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Old 22nd June 2008, 07:15 AM   #1
kanifee is offline kanifee  United Kingdom
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Default tranny repair, is it possible?

ok in need of a little help, somehow ive managed to short my tranny, im getting novoltage across the secondrys atall when plugged into the mains now, im getting a circuit connection over each of the secondrys but not from the primary to the secondeys or beween either of the primarys. have i burnt out a piece of copper wire? is there a way to fix this and will it be to hard?
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Old 22nd June 2008, 08:07 AM   #2
Nuuk is offline Nuuk  United Kingdom
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Congratulations! You may well be the first to come here who has 'broken' a transformer!

But let's make quite sure that it isn't working before you you go any further.

Are you certain that you haven't any bad connections ?

Do you use a fuse and if so is that OK?

Is there a fuse in the mains plug and is that OK?

Best of all would be a photo of things so we can try and spot any errors.
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Old 22nd June 2008, 08:09 AM   #3
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Your measurements indicate interrupted primaries. It is possible to repair transformers. Motor and transformer winders can be found in most bigger cities. The transformer factory will also be able to do a repair.

A new transformer will most probably be cheaper than repairing the old one, however. Rewinding transformers usually makes sense for very big or very exotic transformers only.
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Old 22nd June 2008, 08:20 AM   #4
Nuuk is offline Nuuk  United Kingdom
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Quote:
Your measurements indicate interrupted primaries.
Or an incorrectly wired up transformer that uses twin primaries!

(That's why a picture would be good)
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Old 22nd June 2008, 09:21 AM   #5
kanifee is offline kanifee  United Kingdom
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ok, time to own up to being complete idiot, turns out the leads on the primaries are coated in a non conductive layer that needed stripped
ill duck as you hurl the abuse i feel like an idiot, even more so now, i mesured rails and was getting 37v dc from each of my psu rails so i rigged up my amp board, pop went a cap and i nearly **** my self and then the lm3886 chip poped aswell, luckily i have another board to get things up and running again though ill have to do it a channel at a time, a new chip and cap shouldnt break the bank, now just to figure why it went pop!
All my wiring looks fine, im getting 37 volts dc on each rail from a 230v 2x25v tranny, so the power is about right, my v+/pg+ and v-/pg- are all wired up properly, one + and onw - from each to the amp boards.


Edit, ok i think my rails are coming out reversed on one side of my psu, i went to check voltages again and noticed that on the left sideif i put the posative point of the meter on v- and the negative point of the meter of pg- the indicator trys to go into minuses but if i reverse and put red to pg- and black to v- it shows voltages in the + side of the scale instead of the minus side yet on the right hand side of the psu the rails read red to v+ black to pg+ in the positive side of the scale. does that make sense?

just inacse its releavant the caps that have managed to blow are 100uf 50v
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Old 22nd June 2008, 10:42 AM   #6
Nuuk is offline Nuuk  United Kingdom
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Supplying reverse polarity to any polarised cap will kill it!

A good tip when testing the PSU section is to connect some old caps so if you have got it wrong, you will not kill anything important.

No disrespect, but it sounds like you need to slow down a little!

And don't feel too bad about the enamel coating on the primary wires. I once cut some primaries shorter and made the same mistake! It is 99% our mistakes when something won't work, and 1% a duff component!
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Old 22nd June 2008, 10:48 AM   #7
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As Nuuk said, you need to work more methodological.
Measure ALL your supply outputs against ground, and make a list of what you measure. That will immediately show you if there are any errors.
It'll take 5 mins and beats getting new chips and caps, even if they don't break your bank.

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Old 22nd June 2008, 11:15 AM   #8
kanifee is offline kanifee  United Kingdom
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Good advice, ill mesure all my rails and double check everything, ill report back as im sure ill make a mistake
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Old 22nd June 2008, 11:16 AM   #9
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Kanifee, Those lm3886 chips are going to run quite hot at the 37 volts you are supplying them.
It also might be a good idea to put some light bulbs in the circuit before the transformer to cut back on some of the current while you get things sorted out.
One more thing around here we recommend check, check, check before applying power. Nothing is worse than having to wait a few more days for the ups man while you wonder what went wrong. Have fun that is what it is all about. Tad

P.S. Let us see some pictures as you progress.
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Old 22nd June 2008, 12:19 PM   #10
kanifee is offline kanifee  United Kingdom
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ok got some pics and some voltages sorted, voltages across each of the secondry rails are 28.50v and 27.34v Ac, at the hook up pounts between the psu and amp board im geting 37v dc.

Im using a old cambridge audio A1 case for now untill i can afford a custom one. im also hoping to utilize the input selector aswell.

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

i know the heatsink is a little small for both chips but im using active cooling via a 80mm fan while testing until i can find 2 more suitable sinks.

you may just be able to see were the chip blew

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