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Old 31st Aug 2023, 9:25 pm   #21
ScottBouch
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Default Re: Retro back in day repair and test equipment.

I once was on an oil rig in the North Sea (circa 2010) - I was a visiting to help with a machine repair (14MW gas turbine driven electrical generator) and the need arose for using an oscilloscope to help fault find a proximity vibration probe issue.

I went to see the platform Instrument Techs ("Tiffy's"); half of them looked at me blankly having never heard of one, those who know what one was were bemused as to why I would want one, but they didn't have one. These guys dealt with 4-20mA signals for calibrating instruments so were used to multimeters, and current sources, process calibrators, pressure pumps, and ovens.

After that experience, I went to thought I'd chance it with the telecoms guy, who as it transpired had seen an old CRT scope years ago lurking in a cupboard somewhere, he had a rummage, found it for me and hastened to add he wouldn't know how to switch it on!

So, a quick PAT test later, and the old scope came to the rescue on our vibration probe issue!

Sometimes you need to "see" the signal, which a digital multimeter can't do.

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Old 31st Aug 2023, 9:29 pm   #22
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Default Re: Retro back in day repair and test equipment.

PS: messing around with old aircraft... a modern DMM can give misleading voltage readings at times.

When looking at long cable runs, capacitive coupling can raise the voltage on an open-circuit wire, giving false readings to a high impedance DMM. The load of a moving coil meter does not have the same issue and gives more definite results. This of course could be fixed by adding a resistor across the DMM's terminals, but without this you can get caught out!

Cheers, Scott
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Old 31st Aug 2023, 9:42 pm   #23
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Default Re: Retro back in day repair and test equipment.

That is an absolute example of why I say, NEVER trust what your instruments are telling you. Of course what I really mean is always consider what an instrument is telling you is possibly misleading. Another example is measuring resistances, but for whatever reason there are residual voltages. This can lead to high resistance readings but also negative resistance readings.

What your test gear tells you is a set of clues, not an answer.
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Old 31st Aug 2023, 11:57 pm   #24
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Default Re: Retro back in day repair and test equipment.

Hi Duncan, yes, you always need to apply a certain amount of common sense, and sanity check the readings!
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Old 1st Sep 2023, 9:32 am   #25
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Default Re: Retro back in day repair and test equipment.

Quote:
Originally Posted by ScottBouch View Post
When looking at long cable runs, capacitive coupling can raise the voltage on an open-circuit wire, giving false readings to a high impedance DMM. The load of a moving coil meter does not have the same issue and gives more definite results. This of course could be fixed by adding a resistor across the DMM's terminals, but without this you can get caught out!
That's one of the reasons I like my old Fluke 12 DMM. In voltage mode it has an input resistance of 10 megohms, but in resistance or diode check mode it has a feature called "V Chek" which automatically switches the meter to reading a voltage if it sees one. When it's doing this, the input resistance is substantially less than 10 megohms (I can't remember exactly what). This is really useful for seeing the difference between "phantom" voltages and real ones.

Chris
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Old 1st Sep 2023, 3:42 pm   #26
duncanlowe
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Default Re: Retro back in day repair and test equipment.

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Hi Duncan, yes, you always need to apply a certain amount of common sense, and sanity check the readings!
BUT so many don't!
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Old 1st Sep 2023, 7:48 pm   #27
jamesperrett
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Default Re: Retro back in day repair and test equipment.

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This of course could be fixed by adding a resistor across the DMM's terminals, but without this you can get caught out!
Some DMMs now offer a low impedance voltage input.
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Old 2nd Sep 2023, 10:04 pm   #28
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Default Re: Retro back in day repair and test equipment.

When I first started out in electronics, the only piece of test equipment I relied on was an analogue multimeter with a sensitivity of 20k Ohm/Volt. It served me well for many years allowing me to repair most radios and TVs with simple faults. Even the humble neon screwdriver is useful for checking line output stage activity in CRT TVs. I then built various equipment including TV pattern generators, a CRT tester and ESR meters which have been very useful.

I currently have a large collection of various test equipment including many homemade items. They're all very handy items to have though many aren't used very often but it's good to have a means of testing various components and circuits as and when required.

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Old 4th Sep 2023, 11:46 am   #29
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Default Re: Retro back in day repair and test equipment.

A scope, you can see the waveform and read all the parameters from the screen.

This was designing all sorts of amateur equipment, at work had what they provided.

Can't stand digital scopes though, nowhere near as good as an analogue storage scope. Was recently trying to display the startup current on a 3ph motor, the digital scope would change how it displayed the trace at a low sweep speed, and nothing I could do would give a believable trace. And it was a Tek instrument.
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Old 4th Sep 2023, 2:00 pm   #30
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Default Re: Retro back in day repair and test equipment.

I'm with you on digital 'scopes! Awful things. I nearly rejected a delivery of super expensive Agilent scopes when I worked at Filtronic as they seemed so noisy.... turned out they were supposed to be like that! IIRC these scopes could go on the internet and you could get emails on them... whatever next...
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Old 4th Sep 2023, 2:16 pm   #31
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Default Re: Retro back in day repair and test equipment.

