Help with memory on a snap on tire balancer board

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I have a nice older snap on balancer I use for personal use in my shop. It's always worked great and still does, except recently it started losing the calibration memory when unplugged for longer than a few days. I can get around this by plugging it back it for 24 hours and then going through a long process of recalibrating known weights and spinning a balanced wheel (big pain). It will not recalibrate and hold the memory unless plugged in for 24 hours. I pulled the board out and was hoping to find a board mounted battery or similar....but no such luck. I am thinking that this board must use some sort of capacitor arrangement to hold a residual charge to "keep" the calibration memory? Or would the calibration just be retained in the programming chip? Any suggestions and trouble shooting is appreciated, I know its not a video game...

Model WB250
 
Just spitballing here but Look under that Socketed EEPROM, and see if there may be anything under it.

Also this might use a "super-cap" like the old Xbox's. You may need to look at every capacitor and see if it is the super cap type.
Those are my 2 Ideas for meow. :)
 
Thanks, I shrunk it down but will try to hotlink a higher res pic tonight and I will check out the caps.
 
That's an interesting problem... from the symptoms, I REALLY would have expected a NiCd battery. You need to look at the individual parts on the board and figure out which is the memory. It could be RAM, Serial EEPROM, etc. Once you know that, it'll be much easier to troubleshoot (look for the backup voltage that's missing, replace a bad part, etc).

From the pic, I can see an X24C44P (8-pin chip at U23), which is a serial NVRAM. It shouldn't need power, as it uses an EEPROM for non-volatile memory... but it could just be bad. I'd look at the other parts and see if there's any other NVRAM-like parts... otherwise, I'd first try swapping that part (they're just a few bucks on ebay).

DogP
 
Ok....what about these big guys on the back?
 

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Nah, I doubt those have anything to do with it. Those aren't high enough capacity, and way higher voltage than would be needed for backup.

Can you post some higher res closeups of parts of the board so we can read the chip numbers? IMO, the X24C44P seems like the most likely culprit, but maybe there's another NV memory chip too. I don't see any cap that looks like a backup cap on the board (supercaps generally look obviously different than a standard cap).

It just started doing this, right? I've never used one of these, but some types of machines expect a user calibration every time they're started up (and sometimes periodically during use), figuring the hassle of the calibration is minimal compared to the amount it'd typically be used in a day, when accuracy is critical. And a user calibration may be completely different than the factory calibration.

DogP
 
Thanks for staying with me on this. Yes, it just started doing this, it would hold the calibration before. I will get some better pics tonight. I have owned it for 4 or 5 years.
 
I used the machine again this weekend. Same scenario...had to leave it plugged in overnight before the calibration memory would be accepted.
 
for my nickel i would look real hard at that "spider" chip
common problem is they do exactly what problem u have

ed
 
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