PP2 CPU board (Atari) boot issue

[KPW66]

Looking for some help on a CPU board repair.

I've spent some time over the past few days repairing 3 PP2 sets, and 2 PP1 video boards and I'm stuck on the last board, which is a PP2 CPU board.

I need some help from anyone knowledgeable on the CPU boot sequence. I'd like to confirm it's the watchdog interupting before CPU A resets as opposed to an issue in the CPU A Reset circuit itself.

Here's some info:

PP2 CPU board (Atari)
• on my bench setup, known good
• power is good
• Video board good
• interconnect board good
• all socketed chips good
• some sockets replaced but not all, but pretty sure that's not the issue.
• typical alkaline damage repaired, new parts installed, all confirmed good
• Z80 and CPU B both reset, but CPU A (@3A) does not get a reset (stuck low) and it's not an issue with the LS259 @8E
• when I manually reset CPU A (5v to lifted leg 14) the data lines all come alive so I think the general watchdog kicks in before CPU A's Reset kicks in. I think chasing a CPU A reset problem would be a red herring.

Does anyone know the actual CPU boot sequence? Does CPU B (@4N) boot before CPU A (@3A)? Is it: Z80 then B then A? If yes, then watchdog kicks in before it gets to A.

I've probed around and rams appear good, I know the ROMs and customs are good. The PAL at 5C (and 7C) is good. Not able to get to Self Test so that's no help.

Thoughts?

 

[TimePiloteer]

Yes, it's z80 then B then A. What you can do is replace your video pcb with a PP1 video pcb, which can sometimes get a ram or rom error to appear on the blue screen. Sometime the PP2 sets have an error but it doesn't display with all the other junk on the screen.

 

[mecha]

Looking for some help on a CPU board repair.

I've spent some time over the past few days repairing 3 PP2 sets, and 2 PP1 video boards and I'm stuck on the last board, which is a PP2 CPU board.

I need some help from anyone knowledgeable on the CPU boot sequence. I'd like to confirm it's the watchdog interupting before CPU A resets as opposed to an issue in the CPU A Reset circuit itself.

Here's some info:

PP2 CPU board (Atari)
• on my bench setup, known good
• power is good
• Video board good
• interconnect board good
• all socketed chips good
• some sockets replaced but not all, but pretty sure that's not the issue.
• typical alkaline damage repaired, new parts installed, all confirmed good
• Z80 and CPU B both reset, but CPU A (@3A) does not get a reset (stuck low) and it's not an issue with the LS259 @8E
• when I manually reset CPU A (5v to lifted leg 14) the data lines all come alive so I think the general watchdog kicks in before CPU A's Reset kicks in. I think chasing a CPU A reset problem would be a red herring.

Does anyone know the actual CPU boot sequence? Does CPU B (@4N) boot before CPU A (@3A)? Is it: Z80 then B then A? If yes, then watchdog kicks in before it gets to A.

I've probed around and rams appear good, I know the ROMs and customs are good. The PAL at 5C (and 7C) is good. Not able to get to Self Test so that's no help.

Thoughts?

FPGA catbox will work well with these because the Z80 section needs to function in order for the Z8002's to "wake up".

the 3E and 3F rams are on the video board that I remember. you'll be highly confused looking on CPU board and finding those are one of the sub CPU rom sections like I was.

the very top 7E chip in the ram test is a 6116 part I think, our Pole Position II has an NVRAM

 

[KPW66]

UPDATE: Actually both comments above have helped immensely, let me explain.

First, I installed a PP1 Video board and it booted fine (showing typical graphic issues due to mix-matching PP1 & PP2 boards). So, that alerted me that the CPU board was fine. Then I installed a different PP2 Video board and it worked fine. Thanks @TimePiloteer for leading me down that path.

Next, I went back to the original PP2 Video board (which I wrongly assumed was working fine as it was one my spares that was on the shelf and not one I just repaired) and I swapped out all four 6116 rams and then it booted fine-ish. Thanks @mecha for that tip.

But of course, not I have a new issue with that particular Video board and I cannot figure out the culprit yet. It has graphical issue where all small car and small signs have issues, all related art (objects) are too narrow. Sorta like a horizontal collapse on those objects. I have checked associated chips per the self test table, and custom chips, and counters, and rams, and just about every chip I can think of to remedy this and no success.

 

[Jaydon]

This is from the Pole Position Manual. I wonder if PP2 is the same.

 

[KPW66]

This is from the Pole Position Manual. I wonder if PP2 is the same.

View attachment 862561

Yes, thanks, been all through that. It's less an issue of the actual object (like the car or sign) and more an issue with the width (horizontal) of the rendering of that object. And it appears to only be in the small cars and signs.... but perhaps there is more I am not seeing. I'll post some pics

 

[KPW66]

Here are some examples of issues with the small items (first pic) that then render good (mostly) once they become large (second pic). There are 8 pairs of pics.

The exception is the Pole Position banner (3rd pair of pics) that still has a width issue even after rendering.

I thought it would be easy and just one of the chips mentioned in the table but I've swapped known good chips in and the issue persists. And, as mentioned, I have checked just about every other chip in the circuits and no apparent bad ones are jumping out. I'm using logic probe and piggybacking and not my scope at this point fwiw

 

[KPW66]

you can see the object are there and look correct, they are just super narrow until it flips to the larger object. So, something is off in the small object circuit and I've replaced both 12N and 13N and also the custom at 13H and PROM at 12H. In fact, when I pull 12N or 13N it disrupts the object not the width so those chips aren't responsible for that. I've also gone back and looked at other chips in the circuit and cannot figure this out yet.

 

[mecha]

This is from the Pole Position Manual. I wonder if PP2 is the same.

View attachment 862561

they're the exact same boards so this information applies. I was also going to suggest this reading KPWs post. lol

 

[videodan]

What? A problem with a PP board?! I must be imagining things...