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From: Arfa Daily on 24 Nov 2009 14:30

"Fester Bestertester" <fbt(a)fbt.net> wrote in message
news:0001HW.C731515701323676B0B2D9AF(a)news.eternal-september.org...
>> Parts availablity can be a problem unless you can obtain a parts kit.
>> Parts are not stocked at the local Radio Shack and major suppliers
>> such as Mouser or Digikey may not heve them.
>>
>> PlainBill
>
> Can someone link to a SMPS repair parts kit? I've not seen these.
>
> Thanks.
>

For instance

http://cgi.ebay.co.uk/LCD-PSU-REPAIR-KIT-04TA069I-04TA0691-05TA071B-05TA071C_W0QQitemZ380177344747QQcmdZViewItemQQimsxq20091113?IMSfp=TL091113178002r28571

UK e-bay, but I'm sure a bit of googling or e-bay research would turn up
others in the U.S. or wherever

Arfa


From: Arfa Daily on 24 Nov 2009 14:42

<>>Far better, I think, that the existing power supplies are repaired.
Although
>>diagnosing these supplies is a bit of a black art, contrary to what you
>>believe, most are repairable, and most parts are available, if you look
>>hard
>>enough.
>>
>>Arfa
>>
> There are a few things I would add. Examining schematics of a few LCD
> TV power supplies show a great deal of cross coupling in the
> regulation. Using 5V, 12V, and 24 V supplies and swtiching them on
> without proper care in the sequencing almost certainly will not work.
>
> Parts availablity can be a problem unless you can obtain a parts kit.
> Parts are not stocked at the local Radio Shack and major suppliers
> such as Mouser or Digikey may not heve them.
>
> PlainBill

Interestingly, whole power supplies are available here, sometimes at
ridiculously low prices. For instance, many sets use a Vestel chassis, and
some of these PSUs are being sold brand new for as little as 25UKP, although
you can also find the same PSU at the same vendor for 3 times that, but
listed as being for a different make / model, so it's often advantageous to
know what power supply is used in multiple different manufacturer's sets.
Anyway, the point I was going to make is that a friend of mine whose shop
specialises in repair of LCD TV sets, often buys in these power supplies at
this price, and fits them into sets that they were never intended to go in,
and apparently without any problem. As long as he can find the turn on
signal from the system control micro, and there is physically room to fit a
Vestel supply in the set in question, he just goes ahead and does it, if
necessary, soldering the wires directly to the output connectors.

To take your point about cross-coupled regulation, I have not found this to
be a problem. I repair a lot of Vestel supplies for the trade, and they are
happy to regulate with any load from nothing to full, on any rail, all
rails, or no rails at all. As for the rails coming up in any specific order,
I think all of the ones that I've seen have all of the switched rails come
up together. Certainly, my friend doesn't seem to have ever had an issue
with the actual working of an internal supply substitute.

Arfa


From: PlainBill47 on 25 Nov 2009 11:51
On Tue, 24 Nov 2009 19:42:34 -0000, "Arfa Daily"
<arfa.daily(a)ntlworld.com> wrote:

>
><>>Far better, I think, that the existing power supplies are repaired.
>Although
>>>diagnosing these supplies is a bit of a black art, contrary to what you
>>>believe, most are repairable, and most parts are available, if you look
>>>hard
>>>enough.
>>>
>>>Arfa
>>>
>> There are a few things I would add. Examining schematics of a few LCD
>> TV power supplies show a great deal of cross coupling in the
>> regulation. Using 5V, 12V, and 24 V supplies and swtiching them on
>> without proper care in the sequencing almost certainly will not work.
>>
>> Parts availablity can be a problem unless you can obtain a parts kit.
>> Parts are not stocked at the local Radio Shack and major suppliers
>> such as Mouser or Digikey may not heve them.
>>
>> PlainBill
>
>Interestingly, whole power supplies are available here, sometimes at
>ridiculously low prices. For instance, many sets use a Vestel chassis, and
>some of these PSUs are being sold brand new for as little as 25UKP, although
>you can also find the same PSU at the same vendor for 3 times that, but
>listed as being for a different make / model, so it's often advantageous to
>know what power supply is used in multiple different manufacturer's sets.
>Anyway, the point I was going to make is that a friend of mine whose shop
>specialises in repair of LCD TV sets, often buys in these power supplies at
>this price, and fits them into sets that they were never intended to go in,
>and apparently without any problem. As long as he can find the turn on
>signal from the system control micro, and there is physically room to fit a
>Vestel supply in the set in question, he just goes ahead and does it, if
>necessary, soldering the wires directly to the output connectors.
>
>To take your point about cross-coupled regulation, I have not found this to
>be a problem. I repair a lot of Vestel supplies for the trade, and they are
>happy to regulate with any load from nothing to full, on any rail, all
>rails, or no rails at all. As for the rails coming up in any specific order,
>I think all of the ones that I've seen have all of the switched rails come
>up together. Certainly, my friend doesn't seem to have ever had an issue
>with the actual working of an internal supply substitute.
>
>Arfa
>
I think we were failing to communicate properly here. I interpreted
the plan as to buy three separate power supplies (5V, 12V, 24V) and
use them to replace an integrated 5V, 12V, 24V supply. I do not think
that will work well.

