Robotron not booting

debaser138

Well-known member
Joined
Mar 1, 2009
Messages
1,029
Reaction score
64
Location
Grand Rapids, Michigan
I'm working on a Robotron that was running fine until about 2 weeks ago. It shows the initial rug pattern and then goes to a static screen of red horizontal lines. If you watch the ROM board, it displays 1 2 7 twice and then just repeats 1 3 1. I've tried swapping both of those RAM locations with other RAMs but it doesn't change anything. I also pulled out the CPU board and removed/reflowed the solder on the header pins for the three connections on the top of the board as a few of them were bad.

Measuring the voltage right at the 4116 RAM, I'm getting +4.96v, -5.07v and +11.94v. The machine currently has a Dell computer power supply in it and I can't adjust the +5. I'm going to replace that Dell power supply at some point as I'm not a fan of using computer power supplies. I also want to rewire it so I can easily swap in another switcher in the future.

I've ordered the 4164 RAM replacement kit which will be here by the weekend. Not sure if this will fix the problem but since the machine will be running 16 hours a day, it's good preventive maintenance regardless.

Any suggestions on what else I should look for? Thanks.
 
"Measuring the voltage right at the 4116 RAM, I'm getting +4.96v, -5.07v and +11.94v. "

voltages are fine at the ram - ttl needs 4.75 to 5.25 volts so right in the middle of the range, -5 and +12 nice as well.

"I've ordered the 4164 RAM replacement kit which will be here by the weekend. Not sure if this will fix the problem but since the machine will be running 16 hours a day, it's good preventive maintenance regardless. "

that'll fix any ram issues unless you have a problem with ram sockets at those locations - worth at least checking continuity between the offending ram ic legs and the pcb traces underneath - if you find any continuity issues or higher than expected resistance, clean ram legs and replace socket(s)

maybe also check/recrimp the rom board cable and check/reflow the cpu rom cable header too
 
Last edited:
You can usually tell if you need to recrimp the ROM cable if you can get different results by gently flexing the ribbon cable from the ROM board to the MPU board. If this does change things then here is a link that will show how to recompress the connectors: http://www.arcadesolution.com/ribbon.html

ken
 
Ok, I installed the 4164's and the power adapter and now the game is showing 1 2 5 on the ROM board. The screen shows the rug pattern and then quickly shows a screen of some horizontal lines and then resets and does the same thing over again. I checked each leg of the 4164 at that location to the solder side of the board and everything checks out. I also swapped another 4164 in that location with no change.

I also wired up the 15 pin power adapter to how it was originally and put in one of Bob's Williams switcher kits with adapter (the original linear supply has been removed) and the 4164's are getting a good +5.

One thing I noticed is that with the power connector on the CPU board hooked up, I'm getting 25 ohms between GND and VCC on the 4164's. If I unplug that connector on the CPU board, it doesn't ohm out.

The previous owner soldered in a capacitor looking type battery in place of the AA's. If that thing is having issues would it cause the CPU not to boot properly?

Any ideas on what else I should look at?
 
Ok, I installed the 4164's and the power adapter and now the game is showing 1 2 5 on the ROM board. The screen shows the rug pattern and then quickly shows a screen of some horizontal lines and then resets and does the same thing over again. I checked each leg of the 4164 at that location to the solder side of the board and everything checks out. I also swapped another 4164 in that location with no change.

Try gently flexing the ribbon cable from the ROM board to the MPU board while it is booting. Sometimes the IDC connectors will work themselves loose over the years and will cause address line issues.

Another good test would be to take a known working MPU board and swap it in. Some of the symptoms you are describing sound like some of the addressing chips are failing. Finding the right one(s) can be like playing cat and mouse with a logic probe.

I also wired up the 15 pin power adapter to how it was originally and put in one of Bob's Williams switcher kits with adapter (the original linear supply has been removed) and the 4164's are getting a good +5.

One thing I noticed is that with the power connector on the CPU board hooked up, I'm getting 25 ohms between GND and VCC on the 4164's. If I unplug that connector on the CPU board, it doesn't ohm out.

That sounds like the internal impedence in the switcher. Try just measuring the +5V to ground in the Switcher (when it is not turned on).

The previous owner soldered in a capacitor looking type battery in place of the AA's. If that thing is having issues would it cause the CPU not to boot properly?

Any ideas on what else I should look at?

That sounds like a computer style lithium battery. Measure the output voltage on the battery (with the power off). If it is less than 3V, you can take it out and do the button style lithium battery mod. Or just leave it off until you get the board running right.

ken
 
Try gently flexing the ribbon cable from the ROM board to the MPU board while it is booting. Sometimes the IDC connectors will work themselves loose over the years and will cause address line issues.

Did that but it didn't change anything.

Another good test would be to take a known working MPU board and swap it in. Some of the symptoms you are describing sound like some of the addressing chips are failing. Finding the right one(s) can be like playing cat and mouse with a logic probe.

I don't have another working board available but I just bought one to help diagnose and I should have it within a week. Doesn't hurt to have an extra board on hand anyways.

That sounds like a computer style lithium battery. Measure the output voltage on the battery (with the power off). If it is less than 3V, you can take it out and do the button style lithium battery mod. Or just leave it off until you get the board running right.

I'll take a look at that. Wasn't sure if a bad battery would cause the system not to boot properly or what.
 
Back
Top Bottom