Marshall Valvestate vs265 keeps blowing fuses

[TONY123]

Hi all, i have an amp that recently had reg1 and reg2 replaced and two small capacitors as there was no sound. Then when i got it home it worked for half an hour until i turned on overdrive with foot pedal and then blew shortly after. So i got some new HT 1 amp slow burn fuses. But keeps blowing the fuse as soon as i turn on the amp. i can read schematics and can solder but havent got a clue on how to find the broken components in a methodical manner so i don't have to test every component. Has anyone got any ideas of how to proceed with this? What do i check first?

[Helmholtz]

Please post a link to schematic.

[DrGonz78]

I don't think the site will let him upload files to the site until they have a certain number of posts first. So Tony let us know if this is the correct schematic.

[g1]

So i got some new HT 1 amp slow burn fuses. But keeps blowing the fuse as soon as i turn on the amp.

You say 'HT', but do you mean the mains fuse? It's the only fuse I see that is 1A slow. And it is only 1A where there is 230V mains voltage.

[The Dude]

I'd start by checking resistance from all power supply outputs to ground and see if you detect shorts on any of the supplies. You say 2 small capacitors were replaced. Which ones? Were they installed oriented correctly if electrolytic?

[TONY123]

You say 'HT', but do you mean the mains fuse? It's the only fuse I see that is 1A slow. And it is only 1A where there is 230V mains voltage.

Yes the mains fuse and i'm running 230v in uk

[TONY123]

I'd start by checking resistance from all power supply outputs to ground and see if you detect shorts on any of the supplies. You say 2 small capacitors were replaced. Which ones? Were they installed oriented correctly if electrolytic?

the two little capacitors next to REG1 and REG2

[TONY123]

I'd start by checking resistance from all power supply outputs to ground and see if you detect shorts on any of the supplies. You say 2 small capacitors were replaced. Which ones? Were they installed oriented correctly if electrolytic?

C9 and C10 which are 100uf and yes it appears they are right way round

[TONY123]

I'd start by checking resistance from all power supply outputs to ground and see if you detect shorts on any of the supplies. You say 2 small capacitors were replaced. Which ones? Were they installed oriented correctly if electrolytic?

How would i know if there is a short and do i test with power adapter on?

[Jon Snell]

I would check Q15/16/17/18 the output transistors.
Check you have no short between pins 2 & 3 of each transistor.

[The Dude]

How would i know if there is a short and do i test with power adapter on?

I don't mean to be rude at all, but asking those questions probably means you should take the amp to a qualified tech. Please don't take offense to that statement, but you could do more damage than good if you lack some basic electronics understanding.

[TONY123]

I've checked the transistors and two had blown and one resistor. But now i'm i want to know where is pulling excessive current to fry these, maybe Opamp?

[TONY123]

I don't mean to be rude at all, but asking those questions probably means you should take the amp to a qualified tech. Please don't take offense to that statement, but you could do more damage than good if you lack some basic electronics understanding.

Yeah probably but can't afford it

[Grrrg]

Who replaced the regulators in the first place? They should take care of it. When you try to fix it yourself they will tell you it's your fault.

[TONY123]

Can't seem to get in touch with them anymore