Marshall TSL122 No Sound

[Johnnyrockit]

There is no output from my TSL122 combo, I would like to try and diagnose the problem otherwise an expensive trip to an amp tech maybe needed.

To give a little history of the amp, I have owned it from new which was bought in 2003. The amp head has always got extremely hot in use, too hot to touch. In around 2007 it went back to Marshall for a service, at that time the main board was changed also which is still in the amp, it is revision 6.

Since then it has rarely been used, but recently has been losing power and gain when being used which after research, found is probably due to thermal bias drift, apparently quite common on JCM200 amps. So, I decided to rectify the problem by fitting a valvetubeguitaramps.com bias drift kit. During the fitment, I unfortunately broke one tube so replaced one pair with new. All seemed to go fine except for one problem, I could not obtain any voltage on one side of the bias circuit, even like this, all functions of the amp worked fine, the head was even much cooler than it had ever been.

I triple checked all connections to make sure they were correct and no shorts on the drilled bias pin 5 to the original connections of the main board, but all seemed fine. As a fault finding exercise, I swapped V5 + V6 with V7 + V8 after which the voltage at the bias pins transferred to the other side, so, I swapped one of the old valves with the other old tube I now had spare, There was voltage now present on both sides of bias circuit, though a little unstable on the one side which I put down to cooked old tubes from the bias drift problem. The amp played fine other than a 'wind rush' sound through the speakers for about 20 seconds after switching from standby, which went away.

I then replaced the two old tubes with another new pair which were matched to the first new pair. Upon switching from standby the 'wind rush' problem returned but did not go away, I should add that there was nothing connected to the input at this point, was just adjusting bias.

I expected this to go away as previous when plugging a guitar into the amp (after switching off and back on) but the sound was still there, upon playing a note, the amp made a loud bang and then no output.

I have looked for any signs of damage but can't see any without removing the boards. The power tubes all still glow, V1 preamp tube is glowing brighter than the other 3 which I initially thought were not glowing but are very dim. I have checked the voltage at pins 4/5 to 9 which is about 6.8v on all sockets

When the amp is switched on now, there is a spitting noise through the speakers but still no output from a signal. Even plugging straight into the effects return there is still no output.

Sorry for the War and Peace, I just thought I would give as much information as possible in the hope someone might be able to guide me in the right direction. Any help would be very much appreciated.

 

[Kuga]

Clean with a contact cleaner all valve sockets. All inputs too. Check all fuses. Check all connections and solder joins. Disasemble all amp boards to do It. To check Output transformer take your ohm meter and measure pin 3 on V-5 to pin 3 V-8(without all 4 power tubes installed) should read 20 ohms to 30 ohms.
Best of luck.

 

[Kuga]

What speaker output do you use on your TSL?
Take a look on this. At 28:30.

 

[Johnnyrockit]

Thankyou for the advice so far. I checked the resistance between pin 3 of V5 and V8 which was 31.4 ohms so all seems OK with the OT.
I have checked all the fuses except for F1 which is now underneath the bias mod board so will have to strip to check, however, this is the fuse in the supply to V5 heater and all the pre amp valve heaters so should be OK.
I will strip the boards from the chassis over the weekend and check for damage as suggested.
I have watched Tony MacKenzie's video and do indeed use the 16 ohm speaker connector. Could you tell me if and how removing the speaker lead with no power to the amp can cause a ground fault please? Is this due to the residual power left in the amp?
I will check capacitor C46 when the main board is removed and get back.

I should add that I am completely inexperienced with amp diagnosis and repair, just know a little about electrical circuits and the function of some electronic components to understand some of the amp schematics so if I ask what may seem a stupid question please bear with me.

 

[Dogs of Doom]

before you take it apart...

do you have another amp? if so, try running a cable out of the effects send & into the other amp & see if you get a signal.

also, plug your guitar, straight into the effects return & see if you get sound.

This amp also has a mute button. Make sure it's not faulty. Try working it on/off a few x's.

The main problems usually do not mean no sound, but can lead to that, if they screwed something else up to that point...

Try eliminating a few things 1st, before you go all out.

also, there's a few posts, on here, by madampscientist that give a series of tests you can do, by pulling the power tubes & measuring either ohms (power off - unplugged) or voltage (power on).

Once you go through that & post your findings, maybe someone can give you a prescription, even w/o tearing the whole thing apart.

 

[Kuga]

Thankyou for the advice so far. I checked the resistance between pin 3 of V5 and V8 which was 31.4 ohms so all seems OK with the OT.
I have checked all the fuses except for F1 which is now underneath the bias mod board so will have to strip to check, however, this is the fuse in the supply to V5 heater and all the pre amp valve heaters so should be OK.
I will strip the boards from the chassis over the weekend and check for damage as suggested.
I have watched Tony MacKenzie's video and do indeed use the 16 ohm speaker connector. Could you tell me if and how removing the speaker lead with no power to the amp can cause a ground fault please? Is this due to the residual power left in the amp?
I will check capacitor C46 when the main board is removed and get back.

