Fixing A Broken Postage Scale

[Starhawk] had an old Pitney Bowes G799 postage scale that wasn’t working as it should. After years of faithfully measuring packages and cooking ingredients, the scale stopped working. At first it fell out of calibration. Then the power up sequence stopped working. The scale normally would turn on, light up the entire display, then change to dashes, and finally set itself to 0.0 lbs. In this case, it would get stuck at the dashes and never change to 0.0.

[Starhawk] ended up purchasing another duplicate scale from eBay, only to find that when it arrived it had the exact same power up problem. Using deductive reasoning, he decided that since the scale was broken during shipping the problem would likely be with a mechanical component. He turned out to be correct. The cheap momentary power button was at fault. When pressing the button, the contact would get stuck closed preventing the scale from zeroing out properly. [Starhawk] easily fixed his problem by replacing the switch.

Next [Starhawk] replaced the old scale’s LCD module with one from the new scale, since the old one looked to be on its way out. The scale still had a problem correctly measuring weight. [Starhawk] tried swapping the load cell from the new scale to the old one, but he found that the new load cell had some kind of problem that prevented the scale from zeroing out properly. The solution ended up being to use the newer “analog board” as [Starhawk] calls it.  The end result was the old scale with two newer circuit boards, an older load cell, and a new power switch. Next time it might be easier to just build his own scale.

7 thoughts on “Fixing A Broken Postage Scale

  1. Wouldn’t it have been easier to just use the new eBay scale?

    So his scale was broken, he brought another one, fixed the minor shipping-induced fault in that, then started pulling parts out of it to fix the broken old one.

    Ok, everyone needs a hobby I suppose.

    I guess “compare working new scale against broken old one to deduce the fault” didn’t occur to him.

    Or maybe it’s a case of the summary being wrong again (who could be bothered to RTFA anyway?).

    1. OP here.

      The two scales were different revisions. Comparing got me basically nowhere, because the important part (the Analog Board, if you read the article I wrote) was completely different. Not a whole lot to compare…

      The button problem was on both, and I fixed it on the old scale first. Fixing it on the new scale did not fix the new scale, because the new scale had a problem with the load cell (well, OK, I didn’t know that yet, it had an “unidentified problem preventing it from zeroing” at the time ;) ).

      RTFA, please, I spent some time writing it, and I tried to make it an entertaining read. Lots of dumb jokes / refs / etc.

      Funny thing, I’d forgotten this till now, but I actually at one point had considered rebuilding it from scratch using a PICAXE (I don’t speak Arduino… system-level incompatibility with the C family. I can sort of read it and that’s all)… obviously that scratch-built scale did not happen.

      1. You should try an Arduino, don’t use the Tarduino studio, just use the standard Atmega C environment, I use AVR GCC on windows personally, It will program in C. Once you reflash an arduino to ditch the bootloader you are good to go. Since you are erasing the serial bootloader, why not get an Arduino Nano (Only $2.25 apiece; just an SMD chip and a minimal breakout PCB http://www.ebay.com/sch/i.html?_from=R40%7CR40%7CR40&_sacat=0&LH_BIN=1&_nkw=arduino+nano&_sop=15 )

        To Program you need only a ~$4 AVRISP, just another Atmega loaded with an in-circuit programmer USB software.

        Not hard to do, really, and pretty cheap too.

        1. You know, if I could do C, that would be a great idea… alas, I’m a BASIC boy ;) believe me, I’ve tried, C just ain’t happening. I kinda wish it would, BASIC is kinda, well, basic, but it’s just not in the cards… can’t make my head think the right way.

          Maybe someday that’ll change… we’ll see…

    1. Not a dime a dozen! This scale is a wee bit old… IIRC like a decade. They don’t make ’em any more!

      Cheapest one on fleaBay (the one I bought) was a seasick Jackson. Seller only had the one, as well. (For the record, I did get a refund.) There were two others which were more expensive, and that’s all. Most of the ones up there seem to be the USB kind — which won’t work for me because (a) no computers in the kitchen please and (b) I like Linux. AFAIK (not that I’ve looked much, TBH) that’s one sort of program that’s not open source yet… unfortunately…

  2. You know, I’m honestly surprised nobody has brought this up… but…

    To the “not a hack” folks — define your terms, please. To me, ‘hack’ means, in practice, improvised repair and/or construction of a device, or careful construction of a device ‘for fun’ more than to solve a problem. (Usually that device is technological in nature, but I’m sure there are exceptions — can’t bring any to mind at the moment.) For example — “I hacked together a new remote control for my TV, when the old one broke.”

    I do realize that this definition isn’t official — it’s primarily how I explain it to other people who are used to the term being misused to represent certain activities which are far less legitimate.

    To the “not enough Arduino” folks — I have no defense, sorry. I do own a Mega (traded for it some time ago) but I haven’t used it yet because the C family of languages is very hard for me at best… I grew up on QBASIC ;) my first computer that was mine ALL MINE BWAHAHA — oh, sorry — was a 386… I learned a bunch on it and it was fun :D I’m still using that language, actually — let’s just say I’ve got something kind of interesting and odd in the works and leave it there… my tool of choice (since I’m on Linux on my main box) is a Toshiba 486 laptop that a friend thought I’d like to have (he was very, very right!); I’m using QuickBASIC PDS 7.1 on it…

    To the “too much Arduino” folks — there isn’t one here :P but if you still don’t like it, I’m sorry to hear that.

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