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Marantz 2235B cuts out at roughly 1/2 volume

C

cyber104

Active Member
Hi All:

Not even sure to start looking on this one and I'm certainly not an electronics expert - just a lover of vintage electronics and a basement hack.

I recently picked up a 2235B that works fine and sounds perfect until it gets to roughly 1/2 volume. At that point it kicks the speaker relay and the there is no volume at the speakers. Once you turn the volume knob down a bit, the speaker relay clicks and the sound comes back.

Trying to isolate the problem between the pre-amp and power amp section I plugged the pre-out out of my 2235 directly into the main-in of the 2235B - same thing happens at roughly the same volume setting on the 2235 - so that sounds like the power amp on the 2235B is doing this.

Any thoughts?

Thanks much
Chris
 
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Have you checked the Idle Current and DC Offset? If not, download the service manual and follow the procedure to check it.
 
Connect your phone directly to the main-in at the back through RCA cable. Switch on the receiver and play from your phone. Make sure the volume of your phone is at minimum when you start playing. Gradually increase the volume of your phone and listen to check you are having the same problem at almost the same sound level or not.
 
sanjib said:
Connect your phone directly to the main-in at the back through RCA cable. Switch on the receiver and play from your phone. Make sure the volume of your phone is at minimum when you start playing. Gradually increase the volume of your phone and listen to check you are having the same problem at almost the same sound level or not.
Click to expand...

Wouldn't that be the same test as I tried before - connecting the 2235 "pre-out" to the 2235B "main-in"?
 
Sorry, missed it! Have you done the opposite to rule out Pre of 2235B? Yes, your main amp probably has some leaky capacitors or failing transistors that are leaking DC.
 
My iPhone can't drive it to the volume that it needs - I have a Carver C-4000 that I'll run into it and see what happens
 
cyber104 said:
My iPhone can't drive it to the volume that it needs - I have a Carver C-4000 that I'll run into it and see what happens
Click to expand...
I think you already checked the power amp section of 2235B with your good 2235 and you have the same problem. Am I right? Now to check the pre-amp section of 2235B connect pre-out of 2235B to the main in of 2235 and see whether yore getting the same problem at the half volume setting on your 2235B.
 
I ran another test this AM - using a Carver C-3000 preamp into the "Main In" on the 2235B produces the same issue except that it happens earlier (at a lower volume)

Do you still think I need to test the preamp of the 2235B?
 
Yes - the balance at either extreme does not affect the problem - it occurs no matter what the balance position is
 
I did another test based on sanjib's suggestion above. I took the pre-outs from the 2235B and plugged them into a powered sub. The speaker relay still clicks out at 1/2 volume (speaker sound goes away) but the powered sub keeps thumping along - this seems to me that the preamp is fine but the problem is in the power amp.

Thoughts are most welcome
 
Just an observation - C713 and C714 look like they could be bulging on at least one end. The other end has a black ring around the leg about the size of a pencil eraser (it looks burned to me) - could something like this be causing it?
 
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cyber104 said:
I did another test based on sanjib's suggestion above. I took the pre-outs from the 2235B and plugged them into a powered sub. The speaker relay still clicks out at 1/2 volume (speaker sound goes away) but the powered sub keeps thumping along - this seems to me that the preamp is fine but the problem is in the power amp.

Thoughts are most welcome
Click to expand...
Why aren't you connecting your 2235B (problematic) Pre-Out to 2235 Main-in and check whether the 2235 (good one) relay clicks out at 1/2 volume or not?
 
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