Defender Rug Patten Reset

Stoog

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Got a defender pcb set in for repair and was wondering if anyones seen this before

Before asking yes getting correct voltages ect

Boots up goes to rug patten then second patten black screen reboots owner told me he changed all the rams to 4164 a while back and been working fine since until thic hsppen one day He tried a known good video pcb and still does the same issue.

Each time on either video pcb fitted 4 LEDs on rom card come on when it gets to black screen then resets i cant find any info on this type of fault so thought i would ask here

Any ideas
 
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reseat CPU. if not then, replace the CPU socket. if not then... I don't know, get your logic probe out. I hate Defender now.
 
ribbon cable needs to be changed anyway so I would do that first but that may or may not be the problem. if you plan on keeping the board its nice to cross a potential problem off the list

what did the +5volt measure out at EXACTLY ?
strange that you claim it's getting correct voltages as they hardly ever get EXACTLY +5volts unless the potentiometer modification has been done and I'm guessing yours has not
guessing again here but your +5volt is probably at 4.7 or 4.8 which may or may not be another problem

power supply have new capacitors installed especially the big ones ?
guessing that it may not which means the power supply has cold solder joints all over it and who knows what kind of ac ripple is getting through those old capacitors and making screwy stuff happen

battery is new and modification as been installed ?
coin door switches operating correctly with none sticking ?

hopefully member "Mecha" chimes in on this thread as he is good Williams problem people
send him a PM as he may miss this thread

good luck
 
Thanks for all the replies. Havent really sat down and went over it with a scope/logic probe yet more just reseat eproms and rams so far. I will be taking out all rams and checking them one by one first before going any further to rule out those on both PCBs

Ill look into all the ideas people have given and see what i come up with. If one or more the rams are not working would it show the error message on the LEDs? First time i ever worked on one of these but have in the past fixed a bootleg version of this game

I originally thought the ribbon cable so that will be the next thing ill look into

I am not getting spot on 5.00 volts more like 5.01 to 5.02 and i have it on my test bench so no original power supply/machine.
 
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it sounds to me like it's completing the boot sequence, and then resetting. that implies the rom data is getting there, even though that's a very common failure. it's also not crapping out to a ram error; it should stop at that point.

watch your rom board LEDs, during a proper boot cycle all 4 lights should flash twice getting you to the all systems go screen. or an initial power on, they should all flash once, then it goes through its diagnostic procedure to either generate an error or do the all 4 flash twice.

as a former defender of single wipe sockets, I just can't anymore. the pins break off in the weirdest ways on these. so have a ton of 40 and 24 pin sockets on hand for these occasions. :p
 
UPDATE

After checking all the program roms i found rom 11 to be bad replaced socket/reprogrammed and got it up and running with the known good video PCB he has :) I will end up replacing all the sockets on this PCB but for now just want to get it up and running so i know i am on the correct path

Now fitting his original video PCB with the 4164 ram upgrade i am getting on screen RAM 27 failed

Just finished checking all 4164 rams and all tested ok in my tester along with testing each one on a PCB that uses 4164 rams.

Found that 5K (74LS374) failed replace that and up it came with no issues at all

All fixed
 
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haven't had it happen on Defender, but the Stargate and later stuff will throw obscure ram errors if the horizontal decoder socket is janky. (the one not closest to the header edge, but near the 374 buffers)

never considered a botched rom doing that. I always forget which one is the important program rom you have to have installed.. wanna say 7?

on almost all my repairs I had to wash the rom boards with simple green to get the sockets cleaned up. and clean the corrosion off the rom legs. I had some that worked perfectly and then I went to test them again a week or two later and they started throwing random rom errors. simple reseating helped in a few instances, others it didn't.

I encourage probing ram 27, see if there's any floating pins. do the same for the bank 2 374 buffer. I don't know about a 27, but if you had a 21 I would definitely suspect the buffers or multiplexers then. as per the repair flowchart, pins 7 and 9 on the multiplexers should pulse. obvious first approach would be swapping 27 with another, if still bad, then suspect the socket. I lift the plastic housings off to inspect the socket legs. typically they snap off like cutting a tree down or half of it breaks off and the IC leg won't be able to touch.
 
It would flag ram 27 error on a cold start but if you do a warm reboot would keep changing the error code so tracked it back to that 374 being faulty which repaired the issue

With the rom it was reading back incorrect CRC each time even after cleaning the legs ect so that was causing the resetting all the time
 
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