Sciencemadness Discussion Board

Fixing an Analytical Balance

gdflp - 19-12-2014 at 12:40

I purchased a Mettler Toledo AE160 balance from an industrial auction and received it non-working. The problem according to Mettler, who I called, is that the balance is sensing that the capacity is overloaded on startup, even with removal of the pan. This is shown by horizontal lines across the top of the display. Apparently the balance has been discontinued(surprising that they would do that to a 30-year old model;)) as well as parts and service. Does anyone have experience with fixing balances and know something which often causes this error? Or should I just cut my losses and try to sell it?

Little_Ghost_again - 19-12-2014 at 13:34

Quote: Originally posted by gdflp  
I purchased a Mettler Toledo AE160 balance from an industrial auction and received it non-working. The problem according to Mettler, who I called, is that the balance is sensing that the capacity is overloaded on startup, even with removal of the pan. This is shown by horizontal lines across the top of the display. Apparently the balance has been discontinued(surprising that they would do that to a 30-year old model;)) as well as parts and service. Does anyone have experience with fixing balances and know something which often causes this error? Or should I just cut my losses and try to sell it?


This could be very very simple or a real bitch so decide what you paid for it is worth risking.

Check for simple things first like take ALL wire harness connectors off and spray with proper contact cleaner (The real stuff not something you knock up!) This fix's 40% of stuff I fix.
Next if that dosnt work look really carefully at the sensor if you can get to it without disturbing it, is there a short?

Look for obvious dry joints or cracks in the pcb traces (fixable).

Its most likely to be the first above, then the sensor or at that age I would go looking for tantalum and electrolytic caps.
I would use a ESR meter and test each cap, at that age some will be foofed.
If you cant test them then your gonna have to replace them one by one.
What kind of test equipment do you have access to

[Edited on 19-12-2014 by Little_Ghost_again]

Scrub the above for a bit, read this
http://www.iescorp.com/ae.htm

looks like you have to be real careful inside, so how much electronics experience do you have? I am looking for a schematic for you but I am not hopeful

[Edited on 19-12-2014 by Little_Ghost_again]


WEEEEEEEEEEEEEEEEEEEeeeeeeeeeeeeeee


http://www.iescorp.com/helplinks.htm
have a look at the links :D

[Edited on 19-12-2014 by Little_Ghost_again]

gdflp - 19-12-2014 at 13:47

At home I have a precise meter capable of testing temp, resistance, voltage etc. If I need any other testing equipment though, my dad works for a large government lab as an electrical engineer so he has access to basically anything.

EDIT : Thanks for those links, I might give them a call.

[Edited on 12-19-2014 by gdflp]

Little_Ghost_again - 19-12-2014 at 13:51

I have had a read up and to be honest I would suspect that the load arms are bent from some muppet overloading it in the past, the fact it reads overload isnt great and could be because the arms are bent (they are apparently VERY sensitive), OR............. if it was cheap and if it was me, I would go looking at the op amp comparator circuit. I havnt found a true schematic yet so cant offer much in the way of advice, if you paid a fair bit then it gets tricky

gdflp - 19-12-2014 at 13:54

It was about $200USD, but it seems that these sell for that on eBay even when broken.

Little_Ghost_again - 19-12-2014 at 14:06

Quote: Originally posted by gdflp  
It was about $200USD, but it seems that these sell for that on eBay even when broken.

If you are not good with electronics then dont try and fix it, what does it say on the screen or what is the error code etc?
TBH unless your good with electronics ebay it, it might be real simple like a coil connection of cap thats gone but the problem is those arms, mess with them and its going to have to be re calibrated, they are also very fine which makes me think they have been over loaded and now bent.
I would attempt a fix solely because i have and can use a ESR meter and oscilloscope etc etc. Without that kind of stuff your limited to taking a peak at the coil connection and state of the arms.
But if you stand a chance of getting your money back on ebay then thats the sensible option unless $200 isnt that much to you

gdflp - 19-12-2014 at 14:11

When it's plugged in it shows "OFF 3". When I press the ON button, it displays every line on the display "8.8.8.8.8.8.8.8.", then shows "----" and finally a row of horizontal bars along the entire top of the display and stays that way. I forgot to mention, my dad also has an oscilloscope at our house:D BTW $200 is a LOT of money to me.

Little_Ghost_again - 19-12-2014 at 22:28

Quote: Originally posted by gdflp  
When it's plugged in it shows "OFF 3". When I press the ON button, it displays every line on the display "8.8.8.8.8.8.8.8.", then shows "----" and finally a row of horizontal bars along the entire top of the display and stays that way. I forgot to mention, my dad also has an oscilloscope at our house:D BTW $200 is a LOT of money to me.


If its alot then ebay and recover as much cash as you can, having read the service docs etc I doubt even if you fix it you will get a true reading again.
Most common fault is apparently people putting excess weight on them and distorting the arms, Its a tough one as the company I linked too say just about any can be repaired except those with arm damage as you cant get the arms.
If broken ones get $200 on ebay then do that and jut wait for another to come along.
I still havnt got hold of a schematic but reading the service manual I doubt there is much electronically you couldnt fix. Have you had a peek inside?
Read the doc on the page in the link about removing the main board and about recalibrating etc, then decide if you have the skills to carry it all out.
Having a O scope is good.................if you know how to use it.
But I still think if you stand a good chance of getting your money back then thats the way forward.

aga - 20-12-2014 at 02:11

Before tackling the electronics, have a close look at the mechanical parts.

It may be that some material has found it's way into the load cell, or the mechanism is simply jammed.

Be aware that taking it all apart will require it being re-calibrated, but seeing as it's broken, there's nothing to lose.

DJF90 - 20-12-2014 at 06:05

I had/have the same issue...

http://www.sciencemadness.org/talk/viewthread.php?tid=26247

Mailinmypocket - 20-12-2014 at 06:29

I'm currently dealing with a similar issue. An Ohaus Scout balance that is giving ERR4 when attempting to do a linearity calibration... Not sure if opening it to check for dirt etc is a good idea or not. Annoying.

Little_Ghost_again - 20-12-2014 at 06:33

Quote: Originally posted by aga  
Before tackling the electronics, have a close look at the mechanical parts.

It may be that some material has found it's way into the load cell, or the mechanism is simply jammed.

Be aware that taking it all apart will require it being re-calibrated, but seeing as it's broken, there's nothing to lose.



did you read the links? It details taking it apart etc, it is not easy and the arms are super fine, the problem apparently is that its very very hard to even tell if they have been deformed. The extra bad news is you cant get the load arms anymore.
There isnt a Load cell as such Aga, thats what got me at the start of this as I was expecting a load cell.
The field service manual shows you that there are these two super fine arms and a coil of wire, as the arm approach the coil the field is read via opamps etc (no micro).
Seeing as $200 is alot to him and he can get $200 from ebay for them I would do that.
I would bet my dick that the balance was over loaded and the wires deformed against the coil slightly

aga - 20-12-2014 at 09:53

Ah. OK.

If that's all there is for the sensor, then yes, not much to actually 'fix' i guess.