Repair Logs – Page 53 – JAMMArcade.net

Demon’s World/Horror Story repair log

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Jan 282017

Got this Demon’s World PCB (also known as Horror Story in Japan but game is multi-regional since it can be configured for different regions via the DIP switches) for a repair :

Board was not working, upon boot it showed the typical black/white stripes (common to all Toaplan boards) sign that main 68000 CPU has properly been initialized but then sat on a black static screen :

As said the CPU was properly running on power up but then halted before entering in game, data/address busses were both silent, usally this happens when CPU can’t find addressable devices.So I went to piggyback RAMs on board.When I did it on four 62256 @18F, 19F, 21F, 23F :

I got this error:

I removed the four chips, most of times they resulted good when tested out-of-circuit but sometimes they randomly failed due probably weak cells.Infact when I installed new RAMs I was greeted by this screen:

Board perfectly working, no further issue found.Another repair log archived.

Commodore 64 ‘breadbin’ repair log #7 – bad characters part #2

Jan 262017

This is part two of my C64 repair which documents the replacement of the bad character generator rom using a standard 27c64 EPROM. My local electronics hobby store did not have anything else on hand; I was hoping for a 27c32 because that’s what most folks on the internet seem to be using to get this repair done. I didn’t want to wait, so I settled on the 27c64.

The first step was downloading a c64 character rom ( 901225-01 ) with a checksum of $F7F8 from the internet. There are plenty of sources for these.

After downloading the 4kb binary I ran the following command under Windows to fill up the entire 8kb of address space of the 27c64 ( upper and lower 4kb have the same data ). I couldn’t quite remember which half I needed to burn the contents to so this was a quick and fail safe solution.

copy /b 901225-01.bin+901225-01.bin 901225-01-doubled.bin

I take the 8kb binary ( 901225-01-doubled.bin ) and burn the image to my 27c64 EPROM.

I bend the following pins outward on the 27c64 and cover the window with a sticker once the data is written.

1,2,20,23,27 & 28 ( bent out ).

I made an adapter using a machined pin socket. This is the diagram I used to re-wire the chip which I found on this German site.

https://forum.classic-computing.de/index.php?page=Thread&threadID=4694

2532 pin 18 -> 27c64 pin 23 ( A11 )

2532 pin 21 -> is not connected ( VPP )

27c64 pin 20 -> 27c64 pin 22 ( /CE & /OE tied )

27c64 pin 1,2,26,27 & 28 ( VPP,A12,NC,/PGM & VCC all tied ).

Once I finished wiring it was time to double check my work. I then select a 2532 device on Max Loader, load the original downloaded character generator rom into the buffer; this has a checksum of F7F8 which will be used for verification purposes.

With the wiring complete I’m now ready to verify it’s contents. I will read the device as a 2532 EPROM and if all goes well it should report a checksum of F7F8

With the re-worked EPROM inserted into the ChipMax I hit verify. F7F8 was what I was after.

With that result I was so confident it was going to work that I trimmed the protruding pins and inserted the device into the C64 to produce the results I expected.

Vapor Trail – Hyper Offence Formation repair log #1

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Jan 192017

Sometimes it’s just matter of capacitors…We could call this repair log in this way, let’s read why.

I bought this not working Vapor Trail – Hyper Offence Formation PCB on Ebay:

The board gave a static blank screen on power up:

Like other Data East games, hardware uses as main CPU a custom 68000 marked ’59’ :

Here you can see its pinout figured out by Porchy some time ago:

Data East ’59’ 68000 CPU Info

Probing it revealed static address/data bus, clock was present instead.Since it was not included in the above pinout I spent some time to figure out that pin 59 was the /RESET one.Probing it I found that on power up there was no transition from LOW to HIGH but pin went directly to HIGH state hence CPU didn’t get initialized.RESET circuit is a typical one made of the PST518 voltage monitor IC, a 47uF 50V electrolytic capacitor and a couple of resistors :

Checking in-circuit the ESR of this 47uF 50V capacitor @IC56 gave no reading, value was out of the 100Ohm range of my meter:

I removed it and out-of-circuit testing confirmed this capacitor was bad:

Replacing it restored a proper RESET signal so board successfully booted:

But sound was quiet despite adjusting the potentiometer and some interferences were present on screen too:

I went to measure the impedance of the electrolytic capacitors in analog sound circuit and I found many of them with out-of-specs value:

I replaced them all :

This restored a loud and a clear sound.As said in the beginning, it was only matter of capacitors!

