How high should the +5V before you fry something?

gibbous

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How high should the +5V be before you fry something?

Just curious what others have experienced. I have an Ikari Warriors that I have to crank up to 5.4 AT THE CPU before I get rid of various graphics anomalies. Seems kinda high.
 
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First datasheet for a z80 processor that I could find on google says +4.50v to +5.50v recommended operating range, -0.3v to +7.0v absolute maximum.

I agree, it sounds like you have something in the process of breaking if you need the voltage that high. But I say run it until something actually breaks, then you'll know what to fix.
 
Yeah, that does seem pretty high.

Are there socketed chips in the graphics section of the board? You may have significant oxidation, or worse, corrosion on the metal legs of any socketed ROM and/or RAM chips in your video section. Oxidized and corroded metal does not conduct as well as clean metal... thus you have to turn up your voltage in order for the proper voltage to reach these chips through a resistance that should not be there. Have you tried reseating/cleaning your socketed chips? You may want to replace old sockets if you are handy with a soldering iron. If there are no socketed chips, I would flip the board over and look for cold solder joints on the back side of the board.
 
Shouldn't be that high. TTL specs are typically 4.75-5.25V. Check voltage on the other boards in the stack. Perhaps you're getting drops in the inter-PCB connectors, and that's how high it has to be on the front board in order to keep the back board from dropping too low.

Or... you may have bad RAM causing your gfx issues. A video would help. I had to replace nearly every RAM IC on my IW (6116 and TMM2018) before the gfx probs and resets stopped. But check the voltage on throughout the stack first.
 
I did remove and reseat all the socket chips as part of the preliminary troubleshooting. Didn't notice any major corrosion, but I could've missed something.

I'll have to meter out some more readings. The stuff further away from the edge connector might just barely be getting what they need to operate, while the stuff closer gets too much sounds like a plausible explanation.

Keep an eye at the center of the screen in the first few seconds, and then there's a little blip towards the end in the lower right quadrant.

 
I spliced another +5 tap into the connector on the bottom board and was able to turn the voltage down to 5.26 at the CPU with no glitches. Probably need to check out those connectors eventually, bur hopefully it will run the whole weekend for CAX. :)
 
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