Toshiba 34HF85, M3U01T Chassis

[pfm]

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

 

[Franc Zabkar]

On Wed, 2 Dec 2009 13:09:28 -0800 (PST), pfm <bobh@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.

 

[pfm]

On Dec 5, 8:49 pm, Franc Zabkar <fzab...@iinternode.on.net> wrote:

On Wed, 2 Dec 2009 13:09:28 -0800 (PST),pfm<b...@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