Voodoo Amps - Marshall TSL & DSL Bias Issues

TSL & DSL TROUBLE SHOOTING GUIDE

The information on this page has been accumulated through years of technical experience, trouble shooting and countless live shows. We hope you find this page helpful and that is aids in helping you resolve the problems you are experiencing.

Basics

	Read through our Basic Trouble Shooting Guide first. Many problems can be resolved this way & it's free
	Do not use a 2-prong AC cheater plug
	Be certain you are using a known-to-be-good cables
	Plug guitar directly into amp (eliminate all effects, etc from signal chain)
	If the problem persists proceed to TSL / DSL trouble shooting guide

Brief Check List:

THERMAL RUNAWAY
BIASING
POWER TUBE FAILURE
AMP SWITCHING CHANNELS IN ITS OWN
AUDIO CUTTING OUT
FX LOOP ISSUES

What are your feelings on the "Thermal Runaway" We have worked on hundreds of TSL/DSL's over the years we have not seen any indication of a "thermal runaway" issue. This is usually resolved by properly biaisng the amplifier (IE: most that arrive are severally over biased / biased improperly).

I am trying to bias my amp by using the factory spec chart but the bias never settles and runs away It is very easy to cause unwanted damage to these amps if you do not know how to bias them properly.

Important Do not use the factory spec sheet to bias these amps as it is inaccurate
Doing so will likely result in costly damage to the amp as well as shorter tube life
We do not recommended biasing to a fixed number
Take it to a qualified tech or learn how to properly & safely bias this amp
Please note - It is cheaper to have your amp properly biased ($35-$50) than to pay for a larger repair bill

We recommend the following for biasing a TSL / DSL series amp

Use three (3) digital multi meters (DMM's)
Set up two (2) DMM's to monitor each side simultaneously via the three (3) pins near the power tubes
Set up one (1) DMM to monitor the plate voltage (warning - high voltage!)
Crunch the math and bias accordingly
Note - we recommend making small adjustments to the bias/trim pots as one side effects the other
Continue to crunch the math and rebias until all numbers remain the same
It takes a bit for these amps to settle so be patient
Most lead players seem to prefer setting the bias to 60%-62%
If biased correctly the bias will not drift, run away or go "thermal"

I was playing and suddenly I heard a "pop" and the volume changed. It looked like a power tube shorted so I replaced them. When I turned it on there was a hum that kept getting louder and then the HT Fuse blew. The amp lights up but nothing comes out. Help!

For the sake of this page we will attempt to make this as easy to understand as possible. With regards to an EL34 failing / shorting;

HT FUSE (IE: high tension fuse)
On prior models the "HT Fuse" was often located in series with the output transformer's (OT) center tap on prior models. This was to protect the OT from unwanted damage.
When a power tube would fail the HT Fuse would blow almost immediately thereby protecting the OT, indicating a short in the power supply (IE: a faulty power tube)
Unfortunately the location of the HT Fuse was moved on these models IE: when a power tube fails the HT Fuse does not blow right away
IMPORTANT If you keep turning the amp on you are most likely causing additional unnecessary damage.
We recommend taking the amp to a reputable repair tech who has experience repairing these amps (very important!)

Can I just replace the power tubes? We do not recommend it. A majority of the time there are other components that are shorted on the main PC board. IE: if you install a new power tube into the socket that has sustained damage the odds are you will short/cause a brand new tube to fail.

I looked inside on the board and did not see any burnt components so I should be ok, yes? There may very well be arching on the opposite side of the board that you cannot see as well some other components that are damaged that visually appear fine. IMPORTANT if you continue to turn the amp on you could cause additional damage. By the time the HT Fuse does blow there is almost certainly arching on the PC board, damaged trace(s), faulty components, etc.

What do you recommend? Take or send the amp to a qualified repair tech who has experience repairing these models. Do not continue to turn the amp on.

We understand that players are trying to trouble shoot the amp to get the amp back up-n-running as soon as possible as well as save money (we support this) however we do not recommend this approach on these models as more times than not it leads to a costly repair bill. IE: We have seen far too many of these amps where the OT (output transformer) and/or the PT (power transformer) were shorted due to someone turning the amp on repeatedly attempting to trouble shoot the amp. Take it to a qualified tech, spend a little to save a lot.

My amp is switching channels in its own

Problem - Amp is switching channels on its own
Solution - Unplug your footswitch. If the problem stops purchase a new footswitch
If problem persists - You either have cracked solder joints on the rear PC board where the footswitch plugs into the amp or a faulty male connector.
Solution - Take the amp to a reputable tech who is experienced as repairing this problem
Note - To avoid this carefully connect footswitch to the amp and make sure footswitch cable is not accidently stepped on or stressed. Loop cable through amp's handle to relieve stress
Footswitch - repairs are possible though it may be temporary and/or costly - get price quote first & compare

When I play the audio / sound cuts in and out

For head amplifier heads only (not combos)
Problem - Audio cuts in and out intermittently
Often times this is attributed to cracked solder joints on one or more of the speaker jacks
A - Set Master Volume set extremely low so audio just passes
B - Gently wiggle speaker jack. If this audio cuts in/out see solution
Solution - Solder connections and/or traces on rear PCB of amp need to be repaired
Note - In some cases the speaker jack(s) also need to be replaced
Take the amp to a reputable tech who is experienced as repairing this problem
Note - To avoid this make sure cable is not accidentally stepped on or stressed. Loop cable through amp's handle to relieve stress

Audio is cutting in / out on my FX-Loop

Problem - Audio cuts in and out intermittently
Often times this is attributed to cracked solder joints on one or more of the FX-Loop jacks
Solution - Solder connections and/or traces on rear PCB of amp need to be repaired
Note - In some cases the speaker jack(s) also need to be replaced
Solution - Solder joint(s) on rear PCB of amp need to be repaired or speaker jack(s) need to be replaced
We recommend taking amp to a reputable tech who is experienced as repairing this problem
Note - To avoid this make sure FX-Loop cables are not accidentally stepped on or stressed. Loop cables through amp's handle to relieve stress

Disclaimer All information given herein is for educational purposes only. There is no warranty, implied or otherwise, as to the correctness, suitability, or merchantability of the information for any purpose.

Warning Any and all changes made to electronic equipment must be done by qualified professional service personal. Even an unplugged amplifier contains High Voltages that are easily lethal even to the experienced electronic engineer. Do not remove the cover or chassis from your amplifier without professional assistance.

Voodoo Amps does not provide free tech support via phone or email

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