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Chip Amps Amplifiers based on integrated circuits

Marantz PM30 Problem
Marantz PM30 Problem
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Old 16th June 2011, 07:58 PM   #1
agaricus bisporus is offline agaricus bisporus
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Join Date: Jun 2011
Default 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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Old 27th June 2011, 02:45 AM   #2
! is offline !  United States
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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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