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Old 2nd September 2014, 02:02 PM   #1
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Default Marantz PM 43 dead

I got this PM 43 from a friend. As he said the unit suffered from a thunder damage. Taking a look around I found out that resistors R801 and R802 on the pre power supply section are burnt. The voltages from the power transformer are as they should be, according to the service manual. As my friend recall, as soon as the relay clicks there is a smell of burnt stuff from the amplifier.
The LEDs on the source selector don't light up.
Any suggestions on where to start?

Thank you.
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Old 2nd September 2014, 09:14 PM   #2
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The resistors are at the input to the power supplies for the preamp and other low voltage power supplies. If you have no low voltage power, then nothing can function. Disconnect the main +/-41V supplies to the power amplifiers, then remove the multiway connectors to other boards and replace the resistors, then check all the low voltage supplies are close to those shown on the schematic. If not, you may have to start replacing regulators and other parts too.

You should then be checking that the DC rail voltages reach the preamps when the connectors to each section are gradually refitted, one after another, checking function and current is still within the resistor ratings (measure voltage across the replaced resistors and calculate) as each one is reconnected.

I have seen some simple amplifiers only have a blown fuse and others where almost every semiconductor and microprocessor has been completely blown with lightning damage, yet there was almost no appearance of damage. Keep an eye out for further signs of burning around inputs etc.
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Old 2nd September 2014, 09:33 PM   #3
rayma is offline rayma  United States
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Quote:
Originally Posted by davx975 View Post
I got this PM 43 from a friend. As he said the unit suffered from a thunder damage.
Any suggestions on where to start?
I'll wager that this is not worth the trouble, unless you're looking for a very long term project.
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