Marshall VS65R powers on ..No Sound

[1ampman]

Just had one in with the same problem. The fuse mounted on the circuit board was blown. It's for the heater of the 12ax7 All signals go thru it.... Check for filament voltage .......since it's hard to get to jumper the fuse or solder a quick shorting bridge.

[Begbie]

Thanks 1ampman,
I did test for continuity on the mounted fuses but think I read somewhere that the tube gives a false indication on the fuse.
How do I test filament voltage?
And do you mean : Jumper the fuse as an easier option?

[g1]

The heater circuit and it's fuse can not affect the +15V rail in this amplifier.

[Enzo]

Check for heater voltage by pulling the tube and sticking your meter probes in pins 4/9 and 5/9.

[1ampman]

By a quick jumper. I mean solder a piece of wire to take the place of the fuse. First see if the tube is lighting up? If not the power transformer has a separate winding for the filament (AC) . The fuse is a small round cylinder soldered to the circuit board, that can't checked by looking at it like a normal fuse. I believe it's 250ma. Not a fun easy 2 minute job. I had to pull the circuit board. Getting the board out requires unhooking a bunch stuff. If you mark the wire & board with a colored magic marker, You'll know where the wire goes when installing. So you will need many different color magic markers. The amp does sound good for rock&roll....Hope this helps

[1ampman]

Enzo, the filament is 12vac , so pins 4&5 would be used to check for heater voltage. Make sure your meter is on AC not DC

[Enzo]

Thanks, I didn't look at the schematic. The basic idea was pull the tube and measure whatever was coming its way on the hater pins of the socket.

[Begbie]

Thanks for the help everyone. If nothing else I'm learning a lot more about this amp than I knew before. I'm back to work so my ability to test/try/curse will be limited by over the next few days.
I am so desperate to get this thing working again though so please don't mistake my tardiness in replying for apathy.

Thanks again for all your help, I would be lost without it!

[Begbie]

I'm back!
Ive managed to source a collection of OP amps and have swapped out IC3 the first one near the Input and IC7 because it was the same as IC3.
No joy at all.
The 15v +/- rails are at 5/-7 respectively.
The resistors are still behaving the same way, that is one is getting real hot and the other just warm.

[Enzo]

Are you sure the IC is in the socket facing the right direction?

[Begbie]

Are you sure the IC is in the socket facing the right direction?

I was going to say "I'm sure I checked that" but doubt set in, and Ive actually physically checked that they are oriented right! and yes they are!

[Begbie]

So I managed to change out ICs 1, 2 and 4 in an effort to eliminate them from my inquiries.
I double checked the orientations of the ICs the continuity of my soldering and replugged it all in to test it.
I had a moment of sincere joy as the tube lit up and the LEDs on the front panel illuminated brightly (a symptom of my problem was the LEDs were lighting but at a less bright level than usual -probably due to the bad 15v rails.
I tried to input a signal and no joy
I then tried to switch channels from 1 (clean ) to 2 (OD) and nothing
I then tried the volume pot on the OD channel and all the lights (valve /leds ) dropped out.
Could this all be a Pot issue?

[g1]

Do you have the pots assembled back to the chassis and tightened?
What are your +/-15V rails reading now?

[Begbie]

Do you have the pots assembled back to the chassis and tightened?
What are your +/-15V rails reading now?

I didn't have the pots fastened to the chassis. Dont they ground from the PCB?

15v rails are worse now -2 and 0

[Begbie]

Update
This is getting me down now seems like it's going backwards. But I changed out ICs 1 and 3 and the volume pot on channel 2. Now I have +-/15v rails back yay. No sound still though.

Any suggestions on where to try next. I'm tempted to change out all the pots anyway as they are getting on in years.