Purchased described as “dead”. Started by creating a JAMMA adapter (I hate creating adapters, it is tedious work). Well, the description was correct – she is dead alright: screen has static garbage and required some tweaking to sync correctly on my test bench monitor.
Watchdog is barking, disabling it has no effect on the screen’s contents. Board already had some previous work done in it, solder-side contains more than 20 jumps to connect some RAMs back onto the bus. The Parts side shows the missing/removed/blown traces being jumped.
Started by checking the daughterboard, seems OK. Next I remove, socket and replace the 74LS245s on the board because word has it that they tend to be the cause of most problems, the Galaxian Trouble Shooting Logic Board manuals lists similar symptoms connected to those chips, and the Fluke 9010 troubleshooter says that the address lines are tied. Other than that, I cannot come up with a good way to check them! 🙂
Gotta wait for some replacement sockets and chips to come in…
[07/30/03] Got ’em in, working on the board soon…
[Some time later…] Well, so much for THAT idea; board is still in the same condition, with address line 12 tied low. After taking another look at the schematics, I am going to try replacing the 74LS367s at 7D and 8D and see what happens. Gotta order those now…
[07/31/04] Hmmm! Only took a year to get back to this…! 🙂 Well, replacing them did nothing. I did discover one broken trace and jumped around it.
While messing around with the board I noticed that pushing on the CPU effected the the signals on some of the CPU’s control, address and data lines. For example, my logic probe would have a stronger flash depending on how I pressed on the CPU. Replaced the socket and the game actually does something long enough to prevent the first watchdog timeout from resetting it.
Started taking a closer look look at the board and after staring at it for 45 minutes I noticed a broken connection. Repaired it, and now I have a totally different screen; it went from Figure A, a static garbage display, to Figure B, which is drawing some seemingly random graphics/data near the upper right hand corner with a row of static zeros on the left that go through the bottom to the top of the screen (watchdog is disabled, it does not reset it in this state). Well, at least that is some kind of progress…! Yeah, progress… Right?
These images are thumbnails, click on them to increase their size.
Using the Galaxian Test ROM, the game does not watchdog (uh, I think…), but the Test ROM just seems to quickly fill the screen with what-looks-like-half-circles, briefly clear the screen and then display garbage?
[08/01/04] Used MAME to see what the Test ROM is supposed to do, and realized that I have the wrong graphics EPROMs on the board. Now the Test ROM starts the same as it does in the emulator, but then gets futzed up.
Started examining the underside board again and was about to undo the mods required for the Four Play when I noticed a blob of solder shorting two pins on the back of the board! Removed it, and the board kinda runs the Test ROM, but differently than in the emulator. Tried out the Four Play EPROM and it comes up to a menu(!), but gets hung up there or at least, does not respond to controls):
Notice the kinda-flag looking character and the number ‘3’ near the upper right hand corner of the screen, kinda where I had that random garbage earlier. Hmmm… No controls, possible RAM issues… The 138s?
My eyes get drawn back to the bank of 3 138s and I notice that where I had not repaired where I previously had clipped one of their address lines (as part of an earlier troubleshooting effort). Connect ’em back up and…
Nothing! A blank screen! Further playing around with each of the chips leads me to believe that at least one of them is bad; either at 8M or 8N. Just to be sure, I am going to yank all three and socket & replace them. Anyone got some spare 138s lying around that I can buy?
Also, I am starting to think that my Fluke Z80-Pod is busted… (Yep, it was… See here.)
[08/02/04] Well, well, well… Going through my chip inventory, I found a tube of 138s and another tube of sockets to match! When I removed two of the three 138s (8M and 8N), they literally broke into pieces! Clipped and desoldered ’em, cleaned the holes, dropped in the sockets, put in the new 138s and whadda know… Sucker came right up!
I also figured out why the screen was green; here is a tip: try not to switch your Video Green and Video Sync lines!. She works and plays great:
(Actually, there is one small problem, the background sound (the one that speeds up as you destroy enemy ships) starts getting faster right from the start of a game and get real fast real fast; within 30 seconds, it is faster than I have ever heard it go. Since it happens on all of the games, I think it is something on the board. But that is a tale for another time…)
Solution: Replaced 74LS245s, repaired/jumped broken trace, repaired previous repair attempt, replaced CPU socket, replaced the three 74LS138Ns, removed an unintentional solder bridge. It could also use to have all its sockets replaced… Maybe after I get more skilled with my new desoldering station! 🙂