• Hello MLAers! We've re-enabled auto-approval for accounts. If you are still waiting on account approval, please check this thread for more information.

Fried Macintosh 512k motherboard.

K

KenB123

6502
I did something stupid :(

You know the type of fly back transformers that don't have the bleeder resistor? That caused a big problem for a motherboard that was working fine.

I unscrewed the groud wire from the crt and discharged the crt with it. There was a big arc and it was safe to remove and handle because I was working on an internal hyperdrive anyway.... The issue I'm having now is there's a single horizontal line across the screen. As anyone would think the issue would be a bad analog board... Apparently it's not. Somehow the motherboard is causing the horizontal like across the screen. Also when powered on the motherboard pridudes a normal sounding chime but it's a few seconds longer then it should be. Someone suggested something with the processor circuit not function properly because thr chime is longer then normal.

I also noticed that when I press the developers switch the horizontal line shrinks to the size of the error code that is supposed to show up when you press that button without a os loaded. So I have no clue what's burned up.

I have plenty of dead board so I can try swapping anything that could possibly be it.

It would probably be a chip that control video but I have no clue what one that would be.

Thanks to everyone that has any idea what the issue could possibly be it. I appreciate it!

 
sounds to me like C1 is just bad,  or you were flexing the deflection cables, with a carboned up bad solder connection on the A/B

you could hit it while its on, the picture might come back.  

but you want to replace the 3.9uf bi polar cap there.  C1.  its probably bulged at the top.  i see that so much.

 
Alright I'll try replacing it and see if it helps.

The thing is it was working fine before I did that so that's why I think a cap wouldn't go bad because of a spark. I'll try it anyway and see if it helps.

I tried another motherboard in it and it works fine so it's not the analog.

Thanks for your help everyone!

 
That's more of what I was thinking. I thought it would be some chip but I had no clue what it would be.

I'll try and replace that and see if it helps

Hopefully it's 16 pin or less so I can throw in a socket.

 
Lol I still have no clue what chip that would be. Any idea on the name that it would be?

I haven't looked yet maybe it's labeked mux I'll go see.

Oh, I almost forgot merry Christmas everyone to all who celebrate it!

Thanks everyone!

 
Wait I just noticed chip 1e has vsync and hsync I'm going to assume that's vertical and horizontal sync for the screen.

It's labeled LAG I gu I'll try swapping that chip.

 
Omg it worked!!!! I replaced the chip with one from a dead board And as soon as I flipped the power switch the chime was normal and it came up with the flashing disk!!! I'm so happy this actually worked!!!

I put a socket in and cut another socket to add 4 more pins and the replacement chip from a parts 128k board fit perfectly!

Thanks so much for that schematic without that I would be nowhere!!!

Thank you everyone who helped you made a 17 year old Happy :)

image.jpg

image.jpg

 
Thanks for your help and support! I owe you big time for all the things you have done for me :)

You dont know how much I appreciate all of this!

Have a great holiday!

 
You must log in or register to reply here.

Similar threads

B
Display issues on SE and SE/30 after recapping
Replies
3
Views
897
bibilit
bibilit
larwe
Expected behavior for Mac Classic when power applied?
Replies
12
Views
424
cheesestraws
C
D
Mac Plus CRT voltage issue
Replies
5
Views
313
richmacr
R
F
Black Screen - Macintosh Plus
2
Replies
20
Views
4K
ferko86
F
T
SE/30 CRT vertical foldover woes
Replies
10
Views
2K
obsolete
obsolete
Back
Top