Punch 500a2 distorted channel

[chipper]

I have a problem with the left channel on this amp. Q123 hets to hot and the so does Q113 side that i removed the bad outputs, source resistors. I was checking other components and i couldn't find anything else or i'm not checking right? I don't want to install the new outputs yet because Q123 & Q113.

[Perry Babin]

What's the DC voltage measured 'directly across' R174 and R175?

[chipper]

Originally Posted by Perry Babin

What's the DC voltage measured 'directly across' R174 and R175?

R175: 012.3mV
R174: 012.7mV

And Q113 has 24.03 dc on base & collector. Is that normal???? And it gets really hot!

EDIT: R175 & R174 kept rising.

[Perry Babin]

Do you have any solder bridges between the pads for the outputs?

Confirm with your meter set to ohms that no two adjacent pads read near 0 ohms. Check all of the output pads for this channel.

[chipper]

Originally Posted by Perry Babin

Do you have any solder bridges between the pads for the outputs?

Confirm with your meter set to ohms that no two adjacent pads read near 0 ohms. Check all of the output pads for this channel.

Can I ask where am I getting 24 volts from on the driver transistor? Explains why things were getting hot. I really want to fix this but I am unsure where the source is on this problem. What would be an approximate 'good' reading for the SMT parts when measuring continuity?

I am starting to hate this amplifier.....! -.-

[Perry Babin]

Did you check for the bridges between the pads with your meter?

Things are unpredictable (voltage-wise) when components are missing from the feedback loop (this includes the outputs). If you want to repair this, you need to eliminate one problem at a time.

If you're checking components in the circuit, you can compare one channel to the other (meter on resistance, probe placement identical for each component being checked, no power applied to the amp).

[chipper]

Originally Posted by Perry Babin

Did you check for the bridges between the pads with your meter?

Things are unpredictable (voltage-wise) when components are missing from the feedback loop (this includes the outputs). If you want to repair this, you need to eliminate one problem at a time.

If you're checking components in the circuit, you can compare one channel to the other (meter on resistance, probe placement identical for each component being checked, no power applied to the amp).

I did and I didn't get anything near 0 from gate, drain, source i did get high resistance readings thought from source to drain, drain to source. I also replaced a 2A transistor with another working 2A transistor.

What if the bias pot is turned up?? Could this cause problems?

[Perry Babin]

It should be set fully counter-clockwise until you get the outputs reinstalled and clamped down.

I'd suggest that you install the outputs, clamp them down tightly to the heatsink, insert a 10 amp ATC/ATO fuse in the B+ line and power the amp up.

Does the fuse blow?

Do you have any significant DC across the speaker terminals of the repaired channel?

[chipper]

Originally Posted by Perry Babin

It should be set fully counter-clockwise until you get the outputs reinstalled and clamped down.

I'd suggest that you install the outputs, clamp them down tightly to the heatsink, insert a 10 amp ATC/ATO fuse in the B+ line and power the amp up.

Does the fuse blow?

Do you have any significant DC across the speaker terminals of the repaired channel?

I have new outputs, but i don't want to blow them and the old ones are shorted but I'll give it a try even if it shorts the new ones. And yea I have a 5 amp fuse inserted at all times during testing, trouble shooting. But if it blows the new outputs what does this mean???

[Perry Babin]

If you clamp them tightly to the heatsink and have a 5 amp fuse in the B+ line, there is virtually no way to damage them.