Laney vc30 -112 sound level problem

[g1]

So it would seem the IC was bad. The powered speaker sounds like a simple solution for a signal tracer.
Likely there is now a problem with the +/-15V supplies. Check for voltages, the burning smell may have been R55 or R56. The led's and channel switching relays would be affected if those resistors were bad.
The HT fuse is for the high voltage DC to the tubes only. The heaters will still light up with it removed.
Now the question is why the new problem. Any chance you shorted any IC pins together while trying the test with the powered speaker?

[deci belle]

Old thread~ so what.

Thanks so much for going through all these steps for the OP. Helped me a Lot. After I got to the point of testing for good 15v supplies to the Op Amps and big and little transistors and testing the voltage at the diodes, I ordered the three TL072CP.

I hate getting the solid state things out. Operation improved a little, but still, the volume was low and distorted; the bright switch still didn't do anything.

Then I swapped in a 4k primary OT I had with an 8Ω 2ndary tap: BINGO!! Everything works. The chassis isn't in the cab so I didn't hear the reverb or test the effects loop. Will have to get the correct OT.

Oh yeah, there was some scary smoke wisps coming from under the board when firing up with the Fender OT because the cosmetic tolex panel along the back of the chassis is held in by three way too long screws and one was pressing against the underside of the PCB!!! I pulled that out and got lucky— dang.

[g1]

Oh yeah, there was some scary smoke wisps coming from under the board when firing up with the Fender OT because the cosmetic tolex panel along the back of the chassis is held in by three way too long screws and one was pressing against the underside of the PCB!!! I pulled that out and got lucky— dang.

Chances are that someone replaced them with longer than stock?
I remember on the early GK800RB's, the bottom panel screws also held on the rubber feet. Some folks would remove the rubber feet to rack mount, then re-install the now too long screws. One of them went straight into the speaker jack shorting the tip to ground.
Big smoke, no worky. I'm kind of a stickler about replacing screws with exact type or as close as possible.

[deci belle]

Ouch!!

No they weren't, cuz I compared the length with the other screws, g1.

Those three rear strip-panel screws are exactly the same as the screws securing the chassis to the cab, using the production weld-on fasteners— but crazy too long for sure. They only need to be 1/2" or less in that application, and they are over an inch long …and pointy!!

I think they're 5M1 threads, but since those black oval-head screws aren't so common, I'll be shortening the buggers at least several mm's and re-use them (or maybe just grind off the evil "Uncle Fester" points).

[diydidi]

The Laney VC30's are notorious for dodgy cabling on the boards. Especially the screened wires. On some models the wires are soldered directly to board by hand in the factory. Switch the amp on withe the amp innards exposed. Use a wooden chop stick and while inputting a signal wiggle each and every wire. See if the sound jumps back..
Be careful! High voltages inside!

[deci belle]

hi diydidi-- The amp is a 2005 made in England one. Those wires did look good— also, this version's sockets are mounted on the chassis~ Yay!. Thank you for the heads-up!!

I replaced the screen resistors as part of this repair cuz they looked toasty, and I rewired the pwr tube sockets so even old el84s can be used without self-destructing.

Ya, they don't put the wires into the holes— they just lay them flat on the soldered terminals on this build…

Yes, I did do a lot of poking around and testing as part of the preliminaries cuz the amp was delivered not working.

Thank you for those suggestion, diydidi!