Defender CT freezing up - thoughts?

modessitt

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So a few weeks ago I had a Defender CT in the shop to rebuild the monitor. While I had it in, I looked over the rest of it.

The customer bought it from a shop a year or so ago (who didn't recap the monitor before selling it). The RAM had been upgraded to 4125's (with a trace cut) and the CPU had been modified to composite sync (with a trace cut). It also had a switcher installed, even though the original PS is still in there and has all the power LED's lit. It seems they left it to power the coin door and control panel lights. I also noticed that several of the ROMs had legs that broken off, and had clipped leads solder to them as replacement legs. Since the game seemed to be running fine, I didn't risk removing them to clean the legs, but maybe I should have.

Anyway, I noticed that touching the ribbon cable between the ROM and CPU boards caused the game to reset, so I replaced both ribbon cables with new ones. No more resetting when flexing the cables. I also reflowed all the connectors, fixed a bad wire to the volume pot, redid the monitor, installed new AA batteries, etc and everything was working fine.

Well, the customer called and told me that sometimes - after the game has been on for a while - it will either freeze while he is playing, or sometimes go to the rug screen and stay there. He tells me that when he first turns it on, it comes on just fine and plays fine. But if he leaves it on, later he'll come by and see the rug screen up. Or he'll start playing and it will freeze up. If he turns it off for a little while, it will turn back on and be fine again for a while. Sounds maybe heat-related?

He is the opposite of tech-savvy, so it's no use trying to get him to check the LEDs on the ROM board. He's also an hour-and-a-half away, so I'd like to go down with an idea of what to do when I'm there.

Anyone have an idea? Normally, my first inclinations would be either power supply/voltages, or RAM. What do y'all think?
 
4125's huh? 4164's Brother Mod

When the CMOS RAM fails, it will do this. Easy to tell, as the chip gets smoking hot. Burn the fingerprint off of your finger hot.
 
4125's huh? 4164's Brother Mod

When the CMOS RAM fails, it will do this. Easy to tell, as the chip gets smoking hot. Burn the fingerprint off of your finger hot.

I know - 4164's. I was going to do this, but I saw the 4125's and figured they'd probably be just as good, since they use less power as the 4116's and the game was working fine.

Tired tonight, so anyone care to tell me whether I can sub 4164's for the 4125's without a power mod? At least one trace has already been cut, but I didn't pay attention to which one.

That's a good thought on the CMOS RAM. I'll make sure to take some with me, and I'll have him turn it on that morning before I go so it's on for a while...
 
I don't have time to go look right now, but does the CMOS RAM on this match the ones on the Joust/Stargate CPU's? Or is it particular to Defender?

Oh yeah, I've heard the switchers in Defender can cause issues, too. Any thoughts?
 
I don't have time to go look right now, but does the CMOS RAM on this match the ones on the Joust/Stargate CPU's? Or is it particular to Defender?

Oh yeah, I've heard the switchers in Defender can cause issues, too. Any thoughts?

CMOS in Defender is unique to Defender.

Switcher's in Defender suck pretty bad, but not as bad as the other Williams.
 
CMOS in Defender is unique to Defender.

Switcher's in Defender suck pretty bad, but not as bad as the other Williams.

Defender uses a 5101 CMOS

Thanks, Dave. I have some Defender CPU's around, so I'll pull a CMOS and take it along. I told him to leave it on in the morning so I can check to see if it is hot when I get there.

As for the switcher, the original PS is in there with all three LEDs lit, so I may try changing back to original to see if that helps if the CMOS doesn't help...
 
Check the voltages on the original before you plug it in. The LEDs are just approximate, the voltages could be way high or you could be getting some stray AC if the filter caps are leaking.

ken
 
Well, of course I'd check the voltages. :rolleyes: :D

Had three Defender CPU's of indeterminate function, so I pulled the 5101's off of each of them so I can have some options. Then I went to my loose chips box to see if I had any empty foam to stick them in, and found one with 3 other 5101's in it, so I should be good to go...
 
If you have a spare Defender ROM card, it wouldn't hurt to take that along based on your description of the current ROM card. Or if you have time, just burn a fresh set. EPROMs flaking out can cause the same problems.

ken
 
I'll probably end up bringing the set back and reburning them. Don't have time now. Have to be there in the morning....
 
Well, the 5101 was warm, but not burning up. In fact, all the socketed chips (processor, decoders, RAM, ROMS) were pretty warm. You can turn it off and right back on and it will work fine for quite a while. Shouldn't do that if it's a heat-related issue, right?

I checked the switcher and it was running right at 5.0. I checked the original PS and it was working fine, so I removed the switcher and plugged the original PS back in. It might have been my imagination, but it seemed that the chips were slightly cooler that way. It was running fine for a while, so we left it like that for now, and the customer will let me know if the problem returns or not.

BTW - I also tried pushing and wiggling the socketed chips to see if I could cause it to crash, freeze, or reset, and I could not. I also lightly flexed the boards in various places without an issue.

One problem he mentioned was that the high scores erased themselves and one had some ? symbols in place of initials. The batteries are new, and the diodes seem okay, so not sure what's up with that. Could the switcher cause weird crap like that?
 
could be the switcher, or one of the 74 series chips. I don't recall which one cause that problem, but I am sure Ken knows (YellowDog)
 
Most of the time when I have seen or heard of that, it has not been a chip problem. The battery holders that Williams installed are really good for a while. Then the contacts corrode or crack and all it takes is a little vibration an the voltage drops. The 5101 CMOS chips will hold some of their memory for a couple of seconds and the Defender CMOS checksum sucks, so you can wipe half of it out and it will never catch the problem. The most common manifestation of this problem is the ? marks on the high score table and getting a virtually unlimited number of ships (it's really only like 256 or 512, but for most ADD players that's unlimited).

The 5101 retention issue is why the recommendation to pull the batteries and wait 5 minutes when you need to reset the factory settings. The 5114s used in Stargate and later boards don't hold the memory as long, so powering off with no batteries only takes a few seconds.

Early versions of the Stargate CMOS checksum were allegedly lifted directly from the Defender code so you can sometimes hear of Stargates with unlimited ships. I have not dumped the code though a disassembler so it is just hearsay at this point.

Chip problems are usually related to the "open coin door" message where the memory protect is locked on and it can't reset the factory settings.

ken
 
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