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Marantz 4400 - No sound left - FM Mode

Halisson

Halisson

Member
Hello guys.
I'm working to repair a Marantz 4400 not tuned FM. I located the diode H808C short and after repair the line FM returned to normal.
However, the Left side is muted in the scope and output of the boxes, only returns to play the sound in MONO mode. This problem is only on the FM option. CD4, Phono L + R perfect.
The problem also shows when the FM is out of tune or STEREO light on.

I appreciate any help.
 
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do you have a link to the schematics ? manual i have here is pretty useless .
all i can guess right now the diode you replaced is the zener diode i see on a board layout of power supply and it possibly regulates voltage for fm ..
it could be an alignment issue or you have or something around the mpx gone adrift.
do you have the tools for the job ?
 
Appreciate your help.
WZ140 was the zener replaces the other identical.
I have the service manual, I multimeter and oscilloscope.
Tomorrow will disassemble and validate what is happening.
I will validate the tensions and return as soon as possible. I do not know if it really was in MPX session the possible problem.
Thanks for help me.
 
petehall347,

Solved!
I apologize for the English translation and thank you for your patience.
I posted this help forum because I was not sure if the problem was P300 MPX module for my lack of experience.
From your information, did a scan on the board.
Some Volts IC 1156 were wrong, made replacement of the IC and tensions, such as service manual worked well.
There was no signal detected in J311 pin, so I made changes in the C323 and C325 capacitors, replaces and remained within the parameters, but no sign.
The H304 and H306 transistors are ok and there is no short circuit.
The L301 and L303 seemed so original.
By placing the cable referring to the L or R to J313, or other working channel well in scope-tube.
After testing, the problems have not been solved.
In the oscilloscope, signal after H304, but not after H306. I found problem in H306 (2SA842). BC557 replacement for different pinout, but the perfect job!
I am happy to count on your help, and I tried to explain as much as possible to help other technicians when you see the same problem.
Appreciate your help!
Best Regards!

Um abraço do Brasil!
Halisson
 
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