jcm2000DSL almost on bench

[shooter]

Hopefully a quickie for now;
I have the schematic from Doug's library, and one I found from Plexi50 (ALL.pdf)
also grabbed the one from Doug labeled TSL100, which at quick glance is nice, crisp, key features appear the same.
the box I have is date code 1999 -45, both schematics for DSL are 97.

wondering if someone's got a crisp factory schematic with rev notes into '99-'00.  I can get you and email if the files big.

I'm old eyes and like to have them printed 14X17 so I can color and draw before I get out a screwdriver or solder pencil, and no, I don't make the customer pay for my eccentricities 
thanks
dave

[Ritchie200]

Is it having the dreaded overheating drifting bias problem?

Jim

[shooter]

came in with MV intermittent, wiggle-giggle and BOOM - loud, but the 3rd wiggle giggle no more sound.
If it's like it's ugly cuz the valvestate, EVERYTHING is suspect, and probably bad! 

[Ritchie200]

They are notorious for several issues. Check speaker jacks.  The ground for the 4 & 8 ohm jacks is switched through the 16 ohm jack.  Gets dirty, intermittent, heats up and nothing.  Fix is to solder a buss-type ground wire across the jacks.  You can clean the contacts but from what I understand, it comes back pretty quick.  Crappy jacks that year(s)?  Crappy Jack... Wasn't that a Who song? 

Jim

[sluckey]

♫ Crappy Jack wasn't old, but he was a man
He lived in the sand at the Isle of Man ♪

[shooter]

 
I have enough background noise in my head already, now this!!! 

made my 1st error, listened to the musician  ,  It's a DSL 50!
anyway, the 100shemo follows along so far.  verified with meter, no major flats on the Vol or Gain pots in circuit.  I'll re-test with sig & scope.

notorious for several issues

ya, spent a couple hours reading about all the bias, ground, crap components, etc.
I bookmarked the "fix" pages

gonna verify ohmage through the bias catastrophe circuit.  PA tubes will stay out for now.  I don't wanna be the design Engineer when Karma catches up with Him/Her/Other 

[shooter]

no PA tubes, verified bias at pin 5, adjustable, found them @ -40.xxx, set both to -40.5xx.   speaker jacks were giving me sketchy values, cleaned and ran a plug in/out awhile, solid for the 8ohm for now - testing.  I'll talk with the customer about the ground mod.  put some cleaner in the pots and ran them around the dial awhile, still ohm ok to the knob board.

1st inspection found some crusty white stuff (see pic).  came off easy with dry toothbrush.   fingers and face are frozen since it's 48.7deg upstairs
probably plug in the tubes in the AM for full power on test.

[sluckey]

I have some of that crusty white stuff on one of my peach trees!

[shooter]

 
since I got back to the artic, my skin looks like that 
ah, well, I did come back to a legal state with a 4state 6strain blend so now...... 
troubleshooting to be continued around noon!!!!

[shooter]

so I'm in research mode 

found the correct mainboard schematic for the dsl50.  Lucked out, the mainboard is a UK board, good reviews so far, the one Doug has for the dsl100 works for all the other boards.

[sluckey]

All I can tell you at this point is that crusty white stuff on one of my peach trees is not tasty!

[shooter]

I just scrubbed it an vac'd it up,.....although...In full discloser, the voice in my head did comment; "I bet that tastes bad" 

that board pdf is crispy clean, might want achieve?

back3painting

[PRR]

> that crusty white stuff on one of my peach trees is not tasty!

Round here, we are calling it 'snow', and the dogs love it.

[SILVERGUN]

Is it having the dreaded overheating drifting bias problem?

Jim

They are notorious for several issues. Check speaker jacks. ...

Sounds like a GREAT amplifier brand.
Where can I get one?
I need a place to hide my white powder that has no other use....its perfect

[Ritchie200]

What, you scared by a few flames?  If you were a true craftsman and maybe did some welding or something, a little bit of heat wouldn’t bother you!  Now you take your flock of seagulls hair, your kitty tele guitar, and your line 6 and go sit at the kids table - oh and don’t forget your music stand. I’m sure you think all that sounds good. Good for you!  Just don’t bother the adults in the room....


Your guidance counselor
Jim

[shooter]

we got the same snow here, but the cats hate it 

SG, it's only a dimes worth but if you want it, 4u, i'll pay shipping!, oh, gotta dig it outta the vac 1st 

[sluckey]

Shipping white power stuff may be a lot more trouble than it's worth. 

[shooter]

I figured I'd just send the whole vac bag, that way when the officials get done I'd at least know what got on the amp board 

my working theory, a moth, they have a "dusty" coat on wings, white-ish, I can visualize the poor dude getting whacked by 400vdc, thrown up to the knob board as moth vapor, it's MY story and I'm sticking to it!!!!

[shooter]

ok back to work;

B+ ~ 474vdc
set I at 38.2mA
~~ 72% of 25W

both sides have drifted up .5mA over 1/2hr just idling, tweaked back to 38.2mA, i'll give it another 1/2hr then plug in some audio.

the bias pots are touch sensitive 
 just "think" of the value you want push lightly with tweaker, walla, there!!!

[shooter]

2hr test is ~ ok?
Plate drifts over time 471-475vdc
bias drifts over time 37-39mA
need to verify with customer, but looks like he put in a full set of new tubes, so the drift might be tube burn in 

the red CH(B) is harsher but that's the ultra high gain, use transistors and complex circuit channel, also noise floor higher
the green CH(A) sounds nice, that's the classis gain less junk channel

boxing it up, callin it a day!