Author Topic: Repairing my old multimeter...  (Read 17243 times)

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Offline saturation

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Re: Repairing my old multimeter...
« Reply #25 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

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

« Last Edit: April 27, 2011, 08:49:41 pm by saturation »
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Offline vk6zgo

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Re: Repairing my old multimeter...
« Reply #26 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
 

Offline Kiriakos-GR

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Re: Repairing my old multimeter...
« Reply #27 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)   
 

Offline saturation

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Re: Repairing my old multimeter...
« Reply #28 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/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.  


« Last Edit: April 28, 2011, 08:01:08 pm by saturation »
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Offline Kiriakos-GR

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Re: Repairing my old multimeter...
« Reply #29 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
 

Offline pmrlondon

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Re: Repairing my old multimeter...
« Reply #30 on: April 30, 2011, 09:21:17 am »
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.

 

Offline pmrlondon

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Re: Repairing my old multimeter...
« Reply #31 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.
 

Offline abbtech

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Re: Repairing my old multimeter...
« Reply #32 on: May 09, 2011, 06:12:22 am »
unless you have a high voltage divider probe designed to handle 40KV+ voltage spikes.

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






That probe could be used as a weapon if you are doing service work in a questionable area. :)
Personal projects http://alan-parekh.com
Other cool project ideas http://hackedgadgets.com
 

Offline Kiriakos-GR

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Re: Repairing my old multimeter...
« Reply #33 on: May 09, 2011, 11:59:07 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.  ;) 
 


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