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'[PIC]: Microchip Power Bricks'
2001\01\30@070321 by Michael Rigby-Jones

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> -----Original Message-----
> From: Andy Stephenson [SMTP:spam_OUTandy.stephensonTakeThisOuTspamASAMICROS.COM]
> Sent: Tuesday, January 30, 2001 10:37 AM
> To:   .....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU
> Subject:      Re: Microchip Power Bricks
>
> Michael,
>
> Of the two that failed on me, both cases were an O/C 1W ish resistor.
>
> Can't remember the component ref or value, but have a look around. The
> first one to fail, put a hole in the res body, the second one did not.
>
> Rgds...
>
> ...Andy
>
You inspired me to open them up and take a look!  There is a 200 Ohm 1W
resistor (R3) that on both faulty supplies are well cooked, as is the PCB
underneath.  However, both resistors are functional, and I can see no bad
solder joints.  I also checked the fuse, the surge limiting thermistor, the
diode bridge, and something that looked like a low value fusible resistor as
well.  Nothing obvious at all I'm afraid.  The last one to fail has also
been getting *very* hot around the main switching transistor (MOSFET?), the
PCB is noticeably brown underneath this device.  What has probably not
helped is the nice piece of insulating foam that the PCB sits on, helping to
keep everything nice and hot.

Roman suggested changing the electroylitics, of which there are several, but
to be totaly honest, the value of the supply is neither worth the cost of my
time or the cost of replacements.  I'll chop the low voltage cable (with
power plug) off and use it on a bench supply for now.

I really dislike switchers.  I know they have their place, but any time I've
had to repair one, I hate the point at which I have to plug it in and try
it.  I probably just a big coward, but after witnessing a couple of
"catastrophic failures" (not my own!) I usualy put it on the end of an
extension lead and stand the other end of the bench to power it up!  At
least linear supplies generaly hum quite loudly followed by a waft of smoke
if they fail.

In summary it looks like it is basically a poor design that is not
adequately rated for it's intended use.

Cheers

Mike

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2001\01\30@072444 by dre Domingos F. Souza

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>I really dislike switchers.  I know they have their place, but any time I've
>had to repair one, I hate the point at which I have to plug it in and try
>it.  I probably just a big coward, but after witnessing a couple of
>"catastrophic failures" (not my own!) I usualy put it on the end of an
>extension lead and stand the other end of the bench to power it up!  At
>least linear supplies generaly hum quite loudly followed by a waft of smoke
>if they fail.

       Some time ago there was a common joke in my lab: "Alexandre turned indian" and everyone around would start to "hummmmmmmmmmm" for a long time. That's because I used to fix a switcher that ALWAYS blows the +5v capacitor (when it fails, it raises the voltage to +35V!!!!!) and I get that lovely aluminium can right between my eyes, making that mark of the "third eye" in me. So they say I've got to be an indian :o) Of course I solved the problem assembling a "shield" made of clear acrylic foldable between me and the damm switcher. And now I have a good view of an exploding capacitor, he he he :o)


--------------8<-------Corte aqui-------8<--------------

       All the best!!!
       Alexandre Souza
       .....xandinhoKILLspamspam.....interlink.com.br
       Linux User #85093

--------------8<-------Corte aqui-------8<--------------

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2001\01\30@074131 by Bob Ammerman

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I could be wrong, but I think that mChip supplies a conventional linear wall
wart to those of us in 110V land. Mine are heavy and don't get all that
warm.

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

{Original Message removed}

2001\01\30@075608 by Roman Black

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Bob Ammerman wrote:
>
> I could be wrong, but I think that mChip supplies a conventional linear wall
> wart to those of us in 110V land. Mine are heavy and don't get all that
> warm.

The one I got with my original dos picstart years
ago was a normal one. (I never used it!! original
picstart collectors item anyone??)

The one I got about two years back with the new
Picstart Plus is the awful switcher one but did
come with a US mains lead. Since the mains lead
plugs in I just use an Aussie one.
-Roman

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2001\01\30@094846 by William Bross

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At 11:52 PM 01/30/2001 +1100, you wrote:

I have had a number of their PSUs go bad over the years -- 2 of the big old
switchers on my Picmaster and 3 of the small PSUs on my Promate and
Picstart+.  I normally just call my Microchip FAE and I get a new one in a
couple of days.  You can also fill out the service request on their website
at:
http://www.microchip.com/10/tools/support/service/index.htm

Bill

>Bob Ammerman wrote:
>>
>> I could be wrong, but I think that mChip supplies a conventional linear
wall
{Quote hidden}

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2001\01\30@204451 by Roman Black

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William Bross wrote:
>
> At 11:52 PM 01/30/2001 +1100, you wrote:
>
> I have had a number of their PSUs go bad over the years -- 2 of the big old
> switchers on my Picmaster and 3 of the small PSUs on my Promate and
> Picstart+.  I normally just call my Microchip FAE and I get a new one in a
> couple of days.  You can also fill out the service request on their website
> at:
> http://www.microchip.com/10/tools/support/service/index.htm
>


Sounds like a case of "release a disfunctional product
and just replace the failures"... I could never do that!
It would irk me severely that my name was on a crap
product that is not reliable! Just lucky they fail in
a way that doesn't (usually) destroy the Picmaster...
-Roman

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2001\01\30@210415 by Andrew E. Kalman

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Roman wrote:

>Sounds like a case of "release a disfunctional product
>and just replace the failures"... I could never do that!
>It would irk me severely that my name was on a crap
>product that is not reliable! Just lucky they fail in
>a way that doesn't (usually) destroy the Picmaster...


Some time ago our PICMASTER started acting a little funny, in that
the green power LED would sometimes light and other times not.
Everything else about it seemed to work fine ... 4-6 months later I
decided to investigate, and found that one of the two +5V fuses (the
non-socketed one, of course) had blown. Dunno why. Anyway, replaced
it with an in-line, socketed fuse and all is well again.  The PS is
not a brick, though -- it's a big momma made in Germany.

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2001\01\31@021611 by Nigel Goodwin

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In message <RemoveME3A776D7D.6E02spamTakeThisOuTezy.net.au>, Roman Black <fastvidEraseMEspam.....EZY.NET.AU>
writes
>Sounds like a case of "release a disfunctional product
>and just replace the failures"... I could never do that!
>It would irk me severely that my name was on a crap
>product that is not reliable! Just lucky they fail in
>a way that doesn't (usually) destroy the Picmaster...

I suspect that MicroChip just buy the PSU in - probably from the
cheapest quote!. SMPSU's usually fail 'safe', it's uncommon for them to
damage the product they feed - they often have a 'crowbar' circuit which
kills the supply if the output gets excessive.

As a TV service engineer I repair a LOT! of switch mode PSU's,
incidentally, the first domestic use of a SMPSU was by Ferguson in their
3000 series colour TV's - around 1970, and was totally discrete.
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'[PIC]: Microchip Power Bricks'
2001\02\01@161304 by Peter L. Peres
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>At least linear supplies generaly hum quite loudly followed by a waft of
>smoke if they fail.

You must be one of them lucky guys who evaded being sprayed by a failing
large electrolytic in a linear supply ;-) I don't know what causes asthma
but THAT certainly does it, at least temporarily ! I once worked in a
restricted space and had this happen and I thought I had a 50% chance to
make it to fresh air in time.

Peter

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