Problem Toei cm-r20 Green issue?

[Ronnie Dent]

Been getting this monitor cleaned up and ready to go back in the cab, I was getting a lovely white raster on first test but it soon turned into a green ever narrowing strip. I removed chassis cleaned and re capped it, all were replaced apart from the large smoothing cap and 2 of the four np caps as I only had two! Anyway I was greeted with a silent startup and a nearly full screen green raster, none of the r g or b pots change anything? I’m reading a b+ of 106v at the white ceramic resistor left side, is that too low? Hoping this is an easy fix? This is on the bench with no input and screen volts increased to see image.
Pic is before re capping

Thanks Ronnie

 

[Ronnie Dent]

I removed q16 and tested it, tested ok thinking that’s the green drive and maybe stuck on!

Few more pics as of now

 

[Retroman839]

Maybe red and blue are not putting out ?

Cold solder under side of the colour circuits.
Or caps / resistors / transistors in the blue or red colour circuit.

 

[Ronnie Dent]

Maybe red and blue are not putting out ?
View attachment 39735
Cold solder under side of the colour circuits here

Thanks possible I guess, I did look for bad solder while doing the caps but will check again

 

[Retroman839]

Also check solder on kneck card res and blue input connector,

If not been used for a long period though ,
If you haven’t used it in a while
It worked then didnt …
Seems something was ready to quit.

 

[Retroman839]

You could pull a transistor from
Red or blue and test if it has gone short ?

Maybe be poss to test for short in the colour transistors in circuit but I’m not sure about that .. check schimatic of that transistor.

May be poss to read the emitter volts on the transistor /mossfet green , when chasiss is running ?

Then compare that to red and blue transistor / mossfet emitter when running .

If differing value then something wrong in the red / blue circuit ?

Big cement colour resistors on kneck card are usual suspects too! Normally visual sign of over usage on them.

 

[Ronnie Dent]

Cheers I don’t think there are any components on the neck card
There are some tracks on the component side and 4 of them were corroded under caps caused by the glue not cap leak on cleaning them up all 4 were open so had to bridge those

Never seen this one running, as said on first power up had a nice white raster and after a few mins I heard a high pitched tone and the screen had narrowed and gone green.

The manual is very good for someone who understands the all the steps etc but it’s mostly lost on me!
Cheers Ronnie

 

[Retroman839]

You need red blue and green to make white Raster.

 

[Ronnie Dent]

Yes I know so either green is stuck on or red blue are off

 

[Ronnie Dent]

So did some voltage checks on the r g and b I’m seeing 106v on them all inc the tabs of the transistors and on the neck card for each colour hope it’s not a crt issue

 

[Retroman839]

You sure no colour resistors on the kneck card ?
Photo ?

 

[Ronnie Dent]

Yes just wires I think the 3 big resistors are on
The main board getting 106v one side 98v others reference ground

 

[gunblade]

desolder the green gun pin on the neck card

 

[Ronnie Dent]

desolder the green gun pin on the neck card

Thanks Grant will do that tomorrow 👍

 

[bernoli21]

Sounds like you're on the right track with the recap, but that green raster and unresponsive RGB pots could point to a few things. B+ at 106V does seem a bit low-might be worth checking what the spec is for that chassis (some expect 120V).

 

[Ronnie Dent]

Thanks Grant will do that tomorrow 👍

So with the green removed I get a red raster, hope that’s a good sign🤔

 

[Georgian2]

Do you have an video signal connected? Looks like the flyback is turned to high up.

 

[gunblade]

looks like 200v vid b+ missing or issue on cut off circuits, if you had one gun short it will still be green so its not tube

those chassis are dogs, they suffer from corrosion from cap leakage and the tracks on the pcb are exposed so its likely one of more have been rotted away

 

[Ronnie Dent]

looks like 200v vid b+ missing or issue on cut off circuits, if you had one gun short it will still be green so its not tube

those chassis are dogs, they suffer from corrosion from cap leakage and the tracks on the pcb are exposed so its likely one of more have been rotted away

Ok thanks Grant, I did find 4 rotted tracks under 2 caps, they had not leaked it was the glue that rotted them, they were repaired during the re cap, I will have another look, I did remove the heatsink beside the lopt to get at the caps better and check any traces under glue so confident that area is good.

Thanks Ronnie

 

[Ronnie Dent]

Do you have an video signal connected? Looks like the flyback is turned to high up.

No signal the board is away for repair, I turned the screen volts up to see the raster better

Thanks Ronnie