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Marantz SR 940 no power

T

Tennangler

Well-Known Member
I recently picked this up from someone who gave up on it. When its plugged in the red light next to the power button is on. I read you must push one of the function buttons to turn it on but nothing happens when I do. I also read this is a common issue caused by a bad capacitor in the protection circuit. I think that circuit is on the power supply board.
I have downloaded the service manual and tried to locate some of the boards. This manual is difficult to follow (I'm use to 70s receivers).
Can someone point me in the right direction by telling me what to check first?
Thanks
James
 
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I sent the service manual again yesterday. It seems like it went through but I dont know where it is in the database. Are you able to see it?
James
 
Does the clock show? Have you tried pressing the FM function button? What about hitting FM with the remote?

You could try recapping the "Backup" power supply. It's on page 39 of the SM. Figure 6.17. Check all the voltages shown on that schematic.

Wow! This unit is a strange/complicated beast!
 
The clock does not show. I have tried the FM button but nothing happens. I do not have the remote.
I was hoping someone could tell me what voltages to check to determine if recapping is needed to get it turned on.
Thanks
James
 
The voltages are shown on the schematic, page 39 of the SM. Figure 6.17. Check all of them.
 
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I had to take the plate the transformer is mounted to to access that board. Is this safe with power on?
 

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As long as you make sure nothing is shorted before power on. I would also make sure the transformer mount stays grounded to the chassis with a jumper. Be really careful
 
I have measured voltages at J704 and JP240 With the receiver powered through a dim bulb tester. Will the values be correct or do I need to plug in to regular outlet?
 
Voltages will be lower than normal on a DBT. If the DBT is dimming after power on then you are safe to plug it into the wall socket.
 
The dim bulb never lights at all. I have had it plugged into the wall socket and there was no change. I will remeasure with it plugged in to the wall.
 
Oh yeah. I forgot. You can't turn the unit on. All you have is standby power. The DBT is not much help in this case.
 
I remeasured J704 and JP240 with plug in the wall and the values didnt change much.
J704 I got 22v, 15v, -8v, 0 on pins 1-4.
close to correct values

JP240. -23v, -23v, -25v, 120mv, 0 on pins 1-5
The -23v should be 3.2 off the transformer. 120mv should be 5v.

Does that help so far?
 
JP240 pins 1 & 2 are AC measured between them. Pin 4, I think is the real problem. Its 5v comes from the processor. Processor not turning it on. But who knows? May just indicate the unit is in battery backup mode.

I think it's odd you don't have a clock display. Should at least see 12:00 or 00:00. Have you check the backup battery? Is the compartment totally corroded from battery acid?
 
Are you saying pins 1 & 2 are AC voltage?
The unit appears to never have had batteries in it, very clean. I put new batteries in it but still had no display.
 
Yes, AC. Pins 1&2 come straight of the transformer with no rectification. I can't tell where those lines go or what purpose they serve because the main schematic is so convoluted.

You are probably going to need somebody who has experience with this particular unit. Maybe post in the Marantz forum?
 
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Dave, I posted on the Marantz board but didnt get much response.
I tried ChatGpt and serm to have localized the issue to the standby board. While taking measurments around Q701 I accidently shorted accross two legs of the transistor. The relay clicked and the standby light on the front panel turned off. The display did not come on.
This seems to say the transister is not getting the correct voltage. Could I have a bad cap not suppling the voltage?
Thanks,
James
 
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