Marshall JCM 2000 / TSL60

[w0ttm]

I have on my bench a friends TSL 60 Marshall.
The reported problem was a sudden reduction in volume.
I have done a minimal visual inspection and could see nothing obvious.
Before I dig in to this rather busy amp, I thought it would be wise to see if anyone else has encountered this problem.
I do have decades of experience as a tech and engineer, and a bench full of professional test equipment and tools, and my personal guitar amps were designed and built or modified by me.
Thanks in advance........Rob.

P.S.
This is not the first Marshall to cross my bench, and I am not impressed with their construction.
They may sound great, but I will never buy one.

[w0ttm]

Problem found.
This amp uses DC on the preamp heaters, and it developed a connection issue in the bridge rectifier.
It tested partially open in circuit, but good after removal indicating an internal intermittent connection. (Best guess there)
Replaced the bridge and all is well, or at least what was passing for well before........

[Gtr_tech]

These run hot and can partially desolder themselves from the board. Its getting common to replace the bridge with an uprated part that can dissipate heat better. Some guys will even fit a heatsink if it still runs too hot.

[Amp Kat]

I use a higher rated BRD then the WO4/8 whatever it is and it usually does much better. Very common problem and you can even see the discoloration under the rectifier from getting hot.

[w0ttm]

Thanks big, gooey gobs, guys.
I did replace it with a higher rated part, and raised it off the board a bit.
It did not show any signs of heat damage, but I did not look at the solder joints under a magnifier, and my eyes are over 50 years old
After working on modern versions of amps from Fender, Marshall, and Vox, I'm going to stick to my home built equipment, and my two black face Fenders.
And my Kasino (Kustom) which is almost bullet proof.
Even those have been modified. I guess I'm just too picky.
Next project is another friends Peavy 5150 with reverb issues. I'll let you know.........Rob.