Re: DM501A vs DM502A
It is possible that what happened is that you calibrated out the zerotoggle quoted messageShow quoted text
error caused by leakage at the high impedance input to the LD120
(U1601) using the zero adjustment. R1613 (560k) is in series with the
input and allows leakage to cause an offset error even when using the
200mV or 2V ranges. Then the change in Thevenin equivalent resistance
when the ranges are changed would show up as offset.
You can test this by adding some series resistance while using the
200mV or 2V ranges and seeing if the measurement changes. The leakage
current is then the change in voltage divided by the series resistance
and should be significantly below 1 nanoamp. Leakage should be in the
10s of picoamps.
The leakage does not necessary have to come from the LD120 (U1601) but
it is the most likely source. Since they are difficult to replace, I
would rule out other sources first.
My DM501A displays similar problems but I have not gotten into it yet
to figure out what is going on. I think I am going to go the whole
refurbishment route including cleaning the boards and changing the
aluminum electrolytic capacitors before
On Thu, 3 Nov 2016 19:58:33 -0700, you wrote: