Robotron, lets start with the power

ArcadEd

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Ok, I got a robotron that was out in the weather for a bit (though the wood is in really good shape) I can see the PCBs have a bit of a weathered look to them.

First thing I did was put in all the fuses that were missing. Fired it up and get LED 1 and 2 on the power board to come on, and E1-1 on the Rom board.

I tested voltage on the first Rom chip and the voltage was right around 4.3v.

First few questions.

1. The ISO has a lot of wires coming out, is there a diagram showing which are which so I can test them to make sure the low voltage isn't starting there?

2. If it is the ISO, can I keep it in place for the monitor, but just install a switching power supply for the PCBs? I looks like I will need one with -12vdc as well?

3. If the ISO is ok, what's the next step?


Thanks again.
 
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I'll let the true gurus check me on this, but first of all the ISO (isolation xormer, right?) is *strictly* for powering the monitor so that wouldn't have anything to do with your PCB's voltages.

Yes you can do a switcher for the PCBs, but there seems to be a potential problem with proper saving of high scores. Good recent thread all about that - high scores in Robotron.
 
I've got a Stargate 4 PCB board set up 4 sale on da bay and a Robotron ROM board [tested] that would work if you decided to go that route.

You need to test voltage potential on the RAM chips 4 corners. Back trace from there.

On a Williams cab the ISO is just a part of the AC winding coming of the main transformer. Not likely that the problem is your transformer. Unless you have 4164 RAM installed, with only 2 light lit on the power board... Your not cooking with gas yet...


Ok, I got a robotron that was out in the weather for a bit (though the wood is in really good shape) I can see the PCBs have a bit of a weathered look to them.

First thing I did was put in all the fuses that were missing. Fired it up and get LED 1 and 2 on the power board to come on, and E1-1 on the Rom board.

I tested voltage on the first Rom chip and the voltage was right around 4.3v.

First few questions.

1. The ISO has a lot of wires coming out, is there a diagram showing which are which so I can test them to make sure the low voltage isn't starting there?

2. If it is the ISO, can I keep it in place for the monitor, but just install a switching power supply for the PCBs? I looks like I will need one with -12vdc as well?

3. If the ISO is ok, what's the next step?


Thanks again.
 
OK, so on the Ram chips (I started with 1-1 since that is the error, but checked others).

Pin 1 - -5vdc reads +.53vdc (note, this doesn't read negative)
Pin 8 - +12vdc reads +11.70vdc
Pin 9 - +5vdc reads - Fluctuates between +4.29vdc and +4.15vdc
 
OK, so on the Ram chips (I started with 1-1 since that is the error, but checked others).

Pin 1 - -5vdc reads +.53vdc (note, this doesn't read negative)
Pin 8 - +12vdc reads +11.70vdc
Pin 9 - +5vdc reads - Fluctuates between +4.29vdc and +4.15vdc

These voltages need to be addressed. The -5 is wrong and the +5 is too low.

This is a problem with the board and needs to be fixed first!
 
OK, coming out of the power board I get no reading on the -5vdc, +12 and -12 are good. +5 is at 5.02

So I assume I start with getting the -5vdc working? Where to start with that?

Ed
 
OK, coming out of the power board I get no reading on the -5vdc, +12 and -12 are good. +5 is at 5.02

So I assume I start with getting the -5vdc working? Where to start with that?

Ed

I am not familiar with that hardware (robotron) but there is a regulator or something after the rectifier that will regulate the voltage. Something like a transistor with 3 pins. Usually the left one is the input center is ground and right side is output (-5 in this case).

Did you ohm out the fuses?
 
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Yup, the one fuse I didn't replace was bad. I should no better than to judge a fuse on looks.

Ok with that new fuse in LED 1 no longer lights. so only 2. 1 was actually on and slowly faded off. I don't even power to the Error display anymore.

I think I am going to start with getting the power board rebuilt or buying a new one and go from there.
 
If you happen to have an older computer PS laying around (one with a -5V rail), maybe you could use it to get up and running. Then if you're having problems with the high score save, you could tighten things up by addressing the linear PS.
 
Well I have plenty of power supplies around from arcade machines and some from PCs. But it looks like this requires a -12v, which isn't normally on those power supplies.

Or are you suggesting I just tie in my -5v from another power supply at the point where it exits the power board?
 
OK, so I hooked up a switching power supply for the + and - 5vdc and I made some progress. Game sort of comes up (garbled screen), and the Error Indicator is just flashing random stuff when it boots up, seems to stabilize a flashing 1 (keeping blinking)

I should note, that I am using the existing power board for the + and - 12vdc. Those voltages seem to be fine everywhere I checked.

Not sure if that makes any sense.

Ed
 
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the isolation transformer provides several weird voltages, and it's not just for the monitor. I'm using Joust as an example, cause it's the same hardware and it's all I could find off hand for this.

http://www.cityofberwyn.com/schematics/williams/JOUhar.tiff

there's 3 different AC voltages that come off the isolation transformer and feed into the power supply board. each one handles a different voltage, +5, +12 & +27, and -5 VDC. if one of these voltages isn't present, it will probably cause weird readings or missing voltages.

I believe YellowDog told me that -12VDC isn't required for normal operation... though don't quote me there lol. I've run my Defender without -12VDC on a switcher just fine, I happened to buy a power supply board for it and rebuilt it. I also had to rewire the entire isolation transformer, cause whoever swapped the switcher in cut everything but the 120V wires off.

additionally, if your power supply hasn't been rebuilt, it's most likely going to need to be. consider yourself lucky you have a newer model one with the overcurrent protection, heh, Defender's doesn't have that.


I would go here for more information. like I said, the Joust stuff will be identical for your Robotron. http://www.cityofberwyn.com/schematics/index.htm


information YellowDog supplied me about the iso, I'm going to assume our isos are the exact same: http://forums.arcade-museum.com/showpost.php?p=1739215&postcount=22 he also explains about the -12, you can sub in -5 in its place, but won't be as loud.
 
So I pulled the ram board out to inspect. I think this accomplished 2 things. 1. I re seated all connectors going to the ram board (ribbon cables, power and video). Second, I found a RAM chip in backwards, must have been that way when I got it.

Put 2-1 back in the right way, hooked it back up and got the game to fire up. Got 1-2-1 error on the little error panel.

Switched 2-1 with 3-1. Game booted to Ram Error 31. Switch it around and the error always followed where that chip was.

I guess for now I will just order some 4116 and go from there.
 
Sounds like you're just about there! I've considered doing the swap to (4164?) ram, but I really only get a dead 4116 about once a year or something.
 
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