Some of you remember last fall, a Joust was generously donated to my classroom.

A student has been working on it, and has managed to repair it.

Originally, the game would boot, but would have a lot of vertical garbage lines running through the screen.  You could play the game, but the moment any of the sprites passed through the vertical garbage lines, they would become distorted.  The game would play for about 30 seconds, then reboot.

So...we replaced (bypassed) the linear power supply, with a switching power supply, thinking the linear was somehow causing the problems.  Wrong.

We replaced the RAM with known working 4116 RAM from a spare Williams boardset.  Nothing different.

Finally, I noticed that the Video Decoder 4 ROM at 3G looked funny.  Here's a picture:



I replaced this with an original Video Decoder 4 ROM from the spare Williams boardset, and voila!  The game works properly again.

Now all we have to do is fix an intermittant problem with the sound board (could be a bad connector).

My student is pretty pumped to get it going!



Today, we did the lithium battery mod to the main board, and the machine now is keeping all the high-scores and programming data in memory properly.

We've decided to leave the linear power supply intact, and not bypass it with a switcher after all.  The linear power supply is bang-on with all the voltage outputs.

If you look closely, you can see this is a Robotron style cabinet, that was factory painted as a Joust.

Incredible!

I would like this kind of classroom to be set in a high school near my place! I think this would be really a good thing for childrens who don't like school!

Eric

great work.  i still have that magic worm that could use a little work.  can't wait till your summer starts.  
    tell your students they can always come over to the shop and work on extra credit.

I'm sorry where along the line did I miss the transition of magic worm back to your place Gory?   My hubby still misses it. With a little work on Jim, perhaps Scorpion could make it's way back too, though it has NOS plastics now!

Quoted from Bish

Finally, I noticed that the Video Decoder 4 ROM at 3G looked funny.

Actually, that hacked chip "should" work.

The original William Decoder prom is a 512 byte chip.  

The 2716 eprom used here is 2048 bytes.
By copying the Decoder image 4 times on the 2716,
and setting  the chip-enabled pin low (pin 18 tied to pin 12/grnd),
it "should" work.

The only problem I can think of is that the Decoder prom has a read-access speed of 50ms
whereas the eprom is 100ms.
If the eprom is older, the read-access speed slows down even more,
to the point where is affects the synching of the video.
(...that, or the data on your eprom was simply corrupted... ).

This type of hack became popular because of the near impossibility of finding
the correct replacement Prom.

Glad you found one...

Cheers,
Steph

Quoted from Steph

Actually, that hacked chip "should" work.

The original William Decoder prom is a 512 byte chip.  

The 2716 eprom used here is 2048 bytes.
By copying the Decoder image 4 times on the 2716,
and setting  the chip-enabled pin low (pin 18 tied to pin 12/grnd),
it "should" work.

The only problem I can think of is that the Decoder prom has a read-access speed of 50ms
whereas the eprom is 100ms.
If the eprom is older, the read-access speed slows down even more,
to the point where is affects the synching of the video.
(...that, or the data on your eprom was simply corrupted... ).

This type of hack became popular because of the near impossibility of finding
the correct replacement Prom.

Glad you found one...

Cheers,
Steph

WOW

It shows that you really know what you're talking about!!!

I'm proud to me a member of tihs forum, there's a bunch of people here that know a lot about electronics...not only pinball and video, but everything in regards to electronics!!

Eric

Quoted from Steph

The 2716 eprom used here is 2048 bytes.
By copying the Decoder image 4 times on the 2716,
and setting  the chip-enabled pin low (pin 18 tied to pin 12/grnd),
it "should" work.

I did read up on the decoder hack when I first found it, and as you said, it mentioned that the code would have to be repeated to fill all available space on the chip.  It didn't mention jumpering the chip like this, though.

This is the article I read:  http://www.geocities.com/rhombus2/decoder.html

I'm not sure what the problem was with it, but it really messed the system up, so I'm just as happy to replace it.

Thanks for your insight on this, though.  I appreciate finding out the answer of why this was done this way.  

Quoted from Rider

WOW

It shows that you really know what you're talking about!!!

I'm proud to me a member of tihs forum, there's a bunch of people here that know a lot about electronics...not only pinball and video, but everything in regards to electronics!!

Eric

When testing a 9V battery, lick both terminals to determine the charge left.
Light switches in my house function in both the on and the off position.
Rubbing your feet on the carpet in the winter magically produces electricity.
Hook the red to positive and black to negative when jumpstarting your vehicle.
When unsure if a circuit is live, touch both wires with a screwdriver before handling.


My .02 CAD

Today, we reflowed solder on the header pins of the audio board.  It was giving intermittant sound, and could be heard cutting in and out when we wiggled the speaker and volume control wiring.

We also put a ground wire to the main power switch, put in a new leaf switch for player 1 start, and fixed the wiring that used to go to the back door power-interlock switch (someone had removed the switch, and put the wires together with masking tape!!)

We've given the monitor a good cleaning, used Novus to scrub paint splatter off the marquee, and adjusted the player 1 joystick.

Monday, we're going to replace the power cord.