DIYprojects.info

Doze · Guest

HI,

I have a unit that I just got that doesn't power up. There appears to
be a little bit of brown leakage around the areas of a few of the
capacitors, but removing them from the board shows no damage or area
the leakage could have come from. Testing these on the multimeter, the
ohms increase as they supposedly should into infinity. I have read so
much about the caps going bad on these, especially since it is an older
unit. Any ideas on where to begin checking elsewhere in the power
supply?

Dave H. · Guest

HI Doze,
a lot of manufacturers glob hot-melt glue that goes brown with age
around the larger electrolytic caps to hold 'em to the board before
wave-soldering... if it doesn't power up *at all*, it's more likely to be in
the AC stages of the power supply - have you put a voltmeter on the caps to
see if anything gets that far? If there's no DC on the PSU caps, work back
to the bridge rectifier/diodes and see if there's AC on the transformer
side - if not, is there (mains, dangerous, bites the unwary) AC on the
transformer primary? If so, you may be lucky and find a fuse on the
low-voltage side, conversely the mains transformer may have failed - if the
fuse has blown there's probably a reason - ***DO NOT*** replace with a
higher value, unless you intend discovering where all the
smoke-that-makes-it-work is stored, by making it escape... if the
***correctly rated*** fuse blows, it's time for the schematic and some time
scratching your head, or a trip to a competent tech.

Hope that helps,
Dave H.
(The engineer formerly known as Homeless)

"Doze" wrote ...

Gareth Magennis · Guest

"Doze" <ipedigo@hotmail.com> wrote in message
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Gareth Magennis · Guest

"Dave H." <hopefuldave_doesn't_eat_spiced_meat@hotmail.com> wrote in message
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Doze · Guest

Thanks so much for the input. I'll follow up in a few days to let you
know what progress (or lack of!) I have made. I can't thank you
enough.

Doze · Guest

Well, sooner than a couple of days, I'm back. No blown fuse anywhere.
I've ordered new caps for the output section just to try that out.
I WAS able to find AC on the transformer side, up to the bridge
rectifier/diodes. I can't find DC past that, or anywhere else on the
board for that matter. Should I assume these need to be replaced? Or
that I am testing for DC incorrectly? If they are damaged, would this
mean another problem elsewhere perhaps?

Not ready to throw in the towel yet.

TimPerry · Guest

"Doze" <ipedigo@hotmail.com> wrote in message
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Gareth Magennis · Guest

"Doze" <ipedigo@hotmail.com> wrote in message
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Doze · Guest

Thanks Gareth, for the advice.

I replaced the caps and this has not fixed the problem.
I also replaced a resistor immediately after the recitifer and when I
powered it up, it blew as well as the fuse. I'm not really sure what
is the culprit now.

Any new advice?

Gareth Magennis · Guest

"Doze" <ipedigo@hotmail.com> wrote in message
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GregS · Guest

In article <dssmut$epq$1@nwrdmz02.dmz.ncs.ea.ibs-infra.bt.com>, "Gareth Magennis" <sound.service@btconnect.com> wrote:

JFeenstra · Joined: 13 Oct 2006 Posts: 1

hi, i recently came across one with a dead power supply as well, although the fuse isn't blown i'm having some difficulty spotting the problem...there isn't anything obvious (ie. poor solder joints, leaking caps) so i'm kind of stuck

does anyone happen to have the service manuel for the unit?