PPI A1200

[Perry Babin]

Look at the output with your scope or use a sine wave and use your multimeter.

 

[mike49504]

signal levels are the same .

I checked the outputs again and i only get 6.82 volts of DC on 1 of the negative terminals

 

[Perry Babin]

Is this the side of the amp that oscillates when a speaker is connected to it?

Measure the DC voltage on pins 3 and 4 of the driver board and post the voltages. Place the black probe on pin 7 of the driver board when measuring the voltage.

 

[mike49504]

Pin3:-.006

Pin4:-.108

 

[Perry Babin]

I don't think the DC offset adjustment has enough range but you should at least try to get it zeroed (at the speaker terminals) with that first. If it doesn't have enough range, confirm that the voltage on the outer terminals (not the center terminal) of both DC offset pots have the same voltage.

 

[mike49504]

Which ones are the bias pots in this amp ??

There is 4 pots

VR1
VR5

And 2 between the driver boards marked VR2 VR3

 

[Perry Babin]

The DC offset pots are probably between the driver boards. They are likely 10k (or greater) pots. The bias pots are likely nearer 100 ohms.

 

[mike49504]

I havent messed with the pots yet.

I had the outputs out of the amp on the left channel and just soldered them back in.

Now the amp has 1.95 volts on the output for like 10 secs then goes to 0.2 volts and amp plays fine out of the left channel then after about 2 mins i get 1.95 volts on the output for a min then it goes back to 0


Do i need to adjust the pot still or what do i do from this point?

 

[Perry Babin]

Look for bad solder connections on the large transistors on the driver board. You'll need a lighted magnifying glass to see them, most likely.

 

[mike49504]

Thanks Perry,

I resoldered the big transistors on the driver board amp works 100% flawless