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Electronics => Repair => Topic started by: pmrlondon on April 24, 2011, 01:30:17 pm

Title: Repairing my old multimeter...
Post by: pmrlondon on April 24, 2011, 01:30:17 pm
I am about to buy a new multimeter, but am hoping, once I have it, that I can also repair my old one. The old one appears to have two faults, one of which I have an idea as to what it might be.

The meter is a Precision Gold WG021 - I've had it 15 years and it gave me no significant problems until it stopped working four years ago.

The main fault: the meter seems to be unreliable on AC - giving strange, stuck readings. As AC/DC selection is by a mechanical switch, I suspect either the switch or some of the diodes may have gone wrong. There were stuck readings on most ranges before, but I found a broken resistor and soldered it back together. Now it works OK on DC but not on AC.

The odd fault I haven't a clue about... on the 4000M? range, shorting the probes together gives a reading of 19. On the lower ranges, it reads 0, or on 400?, 0.2 or so, so the reading of 19 has to be something in the meter only applying to that range. (the meter is manual ranging, except on Hz)

Is this meter likely to be worth repairing? Does anyone on the forum have an idea as to what these faults might be?
Title: Re: Repairing my old multimeter...
Post by: saturation on April 24, 2011, 02:33:32 pm
That brings up an interesting question: when should we retire old test gear?  As EE we can maintain our gear far longer than consumers, and even upgrade them to better specs.  In multimeters some sections can be obsolete, like AC, while the DC or ohms is still good.

Thus, does an EE or technician really have to buy new gear if they can maintain old ones, if its cost effective? [ Finding parts in your country versus buying a new item.]

I don't know this model MM, but I presume its digital.  Does it have CAT ratings for safety?  Does it use sheathed banana jacks?  Is its rated accuracy on AC less than 1% on all ranges? Is it true RMS?

If the answer is no to any of them, the meter is obsolete but its still useful if you only use line voltage.  But for tasks requiring measuring AC voltages at many frequencies or wave-shapes, the meter isn't capable.

One issue is cost, if you can afford a new DMM its better to upgrade for the safety features of CAT ratings, even if you can repair this DMM.  One can still buy a meter with similar specs of your 15 yr old DMM for much under $US50 and CAT rated for safety.
Title: Re: Repairing my old multimeter...
Post by: Kiriakos-GR on April 24, 2011, 05:12:00 pm
Hi Phil ,  the link of your web page is not set correctly on your local profile, but i found my way.  :)

Quote
I am about to buy a new multimeter, but am hoping, once I have it, that I can also repair my old one.

What do you have in mind ?

The true good ones, that can be used as true reference , they cost some serious money. 

Title: Re: Repairing my old multimeter...
Post by: pmrlondon on April 24, 2011, 07:40:49 pm
My (already chosen) new meter will be an Amprobe 37XR-A. I will be getting it in a few weeks.

The Precision Gold WG021 is digital, 4000 count. No CAT ratings are marked on it at all. The jacks are sheathed up to the height of the contact. Not true RMS and not sure of the accuracy as I haven't seen the manual for a while. HRC fuses, 500mA and 20A, and there is a PTC in it. It has the virtually useless hFE function, and a body L/C socket rather than being able to measure inductance and capacitance with the probes. Manual ranging, except on Hz.
Title: Re: Repairing my old multimeter...
Post by: saturation on April 24, 2011, 10:57:08 pm
Sounds like time for upgrade and the Amprobe is a fine meter.

One thing with instruments is a matter of trust and daresay, faith.  Sure it works now, but when will it fail? So while repairs can revive an old friend, it may not be the DMM you'd want to take to a difficult job site or underneath a tight crawlspace to measure something and then not trust what you're seeing.




Title: Re: Repairing my old multimeter...
Post by: House91320 on April 25, 2011, 01:01:07 am
pcb pics pleas
Title: Re: Repairing my old multimeter...
Post by: pmrlondon on April 25, 2011, 07:38:01 am
Indeed, the Amprobe will be the one that gets used most. Thinking of possibly hanging on to the PG for those situations where two meters are useful at the same time. The Amprobe will be the one that travels, often to awkward corners of caravans and so on.

I fully intend to at least post pics of the inside of the PG before I start doing any work on it. If I do manage to restore it, I will say what I found wrong.

If my need for an additional meter gets really serious, I intend to save up for possibly a Gossen Metrawatt. I have found few suppliers over here, carrying very few models, but I would have a further look and maybe even check prices in mainland Europe.
Title: Re: Repairing my old multimeter...
Post by: saturation on April 25, 2011, 10:02:08 am
Yep, the way Dave and jahonen use it, it speaks for itself.  Its got many unique features good for EE class of use. 

