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Marantz 240 - Static/Hiss after hours of listening

ocdecio

ocdecio

The proof of the restoring is in the listening.
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Please watch/listen to the following:

https://drive.google.com/file/d/1KQaOjiNePiHS6m_5IobNnFOXsk87f6GF/view

What type of component would usually be suspect in this case? I don't have a scope to get a waveform for it, but will get one if need be. I am inclined towards the small value caps (the silver mica types) since they are in the signal path. I recently recapped the eletrolytics / film and replaced most transistors including outputs (not the drivers yet - could they be the problem?)

If I turn up the volume it seems to get worse and sometimes a loud "pop" would happen as well.
 
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Is there any reason to change most of the transistors? Are they went bad? As far as I know, it is really hard to find the correct replacement for the transistors used in this series of amp. I may be wrong just curious.
 
I hope your problem is not the oscillation! Did you replace the main filter capacitors? Need some Marantz gurus to chime in here!!!
 
@sanjib I pulled the transistors one by one and checked hFE and if they were off spec I replaced them. For example I had a pair of diffs where they should be around 428 and one was 380 and another around 250. The outputs were all over the place - one 48, the others around 150 almost 200. The latest ones I replaced were more in search of the issue you can listen in the video following the troubleshoot steps. I just now replaced Q510 and Q511, they had like half the hFE of their replacements. I am not yet hearing the hiss/static but it is too early to tell.
 
@sanjib I replaced ALL eletrolytics and for the main filter caps I used two KEMETs 22000uf, 100V, no expense spared.
 
ocdecio said:
@sanjib I pulled the transistors one by one and checked hFE and if they were off spec I replaced them. For example I had a pair of diffs where they should be around 428 and one was 380 and another around 250. The outputs were all over the place - one 48, the others around 150 almost 200. The latest ones I replaced were more in search of the issue you can listen in the video following the troubleshoot steps. I just now replaced Q510 and Q511, they had like half the hFE of their replacements. I am not yet hearing the hiss/static but it is too early to tell.
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:trebon:
 
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