845 Meltdown

[ColinA]

Came in tonight to an appalling burning smell.
She says the amp was smoking!
Result total meltdown of mains tranny!!!!!
Will try to post pic.
The amp was running ok so an ideas what to check?

[Paul Barker]

There's an advert for correctly rated fuses.

Check everything now!

Certainly the two lumps of iron in view have had it, remove everything that appears damaged and test everything else, check for dead shorts to ground, particularly electrolytic capacitors, power supply or bipass could have been responsible for that or a short ion the transformer. Check output valves.

It's a thorough and careful rebuild job of one or both channels.

It's also an advert for a well researched safe kit from a respectable UK company like WD aspires to.

[Ianm2]

hmm chinese amps......

bluddy hell!!

current causes heating, big current, short circuit sort of thing....mains tranny short, valve short, anything causing a large current too much for the tx but not enough for the fuse....

is it both tx's or just the one?

and the charring on t'other because the first one got too hot?

....so see what the burnt one connects to and that may yield clues, now tho' what matters is not really what caused it, which is curiosity, but what to do from here....

[Les Reed]

Is this one of the Chinese amps discussed on another thread?

[ColinA]

It's a Yarland
I have asked Ornec,who I bought it through, what their warrenty policy is.

[Paul Barker]

Worthless, it will be an rtb policy, and you see if you don't get charged duty again when it's sent back to you.

I'd say it's one of those things you have to expect when buying an amp sold into a market not correctly researched.

They'll get better at it.

[NickG]

Its maybe not of help, but when trying to fix Pauls example, I first tried a single pair of hexafreds in the 845 B+ supply, they failed, but unlike the diodes that were in the amp before, they failed by going short circuit, and staying short circuit, but not enough to blow a 5A fuse. However the TX didn't like it, and I suspect if I had left it on more than a second, it would have ended up like that. If I remember correctly, the one that has gone in yours is the transformer that supplies the 845 B+.

Of course any number of other things could have caused that to happen :-(

[Global]

Looks like I got a variac just in time!

The mains transformer cover is lots cooler at 220v!

I hope you can do something with it or get some kind of warranty help.

Mark

[Paul Barker]

I'll give you 20 quid for the ashes.

[Global]

Colin

If you do find out the cause, I would be grateful to know as there is one of these sitting in my living room . I have used a variac to bring down the mains a bit and fitted two pairs of 1000v HEXFREDS per Nick's advice. The original diodes were rated 1500v but given UK mains this may have fallen a bit short of safety and I wonder if one or more shorted diodes might be at the root of this as Nick suggests.

Please let us know if you find anything. (and do put the remains in the 'For Sale' section of you can't get it fixed {hope I'm not being too vulture-like!})

BTW, I suspect the supplied fuse is too high in value at 4 or 5 amps.

Again, I hope you have some luck sorting it out.

Mark