100watt Triple Series Lead TSL122
100watt Triple Series Lead TSL122
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Renovation Project
Renovation Project
This is the Marshall attempt to bring all things Marshall into one package, back in the Year 2000. A 100watt combo twin 12 inch, loaded to the max with Celestion Vintage and Celestion XXXXX Speakers . Three Channels, Clean, Crunch and Overdrive all Switchable from a foot pedal, a DI socket, 16, 8 and 4 Ohm Speaker output options, mute switch, Reverb, two FX loops and Mixing for these, plus all the basic Tone, no Tone switches on each channel. You'd have thought is was headed for Stardom...but unfortunately not.
This is the Marshall attempt to bring all things Marshall into one package, back in the Year 2000. A 100watt combo twin 12 inch, loaded to the max with Celestion Vintage and Celestion XXXXX Speakers . Three Channels, Clean, Crunch and Overdrive all Switchable from a foot pedal, a DI socket, 16, 8 and 4 Ohm Speaker output options, mute switch, Reverb, two FX loops and Mixing for these, plus all the basic Tone, no Tone switches on each channel. You'd have thought is was headed for Stardom...but unfortunately not.
Due to classic corporate bungling or lets be fair, bad design and worse manufacturing quality control... the amp has become something of a Fixers pet...can I make it work and if so how much damage am I going to have to sort out.
Due to classic corporate bungling or lets be fair, bad design and worse manufacturing quality control... the amp has become something of a Fixers pet...can I make it work and if so how much damage am I going to have to sort out.
Getting one fixed at the repair shop is going to be your worst nightmare... so they tend to end up in Storage! Suspended between...Oh I'll fix it one day, or may be trade it if I cant fix it, or may be sell it for parts!
Getting one fixed at the repair shop is going to be your worst nightmare... so they tend to end up in Storage! Suspended between...Oh I'll fix it one day, or may be trade it if I cant fix it, or may be sell it for parts!
I bought mine Amp off Ebay at the beginning of Covid-19 Lockdown in March 2020 as a thing to do! It was definitely a punt or pig in a poke as we say... as I knew nothing about them and wanted to broaden my understanding of Amplifiers in general etc. Having repaired my Peavey Delta Blues, this project was another step in the same direction of repairing PCB based Valve amps and looked like a decent challenge.
I bought mine Amp off Ebay at the beginning of Covid-19 Lockdown in March 2020 as a thing to do! It was definitely a punt or pig in a poke as we say... as I knew nothing about them and wanted to broaden my understanding of Amplifiers in general etc. Having repaired my Peavey Delta Blues, this project was another step in the same direction of repairing PCB based Valve amps and looked like a decent challenge.
Background
Background
This amp had been used in a church setting and then abandoned due to HT fuse blowing and Main Valves being destroyed.
It's a classic scenario with these Amps. The Amp came with only two of the original 12AX valves in a dubious state and no others.
The HT fuse was blown and the Reverb Disconnected.
The remaining elements of the story seemed to be that it had sat in a storage locker for several years and accumulated condensation damage / erosion from that.
There were numerous other minor defects, such as cosmetics on the Tolex and front grill, no feet and some knobs being the wrong sort.
Damaged Grille
Overall Main Parts Seemed Ok!
Dirty and Stained Tolex
Wrong Knobs and No Feet!
Investigation
Investigation
This AMP is Heavy, 41Kg!, not a casual busking Amp then!
This AMP is Heavy, 41Kg!, not a casual busking Amp then!
First remove the rear panels in their entirety (helps get access to Reverb Tray and cables as well)
Lay the Amp face down on the floor
Remove the four screws on the top
Slide the AMP case out backwards using the two Transformer cases as primary lifting points.
Take Care when removing the four screws on the top of the amp. The amp sits partly on the front ledge and will rest on the back panel struts. Taking out the screws when the amp is vertical can mean all the weight is on them. Best policy is to lay it Front Down on the floor remove the screws without the weight and slide the Amp out while laid down. Or get someone to help you!
Initial Tests
Initial Tests
Without Valves!
Without Valves!
Without replacing HT fuse I tested the 230v mains supply and transformer secondary voltages which came out OK.
Upon replacing the HT fuse and testing again the HT fuse failed within 30 seconds which meant some PCB short or PCB damage / components damage!
General Internal Inspection: Findings
General Internal Inspection: Findings
When doing an inspection:
Take Photos of the internals, especially Board connections and close ups of specific areas!
When doing an inspection:
Take Photos of the internals, especially Board connections and close ups of specific areas!
Corrosion on Spade Terminals
Solder Joints
What could be heat and tracking damage starting
Important to get General Views
of the connections
Get the Board Serial Numbers for Schematic Reference
List of Findings!
List of Findings!
- Mains PCB loose on supports
- Mains fuse carrier posts weakly soldered
- Blown HT Fuse
- Weakened connections on various Spade connectors on the mains PCB, Motherboard and in general.
- Corrosion on Mains PCB underside, and on Mother board underside, so assume all boards need checking.
- General Dirty and Dusty PCB's.
- 12AX7's looked Black and Damaged
- No signs of Resistor Failure or Track Heating Damage!
