Re: Sys 80 IRQ Still Stuck High (AHHHHHH!)

Hi Ed,

The only activity I get at these chip pins are at Z4 pins 9 and 10. Also the voltage at Pin 14 of Z4 and 36 is 4.06 Vdc. Sounds low. This is the voltage at J1 also. When I take the leads off from my bench top power supply it's voltage jumps to 5.06 Vdc.

Thanks, Dave

GPE wrote:
"David Schulpius" <dschulpius@xxxxxxxxx> wrote in message news:ZNeHf.1256$xZ4.1093@xxxxxxxxxxxxxxxxxxxxxxxx

Hi all,
I,ve been working on a early Sys 80 CPU that was non working when I got it with corrision in the reset and clock area. After rebuilding that area with GPE's kit I now have a stuck high IRQ. Clock and reset tests good when I follow Clay's guides. As of now I've changed everything on the right side of the board except some of the caps. I've replaced the clock and reset section, CPU, the RIOT 's, all chips below them and one bank of dip switches and their resistors and diodes.
Lets see;
The entire clock and reset section including Z36, Z4, Z1 and 3k resistors in that area
U1 (CPU),
U2/U3
RIOT 's U4, U5, U6
Installed a working Prom in Prom 1
Z5 (CMOS Memory)
Chips Z11, Z12, Z13, Z14, Z15
The left most bank of Dip Switches, their resistors and diodes. Tested the remaining dips for shorts and their diodes.
I've checked most resistors and followed most traces.
Checked for shorts between traces and cant find any.
All Data and Address lines pulse at the proper places (CPU, U2/U3, RIOT and Z5) except at chips Z11, Z12, Z13, Z14, Z15. No activity at them except Z12 pins 5, 8 and 11 but these pins are not connected to any traces. I also have activity at Z15 pins 3, 6, 8, 11 depending on if the dip switched are on or off.

I tried testing with GPE's QuickScan after pulling the RIOT 's and Z5. It's read out was 4F, 5F, 6F, 1F. Then I started with installing U6 then U5, U4 and retesting after each. QuickScan would pass the installed chips including U4. Then lastly I installed Z5 and when QuickScan tested it showed F - 4.
I'm about to give up on this one unless anyone has any other ideas. It was suggested that I have this board tested with a logic analyzer. Does anyone know of someone that can do this?

Thanks, Dave



Dave --

You won't get any activity on Z11 - Z15 until the IRQ's are fixed and the CPU is up and running.

Sounds like you have bus contention still. Like 5101 and RIOT are both being enabled simultaneously.
Next place I'd check is Z4 circuitry -- this controls the enables to the 5101. So does part of Z7, Z8, Z10 and Z36. See if you get activity on these:
Z8 - pins 11, 12, and 13
Z4 - pins 8, 9, 10, 11, 12 and 13
Z36 - pins 1 and 2
And measure the voltage at pin 14 of Z4 and Z36

-- Ed



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