IBM 5154 monitor dark image

[romanon]

Hello, i obtained this piece. First I had to replace X2 capacitors in power supply because it was blown, but nothing more was necessary at first sight.
I turned on monitor and connected it to PC. Picture is very dark even though brightness was on maximum. I also tried sub brightness and sub contrast knobs, but it helps only little.
Where can be problem? Despite this, sharpness of picture seams to be fine, but not very stable.

Here is video of current condition:

https://youtu.be/n00P9dhHtTg

 

[T-R-A]

Hello, i obtained this piece. First I had to replace X2 capacitors in power supply because it was blown, but nothing more was necessary at first sight.
I turned on monitor and connected it to PC. Picture is very dark even though brightness was on maximum. I also tried sub brightness and sub contrast knobs, but it helps only little.
Where can be problem? Despite this, sharpness of picture seams to be fine, but not very stable.

Here is video of current condition:

https://youtu.be/n00P9dhHtTg

Quite possibly a flyback transformer. Not a fun thing to fix.

 

[Hugo Holden]

Possibly low screen voltage.

There is a setting inside for the CRT's electrode setup that is called the Screen. Normally this control is physically close to the focus control on the EHT rectifier/tripler assembly and they are labelled.

Scroll to page 11 of this article which shows the two controls on the white plastic block in a 5153 monitor, just below where the EHT cable emerges.

http://worldphaco.com/uploads/INCREASING_THE_UTILITY_OF_THE_IBM_5153_COLOR_MONITOR_TO_AUTO.pdf

I can't recall the inside of the 5154 well enough, but there should be a similar arrangement in there. Leave the focus control alone as the focus looks ok looks ok, try adjusting the Screen setting and you might be able to get a better result with the image. Be aware of the hazardous high voltages that exist in these monitors.

Also an improper setting of a sub contrast or sub-brightness control can cause this problem, but you have checked those.

A low emission CRT is less likely as what I can see looks in good focus, the EHT is likely ok too, so unlikely the flyback/EHT transformer.

 

[Hugo Holden]

On the 5154 the screen (preset potentiometer) is on the pcb that has the socket for the CRT base (see attached picture) If you adjust this make sure to use a good insulated screwdriver or plastic tool better.

 

[Nevets01]

Hugo is correct, the SCREEN pot is on the back of the CRT tube.
However, once you do that, the picture is likely to be out of focus, and you'll have to adjust the focus knob (on a plastic thing near the left bottom of the monitor as you face the screen). It was on mine.
If after you do this, the background (i.e. the parts that should be black) are too bright, you'll have to adjust the "black level", located at the rear of your CRT. It is accessible with the case on.
Also, at least with my 5154, it takes several minutes to warm up. I've noticed that after about 1 minute, it's quite dim, but after 15 minutes it's fine; much more than any other CRT I've owned.