I have a problem with my speccy issue 4b and I guess here I found the answers. First of all my speccy is died 23 years ago. I thing is overvoltage or overcurrent.
Now is time to come to fix this. First I checked the lower ram (-5V, 12V and 5V) and only 5V is appear, so I take a multimeter to measure and find that the TR4 is short. I replace TR4 and TR5, do recap, but the -5V and 12V is still not in place. After deep searching on this and other forums found that maybe the lower ram chips is acting bad. Because I don't have any diagnostic tool only a multimeter, I decide to remove all the lower rams and replace it with new ones. And the -5V and the 12V is back in business.
But the other problem shown up, the faulty ULA. Here is the picture after power up with new lower rams and the faulty ULA:
Luckily I have another speccy issue 4a what I bought 10 years ago and is fully functional. I put my ULA to this fuctional speccy and i got this on screen:
So that is I think the sign for ULA is faulty.
After this the functional ULA from issue 4a put to my speecy, then come out this screen:
So for my point of view the ULA from my speccy is faulty.
My question is what I need to do next with this latest error screen, maybe check the CPU or the ROM? How can I test with these only with multimeter?
Here is my recaped speccy board with new lower rams:
