Sanyo CE21A2 TV arcing in tube neck between anodes at switch-on

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HandyMan 20 years ago

Hi all,

I have a 21" Sanyo TV set (Philips tube) which, when switched on, starts up very briefly and arcs once between the anodes visible in the long uncovered tube neck. The line stage shuts down so quickly that it appears not to start-up at all, but clearly it is doing in order to provide the voltages required for the single arcing. The set then just stays in standby mode with the front LED blinking 3 times in a row repeatedly.

I cannot find blink codes for the front LED, but I can assume it's in a protection mode (unless anyone knows differently?) and need to find the reason for the arcing. Initially I had found that R666 - bad omen or what - (8R2 5W) lifted out from its intact solder joints. Fibreglass-pen treatment to the legs of the resistor and resoldering put that right, but did not affect this fault. The resistor is a surge-limiter in the feed to the line-output transistor (or HOT, if you prefer that terminology). Maybe this is coincidental or a clue as to what may have happened to cause this arcing.

The line-output transistor and its internal diode is fine and so is the snubber capacitor, so they're ruled out as causing excessive-voltage from the flyback. I'm not sure what to do next... LOP transformer or tube defective? I know Philips have been having tube problems for a while now, already written off a 32" one with internal leakage causing a protection fault.

Thanks all, James

PDF service manual for this set/chassis available to download here:

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b 20 years ago

is the power supply Ok? the B+ line not too high?

-B

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HandyMan 20 years ago

Sorry, I should have said.

The B+ line is spot on for its standby voltage. Of course, the line stage stays on for such a short time that I can't check the B+ voltage in the 'On' state, but if the standby voltage is right, I can only assume it drops to the correct level when the line stage pulls some current.

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Franc Zabkar 20 years ago

On 2 Oct 2005 08:19:18 -0700, "HandyMan" put finger to keyboard and composed:

Could it be that the focus and G2 voltages are too high? If so, then this may be due to an open resistor in the bottom end of the screen/focus block on the FBT.

-- Franc Zabkar

Please remove one 'i' from my address when replying by email.

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Skype_man 20 years ago

Likely the picture tube is bad. Unlikely, a crt rejuvinator MAY save it, but not likely.

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Andy Cuffe 20 years ago

I've seen several recent Philips CRTs that were so gassy the necks glowed. They must be having some manufacturing problems. Andy Cuffe

snipped-for-privacy@psu.edu

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HandyMan 20 years ago

Thank you everyone for your replies.

Well, since this message was posted, I noticed arcing from a part of the tube bowl (top-right corner) where glass has been knocked out to the dag, with a long crack emanating from this damage right to the seal between tube bowl and front glass screen.

The arcing at this point only happens once every 10 or so switch-ons, so I hadn't seen it before.

I assume air has got in and the arcing is because there's now no electron beam flow from the cathodes due to air resistance and impedance and so the EHT, with no electron beam current to sate it, is seeking a point of lower potential and finding it in the form of the grids and cathodes. This is only a theory though, since I have not come across a CRT with air in it before. Anyone know for sure that this effect would occur if the tube was absolutely full of air?

Thanks again for your kind help.

Best regards to all, James

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Plague Boy 20 years ago

It's caused by Taco Bell commercials.

PB "Fresh windows units enter the internet backwards, bent over & naked, screaming ?Don?t infect me! It will take me more than 12 minutes to download the security packs!?-anonamin

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clifto 20 years ago

Don't knock 'em. They're the only real example of truth in advertising today. They begin and end their commercials with "Dung!"

If John McCain gets the 2008 Republican Presidential nomination, my vote for President will be a write-in for Jiang Zemin.

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Sanyo CE21A2 TV arcing in tube neck between anodes at switch-on

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