JAMMArcade.net – Page 235

Super Chase repair log

Mar 022012

So I saw this Taito board on eBay. The seller says its broken and unknown but was most likely a Super Chase and supplied a System 16/24 adapter with it, which in its self is very nicely made and they can cost quite a bit.

Only thing is, Super Chase is not a System 16 or 24 pinout.

*pinout supplied by Stefan Lindberg

I made a quick and dirty adapter up with and tested the board, dead.
Now I made a very stupid mistake at about this point. I moved the board down from the test bench and into one of my cabs just to rule out any voltage issues that ive seen before BUT for some unknown reason I left the pinout adapter in the test rig.

After the smoke dispersed I checked the damage.

Power supply is fried. Turns out, without the adapter I tied the +12v line to the +5v line and destroyed the PSU.
At this point I didn’t hold out much hope for the board anymore but tested it anyway.

The board was unsurprisingly still dead.

I check the RESET and HALT lines on the CPU, the watchdog was doing its thing.
Pulled and checked the program ROM’s and 2 didn’t match.
A strange thing here. One has only 1 byte difference right at the end and the other was clearly trashed with random read outs at every read.
I copied the first dump over to MAME and ran it. Turns out this is probably a different region to the one in MAME and that byte difference either displays the country warning screen or not. Mine does not.

I got nothing but a bit of garbage on screen

I fired up MAME and checked what the game should be doing and it does perform RAM checks. I also saw in the code that it has RAM fail messages on screen should it encounter a problem.
Probing around the board in this state didn’t help at all as the watchdog reset everything before I could really see what was going on.
After a quick look at the CPU code I see I can bypass the shared and screen RAM checks very by changing only 1 byte. I did this and replaced the relevant EPROM and watched the game boot

So the screen RAM is at fault. The screen RAMs are the 2 Sony 58257 chips in the center of the board.
I pulled both of these and both failed. Replaced them and the game boots once more.

A narrow escape I think. This will hopefully teach me to slow down a bit, but I doubt it

Taito Super Chase PALs

PAL Updates Comments Off

Mar 022012

Got a broken Super Chase board the other day.
All the PALs were unprotected and have been added. There are 10 in total!

SD2IEC boards

General 2 Responses »

Feb 272012

Myself and my mate StiGGy were wanting another SD2IEC device for a couple of reasons. The other one I have was made by SirMorris and is still going strong but didn’t want to bother him with making a couple more so I asked him if I could have his original schematics which he very kindly supplied.
The result is 4 shiny new boards straight from China. I originally ordered 2 but for some reason they always seem to double up my order but I’m not complaining.

Ive got most of the parts on order but Farnell don’t seem to have the SD slots available that aren’t on US stock order (and extra £15) so ill look else where for those.

Added the last Street Smart PAL

PAL Updates Comments Off

Feb 262012

Today, for no reason other than proving to myself I could, I manually reverse engineered a PAL22L10 from my Street Smart board.
The PAL at location D11 was the only one on this board that was security locked so until now I couldn’t copy it.
Using the ABI to test I went through each pin individually and derived equations.
After my first attempt I thought I actually had it sorted but…..

Altogether it took quite a few hours to do so will probably not do this too often but the option is there should I need to but finally the game booted up and all the outputs on my clone match the original.

Commodore 128 repair log #3

Computer Repair Logs, Repair Logs 1 Response »

Feb 252012

Motherboard clearly had a dodgy ON/OFF switch.
Removed it and replaced it with one from a C64.

On power up I had a blank screen.
Did a few quick checks with the scope and all data/address lines were pulsing properly.
Checked the voltages with a multimeter, the 5v was present but the 9VAC was not. Traced this right the way back to the switch I had fitted.
When I soldered the new switch in, one of the legs musnt have made a connection as they were a little shorter than the original. I resoldered the legs on top of the motherboard as well as the underside and it now boots up.

One of the CIA chips was missing, fitted a new one and C64 mode now works too.

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