SE/30 screen out of focus

[JeffC]

I just recapped the analog board on my SE/30. It had previously been extremely dim, with the brightness knob on the front turned all the way up it was barely visible. The brightness adjustment on the analog board couldn't get the screen any brighter. After the recap it now gets usably bright, considerably less than it should be, but usable. However now the screen is out of focus, and the focus adjustment on the logic board seems to have no effect at all. The adjustment is definitely turning, I can turn it either direction until it runs into the stop and there is no change at all. The disc icon (I don't have a drive hooked up) is also a bit smeared, as you can see in the photo. Both photos are in-focus, the blurriness is the same you see in real life. Any thoughts? Thanks.

 

[Patrick]

I wonder if the the tube is just too far gone ? They are consumable products. Do you have another compact Mac tube you can try?

Otherwise hopefully somebody else with more XP will chime in.

 

[Drake]

I just recapped the analog board on my SE/30. It had previously been extremely dim, with the brightness knob on the front turned all the way up it was barely visible. The brightness adjustment on the analog board couldn't get the screen any brighter. After the recap it now gets usably bright, considerably less than it should be, but usable. However now the screen is out of focus, and the focus adjustment on the logic board seems to have no effect at all. The adjustment is definitely turning, I can turn it either direction until it runs into the stop and there is no change at all. The disc icon (I don't have a drive hooked up) is also a bit smeared, as you can see in the photo. Both photos are in-focus, the blurriness is the same you see in real life. Any thoughts? Thanks.

My initial thought is to move the yoke? Perhaps I'm getting a little dangerous here though!

 

[Elemenoh]

However now the screen is out of focus, and the focus adjustment on the logic board seems to have no effect at all. The adjustment is definitely turning, I can turn it either direction until it runs into the stop and there is no change at all.

Have you measured the potentiometer with a multimeter to see if the value is changing as you turn the dial? You can do that with the power disconnected. If you don't see a change, try cleaning the pot with contact cleaner. If that doesn't work, replace it.

 

[JeffC]

I wonder if the the tube is just too far gone ? They are consumable products. Do you have another compact Mac tube you can try?

Otherwise hopefully somebody else with more XP will chime in.

I do have one I think works so that's my backup plan. I know that CRTs dim over time, though I didn't know they degrade in other ways too.

 

[JeffC]

My initial thought is to move the yoke? Perhaps I'm getting a little dangerous here though!

I'm not too familiar with the yoke adjustments, can the focus be changed that way? I am aware it's quite dangerous to work in there and proper precautions need to be taken.

 

[JeffC]

Have you measured the potentiometer with a multimeter to see if the value is changing as you turn the dial? You can do that with the power disconnected. If you don't see a change, try cleaning the pot with contact cleaner. If that doesn't work, replace it.

I haven't yet, but thanks for the suggestion, I hadn't thought of that. Unfortunately I probably can't work on the machine for a few days, but when I take it back out I'll give that a shot.

 

[JeffC]

I ended up swapping in the CRT from my parts machine and the screen now looks beautiful! The screen has a fair bit of burn-in when you look at it powered off, so I wasn't expecting great results, but I'm quite happy with how it turned out.

 

[YMK]

You may find the focus adjustment still has no effect at all. It just happens to be right for this CRT.

There's a 1M resistor connected to the focus pot that commonly fails open.

 

[Bolle]

Did you swap the neck board with the CRT?
Smearing can be caused by a bad transistor on the CRT amplifier.

 

[JeffC]

You may find the focus adjustment still has no effect at all. It just happens to be right for this CRT.

There's a 1M resistor connected to the focus pot that commonly fails open.

I confirmed that the focus pot on this AB does work, since it properly adjusts the focus on my "new" CRT, but had no effect on the old screen.

 

[JeffC]

Did you swap the neck board with the CRT?
Smearing can be caused by a bad transistor on the CRT amplifier.

Yes, I swapped the CRT and neck board as a pair. With the "new" CRT and neck board installed I confirmed the focus pot does work. Thanks for the info on the CRT amplifier, I'll do some research into that. When I get a chance, I'll try swapping the potentially faulty neck board onto the known-good CRT and see what happens.