Nov 302017
 

Received this Japanese version of Liquid Kids for a repair  running on a different F2 hardware.

 

The game was playing fine but hadn’t any sounds.

Amplifier and preamps were good so I started to probe the sound circuit logic.

The Z80 sound cpu ram had some weak signals

After replacing it , the sound was restored.

Rastan repair log #5

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May 252017
 

The game had some missing background tiles

 

 

At first I thought it was a maskrom problem but once I checked all of them only to find they were good, I started to probe the ram responsible for the background.

A sram @IC31 had some weak data signals so I decided to change it and the guess was right because the game was fixed.

Return Of The Invaders repair log

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Feb 182017
 

Recently I got hold of this favourite game of mine after a long searching. Apparently it is not so common nowadays, so when I saw a sales thread of this pcb  in faulty conditions from an italian arcade forum I took immediately the opportunity and bought it.

The seller posted a video in which the sprites where wrong and the red and blue components were inverted (this latter problem was caused by wrong wiring of jamma adapter)

When the pcb arrived it was in very good conditions with all rams socketed in factory, therefore I immediately tested them out of circuit which unfortunately  were all good (so no easy repair 🙂 )

It had also an horrible hack on the sound amplifier, more on that later.

Therefore I started the troubleshooting without having any schematics and no similar hardware to look for.

Game had this main fault:

and even if it was not seen in the video of the seller, sometimes I got also the logo and some other images messed up

 

The sprite problem I was sure was caused by some wrong addressing of the sprite graphics, therefore I shorted some address line of the eproms on the video board to see which ones contained the sprite graphics and found the four responsible.

Addr 7 and 8 of the eproms 10 to 13 were fixed low. I traced back to a 74ls153@IC38  which had both outputs fixed .

Piggybacking it with a good one restored the sprites, therefore I proceeded with replacing it and fixed the sprite problem

The TTL was from Fairchild (not Fujitsu part!) and it was the oldest one on the pcb, dated 1979!

Now the logo problem, it was strange because sometimes it was shown right, sometimes bad.

After some hours of playing, the logo was not shown right anymore, therefore I asked David Haywood (Haze of Mame fame) where it was contained and it pointed me in the eproms A14 and A15 (different bitplanes which were combined to form the final pic). Both eproms had to be addressed in the same time.

Also he told me that the graphic was bank switched, therefore some logic had to select a particular part of the memory area to show the correct gfx.

I probed their address lines and found the upper one A12, was always fixed low. I forced it high during gameplay and the backdround got corrupted but when the title was shown , the logo was there clear.

So the logo was contained on the upped half of the eproms and the logic was not selecting the A12 bit high or low depending on the situation.

I traced back to the only Fujitsu ttl present on the board, a 74LS259@IC72,  8 bit addressable latch.

Before desoldering it, I tried to understand the datasheet of the part, which is not very common to see on arcade boards , and probes 3 select inputs which were oscillating and the enable line was pulsing everytime it changed from title logo to gameplay.

All his outputs were stuck low, and the HP logic comparator confirmed some outputs were at the wrong logic. Only few are used by the hardware, but I expect in later levels I could get other wrong graphics…

I desoldered it and tested out of circuit:

Turned out Fujitsu was again the source of problems!

I had a hard time to find a replacement, because as said the 74259 is very seldom used by arcade hardware.

At least I found one in the following junk pcbs I had: Rock and Rope boot, Equites and Dig Dug.

I took the one from the bootleg (it is always a pity to cannibalize an original board 🙂 ) and problem was fixed!

 

Since the pcb would go directly in my collection,  the last thing I wanted to fix, was the ugly hack they did by replacing the original amplifier with an LM380 (same used on 1978 space invaders….)

 

This thing worked but it was really ugly!

After spending one hour to clean the disaster with soldering irom and soldering wick, I installed back in place the 2x missing caps and I looked to find the original MB3731 amp among some of mine junk pcbs.

Besides being used on Taito hardware of the era, it was often used on Konami hardware from late 80s/early 90s.

I took it from a junk Main Events pcb and now it looks much better:

 

Liquid Kids repair log

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Oct 312016
 

This game had two problem:

  • Glitchy and noisy sounds
  • Blocky background images

liquidk2

 

Given the high unreliablity of Taito maskroms I immediately tested the ones marked in red which with no surprice some pins not connected internally

 

liquidk

 

C49-04 restored the glitchy sound and C49-02 fixed the blocky gfx.

Replacements to be used are 27c400 (4mbit eproms with maskroms pinout)

Game 100% fixed

liquidk3

The New Zealand Story bootleg repair log

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Apr 172016
 

Got this ugly bootleg for a repair.

TNZS2

 

Game had no sound and the jump button didn’t work.

First of all, this bootleg is known to have the picture upside down and I wonder why the bootleggers left the game in this state.

TNZS

 

Since I had no white noise from the amp I checked the circuit near it and found a capacitor with a leg desoldered. Unfortunately the hole was completely rusted and I had to run an ugly wire to another point on the pcb to restore the sound.

To do: find a thinner wire 🙂

 

TNZS3

 

For the “Jump” problem I traced back from pin 23 of the Jamma connector to input 2A of a 74LS257 multiplexer.

The jump button of the second player, was connected to input 2B of the same 74LS257.

So those buttons has the ouput 2Y of the 74LS257 in common, so to check if the TTL  was working correctly, I ran the input test with the second joystick and infact also the second player jump was not working. The output 2Y was oscillating but evidently not in a correct way.

sn74ls257_s

Given that the game has no first player and second player  playing at the same time, I opted with a simple but effective solution: I shorted 2A and 2Y togheter so that the first player button was connected directly to 2Y.

In this way when you press first player button you press also the second player one but for TNZS is not a big deal because you never play a co-op game 🙂

TNZS5

 

With this solution I could fix the game without bothering to replace the ttl chip