VIC20 repair log

 Computer Repair Logs, Repair Logs  Comments Off on VIC20 repair log
Jan 072012
 

Got Stiggys other VIC20 the other day, it wont load anything via the serial port and just reports back “DEVICE NOT PRESENT”.
According to Ray Carlsen this can be caused by a dodgy 7406 IC and he wasn’t wrong.

I checked all the states of this chip with a logic probe and all seemed to be as it should be so I went through each gate with a logic pulser and checked for its output. The outputs on pins 4 and 6 were stuck.

Removed the chip and eventually found one on a C64c motherboard that was scrap.
Replaced and tested with a demo and a couple of games.

I also took this opportunity to try out the VIC20 JiffyDOS (PAL).
My original test with JiffyDOS on this failed, nothing would load up. Turns out there is an NTSC and a PAL version, the later being significantly harder to find but we got there in the end.

 Posted by at 5:18 pm

Jumping repair log #1

 PCB Repair Logs, Repair Logs  Comments Off on Jumping repair log #1
Jan 042012
 

Got this Rainbow Islands bootleg yesterday.
The game worked when I tested but was told about a dodgy ribbon connector before buying it so decided to take a look. Not sure what happened after that but the board refused to boot.
After finding a few stuck address lines I decided to check the program ROM’s. Found 3 that would not read properly so I replaced them.
In MAME it lists 2 of the program ROMs as being from the genuine Rainbow Islands set but these are double the size so needed to be split into 2 files and burned to 27512 EPROMs.

Probably worth mentioning that if you use the older 2005 ROMIdent program then the dumps from Jumping actually show up as 2 separate ROMs. Must have been like this at one time.
Booting up now gives me a screen of garbage

Every now and then I could make out a “SCREEN RAM ERROR” message. The screen RAM is located on the second board and suspected this is what happens when the ribbon connector got a bit wrong but couldnt get the game to boot again no matter what I did so I decided to socket the 68000 cpu and see what was going on, kinda wish I hadnt now as I got this

Accepting the error just kept flagging more “tied bits” errors. Turns out this was a red herring as these lines are controlled by a PAL20L8 chip and everything passes if this is removed. Wasted a little bit of time on this.

After taking a careful look at the connector it turns out the plastic housing that holds the ribbon cable in place was damaged and this allowed the ribbon cable to come away from the pins. I properly reseated the cable and tested, the board now fires up in all its crazy bootleg glory

The game plays pretty much like Rainbow Islands does but some of the sprites and names are different and I think the secret rooms don’t work too well.

This game has 3 PAL chips on it, unfortunately all are security locked and I am only able to read 1 of them (might be able to read the one on the video board but never tried).

 Posted by at 7:11 pm
Dec 292011
 

After a few different designs and trials I think I’ve finally settled on something I like.
I’ve pretty much got double sided boards sorted but making vias are a pain but it works and looks OK.
As you can see this is destined to be fitted in Stiggy’s machine. It still needs cut down to size but im happy with that.

Sorry, I wont be making these for other people so please don’t ask.

 Posted by at 4:46 pm
Dec 292011
 

This fancy litle thing arrived today.

It was still sealed so was a little bit of a shame to open it but whats the point in that really?
The box included a cartridge, a user port device and a serial port device

Since I love hardware I couldnt resist opening up the cartridge for a peek. Not sure what I expected to find, maybe something fancy and cool? Not likely.

I tried to open the user port device up but the screws have been deliberately sheared but there is a hole at the top where you can see in and it just looks like a load of the lower contacts are soldered together, terminals B – M according to the allpinouts.org.
One strange quirk about this adapter is it doesn’t fully fit into the user port due to the size of the case the edge connector is housed in, you have to kind of mash it in and hope for the best.

The serial port device is also the same but am unable to make out whats connected yet but its very easy to make your own up.
Running the cartridge brings up a nice keyboard test screen where you can press each key on the keyboard and it lights up the relevant key pressed

Pressing the RESTORE key moves on to the Joystick test

And finally onto the computer checks

I didnt have any of the adapter devices plugged in here but they do work, whether they prove anything or not in the event of a real failure remains to be seen.

The manual is pretty informative containing possible problems for each error very similar to the superb info Ray Carlsen has on his site.
There is also a load of order forms for different “Doctor” products for the C64

After a few seconds of google searching I found a ROM dump for this cartridge so it is entirely possible to make up a set of your own should you feel the need to.

 Posted by at 10:48 am

Mortal Kombat PAL dumps

 PAL Updates  Comments Off on Mortal Kombat PAL dumps
Dec 242011
 

Today I found a PLS153 and a couple of PAL16L8 IC’s on my old Mortal Kombat board.
I have added the original PLS153 dump and also reworked it to work with my GAL adapter, both are in the Downloads section.

The 2 PALs were protected so these were dumped with the Boardmaster.

If any of these IC’s are missing from the board, it will not boot at all.

The manual for MK states the following for the chips:
5346-40025-2 => PLD Address Decode
5346-40025-3 => PLD Video RAM Control
5346-40025-4 => PLD Local Control

These have all been tested

 Posted by at 5:30 pm