Greetings,

I acquired an old Snap-On hand-spin wheel balancer machine (WB230/240) and am trying to figure out an issue with the motherboard (pics below). The machine is so old and obsolete that there is very little info out there. The balancer still works but the display will not show the initial settings when you change any one of the three potentiometers. These three pots set the variables for wheel diameter, width, and distance out from a point of reference on the machine. The display is normally just blacked out except the decimal point. When you adjust any of the three pots, it is supposed to show the corresponding numbers. Then, I'm not sure if those numbers are suppose to time out, or if they just stay lit until another dial is changed.

After those variables are set, you simply rotate the tire by hand bringing it up to a certain speed where the machine beeps. At that point, you let it spin until it calculates the weights needed at which point it stops the wheel spin with a brake. Then the display shows arrows indicating how far to rotate the wheel to find the point to attach the amount of weight shown on the display. Everything in this paragraph works fine. The display shows everything properly.

There is another setting that is for different modes (normal, aluminum rim, single plane, fine balance). This mode is changed by rotating the top pot to Zero and as soon as you rotate it off of zero, it changes to the next mode. You repeat this to toggle to the next mode. The modes are indicated by blank/AL/S/F on display. This all appears to work fine.

There is a black button on the back side that switches the machine from grams (no decimal on display) to ounces (decimal lit). That appears to work.

The white button on the back enters calibration mode. That, I believe is supposed to show CAL on the display. It just immediately goes into error mode ("EEE" on display).

Also, if you spin the wheel too fast or in the wrong direction, the display will go into "EEE" mode. When it does, nothing will return to normal mode other than reset by powering down.

Nothing appears to be blown on the board. I don't see any cracked solder joints, blown caps, or burns. J1 Input power can be either the 8.5 VAC adapter plug OR 12VDC battery. Both voltage regulators (lower left) work fine (9.96VDC in / 4.96VDC out). The lower one with heat sink gets quite warm. The largest IC near center gets slightly warm. All three pots get 5v and can properly adjust from 0-5v output.

I am not proficient enough to know what to replace at this point. I assume something senses a change in any of the three pots output voltage and activates the display to read the corresponding value. Would this be the main IC? Should it be getting warm? Or is this a function of another IC on the board? The main IC has a little block on its back that I'm not sure whether it is part of the chip or something epoxied on the back to cover numbers. Other unmarked IC's have sanding marks.

Any help would be greatly appreciated!

Thank you!

Other notes: J1 - power, J2 - unused, J3 (bottom) goes to brake (works), balance sensor unit (seems to work)

 

I did some repairs to a board very similar to this years ago, the top left 74LS174 doesn't look too healthy to me but it may just be an optical delusion.

The issue you are dealing with is most likely the memory cells in the Eprom have started to fail and programming is getting fuddled.
There is a lifespan on these old components and it affects all sorts of old Industrial equipment, EEproms are worse.

 

Oh and replace those old 4,700 µf caps on the foil side of the board, (the other side) and it wouldn't hurt to change out all the electrolytic caps as they no doubt are dried out, especially around the LM340 regulators.

Get some Safety Wash and a hog's-hair brush and clean that board after you are done.

Maybe you'll get lucky and it fires back up!

 

Thanks for the tips!

 

Before blasting that board with any sort of cleaner, I strongly recommend testing to see how the conformal coating reacts. If the solvents soften the coating you could wind up with a hideous mess.

Is there a chance that the CAL function requires a calibration wheel to be mounted or a balance emulator box to be connected instead of the usual inputs from the machine?

 

Turns out I think the biggest problem was lack of information. I think the machine is working OK. The manual I found online is sparse but I think I've figured out how to use it and it appears to work. I previously only had information from the next model to go off of and I assumed it would be the same but I was wrong.

The coating on that 74LS174 is what's making it look damaged but I think it's fine.

The Calibration function can only be entered from the "Fine" mode which I learned from someone who actually has one of these.