Author Topic: Retro teardown - Precision Gold WG021 (multimeter)  (Read 4407 times)

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Offline pmrlondon

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Retro teardown - Precision Gold WG021 (multimeter)
« on: May 07, 2011, 08:22:59 pm »
There is camera shake on some of these - not a lot I can do about it - I made several attempts.

I was planning to try to repair this malfunctioning multimeter, but it fell apart in some more ways as I was attempting to - but I did take photos of the teardown. First, a description of the meter. It is a 4000-count manual ranging meter, capable of current up to 20A - though what its maximum continuous current is, I never knew - with capacitance and inductance (using a front panel socket), as well as hFE (!), logic and frequency, as well as all the usual stuff. Non-latched continuity - that could sound rough, but it worked. It had MAX hold - a little better than simple hold which is what my new Amprobe has but not as good as touch hold. The yellow holster you can see was an optional extra - but one I always had.



Over the years, the foam strip on the battery cover fell off. No great problem. I also have to say the tilting bail on this meter never let me down in any way. The cover is held on by two captive machine screws - yes, this meter has metal threaded inserts.



The battery compartment also gives access to the two HRC fuses - a 500mA and a 20A. There is also a space by the battery for a spare 500mA fuse. Some components can also be seen, including one socketed IC - did they expect such trouble with that as to need to put it socketed in the battery compartment?



The rest of the case was basically clipped together - easy to open. The components are mostly through-hole, but with some surface mount components.
One long wire link seems a bit crazy, but not bad on the whole.



There are no MOVs in this meter, but there is a PTC.



A close-up of the socketed chip - not one I recognise.



The components near the top of the board include a 4000-series.



The back of the case has foil shielding and the buzzer.



On the front of the board, typical arrangements for range switching - lots of it due to manual ranging. Note the split, somewhat shrouded inputs.



The range switch has 9 contacts, and there are two buttons - one for the MAX hold soft switch and one for the mechanical AC/DC switch. The knob is not held in with the board out and depending on ball bearings to make it work well.



So, there's my first teardown.
 

alm

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Re: Retro teardown - Precision Gold WG021 (multimeter)
« Reply #1 on: May 07, 2011, 09:25:16 pm »
The JRC072D is a TL072 (dual op-amp) variant, I think. Possibly for the AC or buzzer function.
 

Offline saturation

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Re: Retro teardown - Precision Gold WG021 (multimeter)
« Reply #2 on: May 08, 2011, 05:53:48 pm »
Great job!  Its appears as a well made DMM for its time.  It doesn't have the spark gap spacings on the PCB which is added for safety for high voltage transients.  If you repaired it to working order, and don't use it only at most to CAT II levels, it could serve as a backup meter, but retiring it is also an option.  It has served you well.
Best Wishes,

 Saturation
 


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