Marantz 1970's "Model 2235" stereo receiver speaker cutting in and out

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Old 08-20-18, 03:54 PM
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Marantz 1970's "Model 2235" stereo receiver speaker cutting in and out

Hi, I have an older receiver that has been sitting on a shelf wrapped in a bag waiting for some TLC for about 6 years.

Prior to that I had used it pretty regularly, however as long as I can remember one of channels has cut in and out (more like the volume wanes in and out) after the amp starts getting warm. This happens with different speaker wires and speakers and with different input sources. I've checked the PCB in the past and didn't see anything burnt or obvious.

I'm not sure where to start troubleshooting this. Can anyone walk me through this?

I found a service manual online and can provide a link. I wasn't sure if I was allowed to do so on this board.

Thanks
 
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Old 08-20-18, 04:48 PM
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Yes... you can leave a link to the manual.
Have you tried the headphones to see if both channels are ok ?
Try them with the speakers turned off or disconnected,
 
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Old 08-20-18, 07:19 PM
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Thanks Pete.

Haven't fired it up for 6 years. Just did now. Speaker connections are spring connections.

No issues with headphones either in stereo or mono.

Trying this at first using alligator clips between speaker wire and spring connections:
No sound from left Main channel, issue is with the Positive (red, - contact) on left Main channel. Thought it was perhaps the speaker, alligator clip. Switched the speakers' alligator clips at the spring terminals and the issue persisted. Right channel functioned fine with both speakers.

Powered off the unit and played with the spring terminals. Both channels work fine with the speakers. Tada! Maybe they have just been really dirty for years?

This has always been an intermittent issue, so I'm going to give it some time to see if the issue comes back. This seems too easy. I'll post back either way.

Thanks for your time.

The manual was found on manualslib.com.
Link: https://www.manualslib.com/manual/10...35.html#manual
 
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Old 08-21-18, 06:53 AM
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I worked at a couple stereo repair shops back in those days. The first one only worked on Marantz. I always loved the build quality of receivers from that era.

The most common problem I encountered with intermittent channels was (is) the TAPE switch. It has a lot of tiny contacts and doesn't get much use so oxidation creeps in until the contacts are too dirty to pass the signal. ALL the selector switches and the volume control can have oxidation issues--especially after 40 years.
Rotate or switch them numerous times & see if that clears it up. If it improves you may want to take it to a pro for a good cleaning.

I can't recall if that unit has Pre Out/Main In jumpers in the back. This is another source of dirty-contacts trouble.

IF the sound ALWAYS works thru headphones, but speakers cut out, this means the entire signal path is OK right through the amplifier section. That only leaves the spring-loaded speaker jacks, A/B speaker switch and possibly an internal protection relay as suspects.
 
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Old 08-22-18, 03:52 AM
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Thanks for the advice Guy. I'm impressed it has been so trouble free after like 45 years. Despite being stored covered when not set up, there is a nice thick coat of caked on dust over most of the components. When you say professional cleaning, what did that typically entail? Contact cleaner and aerosol dusting?
 
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Old 08-22-18, 03:58 AM
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The pots and switches are actually fairly clean as there were a bunch of devices hooked up to the tape and auxiliary inputs that were being used frequently.
 
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Old 08-22-18, 07:05 AM
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The switches & pots are reasonably accessible by just removing the top cover.
If you're handy you can clean them yourself but it's critical you use the right cleaner. A "plastic safe" contact cleaner that leaves behind a thin coat of lubricant is best. Caig Labs "Deoxit" line is great stuff. They have a dizzying number of similar products but there's a lot of overlap and it's hard to go wrong with any of them. Research on their website, buy on Amazon.

If you have any dial lamps out I'm sure they're available on Amazon & eBay.

Go slow. I just saw a Pioneer SX1250 online for sale for $1500. That's a powerful beast from that era but shows how crazy the values of certain old receivers have risen in this age of cheaply-made complicated (errr--make that "feature-packed") digital disposables.
 
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Old 08-22-18, 09:32 AM
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We don't call it cheaply made today.... we call it value packed.

Excellent point on dirty TAPE switches.
 

Last edited by PJmax; 08-22-18 at 09:49 AM.
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Old 08-23-18, 07:04 AM
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What I find suspicious is "back in the day" a 100WPC x 2 receiver would weigh 40 pounds and half the interior volume would be taken up by an enormous transformer & huge filter capacitors.

Today you find 15-pound receivers rated to crank out 60-100WPC X 7 with a transformer that would fit in your pocket and filter caps the size of a roll of nickels.

This doesn't add up and I believe it's part of the reason the old, heavy units are so collectible today. REAL power and built to last. No software to update every couple weeks, either!
 
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