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From: pfm on 2 Dec 2009 16:09
This set suffered a power surge. The set switches on, produces a
raster for a few seconds and shuts down. The SMPS is SOPS type. The
theory of operation is not trivial.

Regulation is from B+ through an opto and TL431.

The B+ open circuit is 138V with the supply making a hum at 595Hz (the
trouble and strife has perfect pitch). Any load, in place of the LOPT
and HOT, causes the supply to groan and shut down. With B+ OC, 431 Ref
is 2.4V, Cathode is 3.8V, reasonable under no load.

Anyone with experience of this set, please?

Thanks
BobH


From: Franc Zabkar on 5 Dec 2009 20:49
On Wed, 2 Dec 2009 13:09:28 -0800 (PST), pfm <bobh(a)pfmbox.com> put
finger to keyboard and composed:

>This set suffered a power surge. The set switches on, produces a
>raster for a few seconds and shuts down. The SMPS is SOPS type. The
>theory of operation is not trivial.
>
>Regulation is from B+ through an opto and TL431.
>
>The B+ open circuit is 138V with the supply making a hum at 595Hz (the
>trouble and strife has perfect pitch). Any load, in place of the LOPT
>and HOT, causes the supply to groan and shut down. With B+ OC, 431 Ref
>is 2.4V, Cathode is 3.8V, reasonable under no load.
>
>Anyone with experience of this set, please?
>
>Thanks
>BobH

Sorry, no relevant experience, but the fact that the TL431's Ref input
is closer to 2.4V than to 2.5V would make me think that B+ is about 5V
too low, even in standby.

Unless the PSU uses discrete transistors, I'd be looking for a PWM IC.
Its datasheet would hopefully have an application diagram that matches
your circuit.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.
From: pfm on 14 Dec 2009 11:07
On Dec 5, 8:49 pm, Franc Zabkar <fzab...(a)iinternode.on.net> wrote:
> On Wed, 2 Dec 2009 13:09:28 -0800 (PST),pfm<b...(a)pfmbox.com> put
> finger to keyboard and composed:
>
> >This set suffered a power surge. The set switches on, produces a
> >raster for a few seconds and shuts down. The SMPS is SOPS type. The
> >theory of operation is not trivial.
>
> >Regulation is from B+ through an opto and TL431.
>
> >The B+ open circuit is 138V with the supply making a hum at 595Hz (the
> >trouble and strife has perfect pitch). Any load, in place of the LOPT
> >and HOT, causes the supply to groan and shut down. With B+ OC, 431 Ref
> >is 2.4V, Cathode is 3.8V, reasonable under no load.
>
> >Anyone with experience of this set, please?
>
> >Thanks
> >BobH
>
> Sorry, no relevant experience, but the fact that the TL431's Ref input
> is closer to 2.4V than to 2.5V would make me think that B+ is about 5V
> too low, even in standby.
>
> Unless the PSU uses discrete transistors, I'd be looking for a PWM IC.
> Its datasheet would hopefully have an application diagram that matches
> your circuit.
>
> - Franc Zabkar
> --
> Please remove one 'i' from my address when replying by email.

Thanks Franc

The supply is discrete and self oscillating, probably designed that
way to save $0.30. The slightest thing and it stops Iworking; fixing
it is like looking for a needle in a haystack.

BobH
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