Wild West C.O.W. Boys of Moo Mesa repair log #1

PCB Repair Logs 2 Responses »

Jan 092017

Received this Wild West C.O.W. Boys of Moo Mesa PCB for repair:

PCB was very dirty with flux residual and rust so I first washed it.After dried I powered it up and was greeted by this screen:

The initial self-test reported a bad ROM @T5 and a bad RAM @J4, obviously the board didn’t boot up but kept resetting.Usually Konami testing routines are very reliable so I went to dump the four program ROMs and actually the one @T5 showed at offset 0x3FFB4 a difference of only one byte (well, one nibble..) compared to the MAME dump:

I reprogrammed the EPROM (a 27C020) and error was cleared but obviously the one regarding the RAM @J4 was still present:

RAM @J4 was one of the three RGB 2K x 8-bit palette RAMs :

Piggybacking it had not effect so, before removing the chip in order to test it out-of-circuit, I checked its connections with a multimeter.All was fine until I could measure a short between pin 21 (/WE) of the RAM and VCC :

This explained why the RAM was reported as bad as it was never be written (write enable signal is active low).The /WE signals of the other two RAMs are generated by the near ‘054338’ custom :

so I went to inspect it with a digital microscope and found two bridged pins:

I removed the bridge and board successfully booted but sound was totally missing:

This is a common issue on these Konami board that use the ‘infamous’ hybrid audio module.This board has the ‘054986A’ one :

Usually you can fix this issue by replacing the capacitors but I opted for a drastic solution removing the module and installing two rounded machine-tooled strips with 1.778mm of pitch:

Lastly I used one of my ready module:

Job done.

Namco System 1 CPU board repair log #2

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Jan 072017

Another Namco System 1 CPU board on the bench after the past one :

Board (coupled with a good ROM board) gave only a black screen with some green lines, watchdog was active :

I checked the three colors outputs and only the green was active, the other two were dead:

We saw in the past repair that there are three 6264 static RAMs, each one for a color, they are addressed by the custom ‘C120’ and data are processed by the custom ‘C116’ which generates the different shades (then formed into a single color and converted to analog signals from some resistor arrays)

Probing the RAMs revealed stuck signals on data pins of the ones @B2 (RED related) and E2 (BLUE).I removed them :

But during desoldering I decided to remove also the GREEN one @D2.They all failed when tested out-of-circuit:

But also with good RAMs I got no improvement, watchdog was no longer active but all three colors still dead.Probing the other RAMs on board, I found no data coming out the two 6264 @D6 and E6 despite address lines were active:

When tested both out-of-circuit actually only the one @E6 failed:

Finally the board booted but with missing sprites and music (ony FXs were present).Here’s a video using a World Stadium ’89 ROM board:

I noticed that if I piggybacked the 6264 RAM @L3 ( used by the custom ’30’ which controls the sound), the rustling sound I had instead of the music disappeared:

So I removed the RAM and it failed the test:

This restored full sound.Now the sprites issue.I noticed that, when using this CPU board with a Galaga88 ROM board, the sprites (that were competely missing when using the World Stadium ’89 one) were visible but garbled and blocky:

The two customs related to objects (the sprites address generator ’48’ and the sprites generator ’39’ ) were good but probing the two 74LS377 @A3 and A4 revealed stuck outputs:

I promptly removed them and they both failed when tested out-of-circuit:

Replacing them restored the sprites and fixed completely the board.Five RAMs and two TTL replaced to achieve this, a nice booty…

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