Distorted left channel - Marantz 2385

jblmar · 25th March 2009, 02:13 PM

Greetings,
I'm in the process of repairing a Marantz 2385 (European version). The amp arrived with both channels blown. Repaired both channels. The remaining problem is that the left channel is distorted.
Looking at a 1K sine wave signal, the top half of the signal is missing.
Looking at the base line on the o'scope, the wave is present below the line but not above. Unusual!
Any suggestions?

h_a · 25th March 2009, 02:50 PM

Quote:

the top half of the signal is missing

Complementary amp with one half shot?

Have fun, Hannes

jblmar · 27th March 2009, 05:04 PM

I measured the voltage at J723 & J725, the base bias of the output transistors. Both measure negitave. J723 should be positive. Reverse biased.
Now's the difficult part. Locating the defect.

25th March 2009, 02:13 PM	#1
jblmar diyAudio Member Join Date: Dec 2005 Location: Brooklyn, New York	Distorted left channel - Marantz 2385 Greetings, I'm in the process of repairing a Marantz 2385 (European version). The amp arrived with both channels blown. Repaired both channels. The remaining problem is that the left channel is distorted. Looking at a 1K sine wave signal, the top half of the signal is missing. Looking at the base line on the o'scope, the wave is present below the line but not above. Unusual! Any suggestions?

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27th March 2009, 05:04 PM	#3
jblmar diyAudio Member Join Date: Dec 2005 Location: Brooklyn, New York	I measured the voltage at J723 & J725, the base bias of the output transistors. Both measure negitave. J723 should be positive. Reverse biased. Now's the difficult part. Locating the defect.

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