I got caught out by DMM input impedance about 6 months ago. I had an issue when designing and building a precision high voltage PSU in that measured output voltages were wrong by 1-2% or so which was not acceptable. We get so used to the very high input impedance of DMM's and (in my case anyway!) think of them as to intents and purposes having infinite input impedance. Of course they do not though and are usually 10M. I was using potential dividers of a few hundred K and, by using SOT resistors in parallel etc, adjusting the output of the PD to specific voltages which had to be within around 0.1%. I was virtually pulling my hair out at the ****** thing when no matter how accurately I adjusted things the final results were out by say 2% after all this careful trimming! I had a sit down and think about this and decided there had to be "a rabbit away" somewhere. Then it clicked.... I recalculated things for "what should it measure if it were being dragged down by 10M resistance"... bingo!
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Old 5th Sep 2023, 11:05 am   #32
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Default Re: Retro back in day repair and test equipment.

One of the most enjoyable things for me (given that electronics is an hobby for me, not a profession - so concerns with time spent is out of the equation) is using the minimal and oldest gear I have to work with, and only reaching out to more recent gear is there's no other way. I like to learn things from the beginning, and using rudimentary equipment taught me a lot so far.

But I believe that a professional nowadays, with such demanding markets, would need to grab the tools that would let them finish tasks quickly, pretty much as it happens in most companies from whatever industry we can find today - and we, buyers, feel the consequences in the resulting quality and difficulty/inability to repair very modern technology... specially because spares are only available for a very short period of time, if there are any to start with anyway. It's sad - but it seems that this is what most of the world is asking for, or at least being complacent with.
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Old 5th Sep 2023, 12:08 pm   #33
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Default Re: Retro back in day repair and test equipment.

High impedance meters are, as noted upthread, easily deceived by leakage.

In times past I have had some wasted hours trying to work out why the lights on a trailer didn't work even though the meter said that there was continuity and 24V was seemingly there. When you're using a 20KOhms per volt meter a bit of damp in a junction box can easily provide leakage enough to convince you that there is power when there isn't.

One of the problems I find with using older test gear though is that you often find yourself spending time fixing it rather than using it to fix the problem you originally set out to fix. And you need new-ish test gear to fix the older test gear...

And anyway, I like having things like a 500MHz frequency counter that runs from batteries and fits in my pocket, rather than something that needs a scope trolley to move it.
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Old 11th Sep 2023, 5:29 am   #34
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Default Re: Retro back in day repair and test equipment.

When I went to sea in the mid 60's as a Radio Officer with Marconi's I was surprised to find that the only bit of test gear supplied was an Avo "Multiminor". The only good thing in the spares cupboard was that there was a spare valve for every one in use including the radar. I can't think of anything that had transistors in it!
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Old 11th Sep 2023, 3:13 pm   #35
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Default Re: Retro back in day repair and test equipment.

From what I saw is the 1960's started with tubes and finished with chips.
I know there was a few transistors in 1950's tubes was still king.

Dave

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When I went to sea in the mid 60's as a Radio Officer with Marconi's I was surprised to find that the only bit of test gear supplied was an Avo "Multiminor". The only good thing in the spares cupboard was that there was a spare valve for every one in use including the radar. I can't think of anything that had transistors in it!
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Old 11th Sep 2023, 3:34 pm   #36
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Default Re: Retro back in day repair and test equipment.

I just post how use a simple RF generator used as a bar generator too. https://www.vintage-radio.net/forum/...d.php?t=203828

Still amazing the few test equipment used in 1950's less in the 1940's.

1) VOM/DMM
2)VTVM w/RF probe
3) tube tester
4) RF generator
5) AF generator for audio work.
6) Oscilloscope for audio work.

Dave
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Old 11th Sep 2023, 3:50 pm   #37
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Default Re: Retro back in day repair and test equipment.

That looks like a lot of test equipment to me. "Back in the day" I'd have been happy with an AVO and an RF signal generator with a 400Hz AF output.
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Old 11th Sep 2023, 4:32 pm   #38
Smithdoor
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Default Re: Retro back in day repair and test equipment.

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That looks like a lot of test equipment to me. "Back in the day" I'd have been happy with an AVO and an RF signal generator with a 400Hz AF output.
The Popular Electronics in first had articles on building a VTVM and RF signal generator.
Later there magazine had building a simple oscilloscope for audio work. My self in 1960's built a AF generator from a magazine.

Never saw any on building tube testing but you could goto the drug store for testing.

The magazine ads and school ads would you believe you need a lot more costly equipment

I had few techs say they start with just a VOM
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Old 12th Sep 2023, 2:32 pm   #39
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Default Re: Retro back in day repair and test equipment.

Back in day you need a bar generator.
All hou need is RF generator and color bar ad a AF generator. Still works today
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