This is a quick double repair log of Liquid Kids, a cute platform game release by Taito in 1990 on “F2 System” hardware.

The first PCB:

It played fine but sprites were blocky:

This Taito board like many other uses 4Mbit MASK ROMs to store GFX data, they are well known to be prone to failure.When I went to read the one @IC54 containing sprites data my programmer complained about pin 32:

The device was internally damaged and its dump was bad so I replaced it with a pin to pin compatible 27C400 EPROM, this fixed the issue and board completely.

The second PCB:

It was dead giving just a black screen on power up.Probing the main 68000 CPU revealed the /RESET and /HALT lines were both asserted all the time.The /RESET signal (and /HALT which is derivated from the first) is generated by the usual circuit made of a voltage monitor (in this case an MB3771) and some external components but it’s not directly tied to 68000 but it goes to the custom IC marked ‘TC0220IOC’  (which handles I/O too) which outputs it on its pin 8 :

Lifting this pin confirmed the custom was generating a stuck /RESET signal.Since by-passing the IC is not possible (device is addressable by main CPU) the only choice was replacing it, this is for sure another part very prone to failure, I can say from my experience that when a board that uses it is not booting then this custom is most likely bad :

This was right also in this repair.Job done.

Got a Dark Seal PCB in a lot of faulty boards recently acquired.For the uninitiated Dark Seal (also known as Gate of Doom in USA) is an action game with isometric perspective and R.P.G. elements released by Data East in 1990.

My board did nothing upon boot giving a solid black screen.Applying pressure on one of the custom ’55’ (the one in the upper right corner) restored the video output, a closer inspection revealed some lifted pins so I did a reflow.I got stable video output now and could play the game but image was rolling, this was a clear sign that SYNC signal was missing :

There are no documentation available but other Data East games share same design.Desert Assaul for example, here’s a snippet from its schematics :

As you can see SYNC signal is generated by pin 157 of the custom ’55’ and then inverted two times by a 74LS04 before reaching the JAMMA edge.I could measure a good signal on this pin :

but nothing on pin 13 solder side of JAMMA connector  :

So the problem was in the middle.Looking at solder side of board I noticed the area of the 74LS04 that inverts the SYNC signal has been badly reworked in order to socket the TTL itself, some rivets were ripped off:

Signal was present on pin 1 of the 74LS04 and correclty inverted on pin 2 but, following the scheme of Desert Assault, it was absent on the adjacent pin 3  (pin 4 is connected to JAMMA SYNC pin via a 47Ohm resistor) so the trace between pin 2 and 3 of the inverter had been severed by the previous attempt repair.I simply bridged these two pins restoring the SYNC on JAMMA.But, once I got a stable image, I  noticed the blue color was very strong and after some time it disappeared causing a yellowish screen:

Color generation circuit is pretty the same of Desert Assault:

As you can see bits of the tree colors from the 8-bit latches are converted to analog by a resistor ladder and, lastly, each color is amplified by an NPN transistor.Signal was absent on the emitter and base of transistor so problem was upstream.Going back I found nothing abnormal until I got to the palette RAMs, three 2018 :

The one highlighted in the above picture was burning hot to the touch, with a termocouple I could measure an external temperature of 69°C  compared to 48°C of the other two (RAMs in palette circuitry run usually warmer than other since they have greater power dissipation due very fast access time, 35ns on these ones)

Analyzing the suspicious RAM with a scope revealed all data lines were stuck low (healtly signal on left, bad on right of the below picture)

Once removed, the chip failed the out-of-circuit test:

Fitting a good RAM fixed board completely.

 

I received some days ago an Ordyne PCB for repair.Game runs on a powerful system called “Namco System 2” made of a CPU board:

and a VIDEO board:

Here are some specs:

• Main CPU: Motorola 68000 @ 12.288 MHz (16/32-bit instructions @ 2.1504 MIPS )
• Sub-CPU: Motorola 68000 @ 12.288 MHz (16/32-bit instructions @ 2.1504 MIPS)
• Sound CPU: Motorola M6809 @ 2.048 MHz (8-bit instructions @ 0.86016 MIPS)
• MCU:
  • Hitachi HD63705 @ 2.048 MHz (8-bit instructions @ 2.048 MIPS)
  • Namco C68 (Mitsubishi M37450) @ 8.192 MHz (8-bit instructions @ 1.024 MIPS)

My board was faulty since it was sitting after performing the SELF-TEST without reporting any error  :

First of all I swapped a good motherboard but this didn’t lead to any improvement so the fault was located on VIDEO board.At a closer inspection I found some scratches on solderside of this board:

One trace was really severed, it was the one connected to pin 9 of the KEY custom ‘176’.Problem was caused due the board has been crushed under some weight hence solder sides of the two boards were touching and scratching each other:

After patched the trace, the board successfully entered in game but I could not coin up.I quickly pinpointed this fault to a missing ‘CUS95’ resistor array @1K near the JAMMA edge:

No further issues were found so board 100% fixed.