Hello all,
I have here a Dana 5004 digital multi meter. It seems to function in DC mode except I get strange drifting on zero that at first I attributed to my 332D not operating correctly. I have shifted focus to my voltmeter and decided to check voltages. I checked some of the marked voltage rails on the PC board and
see AC signals on almost all of them. WTF.
Attached is the PSU schematic, and an image of what I am getting on my scope. I am probing a point downstream of C84, basically TP15 though there is no such test point on my example.
The only DC signal I am seeing is the +5v that seems to be associated with the logic components.
The really crazy thing is I get this small AC voltage with the power off and the mains cord un plugged.
Maybe this is from the memory save batt? EDIT- I get this small AC signal if I touch my fingertip to the probe, so this must be some sort of signal originating from the scope itself? Maybe ill do a self calibration on it.
If I test these points (where is should see +36v DC) with a simple DMM I get voltage readings nowhere near correct.
I did check the voltages on the transformer taps and they are present.
Am I doing it wrong or is there is severe problem with the bridge rectifiers and associated caps in the PSU? CR16 and CR20?...and if so, how the heck has the thing been working at all?