I should add that I am completely inexperienced with amp diagnosis and repair, just know a little about electrical circuits and the function of some electronic components to understand some of the amp schematics so if I ask what may seem a stupid question please bear with me.

If C46 it's wrong the amp sounds but with a lot noise. The primary side of OT seems ok. Check secundary side, I think a yellow wire it's ground or OT common wire( negative wire from speakers output). Take your ohm Meter. Should be about at 4 ohms speaker output 0,4 Ohms, at 8 ohms 0,5 ohms at 16 ohms 0,6 ohms. To make sure OT it's ok check pin3 VDC voltage on power tubes. Without power valves about 470Vdc to 490Vdc. The ground (negative wire from speakers output) connection passes through the 16 ohm speaker output. If this Jack fails or is dirty, the 8 and 4 ohm outputs fails. A cable can be soldered to connect the ground directly to the 8 and 4 ohm jacks. Be aware of residual voltage on caps. You can use a 100ohms 5w resistor to discharge caps.

You know my English level it's poor I try my best.

Good look.

 

[Johnnyrockit]

If C46 it's wrong the amp sounds but with a lot noise. The primary side of OT seems ok. Check secundary side, I think a yellow wire it's ground or OT common wire( negative wire from speakers output). Take your ohm Meter. Should be about at 4 ohms speaker output 0,4 Ohms, at 8 ohms 0,5 ohms at 16 ohms 0,6 ohms. To make sure OT it's ok check pin3 VDC voltage on power tubes. Without power valves about 470Vdc to 490Vdc. The ground (negative wire from speakers output) connection passes through the 16 ohm speaker output. If this Jack fails or is dirty, the 8 and 4 ohm outputs fails. A cable can be soldered to connect the ground directly to the 8 and 4 ohm jacks. Be aware of residual voltage on caps. You can use a 100ohms 5w resistor to discharge caps.

You know my English level it's poor I try my best.

Good look.

Thanks again Kuga. I checked the resistance across the secondary terminals of the OT, I think black is the common terminal of the OT, there are no yellow cables to the OT. I have 0.2 ohms resistance on the 16 and 4 ohm output terminals, and 0.3 - 0.4 ohms on the 8 ohm terminal, from your description above it should be more than this so a possible short on the secondary side? Am I diagnosing this correct?
I can't measure the voltage at pin 3 of the power tubes at the moment as I have disassembled the main board from the amp, the good news is that there are no signs of burnt tracks, blown components or dry joints that I can see. Excuse my ignorance, but when I reassemble the amp, check the voltage between pin 3 and where? I am wary of creating a damaging short. I think I will bridge the ground terminal of the 16 ohm output jack to the 8 ohm jack on the back of the board efore reassembly though, luckily C46 is still OK.
Dogs of Doom, I did plug a guitar into the effects loop return and also used a Pod kidney bean as a preamp into the effects loop but still no signal, as explained above, there is an intermittent spitting/ popping noise through the speakers whether anything plugged to the input/ effects loop or nothing at all plugged in when switched off standby. I don' t have another amp with an effects return to take a lead from the effects send of the tsl122 unfortunately. There is an emulated out on the TSL, I don' t know if this is from preamp only though but would be a valid check to prove preamp integrity if is, I will try after reassembling that amp.
I am concerned that when the amp failed there was a loud bang to me indicating a component failure rather than a connection problem, I hope I'm wrong.

 

[Kuga]

The OT ground wire usually it's black. My bad. Maybe the yellow or orange one was the 16 Ohms output. The resistance should increase when you mesures secundary wiring from OT. I mean at 4 ohms need to be less than 8 or 16 Ohms. When you assembly all amp. Check all it's properly installed. Connect a speaker. Without power tubes check VDC on pin3. Pin3 it's positive VDC, ground wire or chassis it's negative VDC. I will check OT resistence from secundary side on my TSL. I will reported It.

 

[Kuga]

On my '98 TSL100. Ground it's a black wire. 4 ohms a green one 0,3 ohms. 8 ohms a orange one 0,4 ohms. 16 Ohms a red one 0,5 ohms. I check on OT terminals.

 

[Johnnyrockit]

Same colours on my amp, thanks for checking. The readings I took were from the green/orange/red to black. I checked again, definitely not 0.5 ohm red to black 16 ohm output connection, will reduce to 0.1 ohm if testing for a few seconds which I guess is a short internal of the windings?
I will check the voltage on pin 3 of the power valves and get back, am I correct in assuming this is to check the function of the power section prior to Output transformer?

 

[Kuga]

Bad news. Looks like 16 Ohms wiring from secundary side OT it's shorted.

am I correct in assuming this is to check the function of the power section prior to Output transformer?

Yes. Check and report what Vdc voltage you get on pin3 without power tubes. Then you can try 4 ohms speakers output with your speakers and power tubes installed but I think It will doesn't work. I'm sorry.

 

[Johnnyrockit]

Bad news. Looks like 16 Ohms wiring from secundary side OT it's shorted.

