Hippodrome (Data East) PCB repairs
Tools: Logic probe, Multi-meter, soldering iron, 68k pinouts
Problem: Dead board
This is the same DECO (Data East Corp) CPU board, DE-0297-3 used on
Bad Dudes, Dragon Ninja and Robo-Cop. I have a Bad Dudes board set, so I put the ROM
board on the known working Bad Dudes CPU board to figure out which 1/2 of the
board set was the problem. The ROM board worked just fine on the Bad Dudes board
so the problem was isolated to the CPU board. This was an easy way to figure out
where to start. :-)
After putting the board back together, I powered up the board and
looked for Video sync. It was present on the edge connector. Next checked the
reset line on the 68k CPU. It was stuck low. The reset line should be high for
normal game operation. I traced the reset line to the 7405 Hex inverter next
to the CPU and the output on pin 8, which fed the res,Heline of the CPU was stuck
low. It looked like this chip had been replaced before, and soldered straight back
to the board. I checked the pin connections for continuity
with the multi-meter and discovered pin 5 was not soldered at all to the board.
I soldered the pin and reflowed the solder on the other pins. Then I powered on
the board. The CPU came to life! I probed the CPU and the address and data lines
were pulsing, as they should be. The rest of the board was running also, which
was verified by probing several chips and EPROM data lines. But still no picture.
Problem: No Video
I knew I had sync on the edge connector, but re-checked it again.
It was still there. I probed the red, green and blue leads on the connector and
each one was dead. Nothing! I traced them back on the board, and noticed there
was a pretty deep gash in the PCB about 2 inches from the edge connectors. I powered
down the board and grabbed my multi-meter. I used the meter to check the connection
of the red line at the card edge to FB1 were the trace ran. Open! I did the same
with the green and blue to FB2 and FB3 respectively. Open! Looks like the problem.
I ran jumper wire for each trace and checked my work with the meter. Looking good!
The digital multi-meter happily beeped as I tested the traces. Fired up the board
and Viola! Working Hippodrome. A very happy ending and only a couple of hours
work. It was interesting to me that all three traces were broken.
Solutions: Fixed the bad solder joints on the 7405 and fixed three
traces for red, green and blue.
Tools: Logic probe, Multi-meter, soldering iron, Razor blade, 68k pinouts
Problem: Dead board
The board was missing one EPROM on the ROM board and one capacitor at
NF36 on the main board. After replacing the EPROM and testing the ROM board on
the one I fixed above, I knew this ROM board was also good. I installed a 2200pF
filter capacitor at NF35. This cap is the strange 3 legged cap and is commonly
the first component the trace hits when leaving the JAMMA connector. NF35 just
happened to lead to pin C on the JAMMA connector, which is +5. I reconnected the
ROM board and powered up. This got the board to at least power up and get the
CPU running. But I had nothing but garbage on the screen. I gave up for the night.
After looking at the board on and off over the last day, I noticed
the 3 surface mount custom chips had some bent pins with legs smashed together. Using
a razor blade, I straightened out the pins and used a magnifying glass to make sure
no legs were touching. I reseated the ROM board and applied power. One more working
- Replace missing filter capacitor at NF35
- Program and replace the missing 27C512 EPROM
- and straighten out the legs on the three custom ICs on the processor board
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