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Some Sources Introduce Distortion on Marantz Receive

dastinger

dastinger

Member
Hey guys,


The original issue in this thread evolved, so I asked the mods to update the title. If you’d like to read the original problem I had, please read below this edit.

I cleaned the pots and relays, checked the two big capacitors on the picture (they measured just fine), cleaned all the boards and fixed some solder joints that looked old.

Right now, I get sound from both channels form the get go, but some sources introduce clipping both on headphones and speakers. Those sources (DVD player and Chromecast Audio) work perfectly on other receivers and the distortion is introduced independently of which line input it is connected to. Turntable, smartphone or other CD player works fine.

CD1 Direct Mode fixes the distortion. Eg.: Chromecast Audio connected to CD1 input without CD1 Direct mode distorts. With CD1 Direct Mode it doesn’t. CD1 Direct bypasses balance and Source controls so maybe the issue is in there somewhere?

I also tried connecting a pre-out to a line input on another receiver. Distortion still there.

I don’t have a scope, unfortunately. If you guys have any ideas of what I could do further, please advise.

Thank you all!

Previously -

"Yesterday I was going through stuff in the garage and found out a long forgotten Marantz PM-65AV that was not used probably since around 2005. I started searching for its specs and realised that it is quite a bit better than the Marantz I use on my main budget music system, to my delight, so I promptly cleaned it up and tested it.

Main issues:
  • Left channel distorts until I mess around with the volume knob for a bit;
  • Right channel only starts playing after the volume knob passes a certain position (maybe 9/10 o'clock).
There are few things to point out:
  • This only happens when the receiver is first turned on;
  • Once I get rid of the distortion and/or the right channel kicks in, it plays fine for hours;
  • The right channel issue happens at all times. The distortion only some times;
  • Some times it happens both on headphones and speakers. Some times only on the speakers;
  • There doesn't seem to be any channel imbalance. At least to my hearing. I played a Mono record to test and the sound is perfectly centered.
I opened it up and didn't see anything relevant other than what looked like leakage from the main Elna capacitors:"

q4Ma1uG.jpg


But, after reading a bit about this, it looks like that's not leakage. Instead, it's a glue manufacturers used on these? Is this accurate?

So, what exactly is it advisable to do? I'm tech savvy, but not enough to be able to identify potential issues on a receiver. Maybe using deoxit on the volume knob? Is the knobs the only thing I should clean with deoxit, if that is even advisable to do?

Thanks for reading, everyone!
 
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Here try this, exercise all of the controls this could get you back up and running until a proper cleaning can be performed. By this I mean turn all of the knobs back and forth repeatedly a dozen times or more, the same with all the switches etc. Keeping the controls exercised is advisable even when clean, it helps keep them that way.

Perform this task with the amplifier off.
 
Yeah, that's glue not leakage.

Far as cleaning the volume control, possibly if they are mechanical-type controls. If the volume knob is some type of rotary encoder cleaning.innthe traditional sense may not apply.

Also, if there are relays that switch on the outputs, could be the relay contacts are a bit dirty or damaged.
 
Thank you @Grenadeslio !

I did that and didn't help much. When I turned it on this morning, same thing happened. No sound on the right channel until a certain volume level was met.

But something different happened. Today, the right channel distorts/has noise randomly. So, I can play a passage with distortion/noise on the right channel, bring the stylus back, play it again and it's all good. Again, messing with the volume knob seems to help.

I'll test a lot more thoroughly throughout the day. To see if, for some reason, the distortion stops happening after the receiver warms up, for example.

All help is appreciated. I'm really enjoying the sound this unit produces. The low end is a little bit too loose for my liking, but everything else makes it worth it, so I'd really love to see it issue free. With the quarantine, time is what I have the most in my hands so I can mess around with it.
 
whoaru99 said:
Yeah, that's glue not leakage.

Far as cleaning the volume control, possibly if they are mechanical-type controls. If the volume knob is some type of rotary encoder cleaning.innthe traditional sense may not apply.

Also, if there are relays that switch on the outputs, could be the relay contacts are a bit dirty or damaged.
Click to expand...
Thank you for your reply! Saw it after my previous reply so I'm sorry for double posting. There's new info so you might want to read it.

I'm not sure how to check if the knob is rotary or not. Any way I can check and let you know? Same applies to the relay contacts. Again, thank you.
 
This receiver dates back to 1989. All the controls are analog. I think you'd be best served by cleaning all the controls and switches, including the selector switch, with Deoxit. Another possibly could be dirty contacts on the speaker relay, which is a bit more difficult, although theoretically you could use Deoxit on those as well, if you can get inside the relay.
 
Thank you so much, @swechsler!

I will get some contact cleaner today or tomorrow and will clean all the knobs and switches.

I hope this isn't much to ask, but if I get some pictures from the inside, would it help identifying what I could clean to improve it?

-----

Now, some updates.

I have been playing music non-stop for about 3 hours now. I didn't experience any more issues so it seems that once the problem is "fixed", it doesn't come back until I power the receiver off and on again. Does knowing this rings any bells to what it might actually be?
 