Yes. Check and report what Vdc voltage you get on pin3 without power tubes. Then you can try 4 ohms speakers output with your speakers and power tubes installed but I think It will doesn't work. I'm sorry.

I checked the voltage at pin 3 of the power tube sockets without the valves installed as suggested, I have 510 volts on all four positions, is having a little more than advised OK or does it signify another problem? Does having the voltage at the pins signify that the OT is duff, or could it also be the valves themselves?

I also tried connecting one speaker to the 8 ohm connection, when switching off standby with no guitar connected, the 'wind rush' sound mentioned at the beginning of the post immediately transmitted through the speaker at which point I switched the amp off. However, something strange happened, even with both power switches off but with power still connected to the amp, a gradually increasing in volume hum started to come from the speaker so I pulled the power cord at which point it stopped. I reconnected the powder cord to the amp but the him did not return.

I dodn' t try plugging a guitar into the amp for fear of another loud bang as before and causing more damage to the amp.

I hope the description above can shed some more light on my problem, ads always, I' m very grateful for the advice given.

 

[Kuga]

I checked the voltage at pin 3 of the power tube sockets without the valves installed as suggested, I have 510 volts on all four positions, is having a little more than advised OK or does it signify another problem? Does having the voltage at the pins signify that the OT is duff, or could it also be the valves themselves?

I also tried connecting one speaker to the 8 ohm connection, when switching off standby with no guitar connected, the 'wind rush' sound mentioned at the beginning of the post immediately transmitted through the speaker at which point I switched the amp off. However, something strange happened, even with both power switches off but with power still connected to the amp, a gradually increasing in volume hum started to come from the speaker so I pulled the power cord at which point it stopped. I reconnected the powder cord to the amp but the him did not return.

I dodn' t try plugging a guitar into the amp for fear of another loud bang as before and causing more damage to the amp.

I hope the description above can shed some more light on my problem, ads always, I' m very grateful for the advice given.

Don't put power tubes on it. Is It 510vdc on pin3 without power tubes? 510 Vdc could be ok without power tubes but I think OT It's damaged.
I think it would be a good idea to ask a qualified technician for a repair estimate. Telling him that you think It have a damaged OT and ask to check the entire amplifier.

Also will be great install issue 20 main board on it. Existed a kit to replace all boards to issue 20 too. I have all issue 20 boards on my TSL 100. Kit contains clean, crunch, lead boards, rear board and main board. You will have new pots, switchers and jack inputs on It. This last revision has much better components. Metal film resistors. New switching channels design. Better FX loop. It sounds better with issue 20. Still I have stock boards from my '98 TSL 100 in working condition but I use all issue 20 on It.

My '98 TSL 100 still have issue 1 bias board. Three years ago I replaced the two bias pots on this issue 1 board. It works great. I use It ofen.

 

[Johnnyrockit]

Don't put power tubes on it. Is It 510vdc on pin3 without power tubes? 510 Vdc could be ok without power tubes but I think OT It's damaged.
I think it would be a good idea to ask a qualified technician for a repair estimate. Telling him that you think It have a damaged OT and ask to check the entire amplifier.

Also will be great install issue 20 main board on it. Existed a kit to replace all boards to issue 20 too. I have all issue 20 boards on my TSL 100. Kit contains clean, crunch, lead boards, rear board and main board. You will have new pots, switchers and jack inputs on It. This last revision has much better components. Metal film resistors. New switching channels design. Better FX loop. It sounds better with issue 20. Still I have stock boards from my '98 TSL 100 in working condition but I use all issue 20 on It.

My '98 TSL 100 still have issue 1 bias board. Three years ago I replaced the two bias pots on this issue 1 board. It works great. I use It ofen.

Yes, 510 volts without power valves installed.

To give a better description of the 'wind rush' sound through the speakers, if you can imagine the sound you get when blowing over a microphone or trying to record sound in a high wind scenario, that is the sound from the speakers.

 

[Kuga]

Yes, 510 volts without power valves installed.

To give a better description of the 'wind rush' sound through the speakers, if you can imagine the sound you get when blowing over a microphone or trying to record sound in a high wind scenario, that is the sound from the speakers.

Maybe the wind rush sound it's because you have a damaged OT secundary wiring side. I never had a damaged OT on my amps. All have a stock OT.

Do It the wind rush sound without power valves?

 

[Spanngitter]

With the uppermost respect but I would not trust any ohm measurement on the secondary side unless you have a very high quality Ohmmeter which is capable of reading sub single digit resitance reliable and any fat finger influence is excluded.
The only, reasonable and reliable way to check Windings is to supply an small AC Voltage to the secondary, measure Voltage on the primary side and then calculate if the turn ratio makes sense and is correct. Based on this you can calculate the Impedance and check if everything is ok.
Do this for all 3 Output Taps and it will either confirm the OT being good or bad, see also here: https://www.aikenamps.com/index.php...nce,measuring the resulting secondary voltage.