

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