Electronics > Repair

Repairing a Siemens B1045 Multimeter

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Yes, I did it again. Just bought another bench top multimeter off ebay. Of course one that was sold as broken, in the past that has always worked out. I always managed to get them back to life, just trivial failures.

But first things first. The B1045 is quite a nice meter, 5 1/2 digits, auto ranging V-Ohm-Amps, 4-wire ohms function. The smallest range is a bit unusual, it is 0.2, so that effectively gives you a resolution down to 0.00001V, very nice indeed.
This meter also appears to be a genuine Siemens design, not like their handhelds from the same time that were made by Norma in Austria.
My unit was probably made sometime between 1979 and 1981. They are rather rare, they don't show up much either on ebay or at the various used test gear sellers. And if they do and are in working condition they fetch relatively high prices.

I got my meter yesterday, tried it out immediately and found it really didn't work. It only shows random numbers on the display and has some sticking buttons, cosmetically at least it's good.
Tonight I opened it up to have a quick look inside. Nice design with real computer contol, there's a 8085 SBC inside doing all the heavy work. I'll talk about that in a future post, also photos will come later.

The reason I'm writing this now is because I'm somewhat pi**sed off. Somebody's tried to repair it before me and they really made a mess of things. This blithering idiot just bridged a 7812 regulator, thus feeding unregulated 22V into a big part of the circuit |O. Needless to say there are plenty of 4000 series in it. As we all know they're only happy up to 18V. Also needless to say they are not socketed. I pulled two at random and tested them, both fried, of course.

This numpty tried to find a fault in the PSU region, cutting traces willy-nilly, most of them in two places :palm:. Instead of bridging the cuts with a short piece of wire, they created a rats nest of hook-up wires on the bottom of the PCB :wtf:. I had to sort all that out before I could even start my own fault finding. While knitting this mess of wires the idiot jumped across the regulator and made things 10x worse.
At least the SBC is still ok, thanks to its separate 5V supply.

Good luck with the repair, do post pics.


--- Quote from: david77 on March 22, 2014, 01:30:07 am ---they created a rats nest of hook-up wires on the bottom of the PCB

--- End quote ---
Before and after pictures would be appreciated.

Hell yeah very intrresting'!

If there is one thing I really hate, its when an unqualified person has already had a go at a piece of faulty equipment. 'Virgin' equipment is usually pretty 'honest' in that it once worked and then something went wrong . Equipment that has already been 'got at' can end up with a multitude of additional faults introduced by the previous 'tech'. I have discoved chips inserted in sockets, or soldered into PCB's reversed  :o and components that had been replaced by 'compatable' parts that weren't ! Cut traces are an awful discovery as well..... especially if not done in a professional manner. The single worst discovery I made was an expensive bit of kit that someone had just gone around replacing chips in. Fine to a point, but not when they replaced a MPU that contained ROM. The new part was without programming  :'( . That unit ended up as scrap.

I love to see faulty kit with its original calibration seals intact.... its a Virgin  :)


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