Help with Williams Multigame - power problem?

tomservo

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Hi All,

Been away from the vids for a while, but getting back into them a little. About 10 years ago I had a small collection of 10-12, but ended up selling all but three to make room for pins and other hobbies. The 3 I kept are Mad Planets, Tempest, and a Sinistar cab with Clay's multi-williams kit on a set of Joust boards.

I think I put Clay's kit in about 7 -8 years ago and everything has been just fine until a few weeks ago. At the same time I installed the kit, I had also rebuilt the original wms PS with one of Bob Roberts kits.

A few weeks ago, I turned on the Williams Multigame and about 10 minutes later, the screen had turned all blue and had strange hash marks across it. Here is a pic:

https://picasaweb.google.com/lh/photo/yaCSOUPOGhGsfnHjeSPS0w?feat=directlink

If I turn the game off and right back on, it looks just the same. If I turn it off and turn the game back on say a day later, it comes up normally for about 10 minutes, then I get the same strange screen.

Here is what else happens when the screen goes out:
- The alpha LED blanks out. There is no error code when the game boots, it goes right to a "0". But when the screen goes blue with the hashes, the LED digit goes blank.
- Resetting the game menu by pressing P1 & P2 buttons together just blanks the screen for second while the buttons are pressed, but comes right back to the blue screen as pictured as soon as I let up on them.

Here's what I've done so far:
- Reseat all connectors & ribbon cable
- Replaced the 9-pin .156" power header on the main CPU board
- Just the basic "wiggle wires around" while watching the screen, checking for anything loose or any changes
- Took voltage readings on the PS and at the spot where the CPU expansion daughter card +5V and GND wires solder to the mainboard.

Voltage readings at PS TP1: 5.0V, TP3: 11.9
Voltage reading at CPU expansion card: 4.8V

Voltages do not change before & after the screen "blues out".

https://picasaweb.google.com/lh/photo/Id2BVYXBXmcIREbi1FivMw?feat=directlink

Any ideas what else to check? Does this seem like a power issue? I am comfortable using a DMM and soldering iron, and I'm not afraid to troubleshoot, I'm just not that familiar what to look for here. I do have the old RS logic probe, but I will have to try to remember how to use it again, been a while... :)

Thanks!
 
Check the voltages at the 4 corners of the RAM chips. They should be -5V, +12V, +5V and Ground. There are a bunch of things that can happen to the voltages before they hit the RAM chips, so just checking at the input is not always the best indicator.

You should also pull out the logic probe and check on pin 37 of the CPU. It should be solid high and go low for about 1 second when the reset switch is pressed. If it is pulsing, that means that the Watchdog is tripping and you potentially have some memory addressing issues.

One other common issue is the ROM cable. This gets a lot of abuse because everybody grabs the ribbon cable to put the cable connector out. That can pull the wires loose from the IDC blades. You can carefully pull the ROM cable out and recrimp it. The best way is to use a vise to gently squeeze the top back on.

ken
 
Thank you, I will try those suggestions and report back later on what I find.
 
Okay, voltages all good at the ram chips.

Pin 37 is pulsing away on the CPU, but haven't had a chance to go further than that. I take it I need to start checking the address decoders? Any pointers where to go from here?

Just to be be sure, it's been a while since I've used the logic probe, I need to have it set to TTL and not CMOS, correct? There is another switch for "normal" or "pulse". I just keep that switch on "normal"? It is just the simple $12 one that Radio Shack used to carry.

Thanks again!
 
UPDATE:

I removed the multigame kit and put the Joust roms back in to test, just in case the kit was throwing off the diagnostics.

Now as soon as I power up the game, I get the 1-3-1 error and a rug pattern. About every 30 seconds or so, the screen wipes, and the rug redraws. Does that mean anything to anyone?

I pulled the rom board & power supply board and reflowed the power header solder joints. I also recrimped the ribbon cable with a vise.

Voltage on all the rams is the same and not fluctuating. The +5V reads 4.78/9 on all the ram chips. Does this sound a tad low? I'm not sure how close to 5 it needs to be.

Without the multigame kit installed, now the CPU watchdog pin 37 is no longer pulsing, but staying a steady "hi". It drops to low for a second or 2 when I hit the reset.

It still comes up with the 1-3-1.

What to check from here?

Thanks!
 
I changed the ribbon cable out, still getting the 1-3-1 error. A rug pattern comes up, and redraws about every 30 secs.

The 74153 @ 3E does not ring out the same with the logic probe as the others at 3D, 4E and 4F. Based on my rudimentary schematic reading skills, it appears that all (4) 74153's should be ringing out the same.

I have some 74153's on order and should have them this week, so I will change out 3E first and see if that helps.
 
Fixed the error code 1-3-1 on my Robotron.

Replaced: IC1, IC2, C13, BR1 and C15

I replaced several items on the board: BR1 - Bridge Rectifier S5VB, C13 - capacitor 220 MFD 16VDC, C15 - capacitor 47 MFD 50 VCD and replaced both IC1 and IC2 - voltage regulator chips MC1723CP. When I got the game the bridge rectifier was connected by four 8 inch wires soldered to the board and the legs of the bridge rectifier. I removed the wires and soldered a new bridge rectifier back on the board.

This fixed my 1-3-1 error code. I think it was most likely the voltage regulator chips because that was the last items I replaced before the game started working again. The LED 2 was half as bright as the LED 1 and 3. After I replaced the chips LED 2 was as bright as LED 1 and 3, then the 1-3-1 error code went away and I had the correct reading of "0" zero on the display.
 

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