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 Picture Failure on HMV F4 Chassis
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 Return to top of page · Post #: 1 · Written at 5:24:33 PM on 31 December 2021.
Pitchersj's avatar
 Location: Albury, NSW
 Member since 2 July 2017
 Member #: 2134
 Postcount: 172

Can anyone tell me if valve 5AS4 should light up when the set is powered on

I have picture failure on my set and wondering if it could be failed valve

 Return to top of page · Post #: 2 · Written at 7:16:42 PM on 31 December 2021.
Tallar Carl's avatar
 Location: Latham, ACT
 Member since 21 February 2015
 Member #: 1705
 Postcount: 1803

Check the valve filement with your multimeter. Pins 2 and 8.

 Return to top of page · Post #: 3 · Written at 7:26:50 PM on 31 December 2021.
Johnny's avatar
 Location: Hobart, TAS
 Member since 31 July 2016
 Member #: 1959
 Postcount: 491

If you have a picture failure I assume sound is OK?
If that’s the case 5AS4 is working as designed.
Otherwise, measure high tension voltage on 5AS4.
Filaments should be alight.

 Return to top of page · Post #: 4 · Written at 12:22:10 PM on 1 January 2022.
Robbbert's avatar
 Location: Hill Top, NSW
 Member since 18 September 2015
 Member #: 1801
 Postcount: 1693

5AS4 is like a big 5Y3GT, so yes the filaments will glow red across the top and also if you look down into the anodes. They tend to go gassy rather than open-circuit, but if yours isn't lighting up try another one. If you haven't got a replacement, luckily there's literally dozens of pin-compatible types.

Testing procedure:
1. Turn off set, unplug 5AS4
2. Use multimeter to check for continuity of the filament. If this fails, discard.
3. Use multimeter to make sure each anode is NOT touching the filament. If this fails, discard.
4. Use multimeter to make sure the 2 anodes are NOT touching each other (unlikely, but still...). If this fails, discard.
5. Visually check the filament. It should be white - not grey. You might find bits of it at the bottom of the valve. Or you might have low emission.
6. IF you have a working radio that uses a 5Y3G or GT, put the 5AS4 in its place, see if it works. Just don't run it for a while because the filament takes an extra amp (5 watts) of power.
7. If the tube has purple or blue lights, it's gassy. Discard.

If all this passes, you know the 5AS4 is ok. The next thing would be to check the filament voltage in the TV.

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