Improving the Sabtronics 2000
— make a good DMM even better
Easier maintenance is a bonus.
the Model 2000. I found that they noticed the same problem.
Fortunately, the design error is easy to correct I
will describe the necessary modification, plus a relocation of the fuse holder and installation of nicad batteries and a charger for convenience.
After 1 studied the board layout and schematic for the DMM, I tried a few things that looked as if they might correct the trouble. I found that if ! unhooked the +6 volts that powered the decimal points, the meter would zero properly. Apparently, the high level dc line that feeds the decimal points is located too near the low level ac lines on the main PC board. You can see there is quite a mess of traces carrying the various signals to the range and function switches if you check the layout diagrams in the manual.
Before ! describe the modifications 1 made to the circuitry, 1 want to say that I have had no contact with Sabtronics on this matter. 1 hope they corrected the problem in later model runs, but ! do not know. Obviously, you can check to see if your meter has the problem by simply
James D. Powell il N8AMR/4 6400 J Terrace View Blacksburg VA 24060
Shortly after the ad for the Sabtronics Model 2000 digital multimeter appeared in 73 Magazinet I sent in my check for one. I suspect ¡hat quite a large number of other people did the same, since my order was delayed several weeks. When the DMM finally arrived, I assembled the kit and, to my surprise, it worked the first time I
„■ivj ■ p l. m 7« . j!>?. ■ . -"j . i turned it on. After calibration, using the supplied resistors as references, the meter's performance compared quite favorably to that of a more expensive DMM.
I was pleased with the meter for its performance, and pleased with myself for taking advantage of a good deal, until I noticed the meter would not zero on the ac scales. With the input leads shorted, the display would eventually settle down at about 0.5 volts on the 10,0-volt scale. A quick check showed that all of the ac voltage and current scales were affected.
At first I assumed that I had made some mistake in construction, but checking with two other owners of
Photo 1. This is the display board of the Model 2000 DMM, showing the added transistors that drive the decimal points.
Was this article helpful?