Sciencemadness Discussion Board

Scale don't work

quest - 8-8-2011 at 06:57

Hi all,
I got a "E4000D OHAUS scale". I have had it for over 10 years.
Today the scale decided not to work for the first time.
I tried to find out what was wrong, I have connected the power supply to the power and used a voltmeter to see if the wires are cut or the transformer is broken - I couldn't find 2 wires that have 17volts between them. (actually I couldn't find 2 wires with any voltage between them)

And now for my questions:
1) Is there any component in scales that is prone to "die" first? How can I check if it is broken?
2) Does any one know why the scale power supply has 3 electric wires coming out of it and not only 2? (1 positive and 1 negative)
3) If I can't find 2 wires with some voltage between them - does it mean the wires are broken\the transformer is broken like I guessed?


not_important - 8-8-2011 at 07:20

Third wire is ground - 0 V If you can't find any voltages out of it, it is dead. Note that it's more than a transformer, it's also rectifiers to get the DC.

m1tanker78 - 8-8-2011 at 07:58

Also keep in mind that this PS supplies a dual rail +17V | 0V | -17V. Your meter should register +/-34V between the rails and +/- 17V from either rail to the common ground. Are you able to disassemble the PS?

If it really is transformer-based, as opposed to a switching type, then it should be fairly robust. If it's a buck converter (for example), it's almost certainly trash or junk box bound IMO.

Also note that the manufacturer, EDS, disbanded a few years back. Try contacting Ohaus to see if they can offer any help for a replacement PS or check ebay.


weldit - 8-8-2011 at 13:46

This may sound stupid but did you check the outlet. If your outlet has power get another power supply

quest - 10-8-2011 at 14:39

A new PS costs 130$ from the authorized ohaus dealer.
Do you know if it has special part to make it more accurate or this is just a too expensive price?
Can I make a PS with +-17 volt or will it make the scale less accurate because it doesn't have thermal voltage regulator to make the voltage more consistent? (again, I don't know if mine has it, it's just a guess because of the price.)

redox - 10-8-2011 at 15:57

Quote: Originally posted by quest  

1) Is there any component in scales that is prone to "die" first?

I asked my uncle (who is a self-made millionaire in the scale business:cool: ), and he said it is often the load cells that fail first. Are there electronic-fixing stores near you? Contacting Ohaus may also yield results.

If all else fails, it seems buying another scale would be necessary.:(

Also, this may be a noob question, but what is a PS?

#maverick# - 10-8-2011 at 18:08

when he says PS i believe he is referring to the power supply now i may be wrong

redox - 11-8-2011 at 04:23

Quote: Originally posted by #maverick#  
when he says PS i believe he is referring to the power supply now i may be wrong

Thanks Mav, that makes sense.

m1tanker78 - 13-8-2011 at 06:39

PS[U] = power supply [unit].

If the scale performs an auto-zero when it's powered up (don't see a discrete button) then you could probably get away with using a more crude solution for the power supply. Or, you could just 'tare' the unloaded scale as needed. If you have a handle on basic electronics, your best starting point would probably be a 24V center-tapped transformer. These are almost annoyingly abundant in a typical electronics junk box.

Another option is looking for a split rail integrated circuit and working up from there. You'd be surprised at the availability of circuits-on-chip nowadays.

Personally, I'd buy a cheapie Chinese scale and make it work while getting around to repairing or replacing the faulty PS. If you're certain that the PS is dead then tear that son of a bitch apart. You have nothing to lose and may even find the problem and be able to repair it.

Just sayin'