Rockford Fosgate Punch 360a2

[seankane]

Hello everyone.

I have a Punch 360a2 board number PC-2036-C

The power supply and both channels were defective.

I repaired the power supply and all is well.
I repaired the right channel and all is well with that as well.

The left chanel is still defective. I replaced all the outputs, the gate resistors, the source resistors, and a few smd transistors and diodes that were burned.

The left channel has no DC present but it will not bias and only produces the top half of the waveform.

Any ideas where to look next?

 

[Perry Babin]

Did you lift the diode (D104) that allows the protection circuit to clamp the bottom half of the output?

 

[seankane]

D104 was replaced with a new component, but I did not lift it to see if the channel produces the bottom half of the waveform.

Shall I lift it and view the signal through the scope to see if it does?

 

[Perry Babin]

Lifting the diode will allow the audio circuit to operate without the protection circuit. If the audio circuit works perfectly without the diode in the circuit, you know that the fault is almost certainly with the protection circuit components.

 

[seankane]

Lifting D104 allows the amp to produce a clean upper and lower waveform.

I already replaced all the smd diodes and transistors in that channel cause a few were burned. Did I miss something????

 

[Perry Babin]

Double-check the 0.1 ohm resistors. If they're well out of tolerance, the amp will clip the output when driving a load.

If those are OK, double-check the transistors in that part of the protection circuit to confirm that there are no bad solder connections, no bridges and all of the transistors are the right ones for each location.

 

[brandes.cm]

Double check all of the resistors in that section, a 500a2 I worked on had one slightly out of tolerance which caused the same issue you are seeing.

 

[seankane]

All of the source resistors are new and within tolerance.

I guess I will start checking all the smd resistors in that channel as brandes.cm has suggested?

 

[seankane]

OK getting back to this amp after catching up on lots of repairs and bringing it back to the top. Lifting D104 allows the left channel to bias and produce the upper and lower half of the waveform. It also produces clean output on the scope and with a load to a speaker.

As I already stated I replaced every smd transistor and diode in the channel due to several being burnt. I have verified they are all in the correct spot. All of the 0.1 ohm source resistors are new and within tolerance. I have checked alot of the smd resistors and they seem OK.

Any ideas where to go next?

 

[Perry Babin]

Solder the resistor back into the circuit and start desoldering the next transistors in line going towards the 0.1 ohm source resistors. Do this one at a time, reinstalling the one that has previously been removed. At what point does the amp no longer produce clean audio?

 

[seankane]

Solder the resistor back into the circuit and start desoldering the next transistors in line going towards the 0.1 ohm source resistors. Do this one at a time, reinstalling the one that has previously been removed. At what point does the amp no longer produce clean audio?

So re-install D104 diode ? The amp will immediately produce distorted sound with this diode installed. Maybe I didnt understand your request??

 

[Perry Babin]

Yes. That should have read D104 instead of 'resistor'.

With only one transistor out of the circuit at a time, when the following transistors are out of the circuit, which allow the amp to play cleanly?

Q116
Q117
Q118

 

[seankane]

I re-installed D104 and removed Q116 and the amp played clean audio. I have not tried removing Q117 or Q118 individually.

Thoughts?

 

[Perry Babin]

Do the same with 117 and 118.

 

[seankane]

Installed Q116 and removed Q117 and amp produces clean audio.

Installed Q117 and removed Q118 and amp only produces top half of waveform.

Thoughts?

 

[Perry Babin]

With all of these transistors in place, short the base and emitter terminals of Q117. Does that allow the amp to produce clean audio?

Does it produce a clean sine wave with all of the transistors in the circuit and no load?

 

[seankane]

Shorted the base and emitter of Q117 with all the transistors in place and the answer is YES it produces a clean sine wave upper and lower.

 

[seankane]

I decided to remove R153-R159 from the circuit to accurately test them.

I found R155 to be way out of tolerance, I replaced it with a new 1K resistor and the amp plays clean sound with a load and produces and clean sine wave.

Thanks for all you help Perry, when you told me to short the base and emitter of Q117 I did and referred to the schematic and it was obvious what I needed to check.

Thanks to you as well brandes.cm

 

[Atronic]

Hi guys, was wondering if anyone had a schematic for a Rockford Fosgate 360a2.
I have the same problem.
Sorry for my english

 

[Perry Babin]

Please don't post in a repair thread that was started by someone else unless you are trying to help them.

Start a new thread. When you ask for the diagram, include the PC # printed on the board.