Electronics > Repair

Commercial scale help repairing it

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BobLab:
Well, I replaced the bridge rectifier and the filter cap, now we have around 7,40V across that cap, and the LM317T output is measuring 5,84 ~ 5,90V, the adjust pin is measuring 5,35V. I guess the filtering stage is fixed, but still lighting random segments of the seven segments display every time I turn on and off the board, nothing (smart) going on   :-//

fmashockie:
Thats great! So it appears you've fixed the power supply and battery charger for the board.  Now you need to troubleshoot the digital side.  I would see if you can locate a datasheet for that large AMTEL micro/pid.  Do you at least have a user manual for the scale?  Maybe it can tell you what that sequence of LED lighting means (if it means anything).  But without a schematic for this, you'll have to rely on things like datasheets for each of the digital chips and make measurements with your DMM to see if everything is making sense.  Maybe the micro has a reset pin that is pulled high or low causing it to be stuck in reset mode.  You'll have to check for things like that.  You are also very limited with the tools you have.  Do you have an oscilloscope?  If so, you can check to make sure the micro's clock generator or oscillator is working (and you check for a number of other things).  But at this point this is where you have to ask yourself if it is worth the time to keep working on it. 

BobLab:

--- Quote from: fmashockie on September 26, 2023, 02:11:30 pm ---Thats great! So it appears you've fixed the power supply and battery charger for the board.  Now you need to troubleshoot the digital side.  I would see if you can locate a datasheet for that large AMTEL micro/pid.  Do you at least have a user manual for the scale?  Maybe it can tell you what that sequence of LED lighting means (if it means anything).  But without a schematic for this, you'll have to rely on things like datasheets for each of the digital chips and make measurements with your DMM to see if everything is making sense.  Maybe the micro has a reset pin that is pulled high or low causing it to be stuck in reset mode.  You'll have to check for things like that.  You are also very limited with the tools you have.  Do you have an oscilloscope?  If so, you can check to make sure the micro's clock generator or oscillator is working (and you check for a number of other things).  But at this point this is where you have to ask yourself if it is worth the time to keep working on it.

--- End quote ---

I will post the datasheet below, I did a quick read at the pins description, looks like it resets with a high logic level on the pin 9 of the microcontroller, also the signal comes from the collector pin of the PNP transistor(BC328), measuring the pin 9 with the DMM it shows 90 ~ 100mV.
About the user manual I don't have it anymore, I just remember when the scale was turned on(when functional), the brand logo c&f appears on the display, unfortunately like you said, I'm limited with just the DMM no oscilloscope.
The other digital IC's are all receiving the supply voltages, there's another atmel smaller chip no idea what's that for.
I'm working on it for fun when I have some time left, so it's ok, thanks again for helping dude, much appreciated!

fzabkar:
I found the old web site:

https://web.archive.org/web/20100218133427/http://www.cfbal.com.br/paginas_dinamicas/detalhes.asp?iType=82&iPic=641

It seems to have only 1 manual, though:

https://web.archive.org/web/20141222102437/http://www.cfbal.com.br:80/CF_Computadora_2013.pdf

BobLab:

--- Quote from: fzabkar on September 28, 2023, 03:07:16 am ---I found the old web site:

https://web.archive.org/web/20100218133427/http://www.cfbal.com.br/paginas_dinamicas/detalhes.asp?iType=82&iPic=641

It seems to have only 1 manual, though:

https://web.archive.org/web/20141222102437/http://www.cfbal.com.br:80/CF_Computadora_2013.pdf

--- End quote ---
Thanks, that will help!

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