Marshall TSL100 popping crackling static

[BrotherJ]

Hi everyone,

I have a TSL100 (build '00) that has developed a popping static noise. (up until this point it has never failed)

At first this wasn't too bad, and would go away after a couple of minutes. Unfortunately now it's really bad that it blew the HT fuse.

The crackling noise is on all three channels and doesn't matter if anything is plugged into the input jack.

I've cleaned the valve sockets & tensioned them, checked over the board for bad solder connections, resoldered the octal valve bases. Changed all the Valves as well (before the fuse blew this morning)

The noise gets worse when I press in the VPR switch.

Any ideas of what to check for?

[izzybell2810]

At first this wasn't too bad, and would go away after a couple of minutes. Unfortunately now it's really bad that it blew the HT fuse.

The crackling noise is on all three channels and doesn't matter if anything is plugged into the input jack.

I've cleaned the valve sockets & tensioned them, checked over the board for bad solder connections, resoldered the octal valve bases. Changed all the Valves as well (before the fuse blew this morning)

The noise gets worse when I press in the VPR switch.

Any ideas of what to check for?

Hi.
Did it blow the fuse instantly, or did it take a while? Take the tubes out replace the fuse and power up the amp. If it comes of standby and doesn't blow the fuse then check the screen resistors and the new tubes(Just because they're new doesn't mean they work). if it's still blowing, I would check the bridge rect BR1 and Coupling caps. You say you cleaned the tube sockets, were they visibly dirty (carbon)? If so check filter caps!

[BrotherJ]

Hi, thanks for the reply.

In between the Christmas festivities I had got in there again (Before coming back on here)

The amp still had the crackling & popping even after removing the PI tube. I changed the connectors to the other side of the standby switch and still no go.

I changed the caps in the bias circuit (C36,C37 & C42) checked amp and still popping. Checked the Screen resistors & grid stopper resistors - checked fine.

I then changed the rest of the resistors R67,R69,R68 and two that looked a little suspect R4&R5.

Checked the amp and no popping but one output pair (V5&V6) are red plating (Bias showed over 900mV!) other pair V7&V8 were running 150mV.

I switched the amp off quickly!

I think it might be time to take it to the tech!

[izzybell2810]

Pull the tubes and check the neg voltage at pins 5. Should be about -35 to - 50
for EL 34's. It should be OK, as you've checked and replaced the resistors and caps from the PI. If it checks out, then clean and retention the sockets. A badly connected grid will cause a loss of bias.

[pila]

If it blew the HT fuse, you may even have a bad filter cap, even though it's not all that old. The crackling/popping sound could possibly be the noise of a failing electrolytic cap.

[BrotherJ]

Hey guys,

Thanks for the replies! I hate to be a downer but I thought I might leave this one up to the Marshall tech here as it might be stretching my capabilities on this amp - that and I am now having nightmares about pulling that main board any more times

I dropped it off this morning, The tech (Mark @ Megtronics) is great with valve amps and helpful with info... I will report back here the cause of failure

Cheers and hope everyone here have a great new years!

[BrotherJ]

Sorry just a quick question to any marshall repair guys on here, how much are you able to obtain a main board for a TSL100? (The new upgraded type)

Some of the sites are saying around 76 pounds, the Marshall dealer here in Australia quoted me AU$600 (Thats priced to me, im not trade so it might be cheaper for a shop who do their warranty work) but none the less a massive jump on what I expected the price to be...

Thanks!