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Some Sources Introduce Distortion on Marantz Receive

swechsler said:
Doesn't look like the amp has a separate preamp board - everything is on the P701 main amp board. I'm a little confused by the fact that it has an STK3062 hybrid power IC, which feeds what appear to be the output transistors. Maybe they used the STK as a preamp, I'm not sure. But if you look at the schematic, you'll see that WS04, which appears to be the main signal, comes from the front panel input selector board, and feeds the STK on P701.
Click to expand...
That's precisely it! They used the STK3062 as the pre-amp section and it seems like the signal does, indeed, come from that board on the front. Also, I noticed how the last stop before leaving that board is the Muting feature which does not work very well. Sound still goes through when Mute is enabled so I'll definitely start with that board on the front. I'll check all the caps and solder joints. I'll also check the transistors while I'm at it and decide whether I'd like to replace that STK. It's a really cheap part on eBay so why not.

Unfortunately, this receiver does not have a Tape In or else I'd feed the DVD player into it and see if that STK was bypassed. There is a DAT In and Out, but I'm not sure that works the same way as a regular Tape In and Out.

Any other ideas of how to proceed?

Thank you so much for all your help so far!
 
Before replacing anything, I'd start by checking the voltages being supplied to the STK (and possibly all the other voltages coming off the power supply). Do you have a scope? If so, trace the signal path and see if you can determine where the distortion is being introduced. I also note it has a set of surround in/out jacks. I didn't see them in the schematic, but they look suspiciously like preamp out/amp in jacks, so if you have a separate amp, you could pull the jumpers and feed the surround output to that amp and see if you still have the distortion.
 
I thought about checking the voltages last week and even got a voltimeter borrowed from a friend, but then I realised I don't know where exactly I should put the probes and what voltages to expect and, unfortunately, I do not have a scope. It would make life A LOT easier.

I'll try using the surround outputs as pre-outs and see if they work like that, thanks for the idea!

Also, today when I turned on the receiver, I had a loud thump on the speakers. Not when I pressed the button, but a few seconds after turning it on. It went like this: Turn On -> Thump -> Relay click. And this happened every time I turned the receiver on. It seems like every day there's something new going on.
 
The voltages are marked on the schematic, but you'd still need to associate that with the actual circuit boards, which I can't help with. Shouldn't be difficult to find the STK connections, though.
 
@swechsler

Finally managed to dedicate some time to the receiver and I'm about to give up tbh. There are some things I did and some that I did not.

I unplugged those bridge connectors on those surround in and out RCAs and the receiver stopped playing sound so I was pretty sure those were, in fact, a pre-out and pre-in. And you were absolutely tight, they actually were! I connected that pre-out to a line in on another receiver and the distortion was still there so I'm really not sure where the issue is. Using that connection, volume and tone controls are bypassed.

I tested further and the issue is definitely with high voltage outputs. I am able to use the same CD1 input for my phone, DVD player, CD player and Chromecast Audio and get different results. The DVD player and Chromecast introduce distortion, my phone and CD player do not. If I lower the output volume on the Chromecast to about 50%, distortion is gone so I am able to fix the clipping by doing that. I measured DCV on the output of each one of those sources and it was consistently higher on the ones that clip.
  • Now, you may say "Well, then the issue is with the receiver not supporting those high output voltages". Well, I would agree, but with CD1 Direct, it works perfectly;
  • So let's see what exactly CD1 Direct does. It bypasses Balance and Source controls, so maybe the issue is there somehow. I cleaned the Balance pot again and it didn't help.
I got to all the boards and, visually, there are no issues with the capacitors. I fixed some solder joints that seemed a bit old and checked the transistors for continuity between the pins. There isn't any so, while that does not confirm that there isn't an issue with the transistors, it's a basic way of checking if there is something obviously wrong.

Next step would be to try checking all the voltages in the right spots and see if that helps me somehow, but the fact that I can get it to play perfectly using CD1 Direct makes me think that checking those measurements is pointless.

Thank you for all your help!
 
swechsler said:
That would appear to rule out a problem with the STK then, since it is in the circuit after the OUT/IN jacks.
Click to expand...
Yes, it definitely does rule out an issue with the STK and, honestly, I wish it was the STK. Hell, I wish it was those two capacitors. Both were cheap and easy fixes.

Now I don't even know what to do.
 
Maybe it's time for a more simplistic solution: add an inexpensive external switchbox so you can hook everything except phono through CD1, and use CD1 direct for everything (except phono).
 
swechsler said:
Maybe it's time for a more simplistic solution: add an inexpensive external switchbox so you can hook everything except phono through CD1, and use CD1 direct for everything (except phono).
Click to expand...
Yep, that has gone through my mind and I even looked at the prices already. I'll need to decide if it's worth the investment. Thank you!
 
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