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Sartorius vs Technomaniac - who will win ?

Technomaniac

Oct 31, 2020
100
Joined
Oct 31, 2020
Messages
100
Sartorius PMA7200X Electronic Scales.
Hadn't worked for years, been replaced by a new model and shelved in the Panel Shop that used to be across the street. The spray painter used it to weigh out the portions of paint to arrive at the manufacturers paint colour. When I received it as a boat-anchor gift, there was no digital display.lit. The 240 to 12v power supply was epoxy encapsulated and no output, so as I run from 24 volts off-grid, I decided to run it from a 24 to 12 volt regulator. The output cable from the little power box had but two wires, blue and black. Several months ago, I had the thing on the bench, and had been at the display module, which uses what my circle of colleagues calls a BLOB. Its a chip thats built on the PC board and covered with a little hill of epoxy resin. There was a flexible ribbon film involved, and from memory it ended up with several little links and patches to reconnect the display to the blob once again. So I had it working until I lost three little rods which fit between the pushbuttons and their appropriate switches. When you have the thing apart, they fall out, never to be found again. You don't expect them to fall out, you think that the button sits on top of the switch and that's it. But NO, theres these little rods in between. They sit in holes in the buttons. Anyway, I spent several hours looking, and decided that I probably didn't need the buttons to function, and hoping they might appear at some future time.
The project was shelved again. I have a Chinese electronic scale in the office for weighing things to be mailed. I sometimes repair mechanical clocks, and I have several ultrasonic cleaning machines. Prepairing the chemical mix for these, requires the weighing of several chemicals. I have in the past, done this in the office, which I was not too happy about. So I thought this Sartorius could be located in the workshop near the sink, and be put to use again.
I had just received in the mail a couple of Chinese 24 to 12 volt regulators so I connected one up to the scales. But stupidly, it was late in the day, and I was tired, and I assumed that blue was positive and black was negative. It seems I was wrong, as the display didn't light and the smell of burning semiconductors wafted through the workshop.
So thats where the story pauses. The photo shows the two little surface mount devices that are burned beyond recognition. Diodes or chokes or low value resistors, or a mix. At least one smelled like a diode. I have a three- terminal regulator close by and the rail doesn't appear to be to ground. So we might be lucky. Otherwise, no great loss.
I don;t know why they would use such colours, though I can recall some early Oriental gear that had a red earth wire.
SartoriusPC.png SartoriusScale.png
You can just about see the two burned devices at the bottom of the picture. They are in line with each other. I apologise for the photo. It seems that black is positive and blue is negative.
 

Technomaniac

Oct 31, 2020
100
Joined
Oct 31, 2020
Messages
100
Silicon diodes have a particular smell when burning, silicon transistors the same. Selenium diodes (getting rarer) have their own smell as well. Probably both toxic. I couldn't believe how long the burning smell lingered in the workshop after the power to the device was shut off. One thing every electronic engineer should experience is the tantalum capacitor. When put on reverse polarity they go off like a gunshot. I had a friend years ago who was into little theatre stage plays and making movies. He had a row of electrical switches and fuses across the mains to produce gunshot sounds as required.
 
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