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Marantz 1040

set dc volts lowest scale ..black probe to chassis red to each point in turn . power has to be on so watch where your hands are .
 
JRM said:
By the way. I am a new learner to all this and am curious to know what the effect of this erratic DC offset will be?:crazy:
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It basically means something is just not right. If you could measure distortion, it probably would not be in spec. When you checked the diff pair, did you measure hFE? It’s critical that these two transistors be closely matched. They could both be “good”, but have drifted apart in gain. Cheaper meters often have a rudimentary measure of hFE that is good enough. Usually, you buy 20 or so KSA992FBU’s, and test hFE until you find two very close. They only cost a few cents each,
 
Hi Pete. I'm assuming its auto as the only adjustment are the pots I have been working with so far.
 
just the jumper ..then check adjust dc offset again at speaker terminals ...
having that jumper there should stop any stray dc current getting into the amps input for that channel .
 
Hi Pete. With the jump wire the DBT lights up like a Christmas tree so I turned it off and removed jump wire immediately
 
You are right I need to have my eyes checked.

Ok j701 jumped to chassis. Ov DC on speaker terminals. Replaced jumper and put DVM on j707 + and chassi - and DVT started around 40mv than came all the way down to -0.1mv. Left standing for 10 minutes and it stayed there. Removed jumper and fluctuating meter reading came up again on j707 and chassis

Can this help resolve diagnose the problem?
 
bit of further testing ..lift one leg of R701 amp board and check dc offset again . lifting one side disconnects the input to main amp cutting everything before it out of the equation .
 
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