Marshall JCM2000 DSL401 repair (self.ToobAmps). At this stage I had no schematic and I had not worked on this model Marshall before. So I was just gathering info to learn its history. And I had biased the new matched quad tubes down to a more 'within spec' 0.8V, not 1.35+ Volts that Marshall released the amp with. That crackle was still. Amp schematic, (Marshall). Photograph of a JMP 2199. Thanx to Sam. 2200 JMP 100W Lead Combo, 100W 2x12' combo. This amp was in production from 1976 up to 1980. It was an all transistor Master Volume amp. This was the combo version of the 2098 Master Lead head. Pre amp schematic, (Marshall). Power amp schematic, (Marshall). Photograph of a JMP 2200. Reliable 50 watt guitar amp with 2 channels/2 modes option. Built-in guitar effects. Adjustments: Prescence, Treble, Mid, Bass, Deep, and Tone Shift. If thissounds like a dream, it is no longer – now that the JCM 2000 Dual Super Lead range is here. The 100 Watt DSL 100 and 50 Watt DSL 50 Dual Super Lead heads feature two footswitchable channels, Classic Gain /Channel A and Ultra Gain / Channel B. Peace Symbol and American flag type background on Two early / Cabinets, with Marshall 50 Watt Black Amplifier Head. - INSTRUMENTS FOR JOY / guitars would be fun with these. Ten Dollar Man. Jul 23, 2015 60-00 and 60-02 are the same schematics. At least it seems to be that 100 watt and 50 watt use the same circuits. 60-00 and 60-02 are the same schematics. At least it seems to be that 100 watt and 50 watt use the same circuits. So far I don't see.
TL:DR - Fixed a Marshall JCM2000 DSL401 from completely dead to 100% working better than factory.
The long version: I'm not an amp tech by any stretch. However, more than 10 years ago I was involved in a pretty catastrophic vehicle accident that left me unable to walk for two years.
During that time, I learnt to build my own tube amps thanks to the AX84 community, and some local Yahoo groups I joined at the time.
So, my knowledge and skills come purely from basic understanding and eliminating the causes.
I am a subscriber here and I don't often post or comment too much. However, I thought I'd write up about my friends JCM2000 DSL401 that I repaired for him after it had been through years of hell with various 'amp technicians'. I also thought I'd post this for anyone interested in reading how I got the amp working from being completely dead.
I got the amp from him with no lights or anything working at all.
Now, not being an amp tech. I don't have a variac, nor do I have an oscilloscope. I also don't have a tube tester. I have a multimeter and a gas soldering iron.
First thing was to see what life this amp had in it. Nothing turned on at all. This was a very glamorous fix, replace the main fuse.
Next up I got the power light/switch lighting up. Great. Before flicking the standby switch, let's see what the voltages are light inside.
I measured around the place in various spots to get a rough idea, and noted down the voltages. These weren't any special test points, at this stage I had no schematic and I had not worked on this model Marshall before. So I was just gathering info to learn its history.
I noticed that some of the resistors near the tube sockets were blown. 2 of the 4 resistors were black and some were completely disintegrated. I replaced them with the new values (knowing, now that I did some reading, that Marshall requests replacing them with higher value components due to the older DSL401's having been biased incorrectly from the factory.
Next was to see what happened when I turned things on and flicked the standby switch. FIZZLE, BOOM!
The resistors I just replaced fizzled, exploded and let all the magic smoke out.
I decided to leave things on and measure the voltages. What was suppose to be around 18V DC in standby mode and about 375V DC when switched on, was closer to 475+ I turned everything off, let it cool down and bled the caps.
I replaced the resistors again and removed the tubes. The same two resistors blew up. So I swapped around the 4 EL84's. The unblown resistors blew up this time. The new ones I replaced again worked fine.
So, tubes were shot. At this stage, I looked at the tubes and replaced all 4. In fact, considering the age of the tubes, with my friends permission, I replaced the entire set of tubes. All 8. 4 EL84's and 4 12AX7's.
The amp was now running stable and I was getting sound, albeit, extremely crackly. I would work on that later.
Where those original resistors had died, the tracks on the other side were burnt and lifting. So I repaired the circuit board and sorted that all out.
Next, for good measure and because it's so cheap, I replaced the stock bridge rectifier with a higher rated one. Mounting it with a heatsink and a couple of centimetres off the circuit board for heat and ventilation.
The amp was now running well, and I had biased the new matched quad tubes down to a more 'within spec' 0.8V, not 1.35+ Volts that Marshall released the amp with.
That crackle was still there. Time to look around. Poking around with a wooden chopstick, I discovered the volume pot was faulty.
Sadly, I couldn't just duck out and get another one. It's a Stereo pot. So it had 6 pins, and they're 'surface mount', not your standard pot you find in other tube amps or like a volume pot on a guitar.
So I de-soldered it and attempted to repair it. There wasn't much to it, it was just worn but a good clean got rid of most of the crackling. Re-soldering the pot back in most likely helped, as when I was poking around, I swear the noise was mostly from a dry solder joint or poorly soldered in the first place.
Crackle was gone.
The amp now worked almost 100%.
The last thing that needed attention was the channel switching. The lights were not working at all, and the amp was stuck in O.D 2. Which I'll be honest, sounded horrible. There was only one choice, but two solutions.
Play on OD 2 with the gain turned right down for clean stuff.
or
2. What I decided to go with, because I would feel bad giving my friend his amp back with it not working 100%, and that was to fix it.
I'm not very good with solid state stuff at all. To me it's like 'Well, just replaced that IC and see what happens.' Those little black rectangles confuse me with all their functions and wonderment they do.
Anyway, I found three transistors, all seemed to just be 'open'.
So I replaced them with identical components and channel switching worked.
The last thing that had failed with the spring reverb. It wasn't working. But I also noticed some nice springy sounds when moving the cabinet around. So I opened the tank to find what I thought I would, the spring had broken away from the terminal it was 'soldered' on to.
I use the term 'Solder' loosely because this is where I tend to find a lot of springs are broken.
I resoldered it and held it in place while the thing cooled down. The reverb works again.
Marshall Jcm 2000 Dsl Head
I soak tested the amp quietly as it was quite late. Again, mentioning that I have no test equipment, no dummy loads, no oscilloscope. etc. So I just use real life testing and wait for the brown smoke to escape.
2 hours later the amp was still on, and looping a guitar loop I recorded on my loop pedal and went inside to eat dinner and watch Netflix.
The following day, I took it to a busking gig I play with another friend of mine. I figured it will die during the gig if anything is going to go wrong.
Marshall Jcm 2000 Dsl Manual
I turned it on at 10:30am this morning, and didn't turn it off until 4pm this afternoon. 5.5 hours of playing, no turning off, no standby. Just music from start to finish.
The faceplate now gets warm to the touch. Not hot enough to scorch your fingertips. The tubes are running within spec, I checked voltages again when I got it home. Everything is the same as when I tested it the previous day.
My friend who owns the amp even turned up to the gig and listened to it a for a few sets. He's very pleased that a completely dead amp is now working 100% and hopefully with the mods and mistakes I've fixed, and cleaned up will allow the amp to operate for years to come until it needs new tubes.
I hope you enjoyed reading this adventure.