Quote from: pmrlondon on April 25, 2011, 07:38:01 am
Indeed, the Amprobe will be the one that gets used most. Thinking of possibly hanging on to the PG for those situations where two meters are useful at the same time. The Amprobe will be the one that travels, often to awkward corners of caravans and so on.

I fully intend to at least post pics of the inside of the PG before I start doing any work on it. If I do manage to restore it, I will say what I found wrong.

If my need for an additional meter gets really serious, I intend to save up for possibly a Gossen Metrawatt. I have found few suppliers over here, carrying very few models, but I would have a further look and maybe even check prices in mainland Europe.

Title: Re: Repairing my old multimeter...
Post by: Tony R on April 25, 2011, 01:31:20 pm
My policy is to get flukes with a "lifetime" warranty, which basically means at least 10 years. Once it is up, use it until it dies, but nothing where safety becomes an issue on and nothing that requires that much accuracy. don't stick any more money into it just replace it when it dies.

My thoughts are if fluke wont support there product anymore, there must me reasons why...

Being this DMM has not a cat rating on it and is not fully working, it would be fine for measuring some stuff in it, but i wouldn't stick to much cash into it and I wouldn't test your outlets with it.

Plus if you do the math, spend 300 dollars or so on a nice fluke, it will last 10 years, your spending about 30 bucks a year on a DMM, Not to bad really...

I would think about retiring it.
Title: Re: Repairing my old multimeter...
Post by: saturation on April 25, 2011, 05:22:08 pm
I think robustness plays a great deal too in a DMM's success or long service life.  Its made Fluke's rubber sleeve so successful.  Although the 80 series is only IP 30 rated versus 'rugged' being roughly IP 67, its design does take common field ab/use well [ table drops, extremes of climate: hot, cold, humidity, survives rain but needs to be dried before use].  Many DMM in Dave's review survive a table drop, but real life drops happen very often, so not sure if the criteria is one drop, or drop repeatedly at that height.  Since the 80 series has been around over 20 years, its reputation for physical abuse is well known.
Title: Re: Repairing my old multimeter...
Post by: Kiriakos-GR on April 25, 2011, 11:40:58 pm
If some one could speak about DMM abuse , this one could be only an electrician,
by owning the Fluke 28II , I will not have to worry about falling from a ladder . ( not me, the DMM )  :D

At the soft handed professionals, that do only electronic repairs on bench ,
any DMM it will survive from falls ( 1 meter drop ) , but I can not tell the same about the high voltage of a fly-back  ;)  
Title: Re: Repairing my old multimeter...
Post by: tekfan on April 25, 2011, 11:51:11 pm
Quote from: Kiriakos-GR on April 25, 2011, 11:40:58 pm
If some one could speak about DMM abuse , this one could be only an electrician,
by owning the Fluke 28II , I will not have to worry about falling from a ladder . ( not me, the DMM )  :D

At the soft handed professionals, that do only electronic repairs on bench ,
any DMM it will survive from falls ( 1 meter drop ) , but I can not tell the same about the high voltage of a fly-back  ;) 

Don't mess with flybacks. You'll almost certanly destroy your meter unless you have a high voltage divider probe designed to handle 40KV+ voltage spikes.

Recently I saw a bus/car repair technician with a Fluke 123 scopemeter. It was completely dirty (black, not yellow). It must have had a very hard life but it still worked as it should.
Title: Re: Repairing my old multimeter...
Post by: Cj1corbystarlet on April 26, 2011, 04:21:16 am
I have a Fluke 75mk3 from memory, as a Electrician it gets hammered every day at work, 

After 12 years of daily service the battery went flat, replaced the battery and all is good.

Cant beat a good Fluke.

regards
Ben
Title: Re: Repairing my old multimeter...
Post by: Kiriakos-GR on April 26, 2011, 01:34:42 pm
Quote from: tekfan on April 25, 2011, 11:51:11 pm
unless you have a high voltage divider probe designed to handle 40KV+ voltage spikes.

Well i do have it , so to feel complete .  :)

(http://img827.imageshack.us/img827/7558/flukemodel80k4002.jpg)


Title: Re: Repairing my old multimeter...
Post by: Kiriakos-GR on April 26, 2011, 01:36:47 pm
Quote from: Cj1corbystarlet on April 26, 2011, 04:21:16 am
After 12 years of daily service the battery went flat, replaced the battery and all is good.



Hi Ben , I bet that in your message,  the correct word are months instead of years   ;D

My regards to you too.

