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CRT Repair Toshiba CN27D90 Tube Brightness Issue

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I'm trying to get some help with a repair I made recently to my CRT Toshiba CN27D90. I performed a full electrolytic cap replacement and upon reassembly and power up the TV now has issues with the picture tube being very dim and it seems unable to produce any white color. I suspect maybe a power issue but I'm not sure where to start checking, as actively diagnosing issues isn't my forte.

Before the repair the TV did not display the issue described above. It had vertical geometry issues and some red color instability (as in after power on, the whole picture would lose its red channel and become just cyan/green, but this would usually stop after maybe 20 mins).
I've attached some images below to help. I'm using 240p Test Suite for the test images. Colors display but it has issues with white.
Any and all help is appreciated, thank you.

Welcome to the forum  :)

If you have new symptoms after recapping, then review your work you might have bad soldering, wrong capacitor value/polarity or new fractured soldering joints. Connectors as well, that they are not damaged or plugged in wrong during assembly.

Whenever a gun is cutting in and out, I find it's usually bad solder joints on the CRT board/socket. Not a capacitor. While looking at the screen using a mirror, take a plastic poker and tap the main PCB, the crt board, lightly to flush out bad connections. With older sets it's common to use a magnifier and do a visual and go over the solder joints. It depends on the build quality, some sets have good wave-soldering and many do not. With CRT TVs and monitors, I'd always spend 15 minutes just staring at the board and re-touching up dodgy looking solder joints. Every set has them.
Heavy through-hole parts can fracture solder joints from the tossing and flipping around doing the recap. Some people can be a bit too rough.

You appear to have primary colours, green gun is a bit weak- but any mix of them is a trainwreck, especially to make white or yellow. This is odd, I'm suspecting a capacitor on a CRT (common) rail is no longer there and ripple current makes one gun affect the others. This is just speculation.

Do you have the service manual, a scope etc. that kind of thing? While you can troubleshoot the problem, it takes a lot of time. If your only test equipment is your eyes, then it can be faster to review things with a magnifier, and bright bench light.

Ty for taking the time to reply and for the insights so far.  :)

I have been inspecting the board with a magnifier looking at joints, but in order to be thorough, I'll need to fully take the board out again, which I'll do. In hindsight, I should have just worked on small sections of caps at a time, mainly where there was leakage (and there were leaky caps on the vertical geometry segment of the main board). I do not have any tools except my soldering equipment and a multimeter.

I tested the voltage on the filament heater (I think that is the proper term) at the neckboard and coming off the flyback transformer because I did notice that the filaments in the tube are not glowing when the TV is powered on. At the transformer pin, it's outputting ~3.1 VAC. I traced it to a molex type connector which is running up to the neckboard. At the connector just adjacent to the flyback transformer it's measuring 3.1 VAC, at the neckboard connector pin it's 3.1 VAC, then it runs through a very low Oms (0.82) resistor which makes it 2.8 VAC at the neckboard pins just before the filaments.

I have no idea though if these are good values b/c I do not have access to a service manual, as you mentioned.

And as an aside, I took values of the R, G, and B pins at the neckboard: R=184.6 VAC, B=187.5 VAC and G=177.0 VAC

I did find a schematic https://elektrotanya.com/toshiba_cn27c90_tv_d.pdf/download.html and this https://elektrotanya.com/toshiba_cn27c90_tv_d.djvu/download.html

The power supply outputs regulated +115VDC at C897 33uF 160V/F802, which I would check and a few rails the ones with new caps to see how they are doing i.e C889 3,300uF 35V/F803 for audio?, C892 1,000uF 25V for 18.5V and there's a handful of other voltage regulators.

The flyback transformer has a dedicated winding for the CRT filaments, these are usually 6-9VAC but 16kHz AC squarewave which many multimeters do not accurately read. The X-ray protect circuit is also fed by this and somehow gets 20.1VDC from it so it must be higher than what you read.

Ok, great. I'll start looking at those as soon as possible and I will see how they are functioning. Thank you.


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