Marshall TSL122 Extreme Issues

[fishman]

I am new to this forum but it seems that there is a wealth of tallent here. Perhaps one of you could enlighten me as to whats up with this *&)(()^^ amp.

I bought a 2004 Marshall TSL 122 Combo four months ago. It started popping (loudly) three months ago. Replaced tubes. Popping continued. Checked bias. L35 & R48. Replaced tubes again checked bias when left idiling (off standby) time 0 and 1 hour fairly constant. Checked again after playing 2 hours 90 - 120. Tubes cooked again and popping. (Tried fans etc) Brought to tec. Replaced bias pots (not board). Replaced caps, and checked filter caps. Still popped. He basically turned me loose.

Frustrated I disassembled the boards and reseated the connections and changed the contacts on the standby switch to the unused terminals. THe amp worked fair ( no popping but Hum) for 4 hours. Replaced the pre amp tubes the next night and as soon as I powered up the amp popped again. Took out the preamp tube next to the first power tube and put back in the old one. The amp performed again for 3 hours and reverted to popping.

Does anyone know what might be the issue.........is there anyone that can help? At wits end...band and wifey is not HAPPY and 2000$ down the tube is not possible right now. Unemployed ya know!

Thanks for any help that I can pass along to the tech
Fishman

[Sock Puppet]

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

Had a super lead 100 combo two or three weeks ago - nasty construction!

A couple of resistors were out of whack affecting a large bias drift which was killing one tube in particular.

The plated through holes on the power tube sockets had to be soldered on both sides of the double sided board, these had caused more trouble than enough with popping and crackling.

I got a mate to do it at the finish (he was a lot keener than me and has an enviable workshop). I was pleased to see the back of it.

- One of the caps from the P.I. was leaky under test too. Both were changed (.022 500V I think)

S.

[Twist]

Try this to isolate where the problem is, remove V4 (the driver tube) and turn the amp on. If the popping stops then we know it's in the pre amp section. The popping noise could be from high voltage arcing inside a transformer, across tube pin sockets or PC traces. Typically its from faulty tubes. If the amp was functioning ok and you noticed a slight hum there are a few factory mods to remedy that. It involves changes to the FX loop and DI. It sounds like the hum is from improperly biased tubes. If it's possible, could you look at the output tubes when the amp is popping to see if something inside the tubes flashes.

[fishman]

Thanks guys. I will look into this. Honestly I have not had enough time with the amp really working to know just how well it is operating. I suspect that the amp has not sounded right since the first popping incident. This doesnt really sound like the Marshall I expected I used to own a old (60's) 50 watter. I guess this is "progress". The clean channel seems a little weaker than the gain (crunch). Crunch is still good and strong (volume) and cleans up fairly good when the gain is down. I have not observed any flashes in the tubes (that I can see) but will look at that now. I need to get a schematic for the amp for the others...my tech tells me that the schematic listed on line is incorrect and lists the sub standard cap values.
Thanks again.

Anybody got the "real" schematic for this amp with the right values for the caps?

[Pedro Vecino]

Some differences between TSL exist, as the value of grid resistors in power tubes, but it is independent from these symptoms. No relation.
It is very probable that these random noises (pops) come from an bad functioning in one of the first plate resistors (1/4 watt). You can wait that break definitely (!) or to try to detect it.
You can begin for the four first ones (tubes 1 and 2) and try. Maybe need to change all, included those of the driver. Better, use 1/2 watt (or 1 watt) resistors
This is what I have found in two units.
Regards

[fishman]

Pedro thanks for the reply.
Stupid question by tubes 1 and 2 you mean the power tubes or the pre amp?

OOP's my bad...you mean preamp tubes v1 and v2 right?

[fishman]

Hey Guys
Pulled the preamp tube and the amp was quiet. No noise or popping. I could see no flashes in the tubes. Curiously when I put back in the preamp tube. There was a low volume woshing noise but only on the clean channel. The popping is definately louder on the clean than the crunch channel. Also the volume of the clean channel is definately lower than the crunch all settings the same. When the crunch channel popps and I switch back to the clean it is buzzing badly. Once the clean channel popps again the buzzing decreases dramaticlly. I did notice that there is material in the bottom of the power tubes V! - V4. I assume this means the tubes are shot again! 4th set...what can be the casue of the bias running amuck? Will check it, correct me if I am wrong the bias should equal 90 (ie L45 and R45) or be 90 per side?

Thanks...anyone know a MARSHALL wizard in CT I am begining to think it will take magic to fix.
Regards

[oc disorder]

It may be the DC heater supply to the first 2 pre-amp tubes.
Here's a detailed "fix" re a DSL201/401
http://www.historiclespauls.com/musi...d=22&Itemid=48
Look under amps if that doesn't work.
Recently had a TSL with the clean channel humming.
Replaced the bridge rectifier with a higher rated one
and replaced the 3,300uF (x4) with 105deg ones.
Usually with a magnifing glass you can see cracks around
the bridge rectifier solder points.
You may be lucky and re soldering these may fix the problem.
For this you will have to move the top pcb out of the way
by undoing the jack nuts and the screws holding the XLR DI out.
When I replaced the bridge rectifier I mounted it aprox 1 cm up
from the board so I could solder both sides and makes it easier
to remove should there be a next time round.

[fishman]

OC
Thanks man I had a long talk with my tech and he too thought that this may be an issue. I will disassemble tomorrow AM. While I am at it I will be examining the caps and resistors associated with the preamp section. I suspect that since it got worse when I replaced the tubes there may be a stess crack in the board as well. This thing is real sick.
Thanks for the help...rock on.
Rick