Problem Toei cm-r20 brightness Issue?

[Ronnie Dent]

yes to everything

So Q4, 12 and 20 not likely at fault?

I'm struggling to think of anything, the only caps I never changed were c20 and c12 as they are NP and I only had one of the 3 to hand!
Going to remove the heatsink again and look at the tracks around it to double check
It's a nice burn free monitor but with the amount of transistors and other components I think it's going to be a struggle!

Thanks Ronnie

 

[gunblade]

replace those transistors, its a shot in dark time

 

[Ronnie Dent]

replace those transistors, its a shot in dark time

Thanks Grant, replaced the 3 with 2N5401's but it's still the same, was worth a try. I put Q25 back Iguess I could do same for those 3?

It's weird when there is an image there is like a luminace on the whole screen like a haze so the background is not black! hard to describe but the brightness needs to be fully up

Cheers Ronnie

 

[gunblade]

this is when you find out the tube is failing

 

[Ronnie Dent]

this is when you find out the tube is failing

hope not, is it looking likely now

 

[gunblade]

you could really do with the chassis being tested on another tube before going further

 

[Ronnie Dent]

Actually scrub that description above it was the garage light washing out the image it’s pretty good tbh

 

[Ronnie Dent]

It also seems better as in it's not completey dissapearing at the moment and it's been on more than 30 mins, it's just dipping in brightness now and again.
The B+ is about 102v I think it should be 110v? Might not be relevant to this though.
I have a couple 14" tubes will compare those too

 

[Ronnie Dent]

Problem persists!
I found a small crt that has the same neck socket I guess I need to check the coil windings for compatibility but the plug also looks the same, how many windings are in the coils? 4 wires 2 windings?

Thanks Ronnie

Toei neck card top of pic

 

[gunblade]

it will be either high impedence or low, i reckon both yokes will read about 50 ohms on the vertical

 

[Ronnie Dent]

Don’t think it’s looking good as I’m seeing low ohms on the donor 6ohms or so but there is a resistor across 2 of the poles?

 

[Ronnie Dent]

On the toei I read 60 ohms but I’m not sure what to measure to where?

 

[gunblade]

yellow and green are vertical, read those pins

 

[gunblade]

i would imagine the yoke connectors are different anyway so you might have to swap yokes in any case
i don't want to send you on a shit mission though

 

[Ronnie Dent]

So the yoke plugs are the same but the wire colours are not, yellow green on the toei is 60 ohms on the other it's 4 ohms but there is a resistor across the connectors on the yoke?
Thanks Ronnie

 

[gunblade]

look at the spacing of the pins, vertical are normally closer together
doubt you would ever see 4 ohms on a vertical winding, i haven't

 

[gunblade]

they are different yoke header pinouts so yoke swap is only course

i imagine you proved its not the signal from game board dropping out, wierd crap happens with old stuff you know

 

[Ronnie Dent]

No not proved that just assumed it was the screen, I could hook up a 60 in 1 to the toei to see if it persists on the screen?

Don't fancy messing with the yoke tbh! that small tube has weird low ohms on the windings, it came out a universal tabletop and never worked

Thanks again for all your help with this😁

 

[gunblade]

try a different signal origin, need to rule out crazy stuff

 

[Ronnie Dent]

try a different signal origin, need to rule out crazy stuff

Just hooked it to a 60 in 1 still same issue🤬