SSL 611G channel module popping protection fuses **SOLVED**

[radiotech96]

Hey guys,


Has anyone ever encountered an SSL 611G channel module blowing one of the tiny 2 amp protection fuses on the +-18 Volt rail right by the edge connector? I also found a pair of 22 Ohm power resistors burned on the top right corner of the 242 Eq card. I am about to replace the 2 burned resistors, but I have not found any shorted caps or other components on the EQ card so far, but I am still searching. The two diodes connected to the 2Amp fuses in the protection circuit read shorted in circuit, but on desoldering are in fact not shorted. I removed every single card from the 611G module and the culprit appears to be in the 242 EQ card.

anyone seen this problem before?

[nycsudio1]

I had this problem once and it it turned out to be a wire inside the mic pre pot that broke loose and was touching another wire.

[jwhmca]

Check the card for the conductive "heatshrink" looking stuff...

[StarF666]

I had an issue where a wire bridge corroded through the protective lacquer down to a trace and shorted. Was hard to find because it happened only on power on of the desk.

[waltzingbear]

your sleuthing has been good, now you just need to find the problem in the EQ :-)

It wasn't clear to me how far you had gotten, but the next step could be to take an EQ from another channel and substitute it into the one with the problem to ascertain if it really is the EQ. 

Many potential problems can cause the fuses to blow. You could have a failed chip, bad wire, etc. If you can work on it on the bench would be best, but often not easily done.  Physical examination is first, particularly looking for any evidence of heating. Pulling chips may be useful, but not recommended unless you understand the circuit and can pull the "right" ones.

Its "just" a process of elimination of potential causes.

Alan

[xmax]

What the bear said, pull all the cards and put them back in one at a time until it pops!
Hopefully that works and you find what card is causing the problem and you can look
for a shorted component. If not take a really close look at all the wiring and the above
mentioned places that could cause a short. 

[mahavishnu]

It may well be that the failure on the EQ card is un-related to the primary 611 fuses. They are rarely taken out by cards as the card fusing usually goes before it gets to that point.
As is often the case, your first approach should be looking for shorts with a multi-meter.
Usually when only  the +18 V rail fuse goes there is a short in the TR components, so measure between +18 and ground and Logic + and ground.
If the fault is on the 611 motherboard you will still see the fault with all the cards removed.
Finding a fault in the TR components can be a black hole, look for a minor decrease in resistance to ground as you get closer to the culprit, and move all pots and the small fader  through the entire swing (a bad spot can cause this) and all switches up & down when testing, as it is often the case that the faulty component is in a state that does NOT cause the short while you are going at it...

[Matt Sartori]

if it mother board related (ie pops one of the fuse while no cards are plugged in) check around the EQ and COMP engaging switches as those boards can short the pins on the mother board and pop the fuse.

Mattia.

[radiotech96]

Thanks for all your help guys, I found that the problem was a combination of failed caps and resistors on the EQ cards on the +18 Volt bus and deteriorated wiring sheath on a resistor and capacitor on the back of the EQ cards causing shorting to occur. Solved with recapping and reinsulating the resistors on the back.