Trying to fix Data East Captain America and the avengers... Boot looping?

[Jinx]

I got this board of ebay broke, and figured i'd give it a shot.. First attempt no sync no boot nothing but RED LED on the board. Tested some of the base Roms (without tape on them) and they were not returning anything from the rom database.. so i reflashed them with both 1.4 and 1.9 versions (tried both separately) and it gets me a tad further, I now get a sync reported on my OSSC and it looks correct, but on the monitor, i get nothing but a black screen. Although, I get the HDMI Icon my monitor produces, and it flashes on... for a few seconds then off.. then back on again.. inifinity.. Possibly a boot loop? So reflashing the roms got me this far, but now i cant get any further. Any usual suspects to try for this type of error?

Board looks mostly decent shape, no broken traces that I've found as of yet.. some light corrosion on a few pins, but i've checked them and they go where they should.. nothing severe..

 

[TheCrow]

At first check the custom chips (big square chips) if they have any lifted pins , then check EPROMs if the data on them is good as they have no label covering the window , due to exposure to sunlight the data on them could get corrupted, if they return good then check the reset circuit but you need a logic probe or an oscilloscope.

 

[Jinx]

Thanks for your reply. I dont know how to fully use an OSC scope.. i don't own a probe yet either.. Question, Can a osc scope do exactly what a probe does? (i.e. is it better to just invest a few hundred into something like a rygol rather than spend less money on just a basic probe?)

 

[ShootTheCore]

Arcade boards have a circuit called the watch dog that will reboot the board if the game crashes. That’s likely what’s happening here. You could confirm that the watch dog is barking if you probed the Reset line on the CPU with a logic probe, you’d likely see it getting pulsed occasionally by the watchdog circuit.

If the game is indeed getting reset by the watchdog, you’ll want to start by confirming the ROMs that run the game code are valid, the ROMs connections to the CPU are valid, and that the CPU’s connections to the work RAM are valid.

Here is a list from the MAME driver on which ROMs store the main CPU code - you’ll want to dump and compare all of these against a MAME dump.



You’ll definitely want to pick up a logic probe for diagnosing boards. They’re not expensive - around $25 on Amazon. This is the one I use:
https://www.amazon.com/Elenco-Electronics-LP-560-Logic-Probe/dp/B000Z9HAP4

I filmed a tutorial video on using a logic probe to diagnose a malfunctioning board a few years back:

View: https://youtu.be/2PAtTIAijeA?si=iSl-bt554ZJ_Ojtl

 

[Jinx]

Arcade boards have a circuit called the watch dog that will reboot the board if the game crashes. That’s likely what’s happening here. You could confirm that the watch dog is barking if you probed the Reset line on the CPU with a logic probe, you’d likely see it getting pulsed occasionally by the watchdog circuit.

If the game is indeed getting reset by the watchdog, you’ll want to start by confirming the ROMs that run the game code are valid, the ROMs connections to the CPU are valid, and that the CPU’s connections to the work RAM are valid.

Here is a list from the MAME driver on which ROMs store the main CPU code - you’ll want to dump and compare all of these against a MAME dump.



You’ll definitely want to pick up a logic probe for diagnosing boards. They’re not expensive - around $25 on Amazon. This is the one I use:
https://www.amazon.com/Elenco-Electronics-LP-560-Logic-Probe/dp/B000Z9HAP4

I filmed a tutorial video on using a logic probe to diagnose a malfunctioning board a few years back:

View: https://youtu.be/2PAtTIAijeA?si=iSl-bt554ZJ_Ojtl

WOW so much info and great leads here! I will do all this. I tested the basic roms that had windows unstickered.. They were 'blank' so I reflashed them with Mame rom data in two different revisions of the board.. the other socketed roms that had stickers seemed to have correct CRC data on them but the database listed many different revisions of the game that those chips could work with so I do not know the exact version of my game. Untill I flashed those stickerless roms, I couldn't even get sync.. It did nothing, but after flashing those I got to where I am now which does sound like what you are explaining with watchdog.

Does the probe quality matter? Or do you like that one just fine? I will pick one up on Amazon, maybe even the one you linked if you like it well and have no 'wish lists' that it had

Thanks!! I Will report my findings when i get the probe and check it all out.

 

[ShootTheCore]

Does the probe quality matter? Or do you like that one just fine? I will pick one up on Amazon, maybe even the one you linked if you like it well and have no 'wish lists' that it had

The probe I linked is a good bang-for-the-buck midrange probe. Cheaper probes typically don't have audible tones for whether the circuit is reading high or low - you definitely want the tones. More expensive probes have voltage readouts (useful but a multimeter does the same thing), recording features (mostly useless) and signal injection (sometimes useful).

The biggest drawback to the probe I linked is that its power clips are rather large, which makes it tricky to connect to the 5V and Ground rails on the board under test. I personally use an test clip clamped to one of the EPROMs to get my voltage and ground - like this: https://www.ebay.com/p/1463775928?iid=335476800802

Or you can do what @ack does and chop the original power clips off of the probe and connect smaller ones: https://www.arcade-projects.com/threads/wwf-wrestlefest-that-does-nothing.30977/post-435313