Simpsons PCB Dead

troxel

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Got a Simpsons PCB and is showing nothing but a white screen. Can't get into test modes. Checked voltages, which are fine and board is getting a pulse. Gave the board a look over and didn't see anything out of line.

Any suggestions on where to start troubleshooting this? Thanks.
 
What is the reset line on the CPU doing?

Next, what about the /CE and /OE lines on the program ROMs? Do you get any audio or does it try to play blind? If so you may have a bad hybrid on the video output.

All those Konami boards from that era are very susceptable to physical damage - scraped traces, etc... Look it over CAREFULLY with a magnifying glass as those traces are very tiny on that board.

RJ
 
Thanks, RJ.

Clock on the CPU starts low and then goes high, /OE and /CE are pulsing on the program ROMs. No audio tones on power up, and game is not playing blind.

I'll go over the board again here in a bit and look for scratches. It's in pretty good shape.
Any other areas to check?
 
I had this same symptoms as you are describing on a Simpsons board. Worked great, then one day nothing....I couldn't even get to the test screen. Turned out it was EPROM 13C. I ordered a new one from Steph at Hobbyroms.com. PCB now works like a charm!
 
I'm going to agree with troxel on this one. If you've got access to an E/EPROM writer/reader, I'd go through your board and make sure everything is set.
 
I had this same symptoms as you are describing on a Simpsons board. Worked great, then one day nothing....I couldn't even get to the test screen. Turned out it was EPROM 13C. I ordered a new one from Steph at Hobbyroms.com. PCB now works like a charm!

Had same issue om TMNT: TIT... Was a cold solder joint on the bottom of a ROM socket
 
Thanks, guys. I will pull out the Eprom programmer when I have a chance and check the ROM for bad ones for for cold solder joints/bad traces.
 
Whoops. Meant to say the reset not the clock. I will look at this board some more when I have a chance.
 
Whoops. Meant to say the reset not the clock. I will look at this board some more when I have a chance.

I figured that's what you meant since you said /oe and /ce were pulsing. They wouldn't pulse if the clock was dead.

Next step is to check the ROMs, CPU RAM, and the CPU itself....

It's odd that the CPU isn't getting watchdog reset.
 
Have worked on a few of these, the most common failure is actually within the TTL logic, especially if the board is mostly Fujitsu TTLs, these are dropping like flies nowadays. They seem to lose internal connections to their pins, so if an output pin is disconnected it becomes floating, and if an input pin is lost the chip die isnt getting the correct inputs and appears to be doing the wrong thing based on the inputs that can be seen externally. The SRAM is usually Fujitsu MBMxxxx chips which are very robust and EPROM faults are quite rare. The gfx and sound data is held in mask ROMs which are also a common failure but as they do not contain executable code they would not stop the board booting.

Of course all of that is based on what is most likely, that doesnt mean much to a specific board tho.
 
Had a chance to look at this again, and found a couple bad traces on the ROMs. Added two jumpers and game booted right up.

Pin23 on 17c/16c and
Pin 10 16c/15c.
 
Had a chance to look at this again, and found a couple bad traces on the ROMs. Added two jumpers and game booted right up.

Pin23 on 17c/16c and
Pin 10 16c/15c.

Badass, Good job!! I think I'm about to buy a simpsons board cheap with a Rom error. Lets see if I have just as good of luck finding out the problem.
 
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