IIc strange image

WillJac · Jul 2, 2022

I recapped and cleaned this board both the PSU and motherboard. I now get this image on screen when turn on. I moved the rom, cpu, mmu, iou to another IIc and they all work fine. Anyone have ideas what to check for? Some detailed info would be great assistance.
I have removed the ram and put sockets for now. I need to get some spare ram just to have. I have also changed sockets for the rom, cpu and mmu but done all this after the issue started so it’s not the cause of the issue.

WillJac · Jul 17, 2022

I am bumping this to see if anyone has ideas and suggestions as I have been working on this all day today. I checked traces all from rom cpu mmu iou tmg and found no issues. Those were checked pin by pin to their locations and all other places they go. i also tested the rom cpu mmu iou in another machine and they work. The sockets for these 4 have all been replaced. Still getting this same screen. I seriously thinking it’s memory or other bad chip. This is fhe A2M4100 board with 4 memory chips only. Thanks.

Lycus · Jul 17, 2022

Can you boot into system test?

WillJac · Jul 17, 2022

Lycus said:
Can you boot into system test?

No. That image is all I get with keyboard removed or attached. Pressing keys for test does seem to add another large block on the screen. After a bit some lines show up at bottom. On chips I feel some heat on mmu, iou, iwm, memory. Cpu and rom cold.

Lycus · Jul 17, 2022

Do you have an oscilloscope?

WillJac · Jul 17, 2022

Lycus said:
Do you have an oscilloscope?

Yes

Lycus · Jul 17, 2022

Check the RAM data lines, see if any of them are funky

WillJac · Jul 17, 2022

Lycus said:
Check the RAM data lines, see if any of them are funky

Ok I doing some pics of it will post. They look strange on some pins.

Lycus · Jul 17, 2022

If I were you, I'd socket the RAM chips.

Dual wipe I'd go with these https://www.mouser.com/ProductDetai...sion/4818-3000-CP?qs=IGgAdOvCTsRPXNYrGw8EYA==

For machine pin I'd go with these https://www.mouser.com/ProductDetail/Mill-Max/110-47-318-41-001000?qs=5aG0NVq1C4xxoOYTdZ6dOw==

If you're going to get a new set of chips you could probably do machine pin, but I generally prefer dual wipe.

WillJac · Jul 17, 2022

Lycus said:
If I were you, I'd socket the RAM chips.

Dual wipe I'd go with these https://www.mouser.com/ProductDetail/3M-Electronic-Solutions-Division/4818-3000-CP?qs=IGgAdOvCTsRPXNYrGw8EYA==

For machine pin I'd go with these https://www.mouser.com/ProductDetail/Mill-Max/110-47-318-41-001000?qs=5aG0NVq1C4xxoOYTdZ6dOw==

If you're going to get a new set of chips you could probably do machine pin, but I generally prefer dual wipe.

The rams are socketed with the dual version. Even the cpu rom mmu iou I changed to dual. All rested for good continuity.

Lycus · Jul 17, 2022

WillJac said:
The rams are socketed with the dual version. Even the cpu rom mmu iou I changed to dual. All rested for good continuity.

I guess it's time to look at replacing chips

WillJac · Jul 17, 2022

Here are the images for chip 1 out of 4. This the lower end. I did not do pin 1, 9, 18 as these are power and ground and the file names show the PIN number. As this the 4100 board, I am trying to find a clear schematic to get you the pinning info unless you have it already. I do have a schematic but it is VERY bad scan hard to read. I have to send a zip as it seems I can't attach bmp files that come from my scope. The files with B filename is for chip 3 the first in the higher memory part.

WillJac · Jul 17, 2022

Lycus said:
I guess it's time to look at replacing chips

The 4 main being rom cpu mmu iou I know work as I tried them in another board. I get replacement memory on Tuesday.

WillJac · Jul 17, 2022

Here is the pin out for the ram chips.

Lycus · Jul 17, 2022

B4 and A4 look funky for sure.

WillJac · Jul 17, 2022

I as about to post this. This the first chip and file and shows the PIN number. 2,3,15 look good and same type. 17 is upside down. Inverted. This the only one that is different to all chips and the 4 pins for data lines

WillJac · Jul 17, 2022

Lycus said:
B4 and A4 look funky for sure.

4 is the write pin.

Lycus · Jul 17, 2022

Trace down the chip in the chip select circuitry

WillJac · Jul 17, 2022

Lycus said:
Trace down the chip in the chip select circuitry

sorry can you explain it a bit more I am not super advance on this. Trace the pin 4 you mention or the 17 on chip 1 that is backwards?

Lycus · Jul 17, 2022

Can I see the schematic? You need to trace pin 4, the WE pin, it's got some issues in the write enable circuitry

IIc strange image

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