Dana 5004 troubleshooting- voltages all screwy - Page 1
Forum section: electronics / repair

author: valley001
author_rank: Frequent Contributor
timestamp: April 08, 2019, 08:21:20 pm
content: 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 andsee 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?

author: coromonadalix
author_rank: Super Contributor
timestamp: April 08, 2019, 08:27:28 pm
content: are you taking measurement relative to the tp17 ground ?You have many voltages in it, lots of it.Can you post the schematic on a free hosting site ... cant find it easily ?1.64v pk pk is high, but you are on an unregulated line ...

author: valley001
author_rank: Frequent Contributor
timestamp: April 08, 2019, 08:45:50 pm
content: 5005/6 is basically the same I think, I had some luck here:http://www.ko4bb.com/getsimple/index.php?id=manuals&dir=RacalI am taking the reading referenced to ground. Unless I am missing something it should be a 36v DC signal, but I am seeing 1.5v pk-pk AC signal centered around 80mv.Quote from: coromonadalix on April 08, 2019, 08:27:28 pm

author: coromonadalix
author_rank: Super Contributor
timestamp: April 08, 2019, 09:53:02 pm
content: Did you took measurments with an dmm ?do a spread sheet with the ''normal voltages values'' and write down what you have in dc and ac for the ripple

author: valley001
author_rank: Frequent Contributor
timestamp: April 08, 2019, 10:06:31 pm
content: Quote from: coromonadalix on April 08, 2019, 09:53:02 pmI took a reading with a DMM thinking that I may not be using the scope correctly.I will do that. I should not see a full sine wave signal from what should be a DC signal no? Ripple would not appear as a full sine wave would it?

author: coromonadalix
author_rank: Super Contributor
timestamp: April 08, 2019, 11:13:12 pm
content: If you have died capacitors on the line, maybe it could get like this, the capacitor is smoothing the dc line ...While powered off, add an capacitor on the line, say 1000uf 50volts and check how it goes powered on ?