"Gareth Magennis"
"Phil Allison"
"Gareth Magennis"

Looks like someone may have tried to sort this problem out before, but
didn't replace the PCB?

http://www.lynx.bc.ca/~jc/TSL122.html


** The PCB material is definitely the cause of the problem.

It is made from UTTER CRAP !!

However - uber clever fixes involving a Dremel or mounting resistors in
mid air or any similar hare brained ideas are all just re-arranging the
deck chairs on the SS Titanic.

If no new PCB is available from Marshall at a reasonable price - just
add a bloody fan !!!!!!!!!!!!!!!!!

A single 120mm, 240VAC fan blowing directly on the OP tubes from below
cures the overheating / bias runaway problem completely.


New PCB's ARE available from Marshall, at about £60 to the customer if I
buy and fit one. Marshall tell me they sell a lot of them.
I understand costs are much higher outside the UK, however.


** It's not just the cost in dollars or whatever - availability is crucial
too.

Even common Marshall power and output transformers ( the ****ty Indian made
one ones that sit the lams right on the chassis) are regularly out of stock
here in Australia for months on end.

New output stage PCBs are not even on the radar !!!!!!!!!



I totally agree the bodges and drilling malarky - the problem IS the
PCB material.

Charging the customer a whole bunch of labour to bodge a way around this
problem is, IMHO, unethical, as he STILL has a faulty PCB, and has been
charged loads of money not to fix the real problem.

Replacing the PCB is relatively cheap (compared with the alternative
labour costs) quick and easy, and is the only logical solution here.


** See above.

The logical solution is the use a bloody FAN !!!!!!!!

Takes less than 1 hour to fit one to any combo model and the job is DONE !!

An IEC inlet mounted on the lower back panel supplies AC power to the fan
and it is up to the owner to use an extra IEC lead to run it.



..... Phil