US Amps MD3

[caraudioguy2100]

Anyone know what outputs go in this amp ?

Someone worked on it before and there were all FB31N20 in the locations which were blown .

I replaced them and the burn up instantly

 

[Perry Babin]

Do you have a drive signal (with signal in, no outputs)?

 

[caraudioguy2100]

I don’t see any drive signal for the outputs

 

[Perry Babin]

What's the DC voltage between the collector and emitter of Q39?

 

[caraudioguy2100]

0.12 volts

 

[Perry Babin]

What's the DC voltage across R168?

 

[caraudioguy2100]

7.86 volts

 

[Perry Babin]

Are you getting the input signal drive to R136?

 

[caraudioguy2100]

No

 

[Perry Babin]

Pots/switches, enough input level?

 

[caraudioguy2100]

I found some problems on this amp with more testing .

I found at least 3 shorted MPSA42’s in the output section .

I will replace them and see why I come up with

 

[caraudioguy2100]

I have drive on half the outputs but it on the other half .

Q47,48,49,50,51,52 have no drive ar all and I replaced all the drivers

 

[Perry Babin]

Is the drive to the low-side 50% duty cycle?

Does connecting a load to the speaker terminals help see the high-side drive?

 

[caraudioguy2100]

I figured it out I replaced all of the drivers and had 1 that was defective out of the package replaced it and amp is working .

Thanks for helping me with this amp greatly appreciated