Marshall Valvestate VS30- Hum/No Output

[glstarr]

Help !!!! Borrowed a friends amp for a little practice and during the night had an electrical storm that took out a few electronics in the house including my friends amp. When powered up I get a loud 60 cycle type hum and no output. I have some tube amp experience only. Checked dc voltages on chips and all are ok. All components look good. Is it safe to use a 1950's signal gen. and or tracer on these cicuits? Any help would greatly be appreciated!!! Thanks!!!

[oc disorder]

Hi glstarr and welcome to the forum.
The most common fault with this type of amp is the output chip
which can have the exact symptoms you describe.
It's a TDA2050 .
Providing the sig gen you have is safe in itself I see no reason
you can't use it.
The signal should be ok up to C48 which goes to pin 1 ,the input to the TDA 2050.
Can't see how an electrical storm could blow it .
More likely to affect the power supply but if you have checked the dc supply
(+15volts and -15volts) and thats ok and the channel 2 led is functioning ,
I would think it is the output chip.
The easiest way to remove it is to cut the legs off then unscrew it from the heat sink taking care not to damage the thin insulating washer between the back of the chip and the heat sink. Also the little insulator on the mounting bolt shouldn't be damaged although it may use one of those clips instead.
Then its easy to remove the debris cleanly without too much heat not damaging the pcb tracks and pads.
Fit the new one physically to the heat sink first before you solder it in.
That way there wont be any strain later on on the solder joints .

[Enzo]

If it has that TDA2050, and there is a loud hum, check for DC voltage across your speaker. There should not be any. Or watch the speaker copne. When you power on, does it move one direction and stay there? That would be DC. It will burn up a speaker, so don;t leave it on.

And if there is DC there, then just replace that TDA2050.

[glstarr]

WOW !!! Thanks to both of you for the great info. First thing I did was check for dc on speaker, and sure enough there was 15 volts. went to radio shack and picked up a low wattage iron and took out the part and it was a breeze to do the way you said to take it off the board! I will go to the parts house and pick one up tommorrow and reinstall. I've recapped and troubleshot quite a few tube type jukebox amps but this dang circuit with the chips, etc sure had me lost. Guess i best get busy and learn some new circuit theory!! Again, Can't thank you guys enough!!! I'm sure glad I found this forum. Will Post my results when I pick up the part.

[Enzo]

Hey I am an old jukebox guy. REbuilt more old tube Seeburg amps than I can count, plus old AMI and Wurlitzer amps. DOn;t see many Rockola tube amps around this part of the country.

Of course I have also rebuilt a ton of solid state Seeburg and Rockola amps

[glstarr]

Yeah, I did jukebox restorations and repair full time for about 10 years. Quit about 12 years ago when it got too hard to get chrome done. This area seemed to be all ami's in the forties, fifties and sixties,but my favorite has always been seeburgs!!! There must of been alot of seeburgs up your way,I see trashcans from michigan on e-bay all the time!! I made a trip up your way a while back and got a nice blonde trashcan and a seeburg 9800 to restore one of these days!! Well my part won't be in for a week. Also, OC Disorder, thanks so much for the schematic! I'm going to do some tracing this weekend and see if the rest of the amp is ok.

[Enzo]

Yes, Michigan was a big Seeburg market.

Rowe came along long after tubes to become a major player here.

As a company trainer, the 1970s Rockolas were a favorite, I could take those apart not looking.

[glstarr]

If you have the time, you should write an article for jukebox collector magazine!! I'm sure they would be very very interested to here what it was like to be a rockola insider!!And so would us readers!!!!

[Enzo]

I used to have a monthly column in Startech Journal. I wrote a few columns for Playmeter, and a few of my pieces from Startech have appeared in Replay. All long ago.