Q*Bert acting up

ironmike

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Donor 2012
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Hi, everyone.

Just joined this forum to seek help with my dedicated Q*Bert upright.

It was working awhile back but now its on the fritz. I get the "I'm turned on" when I power it up but then the knocker goes haywire and knocks repeatedly. The screen is all garbage, no pyramid, no start screen, just random colors and patterns. After a few seconds of this the knocker stops and the screen goes blank.

Any ideas where to start troubleshooting?

Thanks in advance,
Mike.
 
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Check your power. It sounds like you might have power supply problems. Do you have a multimeter? I'd start with checking the +5.

Don't leave it on a long time with the problems you are having. Power supply failure on Qbert can lead to other problems.

You can search these forums for prior postings about similar problems. It can be very helpful.
 
Thanks, Jon

Hopefully, I can find time this week to run some voltage checks.

I'll report back with my results.

Mike.
 
First verify your voltages on the top two headers of the power supply. Next pull the filter board and check for cracked solder joints. Fix them and retest. If your still having problems its most likely a problem on the main board.
If you need your power supply rebuilt I can do it for you or provide the parts if you wanted to DIY.
 
To perform these voltage tests do I isolate the PS board from the PCB and sound board by removing the connectors? Or do I just leave everything connected?

Thanks,
Mike.
 
To perform these voltage tests do I isolate the PS board from the PCB and sound board by removing the connectors? Or do I just leave everything connected?

Thanks,
Mike.

If im testing a qbert I always unplug the top headers on the power supply for initial testing. If everything looks good plug it back in and power up then test +5 on the main pcb. You will see quite a bit of drop from the ps to the main board and will probably have to adjust the 5v pot up some.
 
That's what I did last night but I was getting odd readings. I attached the black lead of the DMM on the ground strap on the cab and measured the pins on the top connection of the PS board with the red lead using DC V on the DMM. The readings would drop steadily as I kept the red lead on the pins. What gives? No doubt it's something wrong with my method, eh?

BTW - all of the red voltage indicator lights on the PS are lit. Does that really mean anything?
 
BTW - all of the red voltage indicator lights on the PS are lit. Does that really mean anything?


Thats a good sign but it doesnt guarantee the voltages are correct. Look in the manual and you will see the pinout of the power supply headers. Connect the ground lead to the ground header pin. There are a bunch of them, any will do.
 
Here are my voltage test results:

On PS:
Off P3: 5.2V (pins 9-15)

Off P4:
Pin 1: 8.6V
Pin 3: -11.6V
Pin 4: 11.8V
Pin 6: 26.8V (24V zener mod)
Pin 7: 5.2V

On PCB:
Across C27: 4.1V
Across C26: .03V

The schematic sez P4 Pin 1 should be 20V. Is 8.6V too low? It's the coin meter circuit. I haven't checked to see if its working, though I'm not really concerned if it doesn't.

I read in this forum that across C26 on the PCB should be 12V so that is bad. And 4.1V across C27 is a big voltage drop (maybe bad wire/connections?)

Any thoughts on what my next step would be?

Thanks,
Mike.
 
If that 4.1 is for the +5 on the pcb then that is way too low and needs to be brought up. That is usually good news, means nothing is fried.
Next step would be to ohm the connections and see what the resistance is and try to lower the resistance. With power off course. There is probably a pinched/burnt wire and or burnt connector. This is where a little detective work comes in handy and you will have to ferrite out the connection problem.

Here are my voltage test results:

On PS:
Off P3: 5.2V (pins 9-15)

Off P4:
Pin 1: 8.6V
Pin 3: -11.6V
Pin 4: 11.8V
Pin 6: 26.8V (24V zener mod)
Pin 7: 5.2V

On PCB:
Across C27: 4.1V
Across C26: .03V

The schematic sez P4 Pin 1 should be 20V. Is 8.6V too low? It's the coin meter circuit. I haven't checked to see if its working, though I'm not really concerned if it doesn't.

I read in this forum that across C26 on the PCB should be 12V so that is bad. And 4.1V across C27 is a big voltage drop (maybe bad wire/connections?)

Any thoughts on what my next step would be?

Thanks,
Mike.
 
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Dont worry about the 8.6v, its unregulated and can vary from one machine to another depending on the transformer. The one on my bench rig is around 14v which is typically what you will see. Yes yours is low but its not related to the problem your having.
Have you pulled the filter board and checked the solder joints on it?
 
Have you pulled the filter board and checked the solder joints on it?

Nope. That's next.

I would guess that since you suggest checking the filter board that it sits between the PS and the PCB? And a cracked solder joint on it could result in the loss/drop of power to the PCB?

Thanks again all so far for the replies and help!
Mike.
 
Nope. That's next.

I would guess that since you suggest checking the filter board that it sits between the PS and the PCB? And a cracked solder joint on it could result in the loss/drop of power to the PCB?

Thanks again all so far for the replies and help!
Mike.

Yes, all power and all inputs to the pcb go through it. It is VERY common to have cracked solder joints and is likely all thats wrong with your machine. After reflowing the solder joints you might even find that unregulated 20v will be up where it should.
 
Yes, all power and all inputs to the pcb go through it. It is VERY common to have cracked solder joints and is likely all thats wrong with your machine. After reflowing the solder joints you might even find that unregulated 20v will be up where it should.

Same advise Riptor gave me and it was 100% correct. reflowed the solder joints on the filter board and i was good to go.
 
Pulled the filter board tonight and did a visual check. I didn't see any cracked solder joints. Checked the resistance across all pins, top to bottom and all checked A-ok.

Would a cracked solder joint be obvious to the eye?
 
As long as you are looking at it under good/a lot of light. My basement is under-lit. I figured this out when I went to Riptor's and what i thought was a "good" board had a lot of cold and cracked joints on header pins. They were so obvious in his well lit basement.
 
I checked the filter board again under a lighted magnifying lamp and again found no solder cracks. I did see some discoloration on the pin solder points that has an orangy color to it. See the pic. Don't think that is a concern, is it?

Let's assume then that the filter board is working ok. I suppose that my next step is to check the wiring and connections for corrosion and burnt pins to try to find the missing 12V to the PCB. And the source of the 5V voltage drop. Can anyone offer a methodology that works well for them?
 

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At some point, someone reflowed those pins and the orange discoloration you're seeing is left over flux. If' I'm going to pull a board like that, I'll inspect it out of curiosity, but I always reflow the joints to eliminate it as a possible problem. The outermost pins typically suffering from "cold solder" and sometimes the joint is so symmetrical, you'd never suspect if failed. When they do fail, often the pin will overheat due to resistance at the joint, then someone comes along and blobs solder on it, but the joint still has high resistance because the pin's plating was damaged when the joint overheated.

In the time it takes to run a meter on all of those pins, you could have reflowed them. Not trying to be harsh here, but so many guys go into elaborate troubleshooting, and reach all kinds of quantum theories about why the board isn't working, BUT THEY MISS THE MOST BASIC THINGS.

1. Always suspect prior work.
2. Vintage header pins always need attention.
3. Clean, smooth, power at the right places and voltages is a must.
 
i took my filter board out and soldered the wires together and then shrink wrapped...no more filter board possible issues...
 
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