Intermittent static/noise/scratchiness in Marantz 2245 - help needed!

samid

samid

Active Member
Hi guys,

Please help me diagnose a problem with a Marantz 2245 receiver: intermittent scratchy noise that occurs in left, right or both channels. It seems to mostly occur at lower listening levels, varies in severity (from light static-like noise to almost no signal at all just some crackling), and when it starts any number of things can stop it:
- raising the volume;
- turning the balance pot back and forth;
- even just touching the unit with a lead of my multimeter (with the other lead not connected to anything yet). (That's probably the biggest problem, just trying to measure the signal "fixes" it...)

As I said, it can occur in either channel (sometimes in both), apparently randomly. Sometimes it just works, and sounds perfect. I've wasted a ton of deoxit and time on this to no avail... any ideas would be very much appreciated.
 
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Try to find most of the ground points and make sure you have a clean and secure connection. Transformer mount and circuit board mounts are the best starting points. Loosen the fasteners, apply a drop or two of cleaner/deoxidizer and tighten the fasteners. Sometimes a transistor can exhibit a problem like this, also. Using a cooling spray on the transistors can sometimes uncover a bad 'un. Another thing to look for is a parted trace or solder joint. I use a non-metallic probe to lightly push on certain components or areas to try and uncover these. Good luck with the Marantz.
 
johnnm - I DID clean the controls, read my post.

westend - thanks! I will look at the ground points. As for a non-metallic probe, yes I tried that (using a chopstick) - unfortunately, to no avail.

Any other thoughts?
 
If you have the SM check the tone control board. If you have any small TO-92 2sc458 transistors, replace them.
Good subs are ksc1845 Mouser 2sc 2240.
Have seen this in many older units showing similar symptoms.
 
G'day mate, check for the possibility of 'metal migration' across the legs of various small signal transistors.

I had this happen to an amplifier I used to have, giving exactly the same sorts of (audible) symptoms. Regards, Felix aka catman.
 
Try tapping on the speaker protection relay with an insulated tool. If you can make the noise start (or stop) then change the relay. MY2-DC24 (S) should be a perfect fit.

Tom
 
Many thanks for all the suggestions. Will try them out over the weekend.

Catman - I looked up 'metal migration' and think I more or less understand what it is (but then again - maybe not) - but please explain how do I check for it?

Again, thanks to all.

Edit: I looked through the service manual, the only two 2sc458 transistors that I found were on the phono preamp - and I have replaced those already.
 
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G'day mate, 'metal migration' is when the metallic plating from the legs of the transistor migrate to the body of the transistor, causing intermittent issues like noise, partial short circuits etc.

I had it happen on an amplifier built in the early 1980's. In many cases replacement of the affected transistor is the only option. Regards, Felix (vk4fuq) aka catman.
 
catrafter said:
Try tapping on the speaker protection relay with an insulated tool. If you can make the noise start (or stop) then change the relay. MY2-DC24 (S) should be a perfect fit.

Tom
Click to expand...

I think this is it!!! At least after the unit warmed up I could trigger very similar symptoms lightly tapping that relay with a chopstick. Ordered the replacement you recommended from Digi-Key, will report back as soon as... for now at least, I'm hopeful - thanks Tom!
 
catman said:
G'day mate, 'metal migration' is when the metallic plating from the legs of the transistor migrate to the body of the transistor, causing intermittent issues like noise, partial short circuits etc.

I had it happen on an amplifier built in the early 1980's. In many cases replacement of the affected transistor is the only option. Regards, Felix (vk4fuq) aka catman.
Click to expand...

Thanks for the explanation Felix. How would I look for it?
 
G'day mate, sometimes the legs of the transistors will be very discoloured, even blackish. Close visual inspection with a magnifier will usually reveal it, but soldered in a circuit that might be (very) hard to do!

A faulty relay with noisy contacts is also a very definite possibility! Regards, Felix (vk4fuq) aka catman.
 
catman said:
G'day mate, sometimes the legs of the transistors will be very discoloured, even blackish. Close visual inspection with a magnifier will usually reveal it, but soldered in a circuit that might be (very) hard to do!
Click to expand...

Ok, I think I understand now - thanks a lot!
 
catrafter said:
Try tapping on the speaker protection relay with an insulated tool. If you can make the noise start (or stop) then change the relay. MY2-DC24 (S) should be a perfect fit.

Tom
Click to expand...

Tom - just wanted to say MANY THANKS!!! This indeed was it. I replaced the relay and the unit is now working perfectly!
 
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G'day mate, great to hear of your success! Yes the relay was a pretty safe bet. Good stuff. Regards, Felix (vk4fuq) aka catman.
 
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