Track & Field PCB troubleshooting help needed

87 t-66

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I'm working my way through a track and field PCB and am at a point where I need some assistance. The board won't boot at all. All of the socketed chips are known good and the sockets are new. I believe my next step is finding why the WREN bar signal on the 504 custom @ 3E is not happy. Here is what it is doing:



Here's the same signal on a working board



Any ideas what I need to check next to get the signal to generate properly?

20250911_155258.jpg
 
Maybe also worth noting...pin 5 on the 504 custom @ 3E is high on the bad board but toggles on the good one. I started back tracking that AFE input because it was stuck high (toggles on good board), which led me over here:

20250911_165109.jpg

The IOWREN bar output on 5B pin 8 is stuck high (toggles on good board) which led me back to WREN bar on the custom.
 
It's not running code.... Isn't the CPU watchdogging? You're going to see all kinds of crazy shit until you sort that out. Start with the CPU and it's access to ROM/RAM.
 
Yes the reset is pulsing and it's watchdogging. The clock and voltages are good. I'll start going through the chips between the CPU and ROMS/RAMS. Thanks
 
20250911_192219.jpg

For the LS139 @ 7D, on the good board pins 6 and 7 are high, on the bad board they are toggling. Pins 9 and 10 toggle on the good board but are high on the bad board.

Is there something that would explain the two pairs of outputs being backwards?

1757637227457.jpeg

Before I started there was a floating output on the LS244 @ 5C so I replaced it and the one at 5D.
 
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If this were on our bench for repair, in this order:
Swap the CPU with known good one (6809EP)
Desolder the system RAM (2128 @6A) and check in a dedicated RAM tester
Verify system EPROMs using CAT FPGA(this will also verify decoding logic), or using an EPROM reader
Always target Fujitsu and Signetics logic ICs first. These two brands account for probably 90% of all bad ICs we run across
 
The cpu and roms are verified good. There are a shit ton of fujitsu chips on the board. I'm thinking of replacing all of them before continuing. I'll check the ram too. Thanks
 
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I don't have a dedicated ram tester but I pulled the 2128 and put in a socket and swapped in a few from my stash and it didn't make a difference. I pulled the 138's from 6C and 6D and they tested fine. They are Fujitsu chips so I put in some TI's I had on hand. It still doesn't even seem to be trying to boot. What else am I missing?
 
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Making some progress... I noticed the signals on the LS245 @ 3B pins 1,11, and 12 looked a lot different on the scope than my working board and replaced it. Then the game started booting but was crashing after the title screen and looked like what's in the video below. I know the roms are good so I started piggybacking the 2114's and it stopped crashing after piggybacking A10 so I replaced it as well. I'm going to start looking at the sync signals to see if I can find anything to hopefully get it working correctly.

20250917_130621.jpg

 
More progress...I also noticed in the above video some of the graphics were upside down. The FLIP and SYNC both come from a LS244 @ 1C. The FLIP pin was floating so I swapped it and everything is looking normal.

20250917_144059.jpg
 
Maybe also worth noting...pin 5 on the 504 custom @ 3E is high on the bad board but toggles on the good one.
Pin 5 is watchdog reset.
Shorting the split pad shown in the schematic is equivalent to watchdog disable on Atari.

AFE not toggling just meant the code wasn't running enough to kick the dog.

The IOWREN bar output on 5B pin 8 is stuck high (toggles on good board) which led me back to WREN bar on the custom.
/WREN is generated from CLK1, H1, E (pin 3), and R/~W (Pin 6)
 
The last issue seemed to be the button inputs not working. It was another bad LS244 @ 2C in the photo above causing a bad IOEN signal going to the top board. Hopefully that's everything 🤞

good, if this ever becomes a problem in the future I can use your services.

@87 t-66 is elite
What is that saying...even a blind squirrel finds a nut sometimes? Something like that...
 
The last issue seemed to be the button inputs not working. It was another bad LS244 @ 2C in the photo above causing a bad IOEN signal going to the top board. Hopefully that's everything 🤞


What is that saying...even a blind squirrel finds a nut sometimes? Something like that...
it wouldn't be cost effective for me to do it with all the other things I have to cover here.

I notched some unexpected wins too without the aid of signature analysis.
 
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