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twistedsymphony

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So I picked up a Jaleco Mega System 32 and a handful of carts Unfortunately the Desert War cart is causing me problems.

the game boots fine and plays normally but about 1 minute into game play the screen displays garbage followed by a reboot.

Interestingly when letting it sit in attract mode it will go through attract mode fine and then when it goes to the example gameplay it reboots at about the same place it does when playing the game.

the main board works fine with every other cart I picked up so the problem is in the ROM board.
I went into test mode and did a ROM check and everything came back "OK". I opened up the cart and looked for damage, there are a few places where it looks like the pins have been reflowed (they all look good) but other than that the PCB looks like it's in physically pristine condition.

I tried reseating all the socketed chips and even tried running the ROM board without the case but no luck.

Any advise on other things to check/troubleshoot would be appreciated.
 
Im gonna test my cart and see if it does the same.

To start, you could try to dump/compare/reflash the eproms with mame roms. You can also test the eproms in your programmer.
 
I've never seen the inside of one of those, so shot in the dark... sega system32 rom boards have 4 caps on them and I've heard of those failing. So do Jaleco system32 roms have any caps on them?
 
you could try to dump/compare/reflash the eproms with mame roms.
yeah, I was considering that... there are a lot of roms on these boards though ||


do Jaleco system32 roms have any caps on them?
indeed, though they look to be just power filter caps, and they also look like they're in great shape. I suppose it's worth testing. Derick has pictures of his board here: Jaleco Mega System 32 cart conversions?? my Desert War looks identical to his.
 
I've inspected all the pins and the solder joints for the pins.

I tested/reflowed the caps and solder joins on the sockets that looked like they had been reworked.

no change :(

this weekend I'll dump the program roms to check them against MAME to see if there is any corruption.
 
It sounds like it's crashing and then forces the reboot so ROMs are definitely worth looking at - but often power is the issue for garbage/reboot on games too so I think @ekorz might be onto something with those caps. If they're a common type it may well be worth replacing them.

Granted you would think it would freeze up and reboot during attract, but if one of the caps is bad, one of the ROMs may be more sensitive to it than the others
 
It sounds like it's crashing and then forces the reboot so ROMs are definitely worth looking at - but often power is the issue for garbage/reboot on games too so I think @ekorz might be onto something with those caps. If they're a common type it may well be worth replacing them.

Granted you would think it would freeze up and reboot during attract, but if one of the caps is bad, one of the ROMs may be more sensitive to it than the others
it's definitely something in the first level that triggers it. when you reach the first "POW" marker is when it reboots, whether playing yourself, or when the attract mode reaches that point.
 
So...I tested both of my desert war carts, and they both play fine without issues, both go thru attract mode/gameplay no problems.

It shouldnt matter, but my 5v line was at 5.08
 
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remove any shielding / casing and heat it with a hair dryer.
then run selftest .a few times

if that's o.k. run it till it starts crashing and then run selftest a few times.
 
I'm bumping this thread because I've made progress... but still have more to do.

With the recent conversion thread I discovered that the security chip on my Game Heaven PCB was the same as Desert War. Game Heaven had no problem playing for hours so I knew everything was good.

After swapping all of the Desert War ROMs to the Game Heaven PCB it STILL RESET! keep in mind I previously dumped and confirmed every ROM on that board.

From this I decided to buy a new main board I wanted a reliable one so I spent a little more and got one from Sophia Corp. It came in today....
I swapped all of the ROMs back to the original Desert War PCB and installed that cart on the new main board from Sophia Corp and it works perfectly.

----

So what does this leave me with? I have a main board that works with every game I've put on it (Tetris Plus, Game Heaven, and 3 Different Mahjong games) it's run a few of these games or hours without issues, but not Desert War.

I started looking to see if there were any differences between the two main boards and I discovered 2 differences

1. these two caps (51pF) installed on these ICs:
jms32_caps.jpg

2. these 4 resistor packs installed next to the main CPU
jms32_rn.jpg
they're 9-pin I'm assuming 103J means that they're 10K with 5% tolerance, I'm unsure what the other markings (SE8 and RN5) mean.

Neither of those are on my "non-desert war compatible" main-board.

One other thing I noticed is that on my "non-desert war compatible" main board is when booting for a second or two the speakers have a loud buzz like the amp is running at full volume, during this time the screen is black then there's a quick pop before they return to normal and the game starts.

I assumed this was just a quirk of the Mega System 32's boot process but the new main board doesn't do that. it boots immediately into the game, no speaker buzz and no hesitation between power on and game start.


@Derick2k does your main board have these caps/resistors? and when you boot up is there any speaker popping or buzzing?
 
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One other thing I noticed is that on my "non-desert war compatible" main board is when booting for a second or two the speakers have a loud buzz like the amp is running at full volume, during this time the screen is black then there's a quick pop before they return to normal and the game starts.

I assumed this was just a quirk of the Mega System 32's boot process but the new main board doesn't do that. it boots immediately into the game, no speaker buzz and no hesitation between power on and game start.
Looks like a dodgy reset line to me. The signal is probably built with a RC circuit, if so check the capacitor.
As for why the problem shows only with DW, I don't have the answer.
 
Outside of the Audio section there's not much for electrolytic caps on these boards. The only two outside the audio section are a big green cap near the battery which does look like it could be replaced (there's some residue near the diodes here too), and another smaller cap next to a transistor that looks fine.

jms32_caps2.jpg
 
I dont have those resistor packs or caps on the main board I used and DW plays perfectly, so...

Are there any revision markers between the 2 boards?
 
Are there any revision markers between the 2 boards?
I think one of them did have a small paper sticker on it, I give it a closer look tonight.

On yours when you first power on do the speakers buzz for a second?
 
I'll test it, does yours make the buzz/pop no matter what game you put in it?

Also, I have 2 DW carts, both work, I also beleive I have a MB with those resistor pack, etc.. so Im gonna do a round of testing on all of them to see what results I get.
 
does yours make the buzz/pop no matter what game you put in it?
yes


I have a MB with those resistor pack, etc.. so Im gonna do a round of testing on all of them to see what results I get.
I'm interested to see if any of yours have the reset problem that mine does. it's weird that it lets you play for 30 seconds or so before resetting.

take a look at your super cap as well... I've ordered a new one for mine because there is some residue near it.
 
Outside of the Audio section there's not much for electrolytic caps on these boards. The only two outside the audio section are a big green cap near the battery which does look like it could be replaced (there's some residue near the diodes here too), and another smaller cap next to a transistor that looks fine.

jms32_caps2.jpg
C37 my friend next to what seems to be a reset signal generator (3 legs, looks like a transistor).
 
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