Thread
Fried Macintosh 512k motherboard.
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!
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!
There's nothing wrong with doing it that way, I suspect your problem lies elsewhere...
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.
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!
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!
oh ...that is interesting.
Humm.... maybe the video mux I/C got hit on the main board.
Humm.... maybe the video mux I/C got hit on the main board.
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.
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!
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!
lol i am curious my self.
i guess you can follow the video pin from the connector on the mb
http://www.digibarn.com/collections/diagrams/mac-512klogicboard/mac-logic-schematic.jpg
i guess you can follow the video pin from the connector on the mb
http://www.digibarn.com/collections/diagrams/mac-512klogicboard/mac-logic-schematic.jpg
Only thing I would guess would be chip 2e
But that is not based off of anything.
But that is not based off of anything.
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.
It's labeled LAG I gu I'll try swapping that chip.
Those weren't filled with solder so I'm going to try to fill those first.
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
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
haha good job... you are the man!
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 dont know how much I appreciate all of this!
Have a great holiday!