You appear to be discussing using a 5V, 12V, 24V supply designed for
an XYZ brand of TV in a QED TV. I would have to agree, if dimensional
and current ratings are compatible, that should work.

From a personal perspective, I 'grew up' with analog power supplies
(often using vacuum tube rectifiers). These were inefficient, but
easy to repair. The switch to SMPS supplies required more
sophisticated techniques, but in the end was not that much more
difficult, even for the multiple output supplies found in PCs.

At this point I am finding the supplies in LCD TVs to be extremely
difficult to troubleshoot safely and effectively.

PlainBill
From: Arfa Daily on 25 Nov 2009 19:45

<snip>

>
> From a personal perspective, I 'grew up' with analog power supplies
> (often using vacuum tube rectifiers). These were inefficient, but
> easy to repair. The switch to SMPS supplies required more
> sophisticated techniques, but in the end was not that much more
> difficult, even for the multiple output supplies found in PCs.
>
> At this point I am finding the supplies in LCD TVs to be extremely
> difficult to troubleshoot safely and effectively.
>
> PlainBill

Agreed. The key to it seems to be obtaining schematics. I offer a trade
repair service on a particular LCD power supply board, but I am only able to
do that as a result of hours of painstaking research to find schematics to
cover all the variants. I then spent a long time analysing just what made
this supply tick (figuratively, not literally !! ) and then sat down and
designed a test jig and a set of adaptor harnesses to allow the different
variants to all be repaired using that jig. I can pretty much crack most
problems on them in fairly short order now, but still get the occasional one
that gets the better of me. Just yesterday, actually ... I have one at the
moment that has a really odd fault. The PFC supply won't start up at full
supply volts. Turn it down on a variac just 10 volts, and it will start
every time. If you then turn back up, it keeps running, but the PFC supply
starts to squegg, and the 390v rail drops to around 340v. At the same time,
the 24v secondary side rail drops to around 23v, but curiously, all the
other rails stay spot on. That might be the clue to what's going wrong, as
the 24v rail is normally *very* tightly regulated. I would add that the
problem occurs whether there is a load on any of the rails or not. It'll be
an interesting one to eventually find when I have the time, but in the
meantime to get my customer out of trouble with his, I've had to do him a
swapout.

Arfa


From: Chris F. on 26 Nov 2009 10:59
I should have tested more thoroughly before posting. Turns out the power
supply is good - all three output voltages are normal. The problem must be
in the mainboard - the power light comes on but nothing happens. So it looks
like a dead end for this set.
What I might try to do is fit the power supply from this set into another
one, rather than building an external supply....

"Arfa Daily" <arfa.daily(a)ntlworld.com> wrote in message
news:yckPm.17678$9h4.5659(a)newsfe08.ams2...
>
> <snip>
>
>>
>> From a personal perspective, I 'grew up' with analog power supplies
>> (often using vacuum tube rectifiers). These were inefficient, but
>> easy to repair. The switch to SMPS supplies required more
>> sophisticated techniques, but in the end was not that much more
>> difficult, even for the multiple output supplies found in PCs.
>>
>> At this point I am finding the supplies in LCD TVs to be extremely
>> difficult to troubleshoot safely and effectively.
>>
>> PlainBill
>
> Agreed. The key to it seems to be obtaining schematics. I offer a trade
> repair service on a particular LCD power supply board, but I am only able
> to do that as a result of hours of painstaking research to find schematics
> to cover all the variants. I then spent a long time analysing just what
> made this supply tick (figuratively, not literally !! ) and then sat down
> and designed a test jig and a set of adaptor harnesses to allow the
> different variants to all be repaired using that jig. I can pretty much
> crack most problems on them in fairly short order now, but still get the
> occasional one that gets the better of me. Just yesterday, actually ... I
> have one at the moment that has a really odd fault. The PFC supply won't
> start up at full supply volts. Turn it down on a variac just 10 volts, and
> it will start every time. If you then turn back up, it keeps running, but
> the PFC supply starts to squegg, and the 390v rail drops to around 340v.
> At the same time, the 24v secondary side rail drops to around 23v, but
> curiously, all the other rails stay spot on. That might be the clue to
> what's going wrong, as the 24v rail is normally *very* tightly regulated.
> I would add that the problem occurs whether there is a load on any of the
> rails or not. It'll be an interesting one to eventually find when I have
> the time, but in the meantime to get my customer out of trouble with his,
> I've had to do him a swapout.
>
> Arfa
>
>


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