Audiopipe apmi 1800.1, audio problem .

[rhempz01]

I have an audiopipe apmi 1800.1d that Powers up fine draws around 2.2amps of current at idle. All seems fine until I start to adjust the gain pot, the signal beacomes very strange. Sometimes it will even jump into protection. The signal despite 0 gain seems high to me. The gain pots have all been changed. As well as the power supply and output transistors.

 

[Perry Babin]

Does the amp work perfectly if you don't touch the pots on the amp and adjust the level with the signal source (only)?

 

[rhempz01]

All pots turned couterclock wise, down.

 

[rhempz01]

Just a quarter turn up and this happens. Would octocouplers cause this?

 

[Perry Babin]

Is it clipping hard (why not display entire waveform)?

What happens if you reduce the input level?

 

[rhempz01]

Sometimes no audio at all. Right now this

 

[rhempz01]

But no not clipping yet barly turning gain
Power off and on sometimes no audio, sometimes it there.

 

[Perry Babin]

Is anything sensitive to vibration or movement (other than the pots)?

 

[rhempz01]

I'll check perry. It's so strange that I didn't know how to explain to even ask for help. Originally I believe that the capacitors grounded out to the casing and brought the amp down. The leads were long and there was a large burn mark on the casing.

 

[rhempz01]

Nothing loss or vibration sensitive. But its back to flashing rapidly in and out of protection, and will not power up.

 

[Perry Babin]

Which one of the terminals (16, 4, other) of the 494 is pulsing when it's shutting off?

 

[rhempz01]

This is pin 12,

 

[rhempz01]

Pin 4

 

[Perry Babin]

You're looking for something pulsing at the same rate that the amp is shutting down.

 

[rhempz01]

I know they dont show you much. Seems like they all are. My power supply is just clicking and drawing over 2.5amps of current back and forth rapidly? Very quickly

 

[Perry Babin]

Is the 12v from your power supply rock solid? It should be at only 2.5 amps.

 

[rhempz01]

Yes, supply is solid

 

[Perry Babin]

Lift Q23 (after confirming that its collector is connected to pin 16 of the 494). This will disable most of the protection circuit. Be careful.

Does that allow the amp to remain on?

 

[rhempz01]

Ok so no that didnt work either, so i pulled the output transistors, 3 short, 1 octocoupler was short. So i replaced the driver IC'S, the octocouplers both sides and that is it so far.

 

[rhempz01]

Highside