Dc on speaker terminals class ab

[Aqeeb127]

Im getting dc voltage on the speaker terminals class ab amp 4 volts dc and the one side outputs gets hot
And no clear audio comes out of the amp

 

[Perry Babin]

Post a photo of the defective channel.

 

[Aqeeb127]

Its a monoblock

 

[Aqeeb127]

I will take pics now and i apologize if pics is not of best quality because its almost 1 am here in south africa

 

[xenofonn]

Good day from Greece! Please check the output transistors,maybe shorted,at first,at second check the speaker. Good luck!

 

[Aqeeb127]

Thats the best lighting i could do at this moment

 

[Aqeeb127]

Mr xenofonn speaker is in 100% working orderand theres no shorts

 

[Aqeeb127]

The amp has +-60v

 

[Perry Babin]

Clean up everything with a toothbrush and solvent (acetone, alcohol...) and make sure that there are no shorts.

If the problem remains, remove the drivers that directly drive the outputs. Does the problem remain? If not, check the drivers (out of the circuit) for leakage, shorts and open junctions. If they are OK, reinstall them and do the same thing for the next stage back.

I'm assuming that you've confirmed that there is no excessive DC from the preamp section that's causing the offset.

 

[Aqeeb127]

How do i check the dc offset in the preamp section mr babin

 

[Aqeeb127]

And is the drivers the transistors connected to the base of the outputs

 

[Perry Babin]

Does the point where the preamp section drives the input to the amplifier stage have excessive DC offset? About 1/10th of a volt may be OK but several volts would not be (assuming that the preamp ICs use ±voltage on their supply pins).

 

[Perry Babin]

The emitters of the drivers will drive the base of the output transistors, generally through resistors.In the diagram below, Q108 and Q109 are the drivers. They drive the outputs, Q111 and Q112.

 

[Aqeeb127]

Ok the preamp sectiom is 12mv dc

 

[Aqeeb127]

How doni check for leakage as i still dont own a scope

 

[Perry Babin]

You check for leakage with the meter set to ohms, with the transistors out of the circuit. You should read infinite resistance when a junction is reverse-biased by your meter and across the collector/emitter, no mater the probe placement.

 

[Aqeeb127]

Ok thanks no leakage and no blown transistors as soon as i take the drivers out the the dc offset is gone and i tested the pair before that also

 

[Perry Babin]

Reinstall them and remove the next stage back.

 

[Aqeeb127]

Ok so i must test all the stages

 

[Perry Babin]

You have to test until you find the fault.