Bought a Marantz PM7200 - dead channel

[Bert 1100]

I get 3 clicks on/off with the bulb going bright/off bright/off bright/off

My guess is that it's still too little bulb wattage.
I also run on 240V here, and a 50 watt bulb is OK only for the low power stuff (less than 40-50 wpc). Even two 50 watts in parallel won't allow my NAD 216 power amp (125 wpc) to come on, the bulbs stay bright.

And of course class A draws so much current that it's pointless to try it off the DBT.

I would try your 50 watt and the 75 watt in parallel, I think the risk is minimal.

 

[Homer4beer]

My guess is that it's still too little bulb wattage.
I also run on 240V here, and a 50 watt bulb is OK only for the low power stuff (less than 40-50 wpc). Even two 50 watts in parallel won't allow my NAD 216 power amp (125 wpc) to come on, the bulbs stay bright.

And of course class A draws so much current that it's pointless to try it off the DBT.

I would try your 50 watt and the 75 watt in parallel, I think the risk is minimal.

How do I do that? Build another bulb tester? Is there an easy way to link it in to my existing one built like this?

View attachment 901167 View attachment 901169 View attachment 901170 View attachment 901171

This is as basic as a DBT can get, fully insulated, earth/ground loop through, no soldering, no extra terminals required as the base of the HPM socket has two NC (not connected) spare loop through terminals to use, pre-made 10A extension lead you use to save money and wiring/time etc. $15.33 in parts from your local Bunnings, plus an old 60W globe.

 

[Bert 1100]

just wire in another socket for the extra light bulb, parallel to the first one. Then you can use one or the other or the two bulbs together to adjust for different amps.

 

[Homer4beer]

just wire in another socket for the extra light bulb, parallel to the first one. Then you can use one or the other or the two bulbs together to adjust for different amps.

Thanks Bert. I'll go to Bunnings tomorrow and make another one. I really hope it's just the bulbs stopping the amp working. I really have put HOURS and hours into it so far.

MBZ has also been amazing in helping so far as well.

 

[mbz]

Your almost there.
Having trouble following exactly what the status is, too early in the morning.
The DBT limits supply current/gives you an indication of large current draw. I would expect it to be bright immediately after power on (inrush) then dim.
Do you think you still have a short?
Do you get music on either channel in class A or AB?
If the speaker relay does not click then it may be due to a failure in the protection circuit or excessive dc voltage on spkr line. While this is a PITA to track down
it is normally caused by 1 failed transistor, nothing like what you've been through.

 

[Homer4beer]

Your almost there.
Having trouble following exactly what the status is, too early in the morning.
The DBT limits supply current/gives you an indication of large current draw. I would expect it to be bright immediately after power on (inrush) then dim.
Do you think you still have a short?
Do you get music on either channel in class A or AB?
If the speaker relay does not click then it may be due to a failure in the protection circuit or excessive dc voltage on spkr line. While this is a PITA to track down
it is normally caused by 1 failed transistor, nothing like what you've been through.

I may have a short still....not sure.

No music on A or AB as the second relay doesn't clickon to power it. You think I may have a failed transistor still? Hmm where to check?

Yes massive PIA.......quite disappointing.

 

[mbz]

Try the DBT suggestion from Bert1100, might be just a case of not getting enough watts/amps to the amp.

Check for dc voltage on spkr line (DBT power up), measure at 3356 and GND. Repeat for 3355 and GND. More than 700mV or so is bad.

Once spent 200hours and then some trying to get the most out of a NAD3150. Recapped twice, first with Elna Cerafines then Silmic II.
Mains with Nichi KG then KW's. Metal film resistors, cree rectifier diodes, replaced preamp opamp NE5532 with LM4562. It sounded better
but still sounded like cr@p. Learnt a little though.

 

[mbz]

I may have a short still....not sure.

If you had a short then the DBT would remain bright.

 

[Homer4beer]

If you had a short then the DBT would remain bright.

Ok DBT improved with 2nd bulb, 160W total. Same results with the secondary relay not working to activate the main amp.

 

[Homer4beer]

Try the DBT suggestion from Bert1100, might be just a case of not getting enough watts/amps to the amp.

Check for dc voltage on spkr line (DBT power up), measure at 3356 and GND. Repeat for 3355 and GND. More than 700mV or so is bad.

3356 -42V
3355 -9mV

 

[Homer4beer]

Once spent 200hours and then some trying to get the most out of a NAD3150. Recapped twice, first with Elna Cerafines then Silmic II.
Mains with Nichi KG then KW's. Metal film resistors, cree rectifier diodes, replaced preamp opamp NE5532 with LM4562. It sounded better
but still sounded like cr@p. Learnt a little though.

Wow that's dedication! Shame it didn't work out in the end. I've spent at least 30 hours so far I'd say......learned a fair bit so far as well.

 

[mbz]

3356 -42V

Kind of good news. 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...

 

[Homer4beer]

Would headphones still work under this scenario as they aren't.

I assume not

Edit: Voltage measured between resistor 3314 and collector of 7264 is -41V.

Between 3316 and 7266 it's only -37V

A clue?

 

[Homer4beer]

Ok measuring the EXACT other path on the good left channel I get the following;

3315 to 7265 +1.7V
3313 to 7263 -1.7V

 

[Homer4beer]

Further investigation finds resistor 3298 failed open which comes directly from the +52V supply hence no +52V supplied to the circuit. Have we found the problem!

EDIT: It's a 10E resistor....how is that different from a normal resistor and what value is it?

 

[petehall347]

burned resistors will lead you to the short that caused it

 

[Homer4beer]

There isn't a resistor between the +52V supply and the failed one I found?

 

[petehall347]

anything after it . example 2266 wrong way round etc etc

 

[Homer4beer]

anything after it . example 2266 wrong way round etc etc

Thanks Pete. There is an awful lot after it

 

[petehall347]

i think it will be close to it .