VOX AC15C1 smoking fuses

[Randall]

VOX AC15C1 blows mains fuse instantly with all tubes out. Disconnected OT, still blows. Disconnected PT secondaries, still blows. Does not pass the neon bulb test, but I have been fooled by that one before. Before I commit to delivering the news, can we assume this PT is toast? I get no resistance reading between any of the secondaries or to ground.

http://dealers.korgusa.com/svcfiles/AC15C1_Smanual.pdf

[Enzo]

So disconnect the primary wires too, still blow? Transformer likely bad, but we might as well rule out a shorted cap or other bit in the primary mains wiring.

[Randall]

I don't see what disconnecting the primaries will tell us? I see nothing on the primary side that could blow a fuse, do you?

[The Dude]

It's unlikely, but not impossible. Power switch could have a short to ground, etc. Presumably, you have to unhook the primary anyway to replace the transformer, so why not test it unhooked? A wise man named Enzo once said something about not thinking up reasons to not check something.

[Enzo]

Your schematic won't open for me for some reason.

Like Dude says, the wires are coming off anyway, so invest 10 seconds to be sure.

[Randall]

Fuse does not blow with primary wires disconnected.

[The Dude]

Well, ok, that probably proves the same thing, but I would have hooked the transformer primary directly to ac through the LBL or current monitoring variac to test the transformer unhooked from everything.

[Randall]

With transformer connected to nothing except primary directly to AC thru LBL, bulb glows bright. Can I get an Amen for bad PT?

[The Dude]

AMEN!

[vintagekiki]

Is the power transformer for the appropriate main voltage (page 17 Item 38)
Remove fuses F1, F2, F3, standby off.
Do blown main fuse F4.

[g1]

There are a couple versions of PT for this model. Make sure you get one that matches the dimensions so you don't have to drill new screw holes or anything.

[vintagekiki]

http://dealers.korgusa.com/svcfiles/AC15C1_Smanual.pdf

(page 17 Item 38)

1806-4108+0000	TRANSFORMER PWR 240V AUS
1806-4084+0000	TRANSFORMER PWR 230V EU
1806-4107+0000	TRANSFORMER PWR 120V
1806-4106+0000	TRANSFORMER PWR 100V JP

[Randall]

I ordered the Hammond version for the AC15C1, (290CZ) which is advertised as a drop in replacement from CE Dist. They offer several versions. You know if they sell replacements specific for a model of an amp, that the failure rate is high enough to make it a profitable venture. And I would sooner go with Hammond over anything Korg would sell me, which just be more of the same under spec'd crap.

[g1]

There are a couple versions of PT for this model. Make sure you get one that matches the dimensions so you don't have to drill new screw holes or anything.

I may be getting my C1 and CC1 mixed up. There are so many variants of the AC series it's stupid.
Anyway, the Hammond unit 290CZ has screw centers 2" x 2.5". The other size I'm thinking of (maybe for CC1) has screw centers 2.5" x 3.125".

[Randall]

I haven't yet pulled the original from the chassis to get measurements, but if CE Dist tells me the Hammond 290CZ is the replacement for the C1, I am going to take them at their word that it will fit.