Bought a Marantz PM7200 - dead channel

I thought the DBTs only were accurate with regular tungsten lamps and not halogen, no?
 
just remembered something . make sure the outputs have correct voltages . this however only applies with a speaker load and signal applied .
 
petehall347 said:
is amp at idle no speaker load ?
Click to expand...

When I turn the amp on the speaker relay does not come on. I've checked the circuit and found odd voltages. Since then I found the faulty resistor shorted open which may be why the voltage was out of wack.

From previous post;

Sigh.....I'm pretty gutted right now :( I put in a 72W globe with the same results. If I power up with the "class A" on it powers up with a big click but no secondary click as the power amp comes on and music is played. If I then turn the amp off, turn off the "class A" switch and then power the amp back up I get 3 clicks on/off with the bulb going bright/off bright/off bright/off before it turns back on, stays on, with a dim bulb. If I turn the amp off and back on again WITHOUT using the "Class A" function the amp powers on/off normally with out the secondary click for main amp operation. If I then turn amp off and press class A on, it repeats as before.

So so gutted right now......I honestly do not know what to do now. I haven't checked the left channel however I was in the right channel circuit when I shorted it with the left channel working perfectly well prior to the short. Honestly didn't think I'd have stuffed up the left channel :(

Could I have? :dunno:
 
Also can I use a standard 5% tolerance 10 Ohm resistor to replace the 10E one? The only difference is the 10E resistor has a purple band on it (5 band resistor) which I think is a 0.1% tolerance. Service manual says [10E 5% 0.33W]
 
WOOOOHOOOOO! :banana:

IT LIVES!! :music: YOU BLOODY RIPPA! :rflmao::banana:

ON both channels!! :rockon:

That final resistor did it! I am over the moon right now GIDDYUP! :biggrin:

The power up gave me a click........pause.....then another click.....where my heart lept with joy! I plugged in my phone to stream music via the headphone jack to line in and heard silence! Stupid me thought it was on line 2 so I was like "oh no, now what?" Tried line 1 and got music yeehaw!

After HOURS AND HOURS of staring at a circuit diagram, pulling parts to test after I shorted the main amp out (DOH), measuring EVERY damn component (resistors, diodes and transistors) I have glorious music from both channels!

I COULD NOT have done this without the help of you all here, in particular MBZ :bowdown::bowdown: who freely gave of his time to make dozens of posts to advise on what steps to take, interpret my readings and, most incredible of all, EXPRESS POST, AT HIS EXPENSE, parts to repair it (refusing my offer of payment.) :bowdown::bowdown:

This has been an incredible learning experience and I cannot thank you all enough for helping a complete amateur like myself. :)

Now to try the class A mode. I've only tried AB so far. I suppose this will also need some tuning after installation of new components.

Again, THANKS EVERYONE! :beerchug:

EDIT: Class A works perfectly!
 
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mbz said:
You have excessive dc voltage on the spkr line. The protection circuit is doing its job and not connecting the spkrs.
Very unlikely you have a short.

Problem with right channel

These faults are a PITA to track down.
Two basic scenarios.
Component on positive half of amp has failed open so missing expected positive voltage to cancel the negative voltage (from neg half of amp)
Component on neg half of amp has failed short.

Understand that you've diode checked all components, however one is breaking down under voltage.
Will take some time to sort out a test procedure, maybe others will have a better idea.
Maybe take the night off...
Click to expand...

MBZ you were SPOT ON!:rockon: :bowdown:The resistor 3298 had failed open so no +52V at all coming in.

This is how I found it. I measured voltage at MANY different places throughout the circuit and compared the good Left channel with the bad right channel. :idea:

I even tested for continuity to make sure I was testing exactly where I thought I was. I then noted what I found on the circuit diagram I'd printed out and continued my investigation. Continuity checked along a path was highlighted. Parts DOUBLE checked again marked off with highlighter.

Thanks my friend! MIX CD on it's way to you soon :D

Gq1enF.jpg
 
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Excellent news! Most would have thrown in the towel after the short but you systematically worked through the pain etc...
You did it. That's about as tough as it gets. Enjoy.

Thanks to Pete Hall for joining in/contributions and more experianced eyes.
 
Homer4beer said:
Uh oh. Might have celebrated too early .......no sound from speakers only headphones.
Click to expand...
Headphones are connected to the power amp, just like the spkrs.
"only" differences are,
- headphones are higher impedance and an easier load to drive
Try turning the volume up with headphones, does the sound distort?
- speakers have a spkr selector switch, it may be dirty.
Try connecting the spkrs (with the amp powered off) to the B set of spkrs and check for sound
- The amp has separate protection relays for spkrs A,B and headphone.
Maybe the relay has pitted contacts (but was working 5min ago) or there is a fault/failure in the relay circuit, however would probably affect phones as well.
Need to check schematic.
 
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