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Konami Simpsons Watchdogging

DrBackhands

DrBackhands

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I probed IC 051550 and found my Simpsons board is watchdogging
sad.png
RES and RESET just pulse, but when I bridge the JP connecting RES (p5) and VREF (p4), RES is stuck low but RESET (p10) is stuck high.

Additional info: Voltage at VS is 1.4V and the voltage at CT is 1.224V, which as I understand it from the datasheet, should be high enough to not trigger the watchdog circuit. CK is stuck high. I'm getting a healthy 5V and 12V to the IC at pins 9 and 19.

My question: If the JP is bridged and RES (p5) is stuck low, should RESET still be stuck high? Is the IC doing what it's suppose to be doing? And just to confirm, if RESET is stuck high all the way to the CPU, that means the board won't boot, right? I'm not getting low and high confused here, right?

Edit (10/21): I was getting high and low confused. The CPU is getting a high signal on the RES pin which is what should be happening.
 

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The simpsons like many of the Konami boards from that same era will constantly reset if they are not getting the correct signals. Start with the cpu and check all the data and address lines and clock circuit etc. The AFR signal for the reset comes from 10G a 74LS138.
 
Turns out RES should be stuck high. The CPU had a bad trace on Address Line 7 which I fixed. Now I'm getting an upside down test screen telling me ER5911 at 12C is bad. All its input pins are stuck low (EEPCS, EEPCLK, and EEPDI). I traced them back to an LS174 at 10D where the pins were also stuck low, and so I decided to replace the LS174 thinking it was the problem, but that did nothing... I can try ordering a replacement ER5911, replacements aren't rare, but I wonder why the signal would read low at the LS174. If the signal's destination is low, does that keep the source low as well because it's essentially grounded?
 
It is not often that the eeprom fails. One thing to try before doing anything else, is to hold down the test button when you turn on the power and keep holding it down until it says eeprom reset.
If that is not the cause, check the 74LS257's at 9C as its also directly connected to the same lines from that 74LS174. A couple of the output lines from the eeprom also goes to the 74LS257 at 10C


Screenshot_2023-10-27_16-18-36.png
 
That was my thought as well, I have a suspicion it's not that EEPROM.

I've been holding down test button but it just restarts and gives the same "bad" reading rather than resetting the EEPROM... Not sure what would cause that.

Pins 1, 2, and 3 are stuck low on 12C (ER5911), and there is no output at pins 4 and 7. 6 and 5 are low (good) and 8 is high (good). Continuity to 9C seems good, but because it's not getting the right signal, I can't really say if it's busted or not. But I'll double check. My guess is, if it's faulty, it's pulling the voltage from 10D down and killing the signal to the EEPROM.

If a chip downstream is faulty, can it essentially ground the signal in a way that it will be stuck low at the source pin as well? Does that make sense?
 
If 9C / 10C are a Fujitsu chips, it would not be the first time that I have seen them fail and pull down the data line.

So in answer to your comment
DrBackhands said:
If a chip downstream is faulty, can it essentially ground the signal in a way that it will be stuck low at the source pin as well? Does that make sense?
Click to expand...

Yes any IC that is connected to the same signal can pull it down or up when it fails depending on how it has blown internally.
 
I got replacements for 9C 10C and 10D but the issue is persistent. I'm 99% sure it's the EEPROM failure. I sometimes get a weak data signal upon initializing, and everything else is behaving as it should. I just hope the ones I bought off eBay are real, since the ones on digikey have to bought in bulk...
 
That eeprom is only accessed very briefly during startup and then it is not accessed again. Are you getting anything on the Data Output (DO pin4) of the EEPROM?
 
No signal usually, although I did get a weak floaty signal after re-flowing the solder at pin 4 and holding down the test button (not like a pulse, just a weak blip and then nothing). I'll test again today and double check though. Not much else to do since it's gonna be a while before the IC arrives...

You're right, I am getting a momentary blip from pin 4 and honestly, I think it is doing what it's suppose to do. I was just piggybacking for 9C and 10C, I didn't outright replace them so maybe it's not making contact... at the very least, it's definitely not 10D.
 
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A lot of the times, you wont be able to just piggyback those old Fujitsu chips, you need to replace them or at least desolder legs to determine if they are holding signals high or low, but desoldering and getting them to not make contact is often harder that just removing the IC and putting in a socket.
 
These are technically GoldStars on my board, not sure if that relates to their reliability at all.
 
The Goldstar chips seem to be a little more reliable compared to the Fujitsu chips, but given that these boards are now over 30 years old, any IC is going to be running on borrowed time.
 
I had the EEPROM failure on a Simpsons machine that was on-location just a few weeks ago. Stole one from an X-Men board and that fixed it right up. Bought a new one (actually a 5-pack of OKI M16911 on eBay for $10) and that worked in the X-Men as well.
 
After messing with this board a bit, I'm pretty confident it's a busted EEPROM... though I won't know for sure until I try to replace it. It is still giving me a momentary blip on the data line, so I can't say it's not doing anything... If that signal isn't making it to where it's suppose to go, it's even further down the line, which is going to be harder to check for.

Is M16911 equivalent to ER5911?
 
Interesting to hear that you had an eeprom failure. I have fixed literally hundreds of Konami boards which use that eeprom and I have never had to replace a single one. Every single time it has been one or more of the other IC's around it that has been the cause.
 
I'll be sure to share my own anecdote once the new ER5911 arrives. I'm hoping it works, but I'm far from 100% sure it will.
 
cwispy said:
Interesting to hear that you had an eeprom failure. I have fixed literally hundreds of Konami boards which use that eeprom and I have never had to replace a single one. Every single time it has been one or more of the other IC's around it that has been the cause.
Click to expand...
Yep. Even swapped the bad EEPROM into the X Men to check.
 
Well, I swapped the ER5911, held down the test button, and am still getting the same issues. I'm going to continue checking the chips around it.

Also, whenever I hold down the test button to reset it or whatever, the screen freezes with the words "bad test" on the screen. I realize I've never actually seen the test button held down on one of these konami boards in person before, so I'm not sure how abnormal that is.
 
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