This game had two problem:
Given the high unreliablity of Taito maskroms I immediately tested the ones marked in red which with no surprice some pins not connected internally
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
Got this ugly bootleg for a repair.
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.
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 🙂
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 TTLÂ 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.
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 🙂
With this solution I could fix the game without bothering to replace the ttl chip
I bought this faulty pcb from ebay at a very cheap price.
The seller mentioned that it had a “service switch error” and didn’t boot.
When I received it I could confirm the behaviour:
Several Taito games from late 80s to early 90s use a custom chip marked TC0220IOC which handles the inputs.
Looking at Final Blow schematics, the pinout is well documented so I started to check service signal which infact was always low on pin 36 of the custom chip
Before desoldering the custom chip, I checked the continuity of the Taito network resistor RRC4 (on Fighting hawk pcb) and I noticed that it had a very low resistance (less than 1Kohm)Â to +5V in comparison to the other pins which had a 10kohm resistance.
So, for what it costed I proceeded to desolder the network resistor and see if the pcb booted.
The game did boot infact and it was a good sign, meaning that the problem didn’t come from the custom chip.
I found the same network resistance on a scrap taito pcb and the service switch was fixed but unfortunately the airplane was going up and left all the time and fired and thew bombs continuously.
After running the test mode, I noticed that all P1 and some P2 inputs were triggered!
To end the story short, I had to exchange ALL the network resistances except one to fix the game.
Looks like the game was connected reversed at one point and the network resistances probably protected the custom chip.
No further problems shown up
Got this game for a repair.
The pcb was missing one program rom and a graphic rom.
After checking which version was the game, I burned the correct eproms and I got this screen:
A ram was reported bad but I didn’t know which one.
There were 2x 6116 SRAMS and 6x DRAMS type 4464.
When the error message is shown, the game get stuck in a loop and continuously checks the status, therefore I discovered that shorting pins of the DRAM @9L and 9M changed the hexadecimal value of the error.
With a logic probe the signals were oscillating but I decided to desolder them and put some sockets and test other drams I had to see if the problem changed or better could be solved.
Please note that all the DRAMS I had were taken from dead boards and I had no way to test them out of circuit.
So I proceeded to place the sockets and installed some drams chip and I got always different bits until finally it passed the POST test!
Turned out that I had several defective DRAMS chips and I took the chance to use Super Qix as a DRAM tester 🙂
Below are a collection of defective DRAMS, as you can see they are all from different brands…
Back to Super Qix, , after changing the DRAMS, the game passed all the tests without further errors but I got this:
The game had still the gfx messed heavily even if the ram test was reported good.
I shorted two pins of DRAMS @6S and 6R and I could see some better picture beneath the mess, so I decided to change also those two drams
I started the game board without them in place and I got this:
It was a good sign but to be 100% sure there were faulty I placed them back on the sockets @9L and 9M and I got again the error on the post screen!
After placing two good drams I got this:
Decided to go straight to the next two drams @5P and 5M and replaced without any further thoughts and…..
Problem 100% fixed! Game had no further problems
So turned out that the game had all the 6 drams faulty but the game checks only 2 Drams out of 6x.
The other checks are done on the color sram and program sram.
Game booted and could be played but all the screen was full of garbage and flashing.
I found one of the two rams circled in red that was really hot. Data signals were weak so I decided the replace it.
I could now see some parts of the background, so I decided to replace also the other ram and the game this time was fully restored.
