Taramps DS 1200X4 output transistors getting hot and amplifier pulling excess current

[cush man]

This is the reading of the FETs more or less and also the inductors.

Should I solder in the IC and FETs and remove the inductors?

 

[Perry Babin]

After all channels are oscillating, check the voltage on all of these points.

Check the pads like you did the ICs (previous images) to make sure that there are no abnormal readings.

 

[cush man]

With the FETs in or out?

 

[Perry Babin]

FETs in the circuit. The high-side B+ may charge without oscillating but without the FETs oscillating, it won't mean anything. The 4148 diodes are much less than most amps use. Confirm that all are OK.

Also measure the DCV across gate and source terminals of all of the FETs. Do all read approximately the same?

 

[cush man]

They're going to get too hot before I can do any testing. Should I remove the inductors?

 

[Perry Babin]

The inductors shouldn't make a difference.

Clamp the FETs tightly to the heatsink.

 

[cush man]

Okay doing that now give me a few.

 

[cush man]

The 4148 diodes read okay.

 

[cush man]

FETs in the circuit. The high-side B+ may charge without oscillating but without the FETs oscillating, it won't mean anything. The 4148 diodes are much less than most amps use. Confirm that all are OK.

Also measure the DCV across gate and source terminals of all of the FETs. Do all read approximately the same?

Channel 3 and 1 gate and source voltage is less than half a volt. Channels 1 and 2 are 3-3.5 volts.

 

[Perry Babin]

DCV from the last image I posted?

Are all 4 channels oscillating?

 

[cush man]

After all channels are oscillating, check the voltage on all of these points.

Check the pads like you did the ICs (previous images) to make sure that there are no abnormal readings.

A 8.7 volts
B 8.7 volts
C 8.7 volts
D 8.7 volts
E 9.6 volts

 

[cush man]

I don't think the IC is starting up fully.

 

[cush man]

Sorry about the images...

First image is high side gate pin.
Second image is low side drain pin

 

[Perry Babin]

What's the DCV on all 3 terminals of the 12v regulator feeding the VCC and the VCC2 terminals of the IC?

 

[cush man]

I've set the PS to 1 amp so when the amplifier starts to draw excess current the voltage drops down to 7 volts and the rail voltage drops to +/- 22 volts. The regular that produces the voltage for VCC and VCC2 is measuring 10 volts on all pins when I just check it.

Should I allow the amplifier to draw more current?

 

[Perry Babin]

Using a 2 ohm resistor to limit current would likely work better.

You can't starve amplifiers for current and expect them to work properly. If all FETs are clamped, it's very difficult to do any damage unless you have much more current available.

 

[cush man]

2 ohm! Any specific wattage, or maybe an inline fuse?

 

[Perry Babin]

Do you have any dummy loads?

 

[cush man]

No sir.

But it's on my next purchase before the tariffs.

 

[Perry Babin]

A fuse can be a good option. Try a 5 amp ATC/ATO. If you need to, you can go a bit higher.

I prefer the cylindrical wirewound type like the Ohmite 270 series, 100 watt. 2 ohm is good for most amplifiers. For large amplifiers, you sometimes need to go to 1 ohm (two 2 ohm in parallel). I'd also suggest getting a 12v piezo buzzer to connect across it. It gives an audible indication of a change in current flow.

If you don't want the type shown, any large resistors (100w or larger) will work.