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Marantz PM 550DC - Sound/Output distortion?

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PhilMcKay

New Member
Hi everyone!

I took a chance on an online auction in NZ for a Marantz PM 550DC Amp that was at a tipshop (like the recycling part of a rubbish dump) knowing that there probably was an issue. The unit's appearance is in great condition and I used Deoxit on the volume and balance knobs (the balance was a little crackly but this fixed it up beautifully).

The main issue is the sound output. At a low volume there is a distortion (I wanted to say crackle but it's not "crackly per say), then as I up the volume control the sound improves, it cleans up a bit but you can tell it just isn't quite right, then lifting the volume more the distortion cuts back through.

Things to note...
  • Using Marantz 8 ohm speakers
  • Both left and right channels have the same distortion, left/right/together
  • Can hear the same distortion using headphones
  • Using the Phono selection
  • Have tried an iPhone through the Aux channel with the same distortion
I thought of a recap so removed the main power caps (6800uf 55V) and both capacitance was 93% and 97% of tolerance. Then the next larger ones I saw 470uf and one of these was a little odd so i replaced both. This didn't make a difference at this stage. Happy to do a full recap (because that seems fun as well haha).

Here is a great site showing the "guts" of it https://insidehifi.blogspot.com/2017/04/marantz-pm-550dc.html

Any ideas before I buy 40+ capacitors would be much appreciated.

Cheers
Phil
 
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Any ideas out there? Should I be replaced the transistors? Or start with a full recap and go from there?

Any suggestion would be most appreciated
 
Just came across this thread. Sorry no one jumped in to help. I'm currently troubleshooting a similar issue with distortion and low volume on both left and right channels. My system is a 2226B which has separate Main In and Pre Outs so I was able to narrow down the issue to the Tone / Preamp board using a sine wave connected to Aux inputs and checking the signal at various points. Here's the link to my work. https://audiokarma.org/forums/index.php?threads/2226b-low-volume-distortion-both-channels.989010/

Have you made any progress at this point?
 
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