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Marantz Model 22 Issues

M

mrspock23

New Member
I just got a Marantz Model 22 for a nice deal. It's not in terrific shape, some bumps and bruises here and there, but other than it having sat in a garage for several years and accumulating dust it appears to look ok on the inside.

First of all, the thing has a very annoying low volume hiss/white noise sound no matter the input. Even when the volume is zero, there is still noise (and I can still faintly hear the audio playing). It's in both channels, but in the right channel it is louder. I've grounded the receiver and that has not impacted it at all.

Second, the left channel quits after about 5 minutes. First it gets kind of staticky, then it drastically reduces in volume, and then disappears altogether.

Third, the right channel starts getting staticky after a while. It sounds similar to a loose speaker connection (although that is not the issue).Sometimes it cuts out and then comes back.

I dusted, gently vacuumed and got rid of all the dust bunnies inside, and sprayed a little bit of contact cleaner on the controls. Before the cleaning, the receiver lost both of it's channels after about 20 minutes. Since then it hasn't done that. That is the only improvement I can tell.

I'm not new to audio gear, but rather new to repairs. Any suggestions? Any help would be appreciated!
 
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Check out the pinned posts in the Solid State forum on using Deoxit and checking DC offset. The list of things that could be wrong with a 50-60 year old receiver is long.
 
Actually the Deoxit pinned post is in this General Audio Discussion forum.
 
Ok, so I've looked inside and none of the transistors on that list are in it. Still, it's likely that the transistors are the culprit behind the white noise. Something I've noticed is that the left channel will work great for about 5 minutes (the right channel is now working fine), and then it will slowly decrease it's volume and sound crackly over the course of several minutes until it's completely silent. Any idea what might cause that?
 
Might be 2 issues,
1) white noise
Probably a noisy transistor, maybe leakage of audio path cap
2) audio breakup/loss
Possibly bad solder joint, relay would be a long shot, bias problem as amp warms up

A scope would be very handy. I've had mixed results with an audio probe (when my scope was offline)
Maybe monitor bias on problematic channel without audio and note bias when channel drops out (white noise stops). You could try tapping the relay case with something non-conductive(chopstick?)

Try to find a scope, make things a lot easier.
 
mrspock23 said:
Ok, so I've looked inside and none of the transistors on that list are in it. Still, it's likely that the transistors are the culprit behind the white noise. Something I've noticed is that the left channel will work great for about 5 minutes (the right channel is now working fine), and then it will slowly decrease it's volume and sound crackly over the course of several minutes until it's completely silent. Any idea what might cause that?
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Like mbz said, could be a cracked solder joint that as it heats up slowly expands until contact across the crack is lost.
 
If there were a cracked solder joint, which board would it be on that would impact the left channel? I'm trying to figure out where I should be looking.
 
Ok, so I just tried something I read on another post. I plugged in the Tape Out to the Tape In on another receiver, and I plugged in some headphones into that receiver's jack. I'm getting both channels completely balanced and strong without issue. The left and right mono switches are working fine, and so is Tape Monitor. So where would be the source of my problem?
 
I just did the opposite: plugged the Tape Out from my other receiver into the Tape In of the Marantz, and it still has no left channel and the hiss.
 
The tape monitoring function is passive, you are only testing switches not the pre or power amp.

mrspock23 said:
So where would be the source of my problem?
Click to expand...
Preamp or power amp unlikely to be power supply, could be dying component (transistor, cap,,,) or bad connection/solder joint or...

Google "audio probe", prefer you find an oscilloscope.
 
Fixing one issue on these will not fix your problems "down the road." A full rebuild is in order for a receiver of this era is necessary to run correctly and not be a source of frustration. All electrolytic caps, known-noisy transistors, diodes that are known to fail, voltage trimmers, etc. should be replaced.
 
Well, now I've hit another road block. I decided to take the output transistors in the back of the unit out and clean them, because I had cleaned just about everything else. I put them back in, turned the thing on, and in a matter of seconds I heard a pop and then a low level hum. I turned the thing off and smelled a little bit of smoke. Waited 'til this morning to turn it back on, and now I get no sound at all. Guess this fish is too big for me to fry.
 
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I'm guessing one or more of the output transistors blew. I had suspected that they might be the culprit behind the sound issues. I can't see anything on any of the main boards that seems injured (but that doesn't have to mean anything). The transistors are old Motorolas: two SJ2000, SJ2001, and 34-1001. I found another thread from some years ago that mentioned modern replacements for the 2000 and 2001, but would it be safe to say I could also replace the 34-1001 with that as well?
 
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Does this amp have two different output transistors per pair?
If so, you did plug them into the right sockets, right? One would be a PNP, the other a NPN. Check the fuses, dont turn it on again. Other componants are probably fried now.
Its going to need a full restore anyway. Maybe have this thread moved to the Marantz forum.
The model 22 should be a nice little receiver once sorted out. Being as old as it is, its going to need a full recap replacing every electrolytic capacitor and outputs tested at the very leased.
All controls and switches will need a good cleaning with contact cleaner too.
There are some really good techs here on AK you could send it off to and get it repaired if you wanted.
 
Could be its in protection now. I would ask in the Marantz forum to be sure about the replacement for the 34-1001.
 
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