Marantz PM30 Problem

agaricus bisporus · 16th June 2011, 06:58 PM

My trusty old PM 30 blew its internal fuse recently. I replaced it and it blew again, but I noticed one big double resistor - a RGC33 .18oh in the power amp was hot.

Now I'm not an electronics expert but a hobby fixer with a soldering iron and multimeter - I can identify components on a schematic and change them but deep techspeak is going to be over my head. I have got a schematic of this amp.

How far is the damage likely to have gone - and do I stand a chance of identifying and fixing it? I really want that amp back working again!

! · 27th June 2011, 01:45 AM

It probably has a blown (shorted) transistor, either directly on the output or the one driving it is blown or just got leaky over time. You could try testing with a current limiting device like a light bulb in series and measure output, but don't blame me if you electrocute yourself.

I mean be careful working with a live amp.

Otherwise you can desolder and pull the transistors out and test them. On the following webpage is a basic description of doing so, about 2/5ths of the way down the page:
Testing Transistors

16th June 2011, 06:58 PM	#1
agaricus bisporus diyAudio Member Join Date: Jun 2011	Marantz PM30 Problem My trusty old PM 30 blew its internal fuse recently. I replaced it and it blew again, but I noticed one big double resistor - a RGC33 .18oh in the power amp was hot. Now I'm not an electronics expert but a hobby fixer with a soldering iron and multimeter - I can identify components on a schematic and change them but deep techspeak is going to be over my head. I have got a schematic of this amp. How far is the damage likely to have gone - and do I stand a chance of identifying and fixing it? I really want that amp back working again!

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27th June 2011, 01:45 AM	#2
! diyAudio Member Join Date: Jun 2005 Location: Midwest	It probably has a blown (shorted) transistor, either directly on the output or the one driving it is blown or just got leaky over time. You could try testing with a current limiting device like a light bulb in series and measure output, but don't blame me if you electrocute yourself. I mean be careful working with a live amp. Otherwise you can desolder and pull the transistors out and test them. On the following webpage is a basic description of doing so, about 2/5ths of the way down the page: Testing Transistors

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