Repair Logs – Page 75 – JAMMArcade.net

Rainbow Islands repair log #10

Feb 252016

Another Rainbow Islands PCB to repair.

This one had issues with the sprites which were broken up and seemed to be repeating, looked very much like a stuck bit on the sprite addressing;

IMG_20160224_112137583

IMG_20160224_112142174

All tiles and background graphics were fine, so I knew it was something to do with the sprite circuit.

The first thing I did was to look at the area where the sprite data is read from the two eproms. The two 74LS244 buffers checked out fine, but one of the 74LS373 Octal Latches had an output pin stuck HI (pin 9);

IMG_20160224_112155598_HDR

So I desoldered it;

IMG_20160224_113645345

I confirmed the Octal Latch was bad in an IC Tester. So I soldered in a socket and replaced with a fresh Octal Latch;

IMG_20160224_114050662

PCB sprites now restored;

ri_pcb_2

ri_pcb_3

Atari Asteroids Deluxe repair log

PCB Repair Logs Comments Off

Feb 202016

Sometimes lightning does strike twice.

I was recently sent an Asteroids Deluxe PCB which was exhibiting corrupted vectors.

When I got the PCB, I put it on my test rig and was presented with the following in TEST mode;

IMG_20160215_160220667

GAME mode;

IMG_20160215_160158687

The symptoms were pretty much identical to the last Asteroids repair log I posted. Note however this is an Asteroids Deluxe, however it is pretty much identical hardware to Asteroids except that Asteroids Deluxe has a pure digital sound circuit via a Pokey chip (Asteroids is analogue and no Pokey).

I immediately probed the 74LS42 decoder at E6, which had two outputs stuck HI.

IMG_20160215_160124793

So I desoldered it;

IMG_20160215_161027015

Tested it in my IC tester;

IMG_20160215_181037047

Socketed and replaced it with a fresh decoder;

IMG_20160215_161344449

Fire her up again;

IMG_20160215_160348150

Now working, except that the PCB would sometimes crash or refuse to boot. I was able to determine that three of the six ROM sockets were worn. So I replaced all of them for reliability;

IMG_20160215_162641553

IMG_20160215_165025775

IMG_20160215_162807350

Now working 100%.

Poker Ladies repair log #1

PCB Repair Logs Comments Off

Feb 202016

I recently received some faulty Capcom pre-CPS PCBs.As most of you know, these board are well known to commit suicide.As you can read from the Dead Battey Society site, “the way suicide work is that the batteries on board supply power to a bit of RAM that holds a decryption table. This table is the key to decrypting the encrypted program stored in the board’s ROMs. When the battery dies, this table goes away and the program code can no longer be decrypted. The CPU no longer has valid code to execute. The board stops working”.

In particular Capcom pre-CPS boards all use a single 3.6V battery and a custom Z80 marked “Kabuki”.The Kabuki has the RAM with the decryption table built right into it.

My Poker Ladies PCB committed suicided and all I got was a static blue screen:

Poker_Ladies_suicided

After reviving it with the use of patched ROMs available from the Dead Battery Society site and doing some modification on PCB (thanks to Corrado for providing me info), the board successfully booted but showed sprites issue:

sprites_issues

EPROMs containing this part of graphics were reafd fine so my first suspicions were on the custom sprites generator marked “86S105” (84 pin PLCC package) which addresses the devices :

86S105_sprite_generator

I played the card of its replacement taking a spare from a shorted Block Block PCB:

86S105_removed

and I won since sprites were fully restored:

sprites_restored

Bubble Bobble (bootleg) repair log

PCB Repair Logs Comments Off

Feb 202016

I never had a Bubble Bobble PCB in my collection so recently I bought this bootleg board (original one is too expensive for my taste) called Super Bobble Bobble :

Bubble_Bobble_bootleg

When I powered it up, at first glance it seemed to play fine except for the lack of sound which I promptly fixed reseating and cleaning the sound CPU ROM.But playing some games I noticed that screen was yellowish :

color_issue

Shorting some data/address lines of various RAM I could identify the ones related to palette circuitry, two TMM2015 (6116 compatible)

palette_RAMs ha

Probing the lower one with a logic analyzer revealed that some address lines were stuck low:

TMM2015_DATA_bus

This lead me to remove and testing the chip out of circuit where it failed:

TMM2015_palette_failed

TMM2015_recplacing

With a good RAM chip correct colors were restored:

correct_colors

End of job.

Pac-Man repair log #3

PCB Repair Logs, Repair Logs 1 Response »

Feb 162016

Got the second board fixed up today.
This one had a lot more wrong with it and all caused by a previous repair attempt.
Visual inspection immediately revealed this.
20160207_133009

I confirmed these wires were going where they should be and neatened them up a bit.

As with the first board all I got was a blank screen with the board not playing blind. At this point I had my smaller custom replacements verified so could do away with stacking the TTL riser and could just plug the Fluke straight in.
ROM checks were all good but the RAM checks failed straight away.

With the previous repair still fresh in my mind I knew where to look. the 74LS245 at 4H. This had a turned pin socket fitted and a 74HC245 chip inserted. The HC variation means its CMOS logic levels and typically aren’t an ideal replacement for LS parts. If you are going to swap them out you can use the HCT variety which are TTL compatible.
I replace this chip with a 74LS245 but it did not fix my issue. Checking the outputs of the 245 to the RAM led me to suspect a poor desoldering job of the previous chip as several pins weren’t connected to the RAM. I desoldered the socket and found this mess.
20160207_133720

You can clearly see a the traces that have been ripped through. I patched these, fitted a new socket and continued my checks.
The Fluke now reported this.
20160215_203212

Knowing the chip was good and the connections to the RAM were good I focused my attention on the CPU side of this chip.
I knew my custom chips were good and I could correctly read the ROM’s so new the CPU socket was good. This didn’t leave me with many places left to look. I could almost certainly rule out some places as data bits 2 and 6 were across two different chips and the chances of both of the chips shorting together was a bit low. This left me with an 74LS273 at 4D and also to the dreaded crusty flux issue. Cleaning the flux cleared my short.
20160215_205328

Now the game would boot but I get this
20160215_205526
Only the score and credits were showing. If I started a game the lives were also showing at the bottom.

My attention immediately went to the 4 x 1bit RAM chips at 2A-2D and found there wasn’t a great deal of activity and some missing signals.
My heart sank right away as I could see turned pin sockets had also been fitted for all of these which most likely meant the same person had replaced them.
Sure enough there were several traces cut. I did remove one of the sockets just to see what I was up against.
20160216_193306
Some severed traces here and doing a continuity test revealed more and more. I also found one pin not soldered.
20160216_194329

A bit of time later after patching and verifying my work I fired it up and was all ready to feel pleased with myself on a job well done but the same fault was still present.
Confident the fault was still in the area I was already working I set back to work checking continuity and found the ‘Data In’ pin (pin 15) of a RAM at 2A was shorted to pin 1 of the RAM at 2B. Looking back at the picture I had taken I noticed a bit of stray solder bridging the trace that ran adjacent to pin 15 that I had missed earlier. I managed to remove it with a pin and a bit of patience.
After that the board fired right up and plays fine.
20160216_201142

20160216_201150

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