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Help with Tandy 1000ex i/o Err 8259


miniMOJOman

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Hello, I am a super newbie here and just acquired a Tandy 1000ex with color high resolution monitor woo hoo, unfortunately when I turn it on it says the ram up top and then near the bottom of the screen it displays "err i/o 8259"

 

From the little information I could find it sounds like it has to do with the 8259 interrupt controller or the cpu. I would assume that the cpu is fine since it actually powers on... can anyone help me diagnose and fix this issue?? I put a dos boot floppy in the drive but it doesnt seem to want to boot from it, unless I have to press a certain combination of buttons in order for it to boot.. Thank you in advance!!

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Hello, I am a super newbie here and just acquired a Tandy 1000ex with color high resolution monitor woo hoo, unfortunately when I turn it on it says the ram up top and then near the bottom of the screen it displays "err i/o 8259"

 

From the little information I could find it sounds like it has to do with the 8259 interrupt controller or the cpu. I would assume that the cpu is fine since it actually powers on... can anyone help me diagnose and fix this issue?? I put a dos boot floppy in the drive but it doesnt seem to want to boot from it, unless I have to press a certain combination of buttons in order for it to boot.. Thank you in advance!!

 

I think you are probably correct that the 8259 interrupt controller is the issue. A PC compatible floppy drive controller uses IRQ 6 to tell the CPU that it has data to transfer. Fortunately the 8259 is a discrete chip in the Tandy EX, so you may consider replacing it.

 

Do you have a memory expansion by any chance? If you do, that adds a DMA controller. With the DMA controller, the floppy controller can transfer data to and from memory directly without CPU intervention. Without a DMA controller, the CPU has to handle data transfers from/to the memory and floppy controller. Both methods require the use of an IRQ, but perhaps you can remove the expansion board to see if that helps the problem.

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Would the ram expansion be in the little bay that you can access from the back of the unit? I did actually take the computer apart and cleaned the floppy drive. I did not take the shielding off of the motherboard so I didn't see if it had any expansions there, it only has 256k ram I believe is what it said on the top of the screen. So o doubt ram expansion. I'll have to get down to the motherboard and take some pics. Would you be able to help identify the chip that I could try replacing? Appreciate the help.

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Not sure if you have it yet, but the Sams Computerfacts for the Tandy 1000 might have some useful information for you:

 

http://www.colorcomputerarchive.com/coco/Documents/Manuals/Hardware/Sams%20ComputerFacts%20Tandy%20Model%201000EX%20Computer%20%28Howard%20Sams%29.pdf

 

I always like to have one for each of my old computers.

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  • 4 weeks later...

I'm actually leaning towards the onboard ram being bad. I've read that the interrupt controller actually works with the beginning ram address and that might be bad. We will have to look into possibly replacing the onboard ram.

 

Also would anyone actually happen to have the 1000ex/hx ram upgrade for sale?! Id be interested if so.

Edited by miniMOJOman
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  • 7 months later...

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