Pioneer SX-450 DC voltage at speaker terminals

[Randy007]

hello, I purchased a Pioneer SX-450 pretty dirty unit, I cleaned and deoxit all pots and switches. I then measured the output voltage at the speaker output, help I have about 19V on both channels..A and B..I checked voltages in the power supply and they checked out ok...any suggestions. Thanks

 

[Watthour]

The initial guess is that some of the output transistors have failed (shorted) and may have caused collateral damage.

If that is the case, don't power up the unit without performing some further testing. Check the outputs (Q211-214) for E-C shorts, and test the driver transistors (Q207-210) as well.

 

[Watthour]

Incidentally, if you are using an original factory schematic, there is a glaring error in the diagram. Q210 was drawn backward. This schematic has been corrected:

 

[merlynski]

 

[Randy007]

Incidentally, if you are using an original factory schematic, there is a glaring error in the diagram. Q210 was drawn backward. This schematic has been corrected:

OK thanks, I did notice on the P/S board even though my voltages where good, Q302 was getting rather hot....I am using a dbt and the filament is on but not real bright. I'll check the other transistors for shorts. And on Q210 are you saying the the collector should be on the base of Q214?...OK I see, should be same as Q209.

 

[Randy007]

OK thanks, I did notice on the P/S board even though my voltages where good, Q302 was getting rather hot....I am using a dbt and the filament is on but not real bright. I'll check the other transistors for shorts. And on Q210 are you saying the the collector should be on the base of Q214?...OK I see, should be same as Q209.

Problem seems to be solved, I replaced the driver transistors, output transistors seemed to be fine..and Q302 on the power supply....recapped the whole unit and wallah, no DC on the output and the unit sounds great....thanks for all the help!