Troubleshooting Midway 8080-based Games ---------------------------------------. Phil J. Stracke Alex Yeckley John Robertson Rodger Boots James Marous Brendan Keith EPROMs +---------------------------------------------------------------------------. Your Midway 8080 PCB may have 9316 PROMs, 2716 EPROMs, TMS2716 EPROMs, or 2732 EPROMs. Quite confusing really, as Midway failed to document most of their revisions and EPROM strapping information. Space Invaders boards have Jumper 2 ("J2") which can select either ground, AD10, or -5v. It directs one of these signals to all ROM's at pin 21. I am unsure what position the jumper should be to do this as the documentation is fairly crappy, and there were last-minute parts missing/substituted in the address buffer circuits. The correct link point for J2 is that which directs ADIO from F2 pin 8 to all ROMS at pin 21. On regular 2716's pin 21 is tied to +5. If your boards have 2716 EPROMs, then that pin might not be connected internally and thus not care what is connected to pin 21. If you want to use a 2716 in place of a 9316, you should program it as a 2716 (not TMS2716), then connect pin 21 to pin 12 (ground). Bend pin 21 up so that it doesn't mate with the socket anymore. Double check the voltages at pins 24, 21 (both +5VDC), 20 and 18 to be sure that none of those are hooked up to either -5 or +12VDC. You could also re-strap the board so this isn't necessary at all. The strapping inforamtion is documented in the Midway schematics (although they might be misleading?). If the game is currently strapped for the 9316's or 2716's (not TMS2716), a 2732 is just a drop in (as long as the 2732's have a dual image of the program data). If the board rev is an -000L, you can also remove the H socket and install a 28 pin socket, add three address jumpers and have the whole thing run from a single 2764. Much more tedious and not practical unless you have a -000L. +---------------------------------------------------------------------------. Shuffleboard / Space Invaders PC 0800-09000 H & K Mother boards H is strapped for 2716's Only. K can be altered for 2716's or 9316's. -from Bulletin 10/9/78 +---------------------------------------------------------------------------. A normal (non-TMS) 2716 versus a TMS2716 pins out like this: <----- normal 2716 -----><---- TMS2716 pin redefinitions ----> +-----+ +-----+ A7 |1 +--+ 24| VCC <--- Vcc/PE (PE is Program Enable) A6 |2 23| A8 A5 |3 22| A9 A4 |4 21| VPP <--- Vbb (-5 volts) A3 |5 20| /OE <--- A10 A2 |6 19| A10 <--- Vdd (+12 volts) A1 |7 2716 18| /CE <--- S/PGM (chip select/program) A0 |8 17| D7 D0 |9 16| D6 D1 |10 15| D5 D2 |11 14| D4 GND |12 13| D3 +--------------+ +---------------------------------------------------------------------------. Space Invaders multigame (by Brendan Keith) ------------------------------------------- Another fun way is to burn all 4 or 5 images into a 27128 or larger and simply add 4 leads or so to the address jumpers. No cuts needed. I started with a Bally Space Invaders board. S6 ROM jumpers were set to AD11->a, AD12->b, AD14->c I then took a 27256 and burned in both the Space Invaders set and Space Invaders Deluxe. I can do this because I own both boards so don't anyone try to get smart. The ROM set has to be merged and burned in with the H ROM lowest and the higher segments filled with whatever to make up two full 16K blocks. This new ROM can be plugged in to any of the ROM sockets but sockets F and G are closest to the jumpers that we need to connect to. Plug it in with bottom pins lined up. The top 4 pins hang out. Now for the jumpers. They are really quite simple. I used a 28 pin socket, bent out the following pins and soldered wire wrap wire to the legs. The socket itself can then be plugged in to the existing ROM sockets. Pin 1 to GND Pin 2 to AD12->b jumper. Pin 20 to GND Pin 22 to GND Pin 23 to AD11->a jumper Pin 24 to AD14->c jumper Pin 27 to the center pole of a switch between GND and +5 to switch games. Pin 28 to +5 +---------------------------------------------------------------------------. VIDEO +---------------------------------------------------------------------------. One of the most common failures on this system was jerky motion/garbled video (but the game was still working) and was caused by dirty motherboard/daughterboard connectors. You see, the 8080 just didn't have enough speed to shift an image and write it to the RAM. So they sent the data and how many bits to shift it to the daughterboard which had a hardware barrel shifter circuit on it. The shifted result was then loaded to the RAM. When the connectors got dirty some of this data didn't make it to/from the shifters and the