Green Screen Problem mv1

robgest

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OK, I have worked on this board and have nothing. I tested for 5v between 7 & 14 and have nothing. I was going to track down the traces but have no schematics to work off from, so I have no idea if a trace is bad. I have some battery issues with leakage so maybe something else is bad like the crystal. Any ideas beside sending it in to someone?
Thanks,
 

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You should have continuity from pin 14 of the D4990 to pin 28 of each of the backup RAMs. If not, run a jumper.

It's easy to follow the traces backwards from the chip. You just have to peel off the cardboard/foam insulator from the bottom of the board so you can see the traces.... but just do the jumper I suggested. ;)
 
The RAMs are the six 43256 chips right? I have continuity going to two of the chips (pin 28) but non of the others.
 
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The backup battery ONLY powers the backup RAM and the D4990 chip. It does not power the other 4 surface mount RAM.

Take a multimeter and check pin 28 on each of the 4 RAMs with the power off and you'll find that 2 of them have battery voltage on pin 28. Those are your backup RAMs.
 
Well I'm back to scratching my head. I get continuity on the two rams and I can't see any bad traces. I have no power to the d4990 on pin 14 when I touch pin 7 and 14. My battery is dead so I don't have any backup power. When I put all dips to ON I get the WORK RAM TEST and a beeping noise, and with the dips all OFF I get the green screen. As the picture shows, the only thing that looks bad is the crystal but I don't think that is the problem...right?
 

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Well I'm back to scratching my head. I get continuity on the two rams and I can't see any bad traces. I have no power to the d4990 on pin 14 when I touch pin 7 and 14. My battery is dead so I don't have any backup power. When I put all dips to ON I get the WORK RAM TEST and a beeping noise, and with the dips all OFF I get the green screen. As the picture shows, the only thing that looks bad is the crystal but I don't think that is the problem...right?

Sigh...

Did you do this: ???

You should have continuity from pin 14 of the D4990 to pin 28 of each of the backup RAMs. If not, run a jumper.

It's easy to follow the traces backwards from the chip. You just have to peel off the cardboard/foam insulator from the bottom of the board so you can see the traces.... but just do the jumper I suggested. ;)

If you don't have +5v on pin 14 with it powered up... AND you don't have battery voltage with the power off... (which you won't anyway since you said your battery was dead)... then check continuity like I mentioned. If it doesn't exist between the backup RAMs AND the D4990 then run a jumper.

If it DOES have continuity then replace the crystal.
 
Shipping isn't too bad. I sent you the mouser.com part numbers since I don't carry the crystals yet.
 
Thanks for the help.

I did and checked it all. Replaced the crystal with a 32.768MHz 18pF. New battery and checked the continuity on everything to check and still have the green screen. At least now I have 3.8 between 7 and 14 with no power and 5 with. Not sure what else to do.... oh well, thanks.
 
Then you have a bad trace between the D4990 and the rest of the board.. It's time to start checking trace continuity.

It's possible to have a bad D4990 but pretty rare. it's a robust chip.
 
Trace

OK, 1 more question. How far does the traces go? I ran a few and got the below results. I don't want to be a pain but when your new to something you need advice.


A link to each other
1,2,3,14,15
2,3,14,15,1
3,14,15,1,2
4,4
5,5,5,11
6,6
7,a bunch of 7s
8,8
9,9
10,10
11,5
12,12,12
13,13,13
14,1,2,3,15
15,15's,1,2,3,14

Open thumbnail in new window
 

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