Title: Re: Repairing my old multimeter...
Post by: saturation on April 26, 2011, 02:04:10 pm
12 years, if true is truly impressive! Given what I've seen of electricians and service folks who use Flukes, what really kills DMMs is more likely physical abuse than electrical mishap; the latter can happen and lead to injurious consequences for the user but its rarer than dropping a DMM from a ladder 12+ feet off the ground, into a concrete walkway.


Quote from: Kiriakos-GR on April 26, 2011, 01:36:47 pm
Quote from: Cj1corbystarlet on April 26, 2011, 04:21:16 am
After 12 years of daily service the battery went flat, replaced the battery and all is good.



Hi Ben , I bet that in your message,  the correct word are months instead of years   ;D

My regards to you too.


Title: Re: Repairing my old multimeter...
Post by: Cj1corbystarlet on April 26, 2011, 02:59:43 pm
I'm serious yes my Fluke is 12 years old  :)

I do have to admit i work on industrial machinery and control panels, so it does not get abused, but the Fluke is on her 3rd set of probe leads.

I must get a HV divider probe, as i'm working on some rather interesting HV projects at home........

Ben
Title: Re: Repairing my old multimeter...
Post by: saturation on April 26, 2011, 07:15:42 pm
That's great, but did you only change the battery once in 12 years?

Quote from: Cj1corbystarlet on April 26, 2011, 02:59:43 pm
I'm serious yes my Fluke is 12 years old  :)

I do have to admit i work on industrial machinery and control panels, so it does not get abused, but the Fluke is on her 3rd set of probe leads.

I must get a HV divider probe, as i'm working on some rather interesting HV projects at home........

Ben

Title: Re: Repairing my old multimeter...
Post by: Kiriakos-GR on April 26, 2011, 09:08:39 pm
Quote from: Cj1corbystarlet on April 26, 2011, 02:59:43 pm
I'm serious yes my Fluke is 12 years old  :)

Ben


From what you typed , it sounded like that your battery lasted 12 years in it ..  :)
Title: Re: Repairing my old multimeter...
Post by: Cj1corbystarlet on April 27, 2011, 10:59:57 am
Yeah sorry guy's my initial post was a little confusing (Even to me ! :-[ ), First battery did last about 8 years, second one about 4 years, and its got a 3rd fresh battery battery in it now.

I must pre-read my posts before hitting the go button.

Ben
Title: Re: Repairing my old multimeter...
Post by: Kiriakos-GR on April 27, 2011, 11:20:50 am
No problem mate.  :)

Its good having you around.
Title: Re: Repairing my old multimeter...
Post by: vk6zgo on April 27, 2011, 04:57:00 pm
I think people get a bit overwrought when it comes to CAT ratings & the like.

 Out of the huge numbers of Radio & TV Transmitter Techs,EEs & Electricians that over many years have used such things as AVO model 8 multimeters,Fluke 77s,the early Beckmans,etc,the number of people injured due to deficiencies in their meters is vanishingly small.

How many times would the average user really need "true RMS"?
If you need to worry about the waveshape,use an oscilloscope!

OK,if I was buying a new DMM,I would go for all this stuff,but my Fluke 77 still
works,& doesn't have the strange habits  of some cheap replacements.

Dear old UNI-T ! great if you have plenty of spare time to wait for it to deign to give you a reading.Or,I love the way the resistance ranges go inaccurate with a dying battery,BEFORE the low batt indication comes on!

Another cool thing is the way the thing turns itself off when you are in the middle of a reading!'Even the new Flukes do this!(Although you can disable it).

The 77 will turn off if there has been no measurement activity for a while,but not
bang in the middle of a reading.


GRRR.VK6ZGO
Title: Re: Repairing my old multimeter...
Post by: Kiriakos-GR on April 27, 2011, 06:58:39 pm
Quote from: vk6zgo on April 27, 2011, 04:57:00 pm
Another cool thing is the way the thing turns itself off when you are in the middle of a reading!'Even the new Flukes do this!(Although you can disable it).

The 77 will turn off if there has been no measurement activity for a while,but not
bang in the middle of a reading.


GRRR.VK6ZGO

+ 1000 for this info ..  It happened also to me ( 28II) even in diode mode ( the thing turns itself off ) ,
and I was working with it, testing some micro buttons , and the first though was that it died in my hands .

Why in earth to ignores that there is activity , and does not cancel the damn inner timer ?  

Either way brother,  you need an 28II , or else you will continue to feel like a poor relative with a 77 at hand.  ;)  
No matter the small nags about the 28II it is a killer .
The No1 armored multimeter for out door use , and modern and all.  

