16bit ROMs byte swapped

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Apr 132011
 

Just a note to anyone attempting to burn ROMs that are available online.
This mainly concerns the ROMs for 16bit systems such as the Amiga, Atari ST, Megadrive etc.
The ROMs available for use with emulators, like the Kickstart ROMs for use in WinUAE, have all been byteswapped. If you are going to burn these into an EPROM then they needs to be byteswapped. This can be done using many different tools. I use my own drag and drop program to do this quickly but I know Hex Workshop (and probably most other hex editors) can do this too.

CAPCOM Commando repair log #2

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Apr 102011
 

Got sent a Commando board for repair a while back and have finally got around to giving it a test.
I spent a little time going over the board doing the visual inspection prior to booting up. On the bottom board a 74LS245 had been removed and was just sitting in the board loose but most of the traces going to the IC had also been lifted, I suspect during a bodged removal.

image

I refitted the IC (after testing it), cut the lifted tracks off the board and ran some kynar to the relevant points.

After spending a bit of time making another adapter up to run the game I saw the graphics fault.
All the sprites were barely visible and sometimes were gone completely.
There was also some corruption on one of the screens.


The manual for this game is online and in the back of this are the schematics for the game. Nice. Also, as its CAPCOM, the schematics are nicely split and labelled up in sections.
After seeing the fault I was convinced that RAM was to blame. I scoped a section of 4 x 2114 RAM chips on the lower board. All had good looking address lines but the data lines looked very odd like they were struggling to drive the lines low. I interrupted a couple of pins and graphics started to come back so I pulled it and testing it, FAIL. One replacing the RAM only half the sprites came back with jail-bars running through them. I ended up pulling 3 in total which was quite lucky as I ran out of RAM replacements.
All graphics are now returned to normal.

As for the corruption on the screen. Thanks to MAME I was able to determine this to be an unused part of the screen that my RGB to VGA converter decided to throw in there to confuse me. In a cabinet the screen would be adjusted to remove these borders.

More random finds

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Mar 262011
 

Nothing much to write about recently so I’ll share some more blasts from the past found by my mate in his bindle of retro goodness.
First up, the Iomega Ditto


Between 250MB – 10GB of storage, depending on which tape you bought. It used the parallel port to send/receive data with speeds of up to 1MB/sec
Pretty amazing stuff at the time. I used to have the Iomega Zip drive which was 100meg discs. At the time my HDD was 120meg so it was pretty useful.

Next up, the Elsa 3D wireless shutter glasses

I know absolutely nothing about these things. Never seen them before and will probably never get a chance to try them out as they require a CRT monitor. Probably something similar to those dodgy 3D glasses they brought out for the Master System though. Bring on the headaches!

 Posted by at 2:26 pm

SEGA Master System repair log #1

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Mar 212011
 

Got a couple of Master Systems for repair.
This one was completely dead on power up.
First thing to check with a dead unit is voltages. The master system has a voltage regulator which in this case was fine. Second thing to check is the clock signal. The Z80 has its clock signal at pin 6. This was quiet. Traced it back to the large custom chip. Looking at the schematics the custom chip takes the clock signal from the crystal and then outputs a clock to the Z80. I checked pin 30 of the custom and this was also quiet.
On this model the crystal is located under a metal housing that is soldered underneath. I removed this cover and checked the output from the 54Mhz crystal. Nothing. Replaced this and the unit boots again.

Double Dragon repair log #4

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Mar 122011
 

The sound circuits on these DD boards really were bad!
Another one with dodgy sound, music was intermittent and half the SFX were really really low.
Did a full capacitor replace on this board for the sound, half the caps had started to leak. This brought back the music.
The sound effects were a little confusing. Like the last board I could see the data going into the M5205 chips but on IC80 there was nothing coming out of pin 10. I replaced the chip but this time there was no change. The board has had the op amps replaced at some point and there was a little rework done on them. Pin 5 (input) of the op amp at IC97 was shorted to pins 6 and 7 (output) effectively bypassing the op amp altogether, this explained why the sound was really low. Removing the short fixed the sound.
Another one destined for eBay.

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