- No Signs of cabling or PCB component overheating
- Dubious amounts of Old Solder Flux around Valve Joints
- Valve Seats looked unworn and in good condition
Known Faults: to be checked
Known Faults: to be checked
This is stuff I've seen noted about these amps in Forum's, Sites and others experiences and comments!
This is stuff I've seen noted about these amps in Forum's, Sites and others experiences and comments!
Issue 0 to Issue 4 Motherboards having wrong resistors and or Wrong Bias Resistors in particular. Type and Issue Number of Boards needs Checking!
Overheating of Motherboard PCB causes High voltage / Low Voltage Tracking issues - causing variation of BIAS voltage primarily. This is due to Lack of ventilation and Valves being below the PCB and the tracks on the board being thin and very close together around HT pins and Bias pins.
Bias Voltage running away and causing Red Plating.
Difficulty getting BIAS voltage to operate at Marshall Recommended values of 90mv/ma. ( Does depend on the Valves your using and what you want it to sound like ). Adjustment of the Bias Resistors for various types of valves becomes difficult, due to the above and because the associated BIAS resistors are wrong and because there's variation on the various Issue numbers of Motherboard in respect to the Minimum Bias Voltage Resistor being different on Earlier boards.
Failure of the HT Fuse due to above BIAS issues and RED Plating of the Primary Valves
Failure of the HT fuse and Mains Fuse due to Cracking and burning around the FUSE carriers on the Mains PCB.
Failure of the Mains PCB due to Over flexing, its mounted using two screws to the back panel and flex's every time the IEC lead is inserted.
Corrosion and or Loose Spade Terminals causing burning, overheat, loss of connection, in various parts of the various boards
BIAS Voltage variation caused by Overdrive Board Capacitors being weak or under Voltage and breaking down.
16 Ohms Speaker Output ground connection not working when using 8/4 Ohms sockets causing OT fuse to blow and Output transformer damage.
Overheating and Failure of 1K resistors on Motherboard
Motherboard fuses blown
Resistor Variation due to Heat
High Levels of Hum from Deteriorating Filtering Capacitors
How to Solve the Problems!
How to Solve the Problems!
Board Inspections and Repair
Board Inspections and Repair
I removed the Mains, Reverb and Motherboards one at a time and checked these. I cleaned them with Isopropyl Alcohol to get rid of surface corrosion, dirt and old flux residue. This helps clarify the details of any issues.
I found general corrosion and poor soldering joints on the Spade Terminals across all boards. The Spade terminals have two very narrow feet sticking into the board and these weaken when the connector is Twisted for removal. The inevitable side to side motion cause solder joint fracturing!
Re-solder all these Joints!
Check out the Dubious Spade Joints!
Check out the Dubious Spade Joints!
I re-soldered all these and made sure they were at least better than before, they are a poor connection to the board with the two small pins and have to treated with Kid gloves when taking the cables on and off!
After Cleaning,
Looks Better, but not Finished yet!
After Cleaning,
Looks Better, but not Finished yet!
Although this board now looks cleaner and neater there's a lot to check out still. The Condensation damage wasn't as bad as I feared and residue from dust and other " White Oxide type materials, which could be Lead Oxide possibly, cleaned away Ok.
Schematics
Schematics
Board Issue Type
Board Issue Type
One of the Key issues I found was getting clear Schematics for the Boards Issue number. The issue Number is printed on the Board in a White Panel with the Issue number written in the corner.
There appears to be 3 Mains Circuits Diagrams, Issue 4 Issue 5 and Issue 7 and these show varying resistors etc for Biasing as the Manufacturing caught up with the issues.
The remaining diagrams relating to Mains, Reverb, Clean< Crunch and Overdrive Boards are all covered in various Issues....Mostly Issue 4. I've listed them all below with some handy sites for your own research
Schematics Sites for Marshall Amps (Circa 11-2020)
Schematics Sites for Marshall Amps (Circa 11-2020)
Schematics
Schematics
Mains PCB
Mains PCB
The Mains PCB is poorly mounted on two screws holding the IEC socket to the frame. After some research I found that this caused
Flexing of the Joints on the Fuse Holders as these are inserted into the Frame at the front, and soldered to the PCB, when the PCB moves the Fuse holder is levered against the frame and eventually cracks its soldered joints when the IEC lead is inserted.
Loose Spade terminals, these are badly soldered or fixed by very small pins to the PCB.
Solution:
Solution:
I mounted two 3mm hexagonal support pillars under the PCB by drilling a 3mm hold in the base of the frame and finding a space on the PCB to drill a 3mm hole to mount a plastic support stud. I did this in two places toward the middle and rear of the PCB and mounted the studs. This stopped the flexing of the PCB when the IEC lead is inserted
Prior to this I cleaned and renewed all the Soldered joints on the PCB and checked and tested the SPADE terminals for robustness, replacing dodgy ones with very little purchase
I also cleaned the inside of the Fuse Carriers. These get corroded/dirty over time and benefit from some cleaning.
Once replaced the PCB was solid and doesn't move at all now. This should in theory solve the issue of Joints cracking and creating blown HT fuses as well as dodgy mains supply.
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