crt no filaments


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crt no filaments

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dadams14
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Dec 30, 2005, 1:31 PM

Post #1 of 3 (2833 views)
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crt no filaments	Can't Post

I have an 1981 ms pacman monitor... It gets high voltage because I hear the aquadag and I can dezap the crt when I unplug it. The crt filament is very simple... It has a loop inside the flyback transformer and comes out to small inductor in series...there is a small capacitor in parallel with the loop .. Seems like a filter to smooth the ac 15750 hz from the crt....then the wires go directly to the crt board that is plugged into the crt socket. no resistors in series .... I don't get any raster, I don't see any orange glow in the neck and it does not seem to get warm.....I tried to measure the ac voltage across the filament and I get .1 v on my Digital multimeter... I am not sure you can do this and get a reliable reading....
Can somebody who has a set open and is sure the filaments are glowing .. just read the ac voltage and see what they get?
I checked the continuity of the in series coil and it is ok. Also the loop inside the flyback is 0 ohms. the filament pins on crt read 2 ohms.
I wonder if the small capacitor could be shorting or the
flyback is bad, but I think the flyback is ok because I get hi voltage...
Thanks in advance....
Dennis

mel
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Dec 30, 2005, 10:04 PM

Post #2 of 3 (2825 views)
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Re: [dadams14] crt no filaments [In reply to]	Can't Post

If you get an ohms reading across the CRT heater pins with the CRT board unplugged, the filaments are not open. If you have high voltage, it is a pretty good bet that the flyback is OK. It is rare that a capacitor such as this would fail but it is possible. Check the solder joints and disconnect the cap to see if it may be shorted.

rrobor
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Dec 31, 2005, 4:11 AM

Post #3 of 3 (2821 views)
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Re: [mel] crt no filaments [In reply to]	Can't Post

Yup agree with that, chances are the thing is lit and thats not the fault. Getting a reading on AC on that is dependant on your meter, only better grade meters can give accurate readings of voltage at scan frequencies. Pull the tube base off and ohms read the pins as stated, if OK read the tube base across the socket, if thats OK move on to reading Grid and cathode voltages.

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