defender rom error

TheShanMan

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For a while I was getting occasional random resets (over the course of many months). Then I got a couple of lock ups followed by a rom error (rom 6) when I restarted it. I reseated the rom and it seemed good again, but only momentarily.

Now I can't get it to succeed at all. I verified the rom in my rom burner and reflowed the socket's solder joints.

Any tips on how to track down the problem? I've been probing with my logic probe and it seems that 2 of the CE pins aren't firing, but I'm not sure if that's expected or not. I wish I knew more about exactly what happens during the rom test.

I can keep investigating but with other games to fix and a New Year's party coming up, I'm hoping to avoid inefficient use of my time. :)
 
Not a bad idea, although it was replaced 2 years ago. Thanks!

If at all possible I'd like to avoid the shotgun approach though. What I'm really hoping for is some guidance on what I should expect to see using a logic probe and/or oscilloscope with respect to rom 6 so I can say oh, it's not getting CE1 (or whatever), so now I know what is missing at rom 6 and I can trace it back looking for the chip that is failing to produce the output, a signal is failing to make it across the cable, or whatever.
 
Not a bad idea, although it was replaced 2 years ago. Thanks!

If at all possible I'd like to avoid the shotgun approach though. What I'm really hoping for is some guidance on what I should expect to see using a logic probe and/or oscilloscope with respect to rom 6 so I can say oh, it's not getting CE1 (or whatever), so now I know what is missing at rom 6 and I can trace it back looking for the chip that is failing to produce the output, a signal is failing to make it across the cable, or whatever.

Replace the socket. completely...
 
Replace the socket. completely...

And when you do, inspect the traces under it. I fixed one for a guy that kept giving a ROM error, and he did everything you've done so far, and when i pulled the socket I found a cut in a trace on the top side...
 
I considered replacing the socket, but I got connectivity on every pin by touching the chip leg and the solder pad on the back side of the board. But I also figured that while a connectivity test might succeed, high speed digital signals might not. Is that an accurate statement? It's worth doing regardless at this point, but I like to make sense of the stuff I'm trying. :)
 
You need to find where the pins connect to and test that. It is possible to get connectivity top to bottom on the socket, but not get connectivity to the address or data bus because of a cracked solder joint on an adjoining socket or a cut trace on the board leading to the next socket.

The other possibility is that the spring side of the socket is broken or corroded and not making good contact with the ROM chip's leg.

ken
 
I just replaced the socket. No difference. The traces underneath look great too (magnified).

Can anyone shed some light on what I should be seeing on the CS1 and CS2 signals during boot? Some of the chips show these signals toggling with my logic probe but some don't - not just rom 6. So I don't know if that is because my problem is affecting multiple roms but this just happens to be the rom that is reported or because the test stops once it hits rom 6 and therefore doesn't signal the other roms. So far I haven't been able to make sense of what I've seen with the logic probe combined with what I see on the schematics.

Anyone know in what order the roms are tested?
 
I have seen 3 or 4 cases on Defender where a rom would check out fine on the burner, but not work in the machine. The chip may be too slow or whatever, but a newly burned replacement fixed it.
 
This isn't a new set of roms though. They've been working fine for 2 years, plus they're from hobbyroms. I'm not sure if you're guessing that I just put this rom chip in recently or if you're suggesting that this could happen even to a chip that had been working fine for 2 years?

If I can find a spare 2716 I'll give it a try.
 
ok shanman time to get scientific

1. issues
1a getting occasional random resets (over the course of many months).
1b lock ups followed by a rom error (rom 6) when restarted
1c 2 of the CE lines arent "firing"

2. info needs
2a tips on how to track down the problem
2b not sure if what to expect
2c know more about exactly what happens during the rom test.

3. things you have done/tried
3a new rom board ribbon cable coupla years ago.
3b reseating rom6 (IC 6?) settled problem for a while
3b resoldered rom6 (IC 6 ?) socket
3c rom6 (IC6 ?) checked in burner as OK

4. suggestions
4a recrimp rom board ribbon cable ANS: see 3a above.

5. observations
5a. use the correct terminology. when you say rom6 do you mean ic6 on the rom board ?
5b. what rom types is your board using ?
5c. what are the jumper settings on your rom board ? this includes all jumpers.

5d. understand and report the matching terminology between the ic datasheet and the schematic logical labelling. ie relate the correct pins and functions on the IC and logical designations. ie the CE you are rrefering to:
CS1
5e you are not understanding how the CPU starts up
- a motorola 6800/6809 microprocessor book will help you understand the boot process. the processor specifically looks for instructions in the top few bytes of memory for pointers on where to find the starting program code. IC6 (rom6?) contains this startup address and the pointer to the startup code
5f you are looking at the schematic, not reading it. the schematic clearly shows that of the CE lines, only one is wired.
- if jumper w9 or w10 are installed, that effects the behaviour of /CS1
- if w11 or w12 are installed, that effects the behaviour of /CS2 (A11 used as a CE line)
- CS3 is tied HIGH by R3. if r3 is misbehaving or the other ics similarly tied to R3 have a short to gnd externally or internally then this will affect operation of IC6.
what i am etting at here is you need to look at the operational specs of IC6 to determine what it should be doing and the operational environment around IC6 for why it may not be doing it or for clues thereof

run out of time so i will have to come back to this
 
just checkin how you're going on this one! sorry if i sounded terse in last post - i was in a rush...

also, - forgot to mention that there are two roms that show f000 - ffff addresses so it may be either of both of those two roms playing up

damn gotta dash for the train again
 
I haven't gotten back to it yet. Working on other game issues currently (pin and a mr do project).
 
Gee, thanks dad! For pete's sake, I'm coming back to this thread soon, and I do express gratitude for the help I receive, albeit apparently not on a timetable that you approve of. :rolleyes:
 
Well, I feel like an idiot. I misinterpreted what the little defender operator setup booklet says. It seems to say that you read the LED's and the combination of LED's tells you which rom is bad. Apparently that's not the case. Apparently you push MANUAL down and then press advance to see which rom is bad on the screen. So my misunderstanding caused me to key in on the wrong rom. It was actually rom 1 that was bad, as confirmed on my rom burner! Burned a new rom 1 and voila! Woo-hoo!

Interestingly, rom 3 is the rom that the game boots from.

So I very much appreciate all the help given in this thread. I apologize for my misunderstanding which could have easily prevented the need for this thread. I also apologize for the long delay between the last post and this one. I had no idea it would take this long until I would be able to get back to my defender.

Hopefully the presence of this thread will help someone else in the future though. :)
 
That whole 4 LED diagnostic thing has caused more problems. I think that is why they went to the 7 segment LED that can flash numbers. It is not uncommon to read the LEDs backwards and go chasing the wrong components (RAM or ROM). So don't feel bad. That's why we ask what seem to be stupid questions sometimes, just in case ;)

ken
 
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