Robotron boots & blank screen - where to check?

neopolss

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Robotron boots & blank screen - where to check?

I just picked up a very nice looking Robotron cab. Very clean inside, hasn't been used in years. First thing I noticed when it starts is that it would not save the settings. I checked the battery holder, and sure enough, the batteries were starting to leak. Thankfully nothing on the board. I replaced the batteries, and now the machine will start, first screen for factory settings restored" and then "no errors" or something to that effect, and then the screen goes blank. At the very very top of the monitor I can see some alternating colors from the attract screen, but the rest of the screen is totally blank. It displays perfectly during the startup test and inititialization. Where should I start looking on this? My first williams cab.
 
It is displaying a 3 on the led. The manual says CMOS. is that the big chip on the board? The motorola chip (6800?) is pretty hot to the touch. Everything else feels cool.

Staes "initial checks indicate: operational" then "factory settings restored" then blank.
 
The first thing to check is the voltages.

If it has the original power supply, check the power supply board for the 3 LEDs being lit.

Then pull out the voltmeter and check the voltages on the 4 corners of a RAM chip. The voltages should be:
pin1 = -5V
pin8 = +12V
pin9 = +5V
pin16=ground.

If the voltages aren't right, nothing is going to be right.

ken
 
dang, i had my paypal account in hand and ready to buy some Robotron boots...... ;)
 
The three leds are lit, but I will check out the voltages in the morning.
 
Checked voltages this morning. Running 4.9, -5.02, +11.9, fluctuates a little. Figure it won't hurt to replace the power caps and battery convert it. Anything else I should go ahead and do while I have this out?
 
Based on the original symptoms, it could be the CMOS RAM chip or it could be the corrosion on the battery holders is keeping the voltage to the CMOS below acceptable levels. Once the batteries have been replaced you should only get the factory settings restored message one time.

Check the voltages on the CMOS chip with the power down.
Pin18 = +voltage (Should be 2.8V or higher)
Pin9 = ground

If you are not seeing this, you may want to check the voltage at the holder as well.

ken
 
i have a quick question. forgive me if it's silly.

which chip exactly is the cmos ram chip? is it one of the 24 4116 rams or something on the rom board?
 
which chip exactly is the cmos ram chip? is it one of the 24 4116 rams or something on the rom board?

It is chip 1C on the MPU board. When mounted in the cabinet it is on the first column on the right side the 3rd chip from the top of the board, IIRC.

ken
 
Ok, I changed out the old battery holder for a new lithium one, checked the voltages at the holder and they are good, but I get nothing at the CMOS, unless I am measuring the wrong chip. Third chip from the top on the right side correct? I don't get any more reset errors, It just does the initial test, operational, then blank screen. Again though you can see a tiny sliver of the title screen at the very top of the monitor, nothing else.
 
The Stargate drawing set has a picture of the parts placement as well as the schematics. If you don't have one you can download a PDF version from arcarc.xmission.com.

If you are going to muck with these things you need the drawing set.

ken
 
Cool. I'm ordering a power kit from Bob first, and then go from there. I think the +5 dips shortly after being on. Only two leds are lit after about two minutes of being on.
 
Ok, I changed out the old battery holder for a new lithium one, checked the voltages at the holder and they are good, but I get nothing at the CMOS, unless I am measuring the wrong chip. Third chip from the top on the right side correct? I don't get any more reset errors, It just does the initial test, operational, then blank screen. Again though you can see a tiny sliver of the title screen at the very top of the monitor, nothing else.

Can you post a picture?
 
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