Troubleshooting Obsolete Snap-On Motherboard (unidentifiable IC's)

[MtnMann]

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 "ccc" on the display. Instead, 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) and balance sensor unit (seems to work)

[LateLesley]

Are you sure it IS faulty? I found a manual, which has a calibration procedure.

http://davesobsoletetools.blogspot.co.uk/2011/04/wb230wb240-wheel-balancer-users-manual.html

I run through the operational check first, as described in the manual - it says you have to turn the rim diameter knob back and forth 4 times! It may be looking for that before firing up. You could then run the field calibration check.

As for the board, it is looking a bit grubby, it may be worth giving it a wash - I'd probably just use Isopropyl 99% and a ½ inch clean soft paintbrush.

[tautech]

Before doing what Lesley advises (BTW  ) do consider that unexplained and unexpected behavior is often traced to a crook power supply so be sure to check the supply rails are clean of ripple and close to specified voltages.

You can do both 'near enough' with an ordinary DMM. DC voltage setting to check the rails and AC mV to check for ripple.
I'd expect/want to see ripple values well under 100mV.

[Jim Narem]

I have a working snap-on WB240.  When powered up, the display is a decimal point with an arrow pointing up on one side and pointing down on the other side.  When the tire spinner is rotated, the arrows flip every half rotation.  The numeric display is only for the wheel weight size which only indicates a number when a balance cycle is complete.  The three settings knobs (rim diam, width, offset) are pure analog, the dial trim on the front panel has the scales, they do not read out on the digital display.

Note that balanced (constant 0.0 on the display when sucessful) is balanced; it is independent of the settings and calibration.  The balance mechanism produces a vector whose magnitude and direction is offset by the two vectors (the weights) that the machine computes using the three settings knobs and the calibration step with the 3.0oz weight.  When the weights are correct, the imbalance vector magnitude is 0.

Now that I've seen the circuit board, I'm glad mine works since I've never seen anything like that main chip with the offset pins.

If some idiot cleaned the three dial markings off of the front panel, I can send you a hirez picture of the panel.

[shakalnokturn]

IIRC Nec used to make the IC's with staggered pins in the late '70s, early '80s for microprocessors and ASIC's.
Expect to find a µPD78xx marking hidden somewhere.

The staggered package is known as "QUIP" and for the plastic versions was mainly used by NEC and Rockwell.

[MtnMann]

Wow! Great info everyone!

I did figure out that the display is not supposed to show the settings on the dials. This machine has been very well used but I believe the markings on the face are still readable enough to use.

I didn't know about "ripple". I don't see any fluctuation in the power at either regulator.

I did read about QIP (QIL) chips...

The calibration mode is definitely not working as the manual says it's supposed to show "CCC" when you hit the button and it goes directly to "EEE".
It also won't come out of "EEE" without cycling power. The manual says just spinning the wheel in the correct direction is supposed to return it to normal reading mode.

Does it have to have a special calibration weight Jim? Or does just a 3oz. wheel weight work? I see the Snap-On calibration weight from later models for sale but that looks like it screws on the hub on the spindle on those models.

[Jim Narem]

Great info on the QUIP and the NEC 78K family.  I hope I never really need that info to reverse engineer this wheel balancer.

I have never calibrated my WB240, but if I press the cal button, the machine displays "EEE".  I suspect the whole cal procedure must be followed to get the display to show "CCC".  The user manual (pg 9) says that first you must "fine" balance a wheel to  zero with display "000", then attach the 3oz weight to the outer rim at TDC with outer display arrows on.  Then press "cal" and the display should show "CCC".  It's a very specific procedure designed to protect the stored calibration values.  Any problem (like not starting with a known zeroed wheel in fine mode) will cause the process to fault out and display "EEE".  I think your machine is acting normally.

You need to spin some wheels and see what it does.  The calibration may be fine.

The manual says to use a 3oz weight in oz mode and a 100g weight in gram mode for calibration.  You also need to follow the whole cal proc in the manual.

If you're unable to get a wheel to balance in "fine" mode, you might try getting a garage to balance a wheel for you, then spin it on your machine.  Again, balanced is balanced independent of calibration.  As you may know, tire monkeys are pretty low on the automotive service totem pole so getting a correctly "fine" balanced wheel may be hard.  If you show up with a fancy low profile mag wheel they may do a single plane static balance which is NOT good enough to calibrate this machine.  It must be a two plane dynamic balance.  If a known good wheel doesn't spin 000, I'd suspect the balance head.

[MtnMann]

Thanks Jim,

That's really helpful coming from an owner of one of these. I do have a copy of the manual but you made me realize, I didn't pay enough attention to the calibration procedure saying it should be in "fine" mode. That makes sense as to why I was getting "EEE" on the display. I balanced my truck wheels and my X5 wheels and it seemed to work fine. It sure is more accurate than my Harbor Freight bubble balancer (even though that did make my cars drivable at least).

I haven't tested the calibration yet but I will soon just for kicks.

Cheers!

[mtrmn347]

Hello !
   I know bringing this back from the dead !, but did you happen to ever find a resolution to you r problem with the Snap On wheel balancer ?
I have just inherited a nice WB410 that has the same symptoms and just hoping you knew the fix ?