Corrado Tomaselli

No background in electronics. Learned everything by reading pdf books and expecially Video game logic Vol 1 by Atari and in general early Atari and Williams arcade manuals

Defender repair log # 3

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Mar 112019

Again my Defender boardset had developed another fault.

I had already repaired here:

Defender repair log #1

and here:

Defender repair log #2

This time after the screen “Initial tests indicate all unit OK” it rebooted in an endless loop.

The diagnostic LED were flashing two times correctly before resetting, so I thought it was the ribbon cable.

After spraying and moving the cable , game still reset itself after the initial test but after a while it didn’t produce anymore the classic startup sound and all the LED were always stuck lit.

The 6821 PIA on the romboard should send an \IRQ signal to the main CPU after the ram test but the signal was missing, that’s why the watchdog kicked.

Also the 4 LED stuck lit is an evidence that the PIA died.

It’s known to be not very reliable, so I decided to desolder it , put a socket and test the only one PIA I had for spare which luckily made Defender to boot again.

Game was  fixed without any problems ( for the moment )

Outrunners repair log / pinout

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Jan 272019

Got this game from a friend who took out the board out of a rusty cabinet.

The game needed badly a clean, so I dismounted everything before attempting to turn it on and washed everything carefully.

The game has two jamma connectors for player 1 ( Monitor A,left connector looking at the above picture) and player 2 ( Monitor B, right connector looking at the above picture). The connectors share same power lines, so you can connect wherever you want to play as P1 or P2.

Unfortunately board was not working correctly, it showed from a brief moment a garbled text about network connection and then nothing happened.

I decided to start dumping the program maskroms and found immediately one branded SEGA MPR-15539 which had some internal connection problems.

The other one , same type and capacity was dumped good.

After burning a new program rom on a 27c400 ( 4mbit maskrom pinout eprom), game booted perfectly although without any sound.

There was not even a noise coming from amplifier so I decided to desolder it and found immediately the problem

The amplifier was litterally blown

From Mame source I could get the right one to order, a TDA1518AQ, replaced it and finally the game had sound.

Unfortunately some tracks sounded bad with wrong samples.

There were other SEGA branded maskroms used as PCM samples, I read both of them ( 16mbit maskroms) and one of them , IC1, had A16 internally broken.

After buring a new 27c160 eprom with IC1 data, game sounded perfectly again.

No other problems were found

I will share the pinout of the board to play it on a different cabinet than the original one with a filter board ( the manual has only the schematics of the filter board unfortunately).

Game is Jamma as stated, so all power, video and audio pins are the same.

Board is using the following digital pins: on component side pin 22 is for shift up and pin 22 for shift down. On solder side, pin 22 is to select DJ Music or radio, pin 22 and pin 23 to move forward or backward the selection of musics. This is valid for both P1 and P2 connectors

There is an AMP connector in the middle used to drive lamps but I haven’t yet figured out the pinout and to me is not very interesting.

The most interesting part is the analogue controls which is handled but the daughter board 837-7636 which is in common with all Sega System 32 driving games.

I found a partial pinout on a japanese website and decided to expand it with Outrunner pinout

Last Duel repair log

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Jan 272019

Bought this game for personal collection but despite having declared working it had some graphic faults.

In particular the intro had blockly graphics and generally lacked shade of colours. The gameplay was in general fine at least for the first two levels.

I started to check maskroms and found LD13 and LD15 which handled the tiles of the intro. Maskroms were tested good on the programmer.

Data pins went to a 86s100 custom chip which usually is not very reliable ( see bottom right of the pic below)

At this point I decided to put a socket and change it with another one I took years ago from Poker Ladies.

Unfortunately the defect was still there but after another look underneath the board and I saw some borken traces which connected the custom to a 74ls273.

There were 3 traces severed but still the graphics were not fixed at all without a sign of improvement.

At this point I started to probe all the other ttl of the video board until I noticed a floating data pin of a 74ls273 which led again to the custom.

The trace interrupted at some point but I could not see any visible scratch until I noticed it near a silscreened text H1, not easy to find at all

After repairing this track the game was fully restored

Oct 292018

Got another Tumble Pop for a repair, this time with the background totally messed up

The background is stored in one 4Mbit maskrom silkscreened MAP-02

Probing the chip revealed all the data lines were floating.

Decided to desolder it and read it as 27c400. Strangely the programmer didn’t complain about missing continuity on some pins as normally happens

with these maskroms but the read gave only 1F and 00

I put a socket and since I didn’t have a spare 27c400, I programmed a 27c160 (16mbit eprom) and installed it with pin 1 and 42 out of the socket.

In this way the pinouyt exactly matches the 27c400.

With the eprom in place the game was fixed 100%

64th Street – A Detective Story repair log #1

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Oct 292018

This PCB from my collection had a subtle problem after some minutes of being turned on and with voltages more than 5.1V

Some lines of the sprites started to be shifted toward the left


If I lowered the voltage to exactly 5V the sprites were good.

Being a perfectionist I started to find the culprint and eventually I found the circuit involved in the problem.

If I put the oscilloscope tip on pin 2 of 74LS365@IC55, the problem got worse, more lines were shifted to the left.

The chip was good so I changed also all the components which were in the chain, a 74LS245@IC56 and a couple of rams @IC57 and IC58

It must be said that all these components had healthy a good looking signals on the oscilloscope and they were tested good out of circuit but I decided nevertheless to change them with other brands to rule out every possibility

Still same issues after some minutes powered on

At this time I really thought it was either the sprite maskrom or the custom chip which was the source signal of pin 2 of 74ls365 until I noticed that the same signal was also connected to pin8 74LS273@IC94 which was pretty far from the other chips in the chain.

I decided to make a piggyback with a good chip and the problem desappeared completely at all voltages.

I changed it without further checking and still the problem was there!

With the tip of the oscilloscope I touched pin 8 and the problem disappeared immediately.

The oscilloscope probe has some capacitance which delayed somewhat the signal and fixed the problem.

So I installed a ceramic cap between GND and pin 8 and the problem was 100%


I think that this board had always a timing issue that no one addressed and preferred to run it with exactly 5V