Orion HCCA 2500.1 Output Modification Question

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I got this amplifier that has had its output modified between the source and drain on the IRFP90N20's.
Would anyone know the reason why this would be done or has seen this performed?
The notes from the customer state that the amp slowly over time would go into protect and eventually didn't come out of protect. I suspect the output but do not know if this modification is the culprit of the slow death.
Also, the solder-bridged the 10-ohm resistors on the output of 4 voltage regulators for some odd reason. I was thinking one of the cards has been pulling too much current, so they bridged the output.
I don't want to spend a ton of time chasing issues in a modified amplifier if the modifications do not make sense especially since it uses a PIC.


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I'm not sure why it was done but the RC network done was done at Orion. The RC networks are connected between the rails and the output. It's generally done to reduce high frequency noise.

The 10 ohm resistors fail. Bridging them probably doesn't do any harm. I was told that the electrolytic filter caps get leaky but I've never seen a bad one. I thought the failure was due to inrush current. I replace them with the next larger package.

These amps have a strange clipping behavior. No one I know has been able to make it right.
As far as I know, it doesn't cause any problems except for a bit of confusion the first time you see it. If you repair it and you see a strange compression of the speaker level signal at the point where you would normally see clipping, don't bother trying to troubleshoot it.

If you repair the amp, take a short video of the operation for others to see.
Thank you,
By chance does anyone know what the resistor value is of R682 going to the base of Q681 (KTD600K)? It has burnt to a point that is un-readable. I think it is the creation of the -12v which I am missing to the HCCA card.
I will be repairing this as the PIC seems to be ok but I have never made a video before. I am entertaining the idea to acquire the gear to do so. I have sent an email to Orion but we shall see where that goes.


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