Is this a bad CRT? 10BP4

[CJVx]

Hello, after a re-cap on my RCA T-100 chassis, it has came on showing a strange picture that looks like a stone engraving for lack of a better description. Also experiencing significant blooming, what I think are overscan lines and the behavior of the focus control will only show the sharpest focus when the wiper and element are shunted (fully turned clockwise). Unfortunately I do not have a CRT tester at this time, but still gaining experience on vintage TVs, I would like to hear the thoughts of some more experienced people on here. Thanks!

PS, when the video and AGC tubes are removed, just leaving a raster on the screen, I still see similar overscan lines and blooming/ loosing focus when the brightness is increased, indicating there is something else going wrong further down the line.

[Yamamaya42]

Until you can get video on the screen, you can't really judge what you are looking at yet, the health of the CRT included, or even if the ion trap is on correctly.

[CJVx]

If you look closely, there is video, it’s just odd. I tried the ion trap and all possible ways and this is the best I can get it.

[Username1]

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This picture does contain picture information, however, it looks like a AGC
problem + Brightness way too high, and is displaying retrace lines.

But, since you replaced all the capacitors, as you stated, it can be anything
from the wrong part in the wrong spot, mistake in wiring, or something
else..... Along with this on the picture, is there quality loud sound? or
is it low, or does it have some noise mixed with it?

Use clues in pix, & Sound to guide you, + Check your work, + Check AGC.

Looks like sync is locked, Video is pretty weak - find the cause.

I would say the ion trap is fine for now, and the picture tube is fine too.

-----

Addition:

When I say it looks like a AGC problem, I mean - If the set were not
completely re-caped and you know for sure the circuits were not
mistakenly changed to cause this loss of full signal at the point
it's lost now.....

Start by checking your work - especially signal path near and
after the detector circuit + Possibly include the AGC stuff.....
Don't discount possible bad tube, open IF Transformer, etc.

But first check your own work for mistakes....



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[Yamamaya42]

OK, if you have an an oscilloscope. Set it to the horizontal scan rate, and look at the signal going into the grid 1 of the 10BP4 , should be a green wire, the wave there should be 30-40 PtP. If it's not, you have a problem with the video getting TO the CRT, but if it IS correct, you have a very weak CRT.

http://suzaku.live-evil.org/CRT-input.jpg

this is from the RCA630TSService manual, rather close to your TV, also used a 10BP4.

[Kevin Kuehn]

Try turning your room lighting off. Next turn down the TV's brightness control, and see if the picture(contrast) control can give you a more defined with better contrast picture. With the brightness turned down you may get better focus control too. Keep in mind you can't increase screen blackness with the TV's controls unless the ambient room lighting is low. Think of it as a movie projected on a screen, and if you bring the room lights up too bright you loose picture contrast. These early CRT's were never intended to be viewed in a well lit room.

[jr_tech]

I would check the voltages at the base of the crt...if not ok unplug from the crt and recheck...might provide a clue.

jr

[Yamamaya42]

Originally Posted by Kevin Kuehn

Try turning your room lighting off. Next turn down the TV's brightness control, and see if the picture(contrast) control can give you a more defined with better contrast picture. With the brightness turned down you may get better focus control too. Keep in mind you can't increase screen blackness with the TV's controls unless the ambient room lighting is low. Think of it as a movie projected on a screen, and if you bring the room lights up too bright you loose picture contrast. These early CRT's were never intended to be viewed in a well lit room.

true, but the image should not be THAT dim, something is not right here.

example, my set.
http://suzaku.live-evil.org/0226241857b.jpg
Taken with VERY bright light on, but then again my 12LP4 is an exception, having spent more than half of it's life in a basement unused!

[old_coot88]

By golly there is a locked-in picture there. Couldn't see it at first. First thing I would look for is an open peaking coin the video chain, anywhere between the vid detector and CRT. Blooming is generally from HV being lugged down due to a weak HV rectifier.

[Yamamaya42]

reading this page may help

https://antiqueradio.org/RCAT-100Television.htm

This set uses a 12AU7 as the Video amp 1st and 2nd, the sync is taken off after the first, so yeah, to could be a problem with the coils after the 1st video where the sync is taken off, or it could be bad resistors.

[old_coot88]

The schematic's in here -
https://www.earlytelevision.org/pdf/...edata-1950.pdf

There's actually 3 coils tied directly to the 12AU7 -- L103, L105, and L110. Check those for opens.

[CJVx]

Thanks for all the tips guys, I was able to see that L32 was open, and that it couples the 2 halves of the 12AU7… however, after luckily finding the lead wire just needed to be resoldered, I still have the same symptoms. I was all ready to pull the scope and measure the green second grid wire as suggested, but noticed that something didn’t match in the schematic. I accidentally misconnected C53 directly to one end of L36 as the picture shows, I drew a dotted line where it was accidentally connected. I corrected that, and now I have video, but the focus is still terrible, and best at full rotation of the control. The picture seems pretty dim. Any additional brightness increase from the control will cause retrace lines, and even worse focus as well as blooming. Going to look more into it, and make sure there aren’t any resistor issues, but this kind of looks like a very weak picture tube.

Another odd clue is that the wire that I believe is going to the focus coil at one point in another life was arcing against the door knob cap. When I first turned the set on after recap, I got no raster and traced it back to a dead 1B3GT. I would think this arcing could have killed it, but could it have wounded something else?

[Kevin Kuehn]

Have you tried adjusting the AGC control to see how it influences the picture? It's hard to tell from your photo the condition of the CRT because there's no way to know how the contrast, brightness, AGC, and ambient room lighting is all interacting. From what I'm seeing it's not terrible and can possibly be improved. Do you have another CRT you can sub?

[Username1]

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Well that picture looks much better.... If it's still poor brightness, and the 1B3 is new
and you know it to be good, then you have to look and see what the HV is with a
meter, and see if it drops as you demand more from the HV by turning up the
brightness.... You may also just have a weak picture tube, you know it's an
old tv, and it's to be expected.....

For HV there is a special meter you need to measure it, so be sure you get
the right one, either a dedicated HV, or adapter to a DVM whatever you
want to do. Horiz Output circuit provides HV so you can check out
that area if you find HV to be low.... And ebay for another
picture tube....


.

[Kevin Kuehn]

One other thing to check is the 1M resistor in series with the high voltage lead from the 1B3. If that drifts way high it can cause HV sag. It's R125 on the Sams schematic.