Poor, intermittent contact somewhere. The old pots on my Heathkit tube amps create distortion unless exercised back and forth a few times. They probably need cleaning and lubrication. It could also be a switch, of which a relay is a type. Clean the pots and switch contacts. Tired springs keeping contact on a rotary switch (source selection) causes the no-sound symptom for me occasionally, too.
 
sqlsavior said:
Poor, intermittent contact somewhere. The old pots on my Heathkit tube amps create distortion unless exercised back and forth a few times. They probably need cleaning and lubrication. It could also be a switch, of which a relay is a type. Clean the pots and switch contacts. Tired springs keeping contact on a rotary switch (source selection) causes the no-sound symptom for me occasionally, too.
Click to expand...
Thank you so much!

The rotary selector moves a kind of a flat wire along a piece of plastic when I turn it. Where exactly should I apply Deoxit?

I totally forgot that tomorrow is a holiday so everything's closed. I'll probably won't be able to get Deoxit until Monday but, when I do, I'll clean the pots of every knob, the rotary knob of the source selection (if someone enlightens me about it), all the switches and I'll also try getting to the speaker relay.

I can confirm that the receiver worked great throughout all afternoon. But, at night, I tried turning it on again to see how it'd behave and, even though the sound came out of both speakers equally and immediately without any fiddling, it was distorted on both channels. I didn't spend too much time on it, but I couldn't fix it this time.

If you guys have any other ideas other than cleaning it (which I will do regardless), please come forward. Looking forward to your help on trying to fix this unit.

Again, thank you everyone who chimed in so far!
 
faber12 said:
This! Replacing relays has fixed a few amps/receivers for me.

Absolutely clean any switches and pots as well.
Click to expand...
Thank you so much for your reply!

I managed to get Deoxit and I'm about to go in to clean.

I have a question, though. The issues that initially made me open this topic seems to have been fixed now. Every time I turn on the receiver, even after one night with it off, the sound comes out of both speakers immediately. The issue now is distortion. The sound is distorted on both channels and messing with the knobs doesn't help at all. What I'd like to ask is: These issues always occurred both on the speakers AND on the headphones connected to the headphone port. You keep talking about cleaning the speaker relay. Doesn't that affect the sound coming out of the speakers only? If the issue is present on headphones, doesn't that mean that it is probably due to something else other than dirty/damaged speaker relays?
 
I don't know if the headphone jack goes through the relay, but it wouldn't surprise me if it did - the relay is there to protect the speakers from the initial turnon thumps that most amps experience; headphones would be subject to those same thumps. At any rate, it could be one of the switches that's causing the distortion. It could also be caused by caps going bad, or something else. But cleaning switches and relays is an easy and inexpensive fix. If that doesn't work, then you've gotten into the realm of repairs that may not be cost effective (especially since this is a Prologic amp, and so has little market value).
 
swechsler said:
I don't know if the headphone jack goes through the relay, but it wouldn't surprise me if it did - the relay is there to protect the speakers from the initial turnon thumps that most amps experience; headphones would be subject to those same thumps. At any rate, it could be one of the switches that's causing the distortion. It could also be caused by caps going bad, or something else. But cleaning switches and relays is an easy and inexpensive fix. If that doesn't work, then you've gotten into the realm of repairs that may not be cost effective (especially since this is a Prologic amp, and so has little market value).
Click to expand...
Thank you so much for following up with me.

I spent the last two hours or so thoroughly cleaning everything. I cleaned every pot using Deoxit. I cleaned the switches and the source selector also with Deoxit. I got to the speaker relays and went at it too with a piece of paper wet with Deoxit.

Some things of note:
  1. Before I started cleaning, I connected my phone to the receiver (RCA - Jack) and tested with headphones. Right channel was out, distortion still present. After I cranked up the volume (the turning point seemed to be around 12 o'clock), right channel came on. Still distorted;
  2. After I cleaned, everything was normal. Both channels on, no distortion. Turned it off and on a couple of times, switched sources, pressed every button, turned every knob, experimented with different sources. All good. I honestly thought I fixed it for a second;
  3. Top case on, everything screwed together. Connected it to my system upstairs and.... Distortion both on the headphones and speakers.
So yeh, I don't think this is fixable by simply cleaning pots and relays. There's something else going on and I don't know enough about receivers to realise what it is.

I know this has a low market value so it's not worth to fix if parts are expensive. I honestly wanted it to work because it has less harmonic distortion, better SNR and better frequency response than the Marantz I used. More importantly, the phono stage sounded better. It was nice finding out a long forgotten receiver that I could use again.

So, if anyone has any idea of what it might be or if there's something I can look for, please let me know. I'd be willing to spend a bit of time testing this out if it's easy enough. And, if it ends up not being too expensive to fix, I might do it.

Thank you everyone!
 
These intermittent issues are the worst. It sounds like you either have a component that's intermittent, exacerbated by moving the amp around. That or a bad solder joint. Possibly someone who's more well versed in this sort of repair will chime in.
 
@swechsler

Thank you once again!

