More Joust headaches

cwales

Well-known member
Joined
Mar 17, 2010
Messages
2,699
Reaction score
51
Location
Binghamton, New York
My Joust is cursed, I swear. I had problems with the power board, I sent it away to be rebuilt, it worked for a while then it died. I traced the issue to the connector that goes from the transformer to the power board. I just replaced that, it powered up great, My wife and I played a few games and I left it on. It ran for about an hour, now there's garbage on the screen, all power LEDS are on, the number LED thing on the board is dead.

I tested fuses, one was blown, the one right in the middle. So I tested power going to the power supply board, they were all really close or dead on. I replaced the fuse and tested power going off of the power board (RJ2) and everything is great besides the 12v. Both + and - are 13.67. I don't know if that's too high but it seems the game would boot anyhow, wouldn't it?

So.. any ideas? What should I test?

Thanks.
 
Have a meter? Check to see what voltages you are getting at the power connector of each board. If they are okay, then we'll try checking them at the IC...
 
I tested everything besides the sound board power... went to help a customer, came back 5 minutes later and it's all dead now. Guess I'll recheck the fuses and the power from the transformer.
 
So now I get no power out of the transformer. I tested the fuse on it and it's fine. Could the transformer actually have died? There is still power to the cab, I get normal readings off the utility jack in there.
 
So now I get no power out of the transformer. I tested the fuse on it and it's fine. Could the transformer actually have died? There is still power to the cab, I get normal readings off the utility jack in there.

Yes, it's possible, it's just not common. Look for another fuse leading into the transformer (this is often quite separate from the fuse block on the transformer outputs). This fuse might even be in-line somewhere.

If it's not a fuse, then it's certainly possible that the transformer went bad.

If you disconnect whatever is on the inputs and outputs of the transformer and measure each winding (use the schematic to figure out what pins go to what windings), you'll be able to easily see opens, but you may have trouble distinguishing between normal cases and shorts for some windings.
 
Hi. So today with a fresh perspective on things, I looked things over and saw why it was dead. I had taped the door switch open and the tape came loose :) Look, I was tired, it was hot in here and I wanted to go home. anyhow....

The picture is still the same and there is power to everything. The game just is not booting.

Any input?

Thanks.
 
Looks like your +5vdc to the cpu is bad. Test the +5vdc on 1J1 and see what you get. The connector 1P1 is suspect, and probably has a bad socket pin.
 
It looks like the cable from the ROM board to the CPU may need to be recrimped. You have a partial rug test in that pic. Try gently wiggling the ROM cable and see if there are any changes.

ken
 
Pick one of the RAM chips and carefully measure the voltages at the corners. The voltages should be
Pin 1 = -5V,
Pin 8 = +12V
Pin 9 = +5V
Pin 16 = Ground
The pins are numbered starting in the upper left corner, going counter clockwise.

This will at least tell if you are getting the correct voltages to the components on the MPU board.

If you are not, check the power input header. It is not uncommon to have cracks or cold solder joints reduce the voltages from the connectors which measure correctly.

The only other thing I have seen like that involved a dead CPU chip.

Don't you love brain surgery by email? :)

ken
 
This is what I'm getting, I tried it on 4 chips and it's exactly the same:

Pin 1 = -7.08V,
Pin 8 = +9.88V
Pin 9 = +4.85V
 
If you are not, check the power input header. It is not uncommon to have cracks or cold solder joints reduce the voltages from the connectors which measure correctly.

So you mean the power input on which board? Like from the transformer? or into the CPU board?

Don't you love brain surgery by email? :)

I don't LIKE it but I'm very grateful for it. I'd rather just be able to stick a chip in my neck and understand this stuff instantly :)
 
Last edited:
So you mean the power input on which board? Like from the transformer? or into the CPU board?

The power input pins on the MPU board.

The low +12V is probably the culprit for the odd video colors. When the voltage in the video circuit goes below 10V the colors seem to get scrambled.

The +5V is getting down to the point where things are going to be a little flakey as well.

I have no idea why the -5V is actually higher than it should be :confused:

ken
 
I will show my ignorance again: I guess I don't know which board is the MPU board. Maybe what I'm calling a CPU board is it? Which board has 1J1 on it? :)

Testing the power on the CPU board again at 1J1 I found something odd, testing on the connector it's self I get these readings:

pin 5 +12 = 12.04
pin 7 +5 = 4.99
pin 8 +12 = 11.39
pin 9 -5 = -4.99

If I slide the connector out a hair and test on the pins I get these readings:

pin 5 +12 = 11.9
pin 7 +5 = 4.87
pin 8 +12 = 9.74
pin 9 -5 = -5.02

Is this an indication that something is amiss in the pins on that board then?
 
Last edited:
I will show my ignorance again: I guess I don't know which board is the MPU board. Maybe what I'm calling a CPU board is it? Which board has 1J1 on it? :)

Testing the power on the CPU board again at 1J1 I found something odd, testing on the connector it's self I get these readings:

pin 5 +12 = 12.04
pin 7 +5 = 4.99
pin 8 +12 = 11.39
pin 9 -5 = -4.99

If I slide the connector out a hair and test on the pins I get these readings:

pin 5 +12 = 11.9
pin 7 +5 = 4.87
pin 8 +12 = 9.74
pin 9 -5 = -5.02

Is this an indication that something is amiss in the pins on that board then?

- an decrease in voltage (pins 5,7,8,12) means that each socket (wire) has reached a dirtier bit of the mating pin
- an increase in voltage (pin 9) means that each socket (wire) has reached a cleaner bit of the mating pin

a dirty pin means more resistance between the individual socket and pin which means a voltage drop across the resistance. it also means that the pin/socket joint will heat up more

i would clean all the header pins with one of those scotch/brillo bads (the green ones) then spray with a contact cleaner. -

also pop out each socket in the connector plug and clean the contacting portions as well. while they are out, check them for tightness of fit to the pin as well - nip them closed a little for a tighter fit and retest. reasse=mble and test voltages again!

remember, at 4.75 volts and below 74xxx series TTL chips used in these games are no longer guaranteed to behave predictably as per the component specifications.

clean shiny & tight connections = lower resistance and less problems!

incidentally, these voltages

pin 5 +12 = 11.9
pin 7 +5 = 4.87
pin 8 +12 = 9.74
pin 9 -5 = -5.02
are still within specification AT THE PIN HEADER. you should also check the voltages at the power supply pins on the RAM chips and see if they are still within specification there.
also check voltages at the ROM board connectors/ICs, widget board connectors and the sound board connectors
 
I should get some new soldering equipment in the mail today so I am going to wait for that and pull that board this afternoon, check all the solder, clean the pins really well and we'll see how it goes.
 
Back
Top Bottom