PPII High Score Corruption

FrizzleFried

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Well, I've replaced the battery with the proper NVRAM (if that's what it's properly called) only to still have an issue with my Pole Position II, from time to time, corrupting the high scores. What happens is when I power up I get a bunch of garbage on screen and a nasty sound out of the speakers. When that happens, it seems to be a crap shoot as to whether the high score board will be corrupted or not. I'd say it gets corrupted 30%-50% of the time it does that and it does that about every 15-20 power ups randomly (if I sit there and power down power up power down power up it doesn't seem to rear it's ugly head strangely). Any ideas? +5 now comes from a separate switcher and the board has been modded for +5 and GND to hit every test point on both boards... so that's not it (right?)...

It really sucks to lose PPII high scores...
 
What ms is the NVRAM? That plays a roll in the saving, may or may not be SLOW enough...

Not sure of the speed... I got it per recommendation here... but I don't think the NVRAM is the problem as it was doing this crap with the battery pack as well (actually, this problem was the main reason why I swapped to the NVRAM).

Also, the problem only happens at power up... not when saving the scores.

EDIT: BTW-I should clarify... when this happens, it doesn't "CORRUPT" the high scores... it "RESETS" them. Bad explanation above...sorry.
 
One of Mark's comments on the topic that may help you out:

What I'd suggest for PP NOVRAM replacement is the following:

Pull Q3 and replace it with a schottky diode across the collector and emitter pins (band going towards the collector).

Solder a 47-100uF cap across C67 (to make sure the NOVRAM has time to auto store on shutdown).

Pull 7E (and replace the socket if any corrosion hit it).

Replace 7E with a Simtek / ramtron / dallas novram part.

The "Full Story":
http://forums.arcade-museum.com/showthread.php?t=44579
 
BTW, my PPI does the same thing from time to time. I had not tried Mark's suggestion prior to my move. Right now its wrapped in plastic and stored.
 
My PPII does the same things if it is persnickity upon startup (ie garbled screen) I usually have to pull the connector and blow in it just like we had to do to the old NES cartridges and then it boots. One would think that moi should change the connector, but my PPI has no startup issues whatsoever. Probably change it out anyway.

To the point, both my boards have the just the 7E NVRAM upgrade, and when the PPII gags at startup, I lose the High Scores, but when it starts fine, the scores are there. With PPI I have never lost the awesome times I have set... :D
 
Hmmm... I'll have to replace the cap as suggested. Not sure how to do the diode mod as I couldn't tell you what an emitter pin vs a collector pin is nor do I really even know what a schottky diode is vs any other diode or where to get them...

The cap I can do however. But he says "47-100uF cap across C67"... does that mean to solder a 47uf-100uf of any voltage across C67 or does he mean 47v 100uf (sounds like an odd voltage)... and by saying "across C67" does he mean to replace C67 with this cap or leave the current cap in there and solder the additional cap also? Yes... I'm pretty much a newb at this stuff still.

What exactly does the diode mod do?
 
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Hmmm... I'll have to replace the cap as suggested. Not sure how to do the diode mod as I couldn't tell you what an emitter pin vs a collector pin is nor do I really even know what a schottky diode is vs any other diode or where to get them...

The cap I can do however. But he says "47-100uF cap across C67"... does that mean to solder a 47uf-100uf of any voltage across C67 or does he mean 47v 100uf (sounds like an odd voltage)... and by saying "across C67" does he mean to replace C67 with this cap or leave the current cap in there and solder the additional cap also? Yes... I'm pretty much a newb at this stuff still.

What exactly does the diode mod do?

Replace the 6116 RAM at 7E with a Simtek STK25C48. I am 99% sure that you get this at Mouser.

Very similar to the Qbert mod that I did.

From the sound of the diode mod, is slows down the shut down to give a chance for the battery backup up NVRAM to work.
 
the diode mod keeps current from flowing back out of the new cap that you installed to the whole boardset, it only allows the energy stored in the new cap to reach the nvram. It keeps the voltage high enough to give the nvram time to enter shutdown/powerdown/backup (whatever its called) mode, and that voltage decreases gradually (instead of all at once, or nearly all at once).
The shottzky is specced b/c it has a very low voltage drop across it. As far as which pin is which - you can figure that out by pulling the datasheet for the transistor thats being replaced. Without digging through the schematics to figure out what kind of transistor it is, its hard to say, but most transistors have the base as the middle lead. The band side of the diode would go to the lead that goes to the ram +5v socket, and the non band side would go to the side thats connected to the +5 supply.
As far as removing the original cap, or adding the new one across it, i'd add the new one across, as the old one is a filter. Leaving it won't hurt anything, removing it (while unlikely) could cause issues.
 
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As far as removing the original diode, or adding the new one across it, i'd add the new one across, as the old one is a filter. Leaving it won't hurt anything, removing it (while unlikely) could cause issues.
Do you mean "as far as removing the original CAP"? Also... that cap size confuses me... is he saying 47uf-100uf of any voltage? I assume any voltage 5v+? Also, I checked digikey for schottky diode...there are hundreds... any particular size/voltage/whatnot?

Remember... you're dealing with a dumbass when it comes to this stuff.

:D
 
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Do you mean "as far as removing the original CAP"? Also... that cap size confuses me... is he saying 47uf-100uf of any voltage? I assume any voltage 5v+? Also, I checked digikey for schottky diode...there are hundreds... any particular size/voltage/whatnot?

Remember... you're dealing with a dumbass when it comes to this stuff.

:D

yes. i meant the original cap, edited my post to reflect that.
Needs to handle at least 6.3v forward, and a 1 amp current should be more than enough. Mark could do a better job actually speccing a diode, but just looking at it, an 1n5817, 1n5818, or 1n5819 should all work fine.

edit #2 - i'm not sure they make electrolytic caps with voltage ratings less than 6.3v, ergo the any cap statement. But yes, a 6.3v rated or higher cap, with at least 47uF capacitance, upto 100 uF capacitance.
 
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Now comes the problem of finding one local. I won't pay $7.00+ to ship $.24 worth of 2 diodes... That just seems silly. Radiosuck only had 1n4001's... and my only "real" electronics store is a 15 mile journey (after gas and time I might as well order from Mouser).

Anyone here have two of these bad boys they'd be willing to sell me for like a buck or two shipped?
 
Well, I've got a bunch of diodes in my electronics parts box... but I have no idea how to determine what rating they are. I tried google and have come up pretty empty. Is there a way by SIGHT to determine what rating a diode is? Any other way? Obviously I am looking for on of the 3 types mentioned above (1n5817, 1n5818, or 1n5819)
 
The diodes should have a number on them. Might need a magnifying glass to read it though.

ok, so i looked up the datasheet for the MK48z02 nvram. average power dissipation is 80 mA. most diodes have a minimum power rating of 150 mA, so any old diode will do power-wise.
Take your meter and set it to diode test. Go through your diodes and find the one with the lowest number. If it reads less than .3v it should work fine. If it reads closer to .6v then you could try it, but chances are the voltage at the power pin of the nvram will be less than 4.75 volts (which is the minimum for the MK48z02). You could try leaving the transistor as is, and just adding the cap. You could even go up to a 220uF cap and try that, it shouldn't hurt a thing. That might very well work if you don't have any diodes. I just looked through my stock, and i don't have any here that fit the bill. I'd be happy to send ya a couple if i did.
 
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I just ordered from Mouser IN6263 Schottky diodes. It says 15ma 60v. Is that too low for this?
 
15 or 150? 15 is too small. Needs to be around 100mA bare minimum as best i can tell.
 
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