vestel 11AK36 A8 TV - PSU not starting

B

b

Guest
This 14" 11AK36-A8 tv apparently 'just went off.' there was evidence
of a short near the mains inlet, on the print side of the pcb -
probably a strand of wire or blob of solder from the time of
manufcture had been the cause. checked rectifier, removed PTC in case,
replaced fuse. Set dead. 0v at psu o/ps.

checked the obvious in psu primary, no shorted diodes or open
resistors. Removed secondary diodes including HT line.

schematics here (5m). Psu is on page 24.: http://www.fileden.com/files/2007/6/4/1143893//11AK36
FULL.pdf

....not identical but the main aspects are the same.

300v present across mains capacitor, and at R821 (safety) and
collector of Q801.
25v present at c811, suggesting the uPc of the PSU has power.

I don't know where to look now. My next step would be to change the
uPc UC3843, but I don't think I've ever seen a case where the chip
went on its own...

I should probably have tossed this aside by now but I'm just keen to
satisfy my curiosity. So I'm all ears.
cheers,
B.
 
On Fri, 27 Aug 2010 05:05:57 -0700 (PDT), b
<reverend_rogers@yahoo.com> put finger to keyboard and composed:

300v present across mains capacitor, and at R821 (safety) and
collector of Q801.
25v present at c811, suggesting the uPc of the PSU has power.
Click to expand...
If the voltage at C811 is 25V, then one would expect that one or more
of D840 (15V zener), D839 (signal diode) and Q809 are open. AISI, the
combined voltage drop across all three components should be around
16V.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.
 
"b" <reverend_rogers@yahoo.com> wrote in message
news:8f75d703-8667-4259-8068-d91597e86867@q2g2000yqq.googlegroups.com...
This 14" 11AK36-A8 tv apparently 'just went off.' there was evidence
of a short near the mains inlet, on the print side of the pcb -
probably a strand of wire or blob of solder from the time of
manufcture had been the cause. checked rectifier, removed PTC in case,
replaced fuse. Set dead. 0v at psu o/ps.

checked the obvious in psu primary, no shorted diodes or open
resistors. Removed secondary diodes including HT line.

schematics here (5m). Psu is on page 24.:
http://www.fileden.com/files/2007/6/4/1143893//11AK36
FULL.pdf

...not identical but the main aspects are the same.

300v present across mains capacitor, and at R821 (safety) and
collector of Q801.
25v present at c811, suggesting the uPc of the PSU has power.

I don't know where to look now. My next step would be to change the
uPc UC3843, but I don't think I've ever seen a case where the chip
went on its own...

I should probably have tossed this aside by now but I'm just keen to
satisfy my curiosity. So I'm all ears.
cheers,
B.
Click to expand...
The link doesn't seem to get you direct to the schematic. Seems to want a
login from the home page ?

As for '3843s, I have had them go faulty on their own on other Vestel PSUs,
but I agree, it's rare. Have you ESR checked any small primary-side
electrolytics ? Is there anywhere else I can get a squint at the schems, or
can you mail the pdf to me direct ? I do quite a lot of switchers, and used
to do a lot of Vestels from bigger LCD TVs, so I might be able to offer an
insight or two ...

Arfa
 
On Aug 28, 9:33 am, "Arfa Daily" <arfa.da...@ntlworld.com> wrote:
"b" <reverend_rog...@yahoo.com> wrote in message

news:8f75d703-8667-4259-8068-d91597e86867@q2g2000yqq.googlegroups.com...



This 14" 11AK36-A8 tv apparently 'just went off.' there was evidence
of a short near the mains inlet, on the print side of the pcb -
probably a strand of wire or blob of solder from the time of
manufcture had been the cause. checked rectifier, removed PTC in case,
replaced fuse. Set dead. 0v at psu o/ps.

checked the obvious in psu primary,  no shorted diodes or open
resistors. Removed secondary diodes including HT line.

schematics here (5m). Psu is on page 24.:
http://www.fileden.com/files/2007/6/4/1143893//11AK36
FULL.pdf

...not identical but the main aspects are the same.

300v present across mains capacitor, and at R821 (safety) and
collector of Q801.
25v present at c811, suggesting the uPc of the PSU has power.

I don't know where to look now. My next step would be to change the
uPc UC3843, but I don't think I've ever seen a case where the chip
went on its own...

I should probably have tossed this aside by now but I'm just keen to
satisfy my curiosity. So I'm all ears.
cheers,
B.

The link doesn't seem to get you direct to the schematic. Seems to want a
login from the home page ?

As for '3843s, I have had them go faulty on their own on other Vestel PSUs,
but I agree, it's rare. Have you ESR checked any small primary-side
electrolytics ? Is there anywhere else I can get a squint at the schems, or
can you mail the pdf to me direct ? I do quite a lot of switchers, and used
to do a lot of Vestels from bigger LCD TVs, so I might be able to offer an
insight or two ...

