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Pioneer SX-727 Left ch/pin3 on protect bd DC offset fluctuating.

B

B Dragon

New Member
Hi guys. New to audiokarma. Been looking at a lot of your threads on pioneer SX 727 they are helping out a lot. Just bought pioneer SX 727. Recapped everything except for I still have to order three main power supply caps. My problem as mentioned in the topic. Before and after recapping. The DC offset and what appears to be left channel /pin 3 on the protect board is constantly fluctuating. Right channel is solid at 0.
Any idea of what component might be causing this to cut down my troubleshooting time. Or might it be the power supply caps I have not changed yet? Or a bad transistor in the left channel somewhere?
Forgot to mention I have the preamp/ Main in jumpers pulled and doing all my measurements like that so it seems to be for sure somewhere either in the protect circuit or power amp board I am guessing.
 
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You will have to trace back on the schematic and check voltages. Not familiar with Pioneer, ut Kenwood used a lot of zener diodes for voltage control in the amplifier sections and they tend to short. A bad one could be causing your trouble.

Probably not your work, I'd check the transistors for shorts/opens in that channel starting at the beginning. Check for hot resistors too -- a shorted driver can cause excessive heat and pull down the rail voltage.

Do your testing on a DBT just in case -- it's easy to bridge solder points with a probe, and with full power something will pop for sure!
 
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