I took the opportunity to check most of the solders and capacitors (some were inaccessible) and everything looked in perfect order. I'll probably check every capacitor with a multimeter though. In the mean time, I'd love if someone that's used to this kind of repairs would chime in.
 
I managed to record 4 samples so you can understand what's going on. I can confirm that the channels do not go out anymore. I hadn't turned the receiver on for 2 days now and both channels worked right from the get go. That didn't happen before so I guess cleaning made a difference. The distortion is there though.

The clips are as follows:

Love Supreme PM-65AV - FAULTY
Love Supreme SR-73

Umek PM-65AV - FAULTY
Umek SR-73

I decided to record the same song (not the same timestamp, I'm sorry about that) on the faulty receiver and on the one I use regularly. Same source, same recording interface, same recording volume on Audacity. The issue is a lot more noticeable on the Umek sample. The song is brickwalled (as almost always nowadays) so it's a lot easier to hear the distortion. Does this help somehow?

Also, my next step will be checking the caps. I would just like to be able to narrow the issue down to one board instead of going in blind checking every cap. Some boards will also be a pain in the ass to reach so if I can save myself the trouble by knowing where the issue lies, that would be great. Thing is, I don't know how to make sure or even where to start. And looking at the service manual isn't easy. Any ideas would be greatly appreciated.

Thank you!
 
So, I have some updates regarding this, but now I hit another wall.

After cleaning the pots and the speaker relays, the issue that made me open this thread "evolved". Now I get sound from both channels every time, without a single issue. Any noise that would come up while turning the volume knob or pushing the Mute button is gone. Now I have an issue with distortion though. And it is really weird. I'll try to be clear and fast:
  • Phone connected to the receiver does not produce distortion (RCA - Jack cable);
  • Chromecast Audio introduces distortion EVERY TIME;
  • DVD player that I use as a CD player introduces distortion EVERY TIME;
  • No distortion on the phono stage;
  • Using the CD1 Direct feature eliminates distortion when the source is connected to CD1;
  • Different cables used to try this out.
Now, I may be hearing distortion on a CD playing on the DVD connected to CD1. Without turning off the receiver, I change the cables on the CD1 source to a cable connected to my phone. No distortion :dunno: The issue is definitely not with either the DVD player or the Chromecast Audio. Both play just fine on another receiver and while using the CD1 Direct feature.

I also checked those two big Elna caps and they're just fine. They're 8200uF and 56v. Both didn't lose any voltage and read 8210uF and 7800uF. Yes, I did unsolder them to test. I took the opportunity to remove most of that nasty glue that was holding them down to the board. That thing was all over the transistors and resistors.

Now, it seems that the CD1 Direct feature bypasses Balance control and Source Selector so should I be looking at those two boards? Please note that non-defeatable tone controls remain in-circuit.

If you have any other idea of how to proceed, I'd love to hear it. Thanks everyone!
 
Weird that CD direct defeats balance and selector but not tone controls.

It sounds like you may be overloading the preamp section with certain signals. If you increase the output level of your phone while it's connected to the system, can you make it distort (although that's a headphone output, so it may not behave the same)? Do you have any line level component that has a variable output that you can test this theory with?

I'm also confused: you said that the DVD player always distorts, but then later you said that CD Direct eliminates distortion when you use CD1. So when you connect the DVD player to CD1 and turn on CD direct, it no longer distorts?
 
swechsler said:
Weird that CD direct defeats balance and selector but not tone controls.

It sounds like you may be overloading the preamp section with certain signals. If you increase the output level of your phone while it's connected to the system, can you make it distort (although that's a headphone output, so it may not behave the same)? Do you have any line level component that has a variable output that you can test this theory with?

I'm also confused: you said that the DVD player always distorts, but then later you said that CD Direct eliminates distortion when you use CD1. So when you connect the DVD player to CD1 and turn on CD direct, it no longer distorts?
Click to expand...
I'm sorry, I should've been more specific. I'll try to clear it up.

The system is mainly used for vinyl record playing but, with the quarantine, I decided to go through old CDs and gear and hooked up a DVD player I had lying around to listen to said CDs. I connect that DVD player to the CD1 Input which can be used as a normal source or as CD1 Direct:

rNbN8MW.jpg

Sorry about the white rectangle, but I'm in bed now and can't take a picture of my unit and this image had a watermark for another website.

As you can see, you can select CD1 on the main rotary source selector and use it like that. I get distortion when it is being used like that. As soon as I turn on the CD1 Direct option (big button on the lower righthand side), distortion is gone. Please note that the DVD player works fine with other receivers, as I said before.

It definitely seems like overloading with certain signals is what's happening. Having the CD1 Direct option fix the distortion is just adding confusion though. And I can't get the phone to distort even at higher volume levels. I could before cleaning it up. I work on the receiver on the basement and what I use to test is headphones, two speakers and the phone connected to the receiver. Before cleaning that glue up, cleaning the relays and pots really thoroughly and checking those two caps, it distorted, but not after, which is also really weird since some signals still do.

Btw, I'm sorry for asking but I looked at the service manual a dozen times and can't, for the life of me, identify which one is the pre-amp board. Could you please help me with that?
 
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.
 
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