soundstream rubicon picasso 10.2 overload problem

[russdeanlee]

both overload light remains lit no output after screwing down transistors, before that it was working fine without the transistor being snugged to the heatsink i finger tightened them. the before both overload did light up everytime the amp turns on then after 1 second will disappear and everything works as should on both channels. i'm assuming i shorting something to ground?

[russdeanlee]

test speakers are focal component to passive crossover box load is 4ohms

[azvrt]

Just for your information, the correct name for this amplifier is Soundstream Rubicon Class A 10.2
It's not a Picasso.

It's normal that the clipping indicators are lit on Rubicons during the turn-on delay.
I had a 10.2 with an abnormally long turn-on delay of about 4 minutes, during that whole time the clipping indicators were lit.
But that does not imply yuo're having the same problem.
Did you receive my email with the schematics and bias setting, 2 days ago ?

If I understand correctly you just extra tightened the screws that bolt down the transistors to the heatsink ? You did not remove the board from the heatsink ?
If you did not, you might want to remove the board and clean the polyimide, sometimes tiny pieces of metal get stuck in the thermal compound and might cause a short.

With most Soundstreams, you can check for transistors shorting with the heatsink by using a multimeter set to 'ohms', put one lead on one of the screws that make direct contact with the heatsink and put the other lead on all legs of all transistors one by one, to find out whether you have a short due to compromised polyimide.
Unfortunatly, the 10.2 has some legs of the transistors actually shorting with the heatsink so that's problem.

Maybe someone else can help out, I need help with some/most repairs myself.

[EBBCO]

Polymide is almost for sure the issue. It cracks when old. When you tighten transistor down it splits protective layer. Shorts to heatsink.

[azvrt]

Originally Posted by EBBCO

Polymide is almost for sure the issue. It cracks when old. When you tighten transistor down it splits protective layer. Shorts to heatsink.

That's very interesting.
Best to remove the board from the heatsink then, and check the polyimide, either for cracks or for tiny metal pieces and if so, remove then.
If in doubt, replace the entire polyimide and apply thermal compound on both sides of the new polyimide.

Lots of screws that bolt down the board to the heatsink on this particular amp

[Perry Babin]

The tabs of the transistors are connected to the power supply rails so if one was shorting to the sink, it would likely blow the fuse. It wouldn't cause the overload to be triggered.

[azvrt]

Even with the 80 ampere fuse of this amplifier ?

[Perry Babin]

The over-current protection is triggered by having too much current flowing through the output transistors. No current would flow through the semiconductor material in the transistor if the tab was shorted to the heatsink.

There was at least one amp (644s) that had a trace too close to the washers and if the washer wasn't positioned properly, it would short to the trace. I don't know if this is a problem in the amp here but it's something that should be checked.

[azvrt]

You are very right.

Also, at some point I bought a Class A 3.0 and Ref 500 board, they were the very first production units that were very slightly different from later units.
When I replaced damaged boards by these purchased boards, the screws were not positioned right over the screwholes, so we had to enlarge the holes in the board, which made the screws we late put in to bolt down the board to the heatsink short with the traces.

We solved it by putting stuff around the screws, don't know how it is called in english, maybe you can tell me:
http://www.krimpkous.com/foto-krimpkous/aanbieding.jpg

By the way it would surprise me if the 10.2 has this problem, but it's definitely worth checking.

[Perry Babin]

Heatshrink tubing.