JAMMArcade.net – Page 45

Prehistoric Isle in 1930 repair log

PCB Repair Logs Comments Off

Apr 292018

Received from Germany some faulty boards to repair.There was this Prehistoric Isle in 1930 PCB, an horizontal shoot ’em up game developed by SNK and released in 1989.

Game boots up but some foreground graphics had vertical lines through them:

Relevant GFX data are stored in a 2Mbit MASK ROM located on video board:

I dumped the device and it was good.The data of the MASK ROM are read by the near custom silkscreened ‘SNKCG’.A visual inspection in this area reveleaed some corrosion on a trace :

Trace was connected to pin 17 of the custom, it was silent when I put on it my logic probe so either it was a dead output or an input not receiving any signal

I was not able to find where this pin was connected to so the trace was really broken due corrosion.Looking at the other near pins, they were all connected to data lines of the MASK ROM, I found corrispondance for all of them except pin 26 (D6).I run a jumper wire and foreground graphics were restored:

Happy with result I was about to close this repair when, during testing, I noticed that voice samples were missing, I could hear only some crackling noise instead of them:

Looking at sound section on CPU board I quickly found the culprit:

The 640MHz ceramic resonator (which provides clock the uPD7759C speech synthesizer IC) was missing, this a common issue on all boards that use it, it’s very easy that it comes off

I took the spare from a dead Sega System 16B motherboard:

Repair finally completed.

HP 10529A reference card gerbers

Reproductions Comments Off

Apr 252018

Recently Bad_Ad84 had the need for more reference cards for his HP 10529A logic comparator so decided to make his own.
He kindly sent the gerbers to me to be hosted and they can be uploaded to the usual PCB fab places like OSHPark and DirtyPCB

ZIP file can be downloaded HERE
Massive thanks to Bad_Ad84 for these, I know ill be using them.

TumblePop repair log #1

Apr 242018

I got this game for a repair:

The game had some background problems ( unfortunately I forgot to take a pic ) and a sprite problem:

The background problem was fixed reflushing the custom chip 56.

As for the sprite problem, after some time checking the part of the circuit responsible for the sprites, I found a couple of 6116 sram @D5 and D6.

One of them had some weak signals on the data lines and tested out of circuit it was confirmed as bad

After replacing the sram the game was fixed

R-Type II (conversion on Major Title – Irem M82 hardware) repair log

PCB Repair Logs Comments Off

Apr 202018

I’ve been sent from Ireland this R-Type II PCB for repair, actually a conversion on Major Title (Irem M82 hardware)

Board played fine but sound was completely absent:

Here is an overview of the sound circuit:

Someone previoulsy tried to fix the lack of sound by replacing many components.The analog part of the circuit was doing his job as putting my fingers on solder side of the amp produced some noise.Probing the Z80 sound CPU revealed /INT line was stuck LOW.While testing components something strange happened, I got sound fully working :

The IC I was testing with a logic comparator is a 74LS244 @IC13 whose ouptuts are tied to the 8-bit data BUS of the Z80/RAM/ROM/YM2151.Signals didn’t look fine to me:

But when I put the clip of my logic comparator on the TTL they correctly toggled :

Data lines are tristate, this means they can be in high-impedance state (Hi-Z) in addition to the 0 and 1 logic levels.When outputs are tri-stated, their influence on the rest of the circuit is removed, and the circuit node will be “floating” if no other circuit element determines its state. Usually pull-up or pull-down resistors are used to influence the circuit when the output is tri-stated.This even more when a same line is shared among different devices like in my case.The 8-bit data BUS of the sound circuit is pulled-up by a 10K resistor array:

When I went to measure it I got high resistance on half of its pins :

I pushed the array a little and this happened :

It was actually cracked in a not visible way (this explains why the logic comparator fixed the issue, it acted like a pull-up).I replaced it:

This restored the sound, board 100% fixed

Konami ‘051550’ reproduction

Reproductions Comments Off

Apr 172018

Have you ever encountered the following scenario on your beloved arcade PCBs?

Probably sometimes.The cracked component is silkscreened ‘051550’, maybe now the name tells you something :

It’s a custom IC in SIL package that can be found on countless boards manufactured by Konami (from mid 80s to late 90s).Here’s the pinout taken from a TMNT schematics:

As you can see, it performs two functions :

master /RESET generation for the whole system and watchdog timer
coin counters handling

In the below scan of the “naked” component I have highlighted the part of circuit that handles the coin counters.The other part is the /RESET generation circuit which is built around a power supply monitor IC like the Fujitsu MB3773 :

You can read its datasheet here:

https://www.jammarcade.net/files/Datasheets/MB3773.pdf

In this project I took into account only the /RESET function since it’s the most important and vital, coin counters can be now considered obsolete hence I intentionally omitted the relevant circuit.Anyway, for my repro I wanted to keep the dimensions of the original part:

Here’s final testing on a Lethal Enforcers PCB:

See you all to my next reproduction project!

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