Repair Logs – Page 81 – JAMMArcade.net

Heavy Unit repair log #1

Dec 142015

I got a dead Heavy Unit PCB with a white screen on boot:

hvyunit1

Looking at the MAME driver for that game I could see where the program roms were located (5C for the main program rom and 5P for the sub program rom).
I started probing around the CPUs and program roms. The CPUs (2 x Z80) seemed active and the program roms had pulsing signals on most of their pins. A few were inactive and connected to nearby GALs (labeled MD-500 and MD-501). All the I/O pins were stuck low on these two GALs while they had pulsing inputs.

There are 3 GALs in total on that board, MD-500 is connected to the main program rom, MD-501 is connected to the sub program rom and MD-502 is connected to the sound rom.
Surprisingly all these 3 GALs had inactive I/O pins. I got a working Heavy Unit PCB from a friend, compared the signals on the GALs and saw that almost every I/O pins were pulsing on the 3 GALs.

These GALs were not available online so I started desoldering them on both PCBs.
I put sockets on the dead PCB, socketed the GALs from the working board and the game booted ! …but with partially missing graphics (I had colored squares instead of sprites):

hvyunit2

Looking at the PCB I supposed the main program rom at 5C was not original as it had no label. Dumping it revealed it was from a US version. Looking at the MAME driver, I could see that every of the 4 versions dumped in MAME had a different ROM layout and my version was not dumped (the numbers on the labels were not in MAME). Particularly, there was a 512kb ROM at 2F on every versions in MAME that wasn’t soldered on my PCB, although I found its content spread on 4x128kb ROMs at other locations. The main program ROM was probably looking at the wrong location so I soldered a socket at 2F to put the 512kb ROM (from one of the MAME dumped versions and labeled B73_08) and the sprites were back. 🙂

hvyunit3

Here is my PCB with the added 512kb EPROM from MAME at 2F (equivalent to B73_17 + B73_18 + B73_19 + B73_20 on the left):

hvyunit0

ps: I’m still looking for the original program ROM for my PCB (labeled B73_24 and located at 5C) to be dumped so I could remove the 512kb at 2F and use the original 128kb ROMs already present on the board. I suppose it is a japanese version.

ps2: I wanted to dump the GALs from the working board but they were protected. To dump protected GALs I needed to use a method by Charles MacDonald. First, I used this adapter in order to read my GALs as 27C020 EPROMs: https://techno-junk.org/files/adapter-v2.png
Then, I used PD.EXE and WinCUPL to recreate the GALs from my raw dumps: https://dreamjam.co.uk/emuviews/readpal.php
These GALs are now available on https://www.jammarcade.net

Space Invaders (Taito) 3-Layer repair log #1

PCB Repair Logs Comments Off

Dec 102015

I was recently given a Taito 3-Layer Space Invaders boardset by a friend to look over. The problem was that it was not running, completely dead with a clicking sound coming from speaker (sounds like watchdog barking to me).

I powered up the PCB stack on the bench and checked the status of the 8080 CPU. I could see right away from probing pin 19 (SYNC) that the clock circuit was not running.

On the ROM board, I could see that the crystal was intact, so I checked the 74S04 (IC1) which I was sure was drives the clock next to the crystal. I found that most of the pins were floating. Replaced it and I now have a clock (note to myself, 74HC04 will not work), watchdog no longer barking but still no display.

ace_si_1

On further probing, found a bad 74161 counter at location IC6 with pins 11 to 15 stuck HI. Replaced this and I now have a display, but it appears to be doubled up;

ace_si_3

Eventually located the problem to IC28 which is a 74LS83, pins 2, 6 & 9 were stuck LO. Replacing this restored the display;

ace_si_2

Note, I am using the composite input on my Plasma TV, as the PCB is composite only and not RGB.

Space Invaders live to invade another day!

Tatsujin repair log

PCB Repair Logs 4 Responses »

Dec 102015

I have this Tatsujin PCB in my collection :

Tatsujin_PCB

Some days ago I wanted to play it on my Astro City so, before rotating vertically the monitor, I tested the board on a supergun.Game was running absolutely fine but I noticed some wavy lines on screen as it was some kind of interference/noise:

I remembered I had same issue on some boards in the past and fault was due an electrolityc capacitor with increased ESR (the role of a capacitor is to block the DC filtering the AC ).So, with my ESR meter I went to test in-circuit the electrolytic capacitors and I came across a 470uF 16V one @C1 (the one that filters the +12V for the audio amplifier) with a high ESR :

bad_470uF16V@C1

You can see from ESR chart that a typical value for a 470Uf 16V electrolytic capacitor should be 0.2 Ohm while I measured 33 Ohm.So I desoldered and measured it out-of-circuit having confirm it was really bad (53 Ohm measured):

470uF16V@C1_out_or_circuit

With a good capacitor fitted no more wavy lines and finally I could enjoy this cool shoot ’em up on my Astro City.

Jungle King repair log

PCB Repair Logs 1 Response »

Dec 082015

I bought this faulty original Jungle King PCB from a JAMMA+ forums user last year but I never had time to look at :

The game itself is a classic, I remember I was used to play it during my childhood in arcade rooms and on home computer.So, I decided to fix it once and for all.Time to build the needed JAMMA adapter (board use a separate connector for power) and I got this scenario on first boot:

All the sprites were intact but background graphics were all messed up.The RAM test reported no problem :

But, since all the RAMs on CPU and VIDEO board were already socketed, I want to test the chips out of circuit anyway and I found a bad 2016 @IC56 on CPU board:

With a good RAM fitted, the graphics were perfect now but the background music was absent, I could hear only the sound FXs.After some research I found that the CPU board was missing a ROM @IC52:

This ROM is, indeed, responsible of the music and only few games on same Taito SJ hardware have it so probably my board was a conversion from another game which didn’t use it (Elevator Action seem to be the common donor board).Anyway, antoher great classic preserved!

Wardner repair log

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Dec 062015

I got this Wardner PCB for a repair from my friend Zoran:

Gameplay was fine except for some minor sprites glitch in form of some sparkling dots:

Studying a bit the hardware, I could figure out where the sprites circuitry lied:

The four EPROMs were dumped good, the six 2148 RAM were fine as well.But when I probe the three 74ALS169 with my BK550 logic comparator I got trouble on pin15 of the ones @B21 an C21:

I desoldered them but they tested fine in all my programmer.I replaced them anyway and this cleared the sprites issue.Job done.

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