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From: Bill Sloman <bill.sloman@ieee.org>
Newsgroups: sci.electronics.design,sci.electronics.repair
Subject: Re: Favourite Test Equipment
Date: Fri, 12 Apr 2024 17:39:14 +1000
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On 12/04/2024 3:46 pm, Trevor Wilson wrote:
> On 12/04/2024 3:32 pm, Bill Sloman wrote:
>> On 12/04/2024 5:42 am, Phil Hobbs wrote:
>>> On 2024-04-11 13:11, john larkin wrote:
>>>> On Thu, 11 Apr 2024 09:55:18 -0400, Phil Hobbs 
>>>> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>>>>> On 2024-04-10 16:30, Trevor Wilson wrote:
>>>>>> On 11/04/2024 3:42 am, Cursitor Doom wrote:
>>>>>>> On Wed, 10 Apr 2024 11:40:02 +1000, Trevor Wilson 
>>>>>>> <trevor@rageaudio.com.au> wrote:
>>>>>>>> On 1/04/2024 4:41 am, Cursitor Doom wrote:
>>>>>>>>> Hi all,
>>>>>>>>>
>>>>>>>>> I'm starting to get a bit fed up with having my test equipment 
>>>>>>>>> blow up
>>>>>>>>> just when it's needed. This is the drawback with vintage gear; 
>>>>>>>>> if it's not used frequently then it can go *bang* the next time 
>>>>>>>>> you switch it on. It makes for good practice in repairing 
>>>>>>>>> stuff, but wastes a lot of time which could be better spent 
>>>>>>>>> doing other things.
>>>>>>>>> I think it's time I modernised my test gear. I was just 
>>>>>>>>> wondering if
>>>>>>>>> anyone has any recommendations they can share. Is there a 
>>>>>>>>> particular
>>>>>>>>> piece of test equipment you couldn't live without? Something 
>>>>>>>>> you're
>>>>>>>>> particularly impressed with? I'd be interested to know so I can
>>>>>>>>> perhaps acquire said item and thereby reduce the number of 
>>>>>>>>> explosion I experience.
>>>>>>>>
>>>>>>>> **In my 55 years of servicing, I've only blown up one thing: A 
>>>>>>>> Micronta DMM, which I connected to a laser power supply. I 
>>>>>>>> should not have done it. Clear operator failure. Everything else 
>>>>>>>> works just fine. Even my
>>>>>>>> first multimeter. A Sanwa U-50D my dad gave me on my 14th birthday.
>>>>>>>> Still works fine. My first DMM. A cheap 'n cheerful SOAR. Works 
>>>>>>>> just
>>>>>>>> fine. My first Fluke meter. A 40 year old Fluke 85. Works fine. 
>>>>>>>> I've had
>>>>>>>> to clean the switch a few times. Otherwise, no problems. Ditto 
>>>>>>>> my other 15 or so meters. Same deal with my 'scopes.
>>>>>>>>
>>>>>>>> I don't know what your problem is. Test equipment, when treated 
>>>>>>>> properly lasts a long time.
>>>>>>>
>>>>>>> To be fair, these "explosions" are typically capacitors: old, dried
>>>>>>> -out electrolytics in test gear that hasn't been used in a long time
>>>>>>> go bang when the power's switched on - as do old X2 safety caps. 
>>>>>>> Those
>>>>>>> are the chief culprits IME.
>>>>>>
>>>>>> **Oh, I see. You ignore regular maintenance. That makes sense. I 
>>>>>> hope no-one buys a car from you.
>>>>>
>>>>> Whereas all you Ozites are 100% rational reasonable polite beings who
>>>>> are always on top of everything, including predicting the exact date
>>>>> when an old cap will give up the ghost.
>>
>> Old electrolytic capacitors tend to give up the ghost when they have 
>> been left unpolarised for years, and are then subject to their rated 
>> voltage without having been re-formed first.
>>
>> Predicting that kind of failure isn't difficult.
>>
>>>>> Silly me for forgetting. ;)
>>
>> You don't have much to do with clueless newbies.
>>
>>>> You don't routinely replace caps in all your test gear? I'm shocked,
>>>> shocked.
>>
>> You don't replace them, you re-form them -  day or so subject to rated 
>> voltage applied through a nice big resistor (100k comes to mind).
> 
> **It would only be required if the unit has been out of service for 
> quite some time, unless it is very old of course. In any case, if I 
> remove a cap from equipment, it will almost always be simply replaced, 
> unless it is a very large and expensive component.

The only time I've done it was with a "new" capacitor bought from a 
cheap supplier for my home-brew hi-fi. It was a large - it not all that 
expensive - component, and would have been a pest to replace.

The hi-fi worked for about thirty years. It had sat in basement for 
quite a while - my wife eventually judged it too ugly for the living 
room - and when it stopped working it was quicker to buy an off the 
shelf replacement, and we then had the money to do that without thinking 
about it. I did think about finding the fault (in the discrete input 
transistors) but never got far enough to find the actual defective part 
or replace it.

-- 
Bill Sloman, Sydney