Commando PCB problem

GoneMad

Well-known member
Joined
Mar 15, 2011
Messages
1,347
Reaction score
36
Location
Cavendish, Prince Edward Island, Canada
I have my spare Commando PCB. It only boots to a distorted screen of sometimes random images or nothing but mostly zero's. I have narrowed it done to the small outer PCB board. This board only has 6 socketed chips and the rest are surface mount. I reseated all the chips with still the same effect. I then checked the checksum of all them with a set of mame roms. they all come good. Just wondering though, even if the checksums match, could the data still be corrupted. Would it be worth my while to erase and burn new data to these? Anyone have any suggestions as to what I should try?

Doug
 
Dude, if the checksum is good then the data is good too, don't reburn the eproms. How do you know the problem is on the top smaller board? I bet the problem lies in the main middle board that houses the two z80 cpu's, nearly always is when the game does not run.
 
I can't help in anyway troubleshooting this, but once you get it fixed, Souzilla has High Score save kits available for Commando if you are so inclined.

Tom
 
Its not 100% guaranteed that the ROMs are good even tho you get good dumps via a reader, have met roms before that could not drive the data lines strongly enough. Worked fine in my reader but on the board a couple of D lines were very weak. It is not very likely, but dont erase the old ROMs, if there is a fault it will be with the ROM chip itself, not its contents. The only way to 100% rule out a ROM fault is to replace the chip with another burnt with the same data, but there are more likely issues that bad ROMs in this case.

I dont know the board in question but it sounds like a memory or bus contention issue. I have seen ROMs die in a way that stops them responding to the /OE pin so they are always talking on the bus and cannot be deselected, the result is a crashed board. Its another reason why a successful read of a single ROM on a burner does not test that the chip is 100% even if it can spit out the right data when asked.
 
Last edited:
Dude, if the checksum is good then the data is good too, don't reburn the eproms. How do you know the problem is on the top smaller board? I bet the problem lies in the main middle board that houses the two z80 cpu's, nearly always is when the game does not run.

When I put this board on my working board, it stops working. And if I take the small working board and hook into my spare pcb set, it works. So neither PCB's will work with this one small board. I have inspected the board for broken traces and such and it looks good. The only thing is to check the chips with the logic probe, but I have no experience in this yet.

Maybe I will pull the roms off the working board and try them and see what that does.
 
Last edited:
OK. I can rule out the roms. I swapped them out and they work great in the good pcb. The problem lies somewhere on the board. Although it did boot up, it took a few attempts for it to coin up, but when it did start game play, it was missing some background, would change colors, and periodically freeze. The audio was ok. Here are a few pics.
 

Attachments

  • IMG112.jpg
    IMG112.jpg
    103.7 KB · Views: 11
  • IMG113.jpg
    IMG113.jpg
    112.8 KB · Views: 11
  • IMG114.jpg
    IMG114.jpg
    93.1 KB · Views: 16
Ok, problem is definately on the top board then, luckily it is not densly populated. First thing to do is check traces, not with a naked eye but with a Meter. If all checks out it is likely one of the TTL logic IC's has failed, you will need a logic probe for that.

Have you ruled out the ribbon cable and connector (cracked solder joints?) that attaches to that top layer?
 
Its not 100% guaranteed that the ROMs are good even tho you get good dumps via a reader, have met roms before that could not drive the data lines strongly enough. Worked fine in my reader but on the board a couple of D lines were very weak. It is not very likely, but dont erase the old ROMs, if there is a fault it will be with the ROM chip itself, not its contents. The only way to 100% rule out a ROM fault is to replace the chip with another burnt with the same data, but there are more likely issues that bad ROMs in this case.

Thats a valid point, just because the data checks out it don't mean the eprom is good. How would you rule that out? As the eprom would be read fine by a programmer? I guess you would have to probe the address lines using a scope?
 
Thats a valid point, just because the data checks out it don't mean the eprom is good. How would you rule that out? As the eprom would be read fine by a programmer? I guess you would have to probe the address lines using a scope?

Or use a Fluke 9010 to run a checksum on the ROMs in circuit. There's a difference between reading something slow with an EPROM programmer and actually running it at speed in a circuit.
 
Or use a Fluke 9010 to run a checksum on the ROMs in circuit. There's a difference between reading something slow with an EPROM programmer and actually running it at speed in a circuit.

Aha! Once again the Fluke 9010 shows its power, one day I will own one with Z80 pod :)

Just a damn shame the more modern PCBs had CPU's soldered in instead of using sockets like the classics.
 
Well, I fired up the good board and grabbed the logic probe just to get a few readings to compare. When I plugged in the bad board. every chip I checked had different readings from the working board. However on one chip, one of the pins was dead, or now action on probe, so from what I gather, is either a bad level or open circuit. now quite sure where to start on this.
 
OK, I did pull this down from the self today and blew the dust off it. I replaced the working board with this one to try get a few more readings off it. After about 3 minutes, it come to life. But not perfect. All the little banks and cliffs that the men would jump off were all missing and a couple other images. Coined it up a couple times and worked OK except for this. Powered it off for a few minutes and tried to boot again and just went to a screen with random images. None that looked familiar. Any help on this would be greatly appreciated.

Doug
 
Back
Top Bottom