Lanzar Optidrive 4000D problem

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I have an Opti4000D (same board as the SS XXX6500 I hear)
The problem is, that some frequency's sounded a bit like they had a 'stutter' to them. It only seemed to happen from about vol 18/26.
I adjusted the gain to zero and kept the headunit low then adjusted the volume to see if it was the amp or headunit. I then tried this with the gain. I have now found it is the amplifier at fault.
When I turned the gain up to a certain point and the bass went from sounding like a clean signal to a noise which I can only describe being like someone had dubbed over my CD with another bass-heavy track. It was still making bass, just not what I was playing...
It does not do this with the RCA's unplugged.
The amplifier switches on and works every time.

I have since checked ALL fets and output transistors and everything gives correct readings.

Has anybody seen this problem before?
 
Hi Perry, did a few checks with the DMM today.
The RCA shields came back with 0.02Ohms so I assumed that they were OK. I checked and swapped the RCA's for some other known good ones.

I'm not sure if this means anything, I am hoping you can shed some light on it.
I checked the resistance between the RCA outer jacket (whilst plugged in to the amp) and ground. I got about 18-19Ohms. Does this sound about right?
I also noticed that touching a ground source the the shields on the amp (either input or output) gave a slight 'thud' at the sub...

You guessed it, I did a few gut shots of inside the amp which I'm about to upload. There are a few items that appear to have either been added on or fixed at some point... I'll get these uploaded now. Thanks
 
For some reason I cannot seem to edit my posts or upload pictures properly...

146b8dc7.jpg
 
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