Magnavox PTV375 HV goes down

Hi. Got a question for you all. Magnavox PTV375 bigscreen. Hit starter
button - HV comes up just enough to flicker an image on the tubes then drops
off. Sound stays up. I ohm checked the HV device between flyback and
splitter. Reads right about 4 megohm between red and green leads. I don't
have another so not sure what correct reading should be. I know pretty well
open, could 4 meg be enough to bring HVPS down? For the tiny time an image
comes up, sweep looks good. As an ancient set, should have been seen before.

I pulled the HV board and checked over resistors, diodes, etc. Didn't see
anything way out of spec, but I could miss something.

Many thanks in advance,

Danny

 

[Jerry G.]

Check to see if the power supply is over voltage, especially to the HV
drive, and or scans. It is possible that there is a fault in the protection
circuits. It is also possible that the power supply is dropping out because
of a defect. The most common cause are high ESR caps in the various areas
concerned.

--

Greetings,

Jerry Greenberg GLG Technologies GLG
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<djnoble35209@charter.net> wrote in message
news:vtt9mdohlfrh4a@corp.supernews.com...
Hi. Got a question for you all. Magnavox PTV375 bigscreen. Hit starter
button - HV comes up just enough to flicker an image on the tubes then drops
off. Sound stays up. I ohm checked the HV device between flyback and
splitter. Reads right about 4 megohm between red and green leads. I don't
have another so not sure what correct reading should be. I know pretty well
open, could 4 meg be enough to bring HVPS down? For the tiny time an image
comes up, sweep looks good. As an ancient set, should have been seen before.

I pulled the HV board and checked over resistors, diodes, etc. Didn't see
anything way out of spec, but I could miss something.

Many thanks in advance,

Danny

 

[Ol' Duffer]

In article <vtt9mdohlfrh4a@corp.supernews.com>, djnoble35209@charter.net
says...

Hi. Got a question for you all. Magnavox PTV375 bigscreen. Hit starter
button - HV comes up just enough to flicker an image on the tubes then drops
off. Sound stays up. I ohm checked the HV device between flyback and
splitter. Reads right about 4 megohm between red and green leads. I don't
have another so not sure what correct reading should be.

If you are referring to the bleeder, 4 Meg is way too low. Don't
know exactly what it is supposed to be, but if you can measure it
with an ordinary VOM, it's probably bad. These are pretty common
leaky failure with age, and yes it makes HV shut down due to excess
current, although it usually doesn't stay up long enough to see a
picture. Make sure you're not measuring something else, like a
cracked blue tube that has sucked fluid.

could 4 meg be enough to bring HVPS down?

Do the math. 25KV (approx.) squared divided by 4 Meg equals
over 150 Watts!