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A crash of drums, a flash of light, my preamp ain't got no lights

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A crash of drums, a flash of light, my preamp ain't got no lights

Postby mr_luva_luva_shabba » Thu Jan 17, 2013 8:46 pm

Hi all,

I've got a Universal Audio 110 solo preamp that has been working faultlessly for the last 5 years, up until last night that is, while recording drums a flash was seen from the side of the case and it hasn't worked since.

Have done the obvious, changed the power cable, and opened up the case to check the internal fuse, which hasn't appeared to have blown, there doesn't appear to be any obvious burnt out component in there, and thats about the extent of my troubleshooting knowledge. I'm handy with a soldering iron, and have a voltmeter, but to be honest it has only ever had use to test audio cables have been made properly.

So how would you start troubleshooting a problem like this to identify a failed component. Someone suggested that it might be a dry joint and to poke around with a wooden pencil until something lights up, but I'm not convinced because of the flash that occurred before it died.

I know the advice might be, if you don't know what you're doing then don't attempt it, but to be honest if I'd followed that adage my whole life, I would have learnt and achieved nothing, so any practical advice, websites etc. appreciated.

Ta,

Jonathan
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Re: A crash of drums, a flash of light, my preamp ain't got no lights

Postby Jack Ruston » Thu Jan 17, 2013 9:07 pm

Hi Jonathan

Something's obviously popped in there. Even if you could find which component that is, you're unlikely to be able to establish what the value of it was if it's exploded/melted etc. Furthermore, its loss may have impacted on other parts of the circuit. If you fix it, can you be sure that the whole circuit it still working absolutely as it should? Even more crucially this is a valve preamp, and the internal voltages will be extremely high. If you make a mistake it won't be a little jolt...they'll find you in the spring. My advice...get it repaired by Universal Audio or one of their distributors. They may even do it for nothing. You never know.

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Re: A crash of drums, a flash of light, my preamp ain't got no lights

Postby The Elf » Thu Jan 17, 2013 9:13 pm

mr_luva_luva_shabba wrote:I know the advice might be, if you don't know what you're doing then don't attempt it, but to be honest if I'd followed that adage my whole life, I would have learnt and achieved nothing

It's fortunate that you didn't follow the same tenet when mum told you not to stick your fingers in the mains socket!

Seriously, this is a bit of 'learning and achievement' that can cost you (or someone else) your life. Go to an expert.
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Re: A crash of drums, a flash of light, my preamp ain't got no lights

Postby mr_luva_luva_shabba » Thu Jan 17, 2013 9:58 pm

Thanks for your replies, points all taken. Apart from the risk of death there is also the risk of doing more damage to the preamp, I suppose I was hoping for an easy fix.

Just one more thing I was wondering, if the internal fuse hasn't blown, and there are no signs of scorching on the circuit boards (it's the 110 so doesn't have valves), could the issue be before the internal fuse? The only component before this is a Corcom EMI filter built into the power input?
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Re: A crash of drums, a flash of light, my preamp ain't got no lights

Postby Hugh Robjohns » Thu Jan 17, 2013 10:23 pm

The 110 has an internal Switched mode power supply, and when one of those goes pop it's pretty terminal. Even very experienced electronics technicians can struggle to fault-find SMPS'S designs, and there is nothing you can do. It will need to go back to an authorised UA repair centre.

http://www.uaudio.com/support/rma-faq.html]http://www.uaudio.com/support/rma-faq.html]http://www.uaudio.com/support/rma-faq.html

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Re: A crash of drums, a flash of light, my preamp ain't got no lights

Postby Folderol » Fri Jan 18, 2013 12:05 am

mr_luva_luva_shabba wrote:Hi all,
Someone suggested that it might be a dry joint and to poke around with a wooden pencil until something lights up, but I'm not convinced because of the flash that occurred before it died.
Whoever suggested that is probably trying to kill you! Pencils have a graphite core, which is conductive.

Also as Hugh said, switch-mode PSUs are a nightmare. Almost every failure mode results in popped (expensive) drive transistors.
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Re: A crash of drums, a flash of light, my preamp ain't got no lights

Postby dmills » Fri Jan 18, 2013 12:16 am

The Elf wrote:
It's fortunate that you didn't follow the same tenet when mum told you not to stick your fingers in the mains socket!
Or you might have become an Engineer! Hands up all those who failed in following that advice !
My suspicion is that most of those here with an electronics background will have at least one story involving childhood contact with far too many volts, still couldn't recommend it however, the ones that hang out here all survived the experience!

Regards, Dan.
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Re: A crash of drums, a flash of light, my preamp ain't got no lights

Postby mr_luva_luva_shabba » Fri Jan 18, 2013 2:41 pm

Thanks all, back to Universal Audio it is, hopefully that doesn't mean the USA, will email them to find out the nearest distributor who can repair in the UK.

My foray into the world of fixing electronic devices will be put on hold for now, there is a slightly less prestige project to fix a Breville sandwich toaster on the horizon, which is probably a better starting point. It better not have a switched mode power supply or there's going to trouble......
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Re: A crash of drums, a flash of light, my preamp ain't got no lights

Postby Jack Ruston » Fri Jan 18, 2013 5:45 pm

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Re: A crash of drums, a flash of light, my preamp ain't got no lights

Postby Jack Ruston » Fri Jan 18, 2013 5:45 pm

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Re: A crash of drums, a flash of light, my preamp ain't got no lights

Postby Hugh Robjohns » Fri Jan 18, 2013 6:33 pm

mr_luva_luva_shabba wrote:Thanks all, back to Universal Audio it is, hopefully that doesn't mean the USA, will email them to find out the nearest distributor who can repair in the UK.

Source Distribution are the agents in the UK, and as part of HHB I imagine they will use HHB's superb workshop to repair it.

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