Picture/Signal Disappearing Act on My Pilot TV37
 

Just finished a recap on this little tv. It has this symptom when, after initial power up, after a few seconds, raster, sound and picture are present.
Video soon disappears and we're left with just the raster and sound, until, after 1-2 minutes the picture comes back. Usually, this is brought about by some percussion on the set, adjustment of the fine tuning or switching the "high/low" switch.

When the picture returns to the screen, it's a little washed out, sometimes negative.

The picture, after about 5 minutes becomes quite acceptable, with plenty of sharpness, brightness available as well as contrast available. Ostensibly the original 3KP4.

Sams manual suggests it's either the kinescope or one of the IF tubes is defective. I've tested every single IF tube and they test fine in emissions and Gm.

The tubes that needed to have been replaced, all except for the video amp, a 6BA6, which, on my Hickock tested below spec in Gm. I suspect this tube may be the culprit, and is on order, but not sure if it's something else.

I'm not sure why switching the high/low or any percussive action would bring back the picture after a couple minutes.

Has anyone encountered this problem and could give some insight?

https://i.ibb.co/bRXY15K/Screen-Shot...2-07-14-AM.png

Since the problem is sensitive to vibration (and temperature) the root cause would have to be mechanical. Something is loose, could be a solder joint or inside a component like a tube, switch or resistor. Moving a switch may simply be generating the right type of vibration to effect another part. If it is a tube, you would need to recreate the same conditions during use of the tube tester in order to see the problem there.
Another example of why a tube tester can't find all tube problems.
Besides trying a new tube, clean switches and tube sockets, etc.
You may need to monitor some signal(s) during warm-up to track the problem down.

Thanks. I'm thinking it may be a bad resistor. Going to go through them, especially on the IF chain. I'm sure those 68Ω's have drifted up.

Is the loss of picture sudden or a fade out? If a fade out, could be a bad filament connection.

The picture comes in right as the set warms up and after a few seconds it fades away. About 1-2 min later the picture fades back in, either by tapping near the IF side or on the tube itself. The set maintains raster the whole time which leads me to believe filaments might not be the problem, but I could be wrong.

I've checked the continuity of the CRT filaments from the chassis connection to the pins of the socket and all seems fine. I've checked and replaced any out of spec resistors and the set is re-capped. I've subbed and rotated tubes. I've aligned the IF stages with a VTVM and the symptom doesn't go away. That's why I'm led to believe it's the 3KP4.

Waiting on an NOS 3KP1 to arrive so I can check this.

Hard to understand how it could be the 3KP4 if it has a raster.

Look at the filaments of the tuner & IF tubes & see if one is
changing brightness. The other thing on these oldies is the video
detector diode. They are lots of trouble & can give you a negative pix.

Quick hints. Finding tuner vs IF problem. No equipment needed !
A good running set with no signal should give a strong clean snowy
pix & a nice waterfall noise from the sound.
Start by turning channels. You should see & hear crashing of the
switches. If not its probably IF but possibly tuner.
Pull the 1st IF tube. You should see the same thing. If not its the IF.
Do the same with the 2nd & 3rd IF's one at a time. That at least can narrow things down.

Tube testers. As pointed out dont trust them. We had a TOTL B&K
tester but rarely used it. It was for the customers. Behind the main
bench was about a 15 by 6 foot tube shelf. It had almost every modern
tube in multiples. On top was stored grosses of 6GH8, 6LB6 & many others
bought in larger quantity. So you just turn around & try new tubes.

enuf fer now
73 Zeno:smoke:
LFOD !

Zeno these pilots used continuous tuners IIRC so no switch noise changing channels.

Was not aware of that so will say "usually". My experience with old sets
is limited to dump picking when I was a kid. Most were those 10" admirals.
By 1970 almost all sets were junked if they didnt have UHF so didnt
see many before abt 1960 as a payed tech. Just as well. IMHO most of
the sets after PCB's & doughnut chassii started they were miserable POS's
to work on.

73 Zeno:smoke:

I forgot to mention I did replace the diode in the video detector can with a new 1n34.

Now that someone mentions it, there may be another failed component in that can. Worth checking.