Ashton Amp Repair Advice.

[Sonic Mountain]

Hey electrical gurus!

So I've been given a broken amp. It just an Ashton GA50, nothing fancy. They guy who had it was complaining about scratchy pots and intermittent buzzing. I suggested some contact cleaner in the pots might be a good place to start and did say to bring it around and I'd do it for him.

He decided to have a crack himself. He gave them a spray and blew them out and left it all to dry. Plugged it in and had significant improvement.

Getting excited he started spraying everything again, including the power switch..... while it was still plugged in.

Buzz..pop!

So anyway, he's not bothered as it was just a spare one and he realises his mistake, but he's given it to me. If I fix it I can have it otherwise he said dump it.

I actually have another amp I could quite easily transplant into this box (which is better than the current one it's in) so if it's a write off, I can still make use of it.

I am really out of my depth with this kind of electronics. I've done some very basic stuff before with PCB's and I can solder fine, I get the basic concepts but I really don't know where to start here.

I think this is the correct schematic - it's very close at least from what I can tell. The fuses appear to be fine, they are like small old school automotive glass ones. I will double check with my multimeter.

http://schems.com/bmampscom/ashton/ashton_vp50.pdf

and what I mainly suspect is the two diodes in this picture - they are involved somehow in the power circuit and they do look a bit discoloured.



There is also what I think is a capacitor on the switch. I'm not sure why it would be there.. to make the light fade slowly when you turn it off?



Anyway. Any advice or direction welcome. I am leaning toward just modding it with the other amp parts and making a franken amp. But maybe someone will have a good idea of what it needs......

[BigDaddy]

Hey mate - I've built 5 valve amps from scratch following vintage schematics though.... no IC's or transistors like this one. If you are handy with a multimeter and understand the safety procedures, you can quite easily troubleshoot it. Safety is paramount here as you will be dealing with 240v AC on those switch terminals and somewhere around 600vdc on the secondaries of the power transformer. Only ever probe with one hand. Use an aligator clip from your meter negative to the chassis and keep the spare hand in your pocket.

Can you provide a bit more information on the current symptoms since he sprayed the switch? Was it the on/off or standby? Does it power up? The diodes look ok to me in that pic. The discolouration on the board will be from those 2W resistors. Anyway, if you can provide a bit more info, it should be fairly easy to work through.

[Sonic Mountain]

Yeah I am very wary of mucking about at this voltage level. Basically it’s dead as a door nail. No sound no lights.

I don’t know that it has a standby circuit. It just has the one on/off switch on the fascia and a push switch to change channels.

[dave.king1]

Yeah I am very wary of mucking about at this voltage level. Basically it’s dead as a door nail. No sound no lights.

I don’t know that it has a standby circuit. It just has the one on/off switch on the fascia and a push switch to change channels.

No sound no lights indicates no power do the heaters light up

The diodes are just downstream from the standby switch in the circuit you linked and if you say there's no standby switch then it's not the same circuit and the cap on the power switch will be there to reduce arcing when the switch is thrown

Marcel will almost certainly provide more info

[McCreed]

I'm not an amp guy, and there was brief comment on safety from BigDaddy, but no one has specifically mentioned discharging each of the electrolytic caps in there before carrying out any trouble shooting & repair.

I hope you've done this Sonic.

[Sonic Mountain]

Thanks guys...

I'm not an amp guy, and there was brief comment on safety from BigDaddy, but no one has specifically mentioned discharging each of the electrolytic caps in there before carrying out any trouble shooting & repair.

I hope you've done this Sonic.

Haven't done anything more than turn it on and look for signs of life and have a look at the fuses. It came pre-dissasembled. I will have a look at doing this though - just had a bit of a read and seems important for Tube amps.. not sure on this, there don't appear to be any large capacitors, but better safe than sorry. Definitely a case of me knowing just enough to be dangerous

No sound no lights indicates no power do the heaters light up

The diodes are just downstream from the standby switch in the circuit you linked and if you say there's no standby switch then it's not the same circuit and the cap on the power switch will be there to reduce arcing when the switch is thrown

Marcel will almost certainly provide more info

Not sure how to identify 'heaters'? It's a solid state amp, not sure if that makes a difference.

Could well be the wrong diagram. I'll see what else I can find.

EDIT: Ah yes, I'm a dummy. That diagram is for a Valve amp. This one is definitely solid state.

[dave.king1]

EDIT: Ah yes, I'm a dummy. That diagram is for a Valve amp. This one is definitely solid state.

Yep that was my thinking, the diagram was a hybrid beast so not valid

The user Valvehead in this post appears to have the Ashton schematics or at least some of them

https://www.guitargear.net.au/discus...?topic=40901.0

Ashton themselves may help

http://ashtonmusic.com/contact-2

[Sonic Mountain]

Yeah I came across that thread as well. I'm guessing that my lack of any kind of qualification in this area will result in a big no. But I'll see, I've sent a request off.

[McCreed]

...just had a bit of a read and seems important for Tube amps.. not sure on this, there don't appear to be any large capacitors...

That schematic you linked shows 12AX7 & EL34 tubes. (???)

[BigDaddy]

Yep - wrong schematic.

There will still be filter capacitors for the power supply which can poke you. Once identified, you need to check them for voltage and discharge if there is anything present as per McCreed's comment. Can you take a few wider pics of the guts? I assume there is a transformer in there....that may have fried on the short (are you sure all the fuses are OK?)

It may be as simple as replacing the switch. The contacts may have copped it when it shorted.