>>..Final problem was it would not zero properly. The zero circuit uses two diodes to make a +/- 0.6V supply driving the offset pot. The unit was offset so that you could not reach zero and the offset pot had fairly little range. Adjusting the chopper didn't help. I replaced the diodes with three 1.2V reference chips (making a -1.2 to +2.4V supply). This centered the zero adjustment and gave better range... Hi Mark, this problem seems to be related to the mechanical, reed contact chopper. This device had to be replaced very often, when I worked in a cal lab about 30 years ago.. I wonder if the unit realy works oK after your modification. Try to replace the mechanical contact by a FET., like in later Fluke designs.. Frank

As usual the Google translation is awful, but here you get to see the inside of an LTZ1000. There's also a downloadable PCB design (I think) although I wouldn't know the format. Alan