Diode B12

[luigidedom]

i have a diode shorted, its marked b12 cant seem to find any data on it any ideas

 

[Perry Babin]

Photo?

 

[luigidedom]

 

[luigidedom]

 

[luigidedom]

 

[luigidedom]

 

[luigidedom]

diode D204 and D204a this is a 2 channel amp which had fried 1 of the channels, ive replaced the outputs and fitted a new driver card. the unrepaired channel is working fine, the repaired channel doesn't oscillate at all and i found D204a shorting, removed it and its marked B12.
i assume D204a is a 12v zener as D204 measures 12v across it but if i fit a 12v zener in place of D204a i get only 0.65v across it

 

[Perry Babin]

Measuring DC voltage with the red probe on the striped end of the zener, is the DC voltage positive or negative?

 

[luigidedom]

it has a positive 12v on it but it also has a squarewave on it

 

[Perry Babin]

The 0.65v is odd because that is what you'd expect if the diode was in backwards.

I'd check the resistor feeding it and check the circuit parallel to it to confirm that something in that circuit isn't dragging the voltage down.

 

[luigidedom]

ive traced the unstriped end of D204a to the speaker output, the striped end then goes to one side of a 33k resistor, the other end of the 33k resistor goes to pin1 of the audio modulator board like some kind of feedback network

 

[Perry Babin]

Is the circuit something like the one in the attached diagram?

 

[luigidedom]

doesn't look anything like that, the diode is in the output section of the amp, the amp turns on and 1 channel works perfect the 2nd channel that was faulty is non responsive

 

[luigidedom]

found a leaky driver, replaced the pair and the amp works perfectly