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Essential Measuring Instruments for the Newcomer.

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Steve Conner

Mon Oct 05 2009, 09:58AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Ooo, a Perreaux power amp!

I live in a small apartment in the city, and I used to have one end of my kitchen set up as an electronics lab. It got such a mess that I eventually got fed up with it, and moved all the equipment into the lab at work. I don't even have an oscilloscope at home now, which is something of a break with tradition. I haven't lived in a scopeless household since I was about 10.

wrote ...
but everyone seems to take it for granted that once you've got your meter you know what to with it, how to use it strategically to analyse circuit functions, and locate even complex faults.

This is because it's so much harder to teach troubleshooting than to tell someone what test equipment to buy. The most important piece of test equipment you own is between your ears. It's not that we take it for granted, rather that troubleshooting is a skill that comes from a deep intuitive understanding of how circuits actually work, and we can't even begin to scratch the surface in a forum thread.

Harry, you got me there! That was my plan, to use the Avo Model 8 to fend off sharks and bash wild animals on the head. Our technicians still have an Avo 8 and seem to use it regularly, possibly for bashing students on the head

By the way: Fluke when someone else is paying for it

For personal use I have an old ITT Metrix meter that I found in a pawnshop. I love the weird design with both a digital readout and a real analog needle. It also has those big ceramic fuses inside and a fair amount of protection. I've also got a cheap Altai meter, which I bought at a hamfest.

Nicko

Mon Oct 05 2009, 10:10AM

Registered Member #1334 Joined: Tue Feb 19 2008, 04:37PM
Location: Nr. London, UK
Posts: 615

Steve McConner wrote ...

Ooo, a Perreaux power amp!

Weighs a ton. There's a 100W non-inductive dummy load sitting next to it. The amp exploded rather dramatically and the then owner was going to chuck it - I rescued it and rebuilt it from scratch - the room (and probably the neighbours') lights dim momentarily when its switched on and its case visibly flexes. Takes about an hour to warm up before use. Fantastic bit of kit.

Ears are good - certain sounds spell certain trouble - smell is very very important. As an EE you get used to a certain range of aromas that are acceptable, and those that are definitely not. The difference is often subtle, but very important.

Another very good tool: Big STOP button (or dead-man's handle/lanyard). Dry powder/CO2 extinguisher... (always have one in the workshop - make sure its serviced every year).

Steve Conner

Mon Oct 05 2009, 10:38AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Nicko wrote ...

Takes about an hour to warm up before use. Fantastic bit of kit.

Wow, that's "high end" for sure. Even my old valve amps are ready to rock in 2 minutes

Ears and nose, there's two more essential measuring instruments. For instance, when working on vintage gear, the smell of burning dust is OK (in fact my favourite smell in electronics) but the smell of burning transformer varnish is most definitely not!

Another useful body part/measuring instrument is the "calibrated finger" to feel semiconductors and tell if they're getting too hot. If you can't stand to hold your finger on a transistor case, it's probably running too hot and will die soon. Op-amps, logic chips, etc. should be barely warm. When troubleshooting, I often feel all of the ICs on a circuit board to see if any are abnormally hot.

(noob disclaimer: don't try this on high voltage equipment)

(noob disclaimer 2: On tiny packages your finger can act as a heatsink, so the device doesn't feel too hot, even though it is overheating when you're not touching it)

(noob disclaimer 3: don't try this on vacuum tubes, they run happily at over 200'C and cause painful burns)

Nicko

Mon Oct 05 2009, 12:14PM

Registered Member #1334 Joined: Tue Feb 19 2008, 04:37PM
Location: Nr. London, UK
Posts: 615

Small story here about the importance of understanding sound & smell...

When we first moved into our current house, its infrastructure was, how to put it... challenging...

Many things were not good, but the position is excellent - you can change the house - more tricky to change its location. So we left some things until we could do a whole rebuild (which we did during all of 2005).

One morning about 06:30 I went into the utility room to get some milk from the fridge - I was listening to the radio, but in the back of my mind something was nagging at me...

Then I realised what it was - there was a faint smell of hot/burning bakelite (a smell that all older EEs will know and love) and a very faint "fizzing" sound...

Alarmed, I started searching and open the garage doors next to the utility room to be greeted by our 230VAC 100A 3phase main feed acting as a Roman Candle and hosing the main switch board with flames & molten copper. In the garage were a number of items, including gas bottles for BBQs etc. The switch board was in flames - this was trouble...

I got everyone out of the house in about 30 seconds - my daughter's bedroom was directly above the garage - the fire brigade were there in 5 minutes & the house was saved - they walked into the garage, took the gas bottles out, and covered the erupting main with dry powder.

The arcing didn't stop until the electricity board emergency response team physically dug up & cut (with ceramic shears) the main feed - two hours later - it hadn't fused at the substation as the feed is several 100 meters long and the impedance was such that the substation didn't drop out.

So, luck, experience with good sense of smell & hearing almost certainly saved my family's life. Luck, in that if it had happened a couple of hours earlier, the garage would have exploded, and experience in that I knew immediately that the combination of that faint sound & that smell when not expected meant certain BAD trouble...

Problem was the 50 year old utility fuse & 3phase termination was bakelite and with the damp in the garage had carbon tracked, before finally arcing over.

Not good.

tobias

Mon Oct 05 2009, 01:05PM

Registered Member #1956 Joined: Wed Feb 04 2009, 01:22PM
Location: Jersey City
Posts: 172

Guys

Since this thread is for newcomers I have to ask you:

What are the real alternatives to a scope for those that lives where traditional oscilloscopes are just too expensive for a new hobbie? (a new tektronix scope is around $1 500 around here)

I'm not interested on sound card nor DIY stuff and it has to be 20 MHz or more. I searched for USB based scopes and found stuff from $20 to $1 000 and confusing brochures with a lack of technical details..

Here in Brazil I did not found anything interesting regarding PC based scopes to buy. I can buy in US but keep in mind that the taxes doubles the price.

A used good branded scope is around $1 000. It's that the cheapest solution that I've got?

Steve Conner

Mon Oct 05 2009, 01:14PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

No, get a used cheapo unbranded one. I refuse to believe there are no cheap oscilloscopes in Brazil.

BK Precision are a typical cheap brand:

but there's also the Hitachi V-212.

Mon Oct 05 2009, 01:17PM

Registered Member #2372 Joined:
Location:
Posts: 62

Here is a link to a document that describes how scopes work and can be used in a fair amount of detail, it might be useful if you havent used a scope before. It is from a company, but most of the info is generic.

tