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Toshiba 34HF85, M3U01T Chassis

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

Reply to
pfm
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On Wed, 2 Dec 2009 13:09:28 -0800 (PST), pfm put finger to keyboard and composed:

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

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Reply to
Franc Zabkar

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

Reply to
pfm

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