Racal-Dana 5004 multimeter (was display segments, now on to others probs)

[valley001]

Hello all,

I got a Racal-Dana 5004 multi meter incoming for what I think is a decent price.  One thing I know is wrong with it is one segment on each display digit does not light.  It appears it may be the same segment on each digit.  I am wondering if anyone has had experience with this fault in the past, and what I should look at when it arrives.   Is this a multiplexing fault of some type? 

[coromonadalix]

Most display instruments are somewhat multiplexed, that way you can save on many pcb space, data lines  etc ...

If the same segment is off on many displays, you know its multiplexed in a way,  you'll have to find the schematics or try to decipher how your display is working, drivers ic's  etc ...  maybe a bad solder, a broken trace, failed driver ...

I only found out a 5001 model ??

[valley001]

So it turns out the display is just fine, all segments operating normally. 

I assumed the internal calibration factors would have been lost due to the age of the 3v lithium batt, but they are intact.  The batt looks sort of like a cr123, I wonder if I could simply replace the original with a fresh cr123?  Amazingly it still shows 3v on my DMM.

I bought this because it was cheap and in very nice cosmetic condition, but also to use as an additional comparison for my Fluke 332D.  With the 332D set to 1v the Dana 5004 dithers 20-40 counts above and below 1.00000 but it never settles.  I am wondering if this could be a fault with the meter.  I have been browsing the manual and it appears it should be able to display a stable reading. 

If this is indeed a problem, does anyone have advice on where to look first? 

I did notice three large electrolytic caps (C82, C80, and C77) on the mother board show evidence of heating, their outer plastic shrink wrap coating has melted through in spots.  I checked them in circuit with my component tester and they test in spec with low ESR. So?  I think these are PSU filter caps so could ripple impact the stability of the meter?

Edit:  I checked the output of the 332D on my scope I am seeing around 16-20mv p-p ripple. 

[Chris56000]

H?

I would definitely have a look at your 332D's bookwork again – 15–20mV on a calibration source is definitely a bit much for that type of instrument and  may well be enough to cause the LSD on the display to jitter – especially with modern a/d converters!

Are you sure the 15–20mV p–p isn't simply "grass" from the oscilloscope amplifier itself that you monitored the calibrator's output with?

Chris Williams