Arfa
Click to expand...
thanks. try this link:
http://www.fileden.com/files/2007/6/4/1143893/11AK36%20FULL.pdf

I got this from eserviceinfo originally, I think.
Re: electrolytics, besides the mains filter cap I think there's only
the one I mentioned (c811)
cheers
Ben
 
"b" <reverend_rogers@yahoo.com> wrote in message
news:e4159d34-fc6a-4427-800f-17350cf3a391@t20g2000yqa.googlegroups.com...
On Aug 28, 9:33 am, "Arfa Daily" <arfa.da...@ntlworld.com> wrote:
"b" <reverend_rog...@yahoo.com> wrote in message

news:8f75d703-8667-4259-8068-d91597e86867@q2g2000yqq.googlegroups.com...



This 14" 11AK36-A8 tv apparently 'just went off.' there was evidence
of a short near the mains inlet, on the print side of the pcb -
probably a strand of wire or blob of solder from the time of
manufcture had been the cause. checked rectifier, removed PTC in case,
replaced fuse. Set dead. 0v at psu o/ps.

checked the obvious in psu primary, no shorted diodes or open
resistors. Removed secondary diodes including HT line.

schematics here (5m). Psu is on page 24.:
http://www.fileden.com/files/2007/6/4/1143893//11AK36
FULL.pdf

...not identical but the main aspects are the same.

300v present across mains capacitor, and at R821 (safety) and
collector of Q801.
25v present at c811, suggesting the uPc of the PSU has power.

I don't know where to look now. My next step would be to change the
uPc UC3843, but I don't think I've ever seen a case where the chip
went on its own...

I should probably have tossed this aside by now but I'm just keen to
satisfy my curiosity. So I'm all ears.
cheers,
B.

The link doesn't seem to get you direct to the schematic. Seems to want a
login from the home page ?

As for '3843s, I have had them go faulty on their own on other Vestel
PSUs,
but I agree, it's rare. Have you ESR checked any small primary-side
electrolytics ? Is there anywhere else I can get a squint at the schems,
or
can you mail the pdf to me direct ? I do quite a lot of switchers, and
used
to do a lot of Vestels from bigger LCD TVs, so I might be able to offer
an
insight or two ...

Arfa

thanks. try this link:
http://www.fileden.com/files/2007/6/4/1143893/11AK36%20FULL.pdf

I got this from eserviceinfo originally, I think.
Re: electrolytics, besides the mains filter cap I think there's only
the one I mentioned (c811)
cheers
Ben
Click to expand...
On some of the Vestel supplies that I've worked on, I have had problems with
the high voltage polyester caps going open. That 47nF 630v one, C812, would
be a prime one to check, particularly if it's a bright blue 'boxy' one,
rather than a brown epoxy coated type. I'll have a bit closer look tomorrow.

Arfa
 
On Aug 29, 12:49 am, "Arfa Daily" <arfa.da...@ntlworld.com> wrote:
"b" <reverend_rog...@yahoo.com> wrote in message

news:e4159d34-fc6a-4427-800f-17350cf3a391@t20g2000yqa.googlegroups.com...



On Aug 28, 9:33 am, "Arfa Daily" <arfa.da...@ntlworld.com> wrote:
"b" <reverend_rog...@yahoo.com> wrote in message

news:8f75d703-8667-4259-8068-d91597e86867@q2g2000yqq.googlegroups.com....

This 14" 11AK36-A8 tv apparently 'just went off.' there was evidence
of a short near the mains inlet, on the print side of the pcb -
probably a strand of wire or blob of solder from the time of
manufcture had been the cause. checked rectifier, removed PTC in case,
replaced fuse. Set dead. 0v at psu o/ps.

checked the obvious in psu primary,  no shorted diodes or open
resistors. Removed secondary diodes including HT line.

schematics here (5m). Psu is on page 24.:
http://www.fileden.com/files/2007/6/4/1143893//11AK36
FULL.pdf

...not identical but the main aspects are the same.

300v present across mains capacitor, and at R821 (safety) and
collector of Q801.
25v present at c811, suggesting the uPc of the PSU has power.

I don't know where to look now. My next step would be to change the
uPc UC3843, but I don't think I've ever seen a case where the chip
went on its own...

I should probably have tossed this aside by now but I'm just keen to
satisfy my curiosity. So I'm all ears.
cheers,
B.

The link doesn't seem to get you direct to the schematic. Seems to want a
login from the home page ?

As for '3843s, I have had them go faulty on their own on other Vestel
PSUs,
but I agree, it's rare. Have you ESR checked any small primary-side
electrolytics ? Is there anywhere else I can get a squint at the schems,
or
can you mail the pdf to me direct ? I do quite a lot of switchers, and
used
to do a lot of Vestels from bigger LCD TVs, so I might be able to offer
an
insight or two ...

Arfa

thanks. try this link:
http://www.fileden.com/files/2007/6/4/1143893/11AK36%20FULL.pdf

I got this from eserviceinfo originally, I think.
Re: electrolytics, besides the mains filter cap I think there's only
the one I mentioned (c811)
cheers
Ben

On some of the Vestel supplies that I've worked on, I have had problems with
the high voltage polyester caps going open. That 47nF 630v one, C812, would
be a prime one to check, particularly if it's a bright blue 'boxy' one,
rather than a brown epoxy coated type. I'll have a bit closer look tomorrow.

Arfa
Click to expand...
thanks, will follow that up sometime in the next fortnight
cheers, B.
 
You must log in or register to reply here.

Welcome to EDABoard.com

Sponsor

Back
Top