data stored to the RAM (that you saw on the screen) would get garbled. Wasn't hard to fix once you knew what was going on. The video out of Space Invaders is a composite signal, so you can't just connect the video signal to one or more colors of the color monitor, and the sync to the sync because there is no separate sync signal off of the space invaders PCB. I was able to get the color monitor to work, so it is possible. I'll give you a hint - pin 8 off of the 7455 located at A-6 is the sync signal. If you hook RGB together, you get black background and white foreground. Your monitor looks b/w at that point. I've used color monitors in space invaders many times. If you get the video signal just before it's AND'd it works fine. TESTING +---------------------------------------------------------------------------. Before you do any testing on your Midway 8080 boards, you should review the Midway 8080 Standard Test Procedures and any relavant schematics. Why can a newer motherboard (like Space Invaders) be used with properly strapped ROMs, but a sound board from a Space Invaders won't work with an older mother board (like 280zzzap) even with proper ROMs for testing purposes? You would think it would come up, but not have correct controls or sounds. The Space Invaders sound board has a watchdog on it. The 280zzzap software has no provision to reset a watchdog, so the program code would run for a while (70ms IIRC), then the SI watchdog would kick in and foul up your test. Forcing the watchdog high *probably* won't work (because of all the things that do need to get properly reset), but YMMV. If it's just for testing, you could re-strap the motherboard to run SI code with the SI sound board, and everything would be OK. Lots of people run into problems restrapping however, because the SI schematics are "misleading". You cannot convert a regular SI set to play SID. Custom circuitry (data shifter) was added to the sound/IO PCB to prevent this. Also, an extra chip was added to the CPU PCB. POWER SUPPLY TESTING +---------------------------------------------------------------------------. See the section on http://www.elektronforge.com TESTING RAM +---------------------------------------------------------------------------. To fix Space Invaders family of game boards, first remove ALL the game ROMs, then turn the game on. You should see a repeating pattern of a thin and fat lines across the screen. Next close the Slam switch for a moment, this pattern should change, but still be solid lines (thin or fat doesn't matter, but they repeat). Now if any lines are flickering, or there are dots on the screen that are sometimes covered by lines but reappear when you "Slam" the switch, then you defiantly have RAM problems. Next, try momentarily shorting pin #7 of each RAM chip to ground until you find the one(pair) that when shorted either make solid the flickering line or cover the dots. Now you just have two suspects to replace. Sub one at a time, then alternate. It is only one of the two Ram chips that share the pin #7 output that should be bad. Any of the following are suitable RAM replacements: AM9060, D2107C, UPD411, MM5280, TMS4060 If you've got a completely blank screen with all of the ROMs removed, then you have a more root cause of your problem than just bad RAMs. Check your clock generation circuitry with a scope first; have you checked the power supply yet? Also try swapping out the 8080; it should be socketed. MISCELLANEOUS FIXES +---------------------------------------------------------------------------. [see page 63-66 of Midway Service Bulletin #2 on Spies] REPLACEMENT PARTS +---------------------------------------------------------------------------. Unable to find a source for D3245 or DS3245 chips (quad clock driver chip)? You can use two 8-pin dual driver chips instead, on a little adapter board and it should work fine. Here are some IC part numbers off of a Space Invaders board. --------- B3 - P8216 Schottky 4-Bit Parallel Bidirectional NonInverting Bus Driver *breath* Same as the 8T26. C7 - F 9310 PC Also a 74160; Presettable Synchronous Decade Counter w/ Direct Clear C5 - D3245 (Very faded) Looks like some type of dynamic RAM controller; don't know anything more. The schematic also lists something like M**4060, but its definitely not a ram chip (can't make out what the ** is). It's an inverting MOS clock driver, used to drive the two phase clock on the processor. D5 - F 9316 PC Also a 74161; Presettable Synchronous 4-Bit Binary Counter w/ Direct Clear E5 - (3 Lines) S7549 Then N9316B Then 7-6974 Another 9316 fer sure. F7 - F 9322 PC A Fairchild quad 2-line-to-1-line data selector/multiplexer. Same as a 74157.