Macintosh SE 30 display half screen

[Roberto]

Hi everyone, I'm new to the forum and I hope to be in the right place for the help you want to give me.
I introduce myself here, since I honestly didn't find the presentation area. My name is Roberto I am Italian and for some time I would like to fix my macintosh SE 30, which has an unusual problem, that is, you only see half of the lower screen.
It is very strange because, according to what L. Pina writes in his book, it is not a part of the screen that collapses (in fact, the horizontal central line is not visible), this last problem is in fact due to a problem of the analog card. Here instead we see a part of the screen that is missing and has not collapsed.
I tried to replace it with another analog board and the result is the same, so I assume it is to be attributed to the logic board. In the logic board I haven't done any intervention at the moment. Has anyone experienced such a thing?
I thank all those who want to make their contribution to understand where the breakdown is.

 

[Bolle]

Now that’s a weird one.

Not sure if anything on the logicboard could cause this.

My first guess would be to check the two 74LS393 video address counters at UF8 and UG8. One of them might be broken or does not receive its clock and reset signals due to broken traces.

Did you do any work at all on the logicboard yet? It should be recapped and cleaned before any troubleshooting takes place.

 

[Roberto]

Thanks Bolle, for your interest, I think I'm sure it's the logic board because I tried to change the analog card (including the card that goes behind the CRT tube), and the problem is exactly the same, so I conclude that both the logic card and the cause. Today I will change the two 74LS393 as you would like. However I have not done any kind of recap regarding the logic board, even if it seems to the naked eye that the board is perfect.

 

[Roberto]

Now that’s a weird one.

Not sure if anything on the logicboard could cause this.

My first guess would be to check the two 74LS393 video address counters at UF8 and UG8. One of them might be broken or does not receive its clock and reset signals due to broken traces.

Did you do any work at all on the logicboard yet? It should be recapped and cleaned before any troubleshooting takes place.

Bolle, do you mean these two?

 

[Bolle]

Yep, it's those two.

However that board doesn't look perfect to me. A lot of dull looking solder spots that look like they already started corroding.

Depending on how the board was stored you won't always see the goo that leaks from the caps

I would recap the board and give it some good cleaning first. If it's still having the same issues afterwards you can go and grab the schematics and trace all signals going to those two chips.

If all signals are good swap them for new ones and see if the problem goes away.

 

[Roberto]

thanks, I will give a general cleaning and maybe a new welding point and then eventually I will change those two components