Repair Logs – Page 116 – JAMMArcade.net

The Lost Castle in Darkmist repair log

Apr 122012

Ive had this board for absolutely ages and originally never bothered trying to repair it as the game is rubbish(IMO).
Since then I forgot all about it until yesterday when I was having a clear out of old boards. So today I thought id have a go at fixing it up.

It had a few issues.
First, the graphics had jailbar lines through them
Second, the colour palette was wrong
Third, the pad at the edge connector for Speaker+ was completely missing

I removed the smaller sound board from the top and started looking into the jailbars.

Jailbars are quite often a sign of a dodgy ROM. These disappeared when I touched the back end of the board. I narrowed it down to a ROM marked “2”.

Simply pulling it and reseating fixed this problem.

On to the palette issue.

There are quite a few PROM’s on this board that are responsible for the colour tables, if one of these was gone I probably wouldn’t have bothered fixing it as they are becoming super rare and expensive. As it happens I traced the fault back to the two TMM2015 palette RAM chips.

The both looked fine on the scope so I had to pull the pair of them. Sure enough one was faulty. Replacing this fixed all the graphics problems.

There isn’t a great deal I can do about the missing pad at the edge connector. I’ve currently got a flying lead soldered onto my test rig connector.
I will probably end up soldering a 2×28 way connector onto the original edge, run a wire from the sound output to the new connector and fit one of those small finger boards.

The game is still rubbish though!

WWF Wrestlefest repair log #1

Mar 242012

Been after a genuine board of this for a bit now and this one came along. I thought it might be in full working order but once again eBay lets me down.
This one had jailbars through all the main sprites.

More often than not this is a bad ROM and this was ended up being just that.

In the corner of this board there is a bank of 8 MASKROMs that contain the graphics. Unfortunately none of these are in sockets and as I couldn’t really see anything hugely wrong on the scope.
This game doesn’t have a test mode nor does it carry out any RAM/ROM tests on start up so I wrote a little self test program myself in assembly that tested the sprite RAM at location 0x0c2000 – 0x0c3fff in the address map and simply would display a “P” for a pass or “F” for a fail.

This passed no problem so my hope is for one of the ROM’s to be dodgy as opposed to one of those custom chips.
I set about desoldering them one at a time and checking along the way. After the fourth one I found my problem with a bad ROM dump.

My dump is on the right and the MAME set dump is on the left. As you can see, bit 0 is stuck on.
I fitted a socket and reinstalled the ROM but with data line D0 lifted and checked it out with the scope.

On a closer inspection it shows that the logic level isnt dropping below 2v.
The MASKROMs are pin compatible with 27C080 EPROMs of which I have none. I have ordered some so will hopefully receive it early next week

EDIT: EPROM came today, the game is now fully working

Virtual Boy repair log #2

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Mar 112012

As with all VB’s and in my previous repair, one of the screens goes a little strange, in my case it was the left screen.
I initially used the oven fix method which worked well but only for a short amount of time.

I fired it up today and was greeted with the same left screen showing garbage.
Rather than use the oven trick again I decided it was time to try one of the more adventurous methods out there.
Turns out there is a nice video on YouTube of how to fix it using a soldering method.

Instead of dropping a load of solder onto it I used some liquid flux and a small amount of solder. You can see it working quite easily and no braid was needed to mop up the excess.

The whole thing only took a few minutes and worked perfectly when I put it back together.
Time will tell how long this lasts but I don’t see why it should cause issues again.

SEGA Master System repair log #2

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Mar 102012

Stiggy dropped round today for a cuppa and brought his sick Master System with him. I have 2 of the mark 1 MS units so we did a swap.
Basically this system was always seeing the UP direction pressed on port 1 even with no controller connected.
Looking at the schematics it would appear that the custom IC 315-5237 has an internal pull-up resistance on each pin and the controller grounds this to register a button press. As I found the pin giving out a permanent low signal chances are something has gone wrong internally.
What I did was fit a resistor between this pin and VCC which changes the default state to a logic HIGH but will still allow the controller to drive it LOW for the button press. Almost certainly not the ideal way of doing it but I don’t know the MS very well at all so this will have to do.
The system now works perfectly. This MS also has a couple of built in games which my old one didn’t.

Jumping repair log #2

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Mar 042012

As mentioned in a previous post, when I converted my Jumping board to Rainbow Islands I noticed that all the text in game was black. Going back through some pictures I took when I first got the board I see its present there too.

So where do I start?
I know from making my conversion that the palette values are stored in the program ROMs and they are pushed out to the palette RAM at address 200000.
I looked at the RAM with a scope and all seemed fine plus all the other colours seemed fine.
I also know that all the values required for this text colour is when the 2 least significant bits (A0 and A1) are active, so I traced these out down to the video board.

After a long session of following various signals I came across a 74LS374 chip.

This had all its inputs stuck low but according the the scope had a fair bit of noise on them, enough noise in fact to make my logic probe see it as pulsing HIGH/LOW. Following these inputs over to the chip next door I see a 74LS273 with its outputs giving off this crazy signal.
I replaced the 74273 and booted the game

If you look carefully you can see the lower part of the text is missing and a bit scrambled. Taking another look at that 74374 chip and its outputs are still crazy despite having good inputs. After a quick desolder and replacment I got this

All fixed and now my conversion is totally complete.
I have left one bit of graphics the same as the Jumping. If you play the game, in the lower left corner, you number of current lives is displayed as blue stars. On the original these are small rainbows. Just a note in case I ever release my modified files and someone tries to sell it as an original or something.

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