Marantz 2215 MPX issue...please help!

[willyrover]

I have been working through a 2215 "barn find" and other than new trimmers that are on the way, I have one issue left to address and I'm stumped.

FM Stereo isn't working. I don't have FM alignment equipment but I was able to confirm that the 19kHz pilot signal is arriving at the MPX board and the doubler to 38kHz is working.

I have pulled transistors and capacitors and they test ok. I've check diodes and resistor values.

The muting IC on another board is also working and I am able to adjust the muting threshold. The same voltage that switches the muting IC is supposed to switch H403 and arrives at the MPX board at pin J404. When the wire is connected to J404 I am only getting 0.6volts. When I lift the wire off the pin, I get 8volts.

I tried feeding pin J404 with an external DC power supply and couldn't get more than a volt or so out of it - as though something is shorted.

Another oddity is that I am reading 39VDC across C415 and C416. These are rated 16V on the schematic and 25V in the amp. They test fine.

Does this issue sound familiar to anyone?

 

[catrafter]

The voltage at J404 is being clamped to 0.6V by the base-emitter junction of H403, this is perfectly normal. H403 is on and allowing the doubler circuit of H402/L402-1 etal. to work.
Perhaps you are missing a ground connection to part of the P400 board?
I believe there is an error on the schematic diagram as I can't seem to find the power supply feed to H406 thru H411 circuits, J406?.

 

[catrafter]

Or a missing P800 ground.
Tom

 

[willyrover]

Thanks for your reply Tom. I will check the grounds on P400 and P800.

Unsure what you mean about J406. There is 39V at J406. This passes through a R454 before feeding H406-H409.

 

[catrafter]

I was asking where the wire that is connected to J406 goes, I think the schematic is in error.

Tom

 

[willyrover]

It goes to J808 on the power supply board. (Which feeds several other boards as well.)

 

[willyrover]

I have been probing further with a scope and comparing the description of operation for the MPX board in the service manual with what is happening on the actual board.

I have 19khz coming into the board and H412/H413 appear to be putting out a rectified 38khz signal to the base of H404.

This signal drops to nearly nothing at the collector of H404, while if I am understanding the manual correctly, it should be amplifying the 38khz signal. Pulling H404 - it tests good.

Can a transistor test good, yet still not amplify?


H405 when switched on, appears to provide ground to the stereo indicator. The collector of H405 has 15VDC sitting on it. H405 tests good.

So H404 is not amplifying and H405 is not switching.

 

[catrafter]

If L402-2 is defective, it won't resonate at 38kHz and H404 won't effectively amplify, then you will have no 38kHz 'drive' to the switching matrix diodes to decode stereo.
Yes, H405 turns on to light the stereo lamp, I believe this is due mainly to current flow in the center tap of L402-1, but I'm not sure.

Tom

 

[willyrover]

If L402-2 is defective, it won't resonate at 38kHz and H404 won't effectively amplify, then you will have no 38kHz 'drive' to the switching matrix diodes to decode stereo.
Yes, H405 turns on to light the stereo lamp, I believe this is due mainly to current flow in the center tap of L402-1, but I'm not sure.

Tom

That's what I was afraid of. L402-1 and L402-2 are combined into a potted circuit and I don't suppose finding a replacement will be easy.

 

[wlhd1610]

They're available.

Bob

 

[willyrover]

They're available.

Bob

Do you have a source?

 

[wlhd1610]

PM me with a pic of yours.

Bob