JAMMArcade.net – Page 31

TumblePop repair log #2

Oct 292018

Got another Tumble Pop for a repair, this time with the background totally messed up

The background is stored in one 4Mbit maskrom silkscreened MAP-02

Probing the chip revealed all the data lines were floating.

Decided to desolder it and read it as 27c400. Strangely the programmer didn’t complain about missing continuity on some pins as normally happens

with these maskroms but the read gave only 1F and 00

I put a socket and since I didn’t have a spare 27c400, I programmed a 27c160 (16mbit eprom) and installed it with pin 1 and 42 out of the socket.

In this way the pinouyt exactly matches the 27c400.

With the eprom in place the game was fixed 100%

64th Street – A Detective Story repair log #1

PCB Repair Logs, Repair Logs Comments Off

Oct 292018

This PCB from my collection had a subtle problem after some minutes of being turned on and with voltages more than 5.1V

Some lines of the sprites started to be shifted toward the left

If I lowered the voltage to exactly 5V the sprites were good.

Being a perfectionist I started to find the culprint and eventually I found the circuit involved in the problem.

If I put the oscilloscope tip on pin 2 of 74LS365@IC55, the problem got worse, more lines were shifted to the left.

The chip was good so I changed also all the components which were in the chain, a 74LS245@IC56 and a couple of rams @IC57 and IC58

It must be said that all these components had healthy a good looking signals on the oscilloscope and they were tested good out of circuit but I decided nevertheless to change them with other brands to rule out every possibility

Still same issues after some minutes powered on

At this time I really thought it was either the sprite maskrom or the custom chip which was the source signal of pin 2 of 74ls365 until I noticed that the same signal was also connected to pin8 74LS273@IC94 which was pretty far from the other chips in the chain.

I decided to make a piggyback with a good chip and the problem desappeared completely at all voltages.

I changed it without further checking and still the problem was there!

With the tip of the oscilloscope I touched pin 8 and the problem disappeared immediately.

The oscilloscope probe has some capacitance which delayed somewhat the signal and fixed the problem.

So I installed a ceramic cap between GND and pin 8 and the problem was 100%

I think that this board had always a timing issue that no one addressed and preferred to run it with exactly 5V

Pacland repair log #2

PCB Repair Logs, Repair Logs Comments Off

Oct 282018

Received a pacland board for a repair which was stuck with a 0 2 0 error at boot.

Normally the middle digit means it’s an program rom error and infact the second prg rom @8D had no sticker and I immediately checked it.

Romident showed it was a Pacland midway rom, but the other prg roms belonged to the japanes new version.

After burning the correct 2nd rom from the jap set I was welcomed with this screen which is the service one.

The dipswitches were all set OFF and after verifying they were working correctly I decided to change all the FUJITSU 74LS257 near them which had dead outputs infact.

In the end all the Fujistsu chips has been changed because faulty: @1L, 2L and 2J!

With good ones changed the game finally booted but the palette was very tinted and the sprites were corrupted:

Verifying the sprites roms 8,9,10 and 11 these were a mess of different revisions, so using a broken pacland I put the matching roms from the new japanese set

Still the sprites were corrupted and eventually I found a bad 74ls86 ( again Fujitsu) @10F

With good one installed I got finally good sprites but still the palette was tinted:

I proceeded on the colour prom section and found that the chip PL1-2 had some outputs dead

Using one from another Pacland board fixed the game 100%

Decrypted SEGA files removed!

General Comments Off

Oct 272018

Due to certain things that have been going on elsewhere on the internet I have made the decision to remove the SEGA ROM’s from this site.
I have not personally been asked to take these down but given what I’ve seen happen recently involving SEGA ROM’s and previously with Nintendo too I thought I would play it safe and remove these files.

Sorry for any inconvenience

Bucky O’ Hare repair log #4

PCB Repair Logs Comments Off

Oct 212018

Received from Greece this Bucky O’ Hare PCB :

Owner told me the PCB developed some sound issue so he wanted the ‘054986A’ audio module replaced with a repro of mine.This is what I did but it didn’t cure the problem, the sound samples were corrupted and some of them missing too :

The MASK ROMs test reported two bad devices @A6 and B6:

They are the 16Mbit MASK ROMs that stores PCM samples:

This wass unlikely but possible so I removed and read them resulting in good dumps.At this point there was nothing else to check, the PCM samples data are processed by the near custom ASIC marked ‘054539’ which was most likely faulty.I prepared the board and desoldered the chip with hot air :

Then cleaned the area and soldered the spare taken from a donor board:

Sound was back clear and complete again.End of repair.

Older Entries Newer Entries