Marantz PM-75 integrated amp. Fault

[alanb]

Can anyone help please?
Only the power light now comes on, the remaining LED,s do not light.
Power is getting to all the main boards, but I only have a circuit diagram and need a component layout service sheet to check thoroughly.
It has happened in the past and corrected itself. I did find at that time, that there had been a short across the 75 ohm input lead from the turntable.
the lead was replaced. That was about 2-3 years ago and it's been OK up to now. There are no earth loops on any of the leads now.
Advice much appreciated. Thanks

[fink]

Usually an input short would have little to no effect on the preamp/amplifier.. in fact input shorts are commonly used to totally mute an input if it may be causing noise or rf issues.

Having said that I can't say what the problem is but if it's affecting many stages of the amplifier I'd lean towards a power supply problem.

[alanb]

thanks Fink,
I didn't know that.
I must get a schematic diagram to check the power to each board

[fink]

http://www.eserviceinfo.com/download...antz_PM75.html

[alanb]

Thank you.
Got it!
I will work on it soon and post my findings

[alanb]

I have found the problem.
The rectifier diodes are burnt, on the low voltage supply.
The output was down to 1 volt. I will also replace the smoothing capacitor when I can get the board out, since this may have caused the breakdown. It will take some time, there is so much to remove first.
Thanks for the link to the scematic diagram.
I'll keep you posted

[fink]

Good luck

[alanb]

Thanks for your help.

I finally got the parts and replaced the burnt out diodes and 3 capacitors that had lost their wax due to the heat,
A tricky job, but worth it

[fink]

No problem