845 SET monoblock stone cold dead - any idea who can service these?

Hey folks,

Well, it appears that one of my Ming-Da 845 monoblocks has died. Tried changing plugs/fuses/valves, all to no avail. It's dead as a dodo! Before you ask, it is a 240V model. Though of course, I have no way of checking this and it could very well be a re-badged 220V model. I wouldn't put anything past those Chinese manufacturers! Incidentally, the other monoblock works perfectly and shows no signs of dying. Yet...

I bought them from Ben at Chinese Hi-Fi and have e-mailed him as they are still under warranty. However, I really don't fancy sending them all the way to France, what with the customs/costs/risks involved.

So I was wondering if you know anyone that has serviced this type of SET before (ideally in London, but not essential)? I should be able to get the circuit diagram from Ming-Da. Any idea what it would cost to fix? Ballpark figure?

Cheers,
DT

 

Have you had a look inside to make sure nothing has come off? If it is just dead i.e. no smoke after a while, no tubes lighting up anywhere etc. it has to be right back at the start of the circuit somewhere round the PSU. If your mains TX had died you'd probably know about it- black markings, smoke, something like that, so I think its worth having a look to make sure everything is firmly connected to the boards, no burnt components and so forth.
What happened- did it shut off in use or was it a working the other day, not today type problem?

 

Give Geoff at Service sound a call

www.servicesound.com

He is in Bexhill 01424 216245

 

No - thank God it died quietly. One of the things that always terrified me about these amps was that they would go down in a blaze of glory.

Would never poke around inside one of these - too much voltage flowing around. No electrical training etc. and don't much fancy getting zapped by a capacitor or something !

However, on this occasion, it was silent, smokeless and odourless.

DT

 

Ah that's grand, Addict. Will do

 

You'll kick yourself if it is just something fallen off inside and you send it off and pay for repairs You don't have to poke anything and you unplug it first. If it has had a few hours switched off but still plugged in (earthed) it should have discharged. Just take the lid off and have a look, you've got nothing to loose.

 

could be an internal fuse as well as the one in the plug and iec receptical...buit if you've blown a fuse it has to have a cause !

just thought if theres no glow it could be the heater curcuit thats given up

 

Maybe not necessarily, my Audions hava a really tiny value fuse which can blow if there's a bit of a mains surge on starting up.

Jeff

 

I think you're right not to poke about inside, it's not a job for an amateur (myself included!).

Honestly, the circuits inside a SET amp are (normally) so simple, any decent valve repair guy could do it. Guitar shops normally have one on the books if the above guy can't do it.

I'd reccomend getting a quote first too.

'boutique' repairers might charge £200+, for a bit of labour and a blown resistor, I'd expect more like £30-£50!

 

Well, against my better judgement I popped the top yesterday to see if there was any visible damage and it appears that one of the internal glass fuses has burnt through. It's not a standard UK type fuse - it's smaller and has a glass sleeve, but it is stamped "3A 250V". Just wondering where I can get a replacement. Will try Ryness and/or Maplins to see if they have any....

Panic over!

DT

 

...but what caused the fuse to blow?

 

Is a very good question! There's no guarantee it won't blow again the minute I turn it on, in which case the panic won't be over.

The amp is plugged into a Belkin surge protector, and none of the other equipment failed, nor did the Belkin's protection kick in, so I doubt it was a mains surge.

Guess we'll have to wait & see....

DT

 

beat me to it ...fuse blow for a reason ......normally high curent draw....but hay fuse are cheap maplins have a good selection ..but make certain you get the identical sort .

 

make sure they are 'slow blow' fuses you get,
with a bit of luck the old one was just tired

 

I was just about to say...

If you look around one end they usually have a 'T' just before the rating. Another give away is they sometimes have a thinker coil or are spring like.

I have some 3.15A/250V timelags (30mm long) kicking about if you get stuck for some. Would reccomend you take your dead one along to Maplin for a match.

 

Well, I just bought some "3.15 Amp 250V" 20mm glass fuses from Ryness. I trust these will be OK to use, or do I absolutely have to use 3 amp versions?

 

Should be fine.

 

That's what I was thinking too.

Oh, btw - they're "quick blow" fuses. Definitely no spring/spirally things going on here. Just a straight wire....

And maplin don't do 3A either. Only 2.5A or 3.15A.

 

See my post #8. My Audion fuses went a coupple of times. put a slightly higher value in and they haven't gone since so I think you'll be fine.

Jeff

 

I would go for 3.15 that will be fine,
yours still could be a slow blow they don't always have a spring,
you need a slow blow because of the surge at turn on,
a normal one could blow at turn on