Mac Classic - will it ever run again!!

[stephen_usher]

Well, the video circuitry *may* be reading video memory from that pattern. Apparently if nothing gets initialized you should get a chequer board pattern, so the system may be starting a memory test and halting.

[rubber_jonnie]

Well, the video circuitry *may* be reading video memory from that pattern. Apparently if nothing gets initialized you should get a chequer board pattern, so the system may be starting a memory test and halting.

Yep, I agree, it looks largely like the pattern is something in RAM. I did have the chequerboard pattern previously until it died from a video perspective. Interestingly both the new board from Tom and the original board exhibit the same behaviour, I have another board that was donated, I'll see what that does tomorrow, but for now, sleep!

I'm quite pleased that the CRT is at least working though, I was a little concerned about it. Also slightly reassuring that there is a decent size/shape image on the screen.

[Tomswork]

Interesting image on the screen I have never seen that pattern before it looks like v sync or h hold is off. The checker board or sema sema is mostly clear and not a blotchy screen pattern. It's good that you fond that Tracee those boards are under a lot of high frequency vibration from the flyback and take a beating.

Tom

[rubber_jonnie]

Interesting image on the screen I have never seen that pattern before it looks like v sync or h hold is off. The checker board or sema sema is mostly clear and not a blotchy screen pattern. It's good that you fond that Tracee those boards are under a lot of high frequency vibration from the flyback and take a beating.

Tom

Interestingly I tried a battery damaged board this morning and it gives a checkerboard. I think the analog board is good as far as delivering an image on the CRT, the rest, well I'll have to get checking. It'd be nice to have a working one to compare against, but sometimes you just have to follow the docs etc.

[stephen_usher]

Interesting image on the screen I have never seen that pattern before it looks like v sync or h hold is off. The checker board or sema sema is mostly clear and not a blotchy screen pattern. It's good that you fond that Tracee those boards are under a lot of high frequency vibration from the flyback and take a beating.

Tom

I'm pretty sure that's the memory test pattern that you don't usually see as the screen hasn't come on by the time it's been cleared. It looks like a "write own address to memory" type test pattern.

[rubber_jonnie]

Very quick check off the voltage rails, and we have 4.58v and 11.66v, so something not right there. Need to find my long plastic pot adjuster as the voltage adjustment pot is rather too close to stuff like the flyback transformer for comfort!!

[rubber_jonnie]

@stephen_usher Well I just found out this symbol on the Bomarc schematics is earth.

Screenshot 2021-12-15 at 15.53.21.png (140.27 KiB) Viewed 2122 times

Now I already had my suspicions, but they also use the more traditional symbol too:

Screenshot 2021-12-15 at 15.57.59.png (133.93 KiB) Viewed 2122 times

Whilst you can see the relationship between the 2 symbols, it makes you wonder what else has been mixed up.

[Tomswork]

Maybe back to the old days with hot frames ? Ground what !

Tom

[rubber_jonnie]

Well this is looking positive:

IMG_20211215_212555.jpg (131.58 KiB) Viewed 2099 times

Now where the hell did I put the RAM card!

[Tomswork]

There is a boot a os boot in the rom on the classic I forgot the key command

Tom