About the Dear old UNI-T , yes they are a bit slow , but is the best choice for starters ,
price / performance ,  so your nags about it , is not that justified.
But you are correct up to a point.

 
Title: Re: Repairing my old multimeter...
Post by: Ernie Milko on April 27, 2011, 07:01:13 pm
To answer the OP's question. Yes. I think you should have a look at repairing your DMM. Those old Precision Gold meters (Maplins, I presume?) were pretty good.
Chances are it's just dirt on the switch contacts. Take the meter apart and clean them with a cotton bud and some IPA.
If it's not the contacts, it could be a dry joint. Check the meter over in bright sunlight.

In this day and age, where everyone throws everything away and repairs nothing, and people upgrade every other week to the latest iphone, I think people should be positively encouraged to repair things.

And I agree 110% with VK6ZGO, above. VK6ZGO struck a chord and made me post to a thread I've read but wasn't going to post to.
Everyone gets far too excited about CAT ratings and true RMS.
When I first started (work I mean, not hobby tinkering) 30 years ago, meters were naff-all rated. And true RMS meters were made by Fluke and Bill and Dave, lived in the lab and cost five grand, and some.

And there are true RMS meters and true RMS meters. My Fluke 87IV can measure the AC and DC components of a non-sinusoidal waveform.
Many true RMS meters (such as the Fluke 179, and probably the Fluke 87V, although I haven't checked; before all you 87V fanboys jump down my throat) can only measure the AC component.
For, as it were, true, true RMS measurements, you need a meter with a thermal converter, such as a Fluke 8920, or an 8520.
And, as VK6ZGO says, if your waveform is that distorted; you're probably better off with a scope.
Title: Re: Repairing my old multimeter...
Post by: Kiriakos-GR on April 27, 2011, 07:15:59 pm
Quote from: Ernie Milko on April 27, 2011, 07:01:13 pm
before all you 87V fanboys jump down my throat


 :D :D :D :D

I loved the all message , but this part mostly.

I stand in the middle, and love and keep anything useful , no matter the manufacturing date.
But since the time that the transformers ( made of copper ) had almost stopped to exist in any modern PSU,
the need for True RMS DMM become an necessity .
I can found and many other examples , but I do not need any analog fanboys to jump down on my throat .  ;) 
Title: Re: Repairing my old multimeter...
Post by: saturation on April 27, 2011, 08:47:16 pm
I think the key issue isn't that when something breaks, you should buy rather than repair, since an EE or tech can repair quite a bit of their own stuff.  It was mentioned fairly early:

https://www.eevblog.com/forum/index.php?topic=3211.msg42897#msg42897 (https://www.eevblog.com/forum/index.php?topic=3211.msg42897#msg42897)

If a major failure happens, one should ask why did it happen?  Is the failure due to a substandard part?  Assembly?  An overvoltage or current event?  If it was spontaneous, one now has to consider if other subtle failures exists downstream from the failure point that affect the electronics' reliability due to substandard parts, exposure to higher voltages, poor engineering, assembly etc..  

Even without electrical stresses or ambient stress to initiate the failure, old electronics may have areas of whisker formation or dendrite migration.  There may be subtle stressed on junctions of many semiconductors, and none of these issues will show up immediately.  So, the question is do you wait until the overt failure is too big to ignore or already plan your backup and get another DMM as your new primary, and repair and use this meter for less critical tasks or trash it instead?

http://www.residues.com/picture_library.html (http://www.residues.com/picture_library.html)

Title: Re: Repairing my old multimeter...
Post by: vk6zgo on April 28, 2011, 02:33:24 am
In the big,bad world where Technicians exist,"fix" is often the only option,because the "suits" who control the money supply won't let us buy new stuff!

In TV Broadcasting,most equipment is extremely expensive,& is usually expected to have a useful life of around 20 years.

TV equipment made by reputable manufacturers ,when refurbished,gives results equal  to new,so there is some justification for the "just fix it " policy,which spills over to Test Equipment as well.

TV stations no longer have large Technical staffs,so rely on contractors to
come in & fix things,but it is still cost-effective,& more importantly,faster to
repair rather than replace.

With the move to digital TV,hopefully the new stuff needed will last longer
between faults,but don't be surprised if Techs are still being told to "just fix"
the current stuff when it is 20 years old.

VK6ZGO
Title: Re: Repairing my old multimeter...
Post by: Kiriakos-GR on April 28, 2011, 11:44:18 am
Well VK6ZGO I do understand your point.

But I will not blame just the "suits" who are buying the gear,
I also blame the "suits"  who makes the Gear ( TV systems).

They do not share any of their knowledge and parts , with unrelated technicians other than the ones working for the brand.
And this causes an very close circuit of people who are related with technical support.   

And this happens with everything, and makes almost impossible the new blood of technicians,
to find their way about working on those products - tasks .. ( what ever you call them)   
Title: Re: Repairing my old multimeter...
Post by: saturation on April 28, 2011, 07:56:18 pm
Here's more about 'old' electronics, in this case semiconductors.  Its interesting few have heard about it and assume chips will last for a lifetime or more.

There are different causes of aging for other components such as resistors, capacitors or the PCB itself.

Since age related injuries to semiconductors are many, 'overuse' is one key cause and a simplified way to see it, it has too many 'miles' on its engine.  Another is exposing the chips to high ambient temperatures over its operational lifetime.  It may be possible to prolong its life with less use, or if its run substantially cooler or at slower clock speeds or lower voltages.  However, these issues are being offset by higher chip densities, so the probability of failure increases given the billions of transistors in every chip, this is then compounded by the use of multiple chips in a device.

http://spectrum.ieee.org/semiconductors/processors/transistor-aging/3 (http://spectrum.ieee.org/semiconductors/processors/transistor-aging/3)

http://spectrum.ieee.org/semiconductors/devices/an-odometer-for-silicon-chips (http://spectrum.ieee.org/semiconductors/devices/an-odometer-for-silicon-chips)

Note, this assumes the chip is working correctly, and that the cause of the failure in your device, was not due to a defect in the actual chip you had in the first place.

The bottom line is, even if all is well, a spontaneous failure can still happen and its more related to simply aging than doing something wrong with your device.  So once your DMM fails due to no obvious reason: overvoltage, a bad fall etc., aging is a consideration.  Its very difficult to test for, devices do not age at the same rate, so a 20 year old DMM by XYZ in one person may have more age defects than the same model with another, as the causes for the components continue to be studied and how the device is used and cared for can modify the rate of aging too.  


Title: Re: Repairing my old multimeter...
Post by: Kiriakos-GR on April 28, 2011, 09:06:36 pm
Well aging could be an possibility , but this damage its not justified by aging at list to me .. ( check the link below)

I will call it as human error in the design,
and I would prefer all the damaged DMM to had such type of damages.
Simple because the repair tactic would be an commonly  known.

https://www.eevblog.com/forum/index.php?topic=718.msg10943#msg10943 (https://www.eevblog.com/forum/index.php?topic=718.msg10943#msg10943)
Title: Re: Repairing my old multimeter...
Post by: pmrlondon on April 30, 2011, 09:21:17 am
Quote from: Ernie Milko on April 27, 2011, 07:01:13 pm
To answer the OP's question. Yes. I think you should have a look at repairing your DMM. Those old Precision Gold meters (Maplins, I presume?) were pretty good.

Indeed, Maplin's own brand. The WG models were the "White Gold" series and had white cases. The WG020 is still on sale, albeit with a black case these days. Conversely, the WG021 was I think the first to be discontinued.

Quote
Chances are it's just dirt on the switch contacts. Take the meter apart and clean them with a cotton bud and some IPA.
If it's not the contacts, it could be a dry joint. Check the meter over in bright sunlight.

The cleaning is part of my general overhaul procedure anyway. Dry joints will definitely be checked for. The new meter will be needed for component checks, of course, but there might not be a component fault, beyond perhaps the diodes.

Title: Re: Repairing my old multimeter...
Post by: pmrlondon on May 02, 2011, 07:21:17 am
I have now ordered the Amprobe at a cost of £82.80 - that seems a good price.
Title: Re: Repairing my old multimeter...
Post by: abbtech on May 09, 2011, 06:12:22 am
Quote from: Kiriakos-GR on April 26, 2011, 01:34:42 pm
Quote from: tekfan on April 25, 2011, 11:51:11 pm
unless you have a high voltage divider probe designed to handle 40KV+ voltage spikes.

Well i do have it , so to feel complete .  :)

(http://img827.imageshack.us/img827/7558/flukemodel80k4002.jpg)




That probe could be used as a weapon if you are doing service work in a questionable area. :)
Title: Re: Repairing my old multimeter...
Post by: Kiriakos-GR on May 09, 2011, 11:59:07 am
Quote from: abbtech on May 09, 2011, 06:12:22 am
That probe could be used as a weapon if you are doing service work in a questionable area. :)

In this case the " questionable area " has my permission , to move the photocopier with out my  help ( that weights 200 kilos ) ,
out in the street , so to adjust to it, the HV elements around the drum unit.  ;)