Re: Anyone Have the Pleasure of Working on a Marshall TSL100?
- From: jh <jh-audiop_NOSPAM@xxxxxxxxxxx>
- Date: Thu, 17 Apr 2008 06:18:06 +0200
Elvis Kabong schrieb:
This amp is insanely and ludicrously designed
and constructed. And the schematics suck too.
I told the owner he should just take a sledge
hammer to it, box up the carcass and debris,
piss and shit and puke on it, then ship it to
Marshall headquarters specifying that it go
to the engineer who designed it.
But since it belongs to a friend of mine,
I'm going thru the drudgery of fixing it anyway,
but what a POS PITA! *Seven* separate PCBs
with and jumper connects all over the bleedin'
place!
Here's what it's doing - after setting the bias on
*any* set of EL34s, then letting them cook awhile,
the bias starts climbing and keeps on climbing
thus overheating the tubes, even while continually
adjusting the bias trimmers. If I was to continue to
let the bias climb, it would eventually burn out the tubes
then the HT fuse would have blown. In case there was some
leaky component, I shotgunned the entire bias circuit -
the diodes, caps and resistors. But it still does it!
So referring to the "brilliantly" organized schematic
I look for the source voltage and come to connector 14
and what does it connect to? Connector 2 on another
page. Well, another page is understandable, but why
not call the other end connector on that page also
"connector 14"? Sheeks! I'm having enough problem
trying to solve the malfunction of this stupid amp and the
schematic is like some childish maze one has to waste
even more time finding interlinkages. Then I look on the
PCB and find some other links and notice they're going
to what appears to be last minute add-on taps to what
seems to be a JCM900 PT.
So I take a look at what goes to "Connector 2" on page 2
and it goes to a +&- 15Volt supply which is fused and
figured it was not drawing much current or it's fuses would
have blown.
Then there's Connector 12 which goes to Connector 20
on some other page and from there to Connector 19
to somewhere else. Sheeks, what do I have to do to
localize frickin' problem? Check out every bleedin'
component on the entire amp? Damn!
So, I'm thinking why not cut traces, make a typical Marshall
bias circuit with just one trimmer on some perf board and stick in
there...then I realized if I hooked it up to the same source,
the bias would *still* climb until I find real source of the
problem.
So if any of you guys of lime can help this yank-off
with the answer if having already dealt with this same problem,
or any of you fellow yank techs, it sure would save me
lots and lots of time tracing down the real culprit and
would be *greatly* appreciated.
Ed
Hi Ed,
BTDT
take look at the grid stoppers, i bet they are 220k in this particular unit....
change them to a standard value and have a look. Although Marshall would tell you the 220k is there on purpose, I still consider it a design flaw.
Second glance: the small ceramic snubber disk at the finals. Voltage rating is too low IMHO, but the symptoms of your particular unit are not quite matching.
regards
Jochen
.
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