Board initially seemed dead, no rgb video or sync output at all. Logic probe showed that there was actually some CPU activity, but a lot of the graphics chips had no clock signal.
Probing some TTL around the graphics crystal revealed a LS75 chip that seemed to have a stuck output. This is a latch that outputs both Q and ‘not Q’ for input D. The logic probe shows both D and Q pulsing, but ~Q was stuck low. Replaced with another chip and it behaved exactly the same. I have to assume ~Q is intentionally grounded out somewhere on the board and isn’t used.
I decided to trace out what controls the sync signal on the board. The path runs from the edge connector to the diode at FB4, then the resistor at R13, then the LS04 chip @ L11. The LS04 is used as a double invertor and the input comes from the custom graphics chip 55.
There are no schematics for Gate of Doom online, but there are for Desert Assault which is from the same era and also uses the 55 custom. This shows the same setup with sync coming from pin 157 then a double inversion, so it seems to be the same design. The schematics show the inputs to the custom – 14MHz clock to pin 11 – this was present and correct, reset on pin 15, again tested ok. Various +5V lines also tested fine. So unfortunately it seemed the custom chip was not working.
All of the other inputs to the graphics custom chip 55 come from the PAL’s on the board. And they run hot – a couple quickly shooting up to 43C – so I decided to replace them all with GAL’s. I didn’t really expect much from this, as the Data East PAL’s of this era often run very hot, and I’ve never seen a failed one. Indeed this had no effect, but the GAL’s do run much cooler.
Examined the custom 55 again – applying some horizontal force to the pins revealed a handful of them moving – therefore not making good connection to the pads on the board. Really I should have noticed this before, so I reflowed the solder with a hot iron on the pins to stick them to the pads again. Success! Everything now working 100%, including sound. So even though the sync line was connected, some other control signals to the custom chip must have been disconnected.
There’s a wealth of information on old black & white vector monitors on the internet, so when the picture on my Asteroids ‘bloomed’ up much larger than it should be and became unstable I quickly found tips suggesting the high voltage diode was at fault. However.. most of this information was actually written in Usenet times – text only documents! I couldn’t actually find a picture anywhere of where this diode is.
So for anyone else searching, I’ve circled it in red in the photo. I used a diode marked ‘VARO H598′ bought from Ebay which is not the original part, but comes recommended as a replacement, and indeed it works perfectly.
I should also point out you should make sure the monitor CRT is fully discharged before going near this part as the high voltage can be present even when the monitor is powered off. Info on that can be found elsewhere on the internet.
Cab wasn’t terrible when I got it – two chunks of wood missing, lot of mold and dust, but the wood and vinyl fundamentally ok, so I decided to paint it rather than re-apply vinyl or laminate.
Tried out ‘wood’ Bondo rather than regular Bondo to patch up scuffs and missing pieces. I used some spare t-molding as a guide to fill the missing chunk at the control panel, worked out quite well. Also filled in the holes from those big ugly lock bars, not putting them back on.
Some painting, then sanding, then more painting.. Plus new t-molding all-around, and replaced faded marquee with a reproduction.
I swapped out the plain joystick tops with some burn marks for some Data East logo tops I’ve had sitting around for a while. They aren’t perfect but better.
Reproduction control panel overlay added and NOS side-art that I’ve been hoarding for a while. Original bezel remains even though it has some stains and a rip. Might change it out later.
Coin door was fully disassembled, some rust cleaned up, repainted and new locks added.
End result! It’s not a 10/10 maybe an 8 out of 10, but good enough
Bought as a non-working board for $9.99 – the most obvious problem is that no CPU was present so clearly the game wasn’t going to do much without that! With a replacement 68000 in hand (again from Ebay for only a few $) the game booted to garbage.
A logic probe on the CPU address and data lines showed zero activity, so the CPU clearly wasn’t doing anything. Power and ground tested as good. The reset and halt lines on the CPU were pulsing, so it seemed something on the board was trying to kick the CPU into life. Testing the CLK pin on the 68000 showed it to be stuck low. I traced out where this pin went and it connects to the output (Q) of a LS74 next to the oscillator. The logic probe seemed to show this chip had failed, as a CLK was pulsing on the LS74 input, but the outputs remained stuck (one output feeds back into a LS74 input, so the output should toggle hi/lo every clock in order to form the 68K clock).
Tested off-board – failed – replacement from Dragonninja parts board soldered in – board boots right up! Quickest TTL level fix I’ve ever done.
At first I thought there was a graphics problem as the title screen was corrupt – though it’s strange all of the other screens were perfect. Then I remembered I’d seen this a long time ago in MAME.. If you boot the English language ROMs with the Japanese dipswitch enabled the title screen is corrupt (because it expects the Japanese character ROMs).
Unfortunately this board is stuck in Japanese – because the dip-switch isn’t being read by the software. A previous owner has removed resistor packs for the dip and the jamma inputs, presumably to repair something else!
That shouldn’t be too hard a fix – to be continued.
Pacman did not appear, and two of the ghosts did not appear. Additionally the text at the top of the screen (Hi Score) and the bottom (Credit) were corrupt. A tip on the KLOV forum suggested this was likely to be the VRAM addresser daughterboard. Nothing looked wrong with a logic probe so I decided to remove the LS157 and LS86 chips as I have a plentiful supply from a Dragonninja parts board.
As it turns out I didn’t even get to the LS86′s as one of the 157′s tested bad when removed, and replacing it solved the problem!
Sound would go quiet after a few minutes, and it seemed like different elements of the sound would have incorrect volumes (drum track, music, explosions). I think that’s because the sound chip outputs multiple channels which are mixed externally before the stereo amp but didn’t look too much into it.
Instead, I just swapped out all the capacitors in the audio section – I think all are 100uF, 25V. This seemed to fix all the audio problems.
The battery is barely mentioned in the manual, but test mode will tell you if it has failed. Just replace the IC in the picture which is on the board with the jamma connector – it’s in a socket even though it doesn’t look like it is. Part number is M4T28-BR12SH1.
Renegade is a JAMMA pcb and the predecessor to Double Dragon. Initially it seemed the vertical sync was broken on this board – the image rolled vertically very fast. I traced the sync line from the JAMMA connector back on the top board and found it goes to the bottom (video) board. After cleaning up a lot of dirt and dust, a massive gouge in the bottom board became clear! Must have been a fairly heavy impact as you can see two TTL pins are sheared clean off.
Bridged the broken traces with wire and sync was restored but the image was cut into three pieces.
Re-checked the repair with a logic probe and found no activity on one of the repaired traces. There was actually a through-hole to the other side of the pcb in the damaged area that need soldered back on the trace. Then everything worked 100%.
This is the Data East MLC package – which is a two layer pcb inside a protective plastic box. Unfortunately this one seems 100% dead – no video or sound output at all. Components are actually surface mounted to all 4 surfaces on the two layers – the main CPU (an encrypted ARM) actually sits on an inside surface so it’s hard to diagnose directly.
Using a logic probe with the game powered on shows that the data and address lines on the program EPROMS are pulsing – so the CPU is definitely trying to do something. All the graphics hardware (ROMs, custom chip) probes as completely dead – that doesn’t prove for sure that it is dead – it may be the CPU is actually failing for some reason and not instructing the graphics customs to start up. My immediate theory would be one of the main RAM chips for the CPU has failed – these are 4 Winbond chips on the main board. The ARM is a 32 bit chip and these 8 bit chips run in parallel so a failure in any one of them would cause the CPU program to immediately fail.
Hoops isn’t that great a game, so I’ve no plans to probe further – this can wait until I find another MLC game and swap the top & bottom boards and see what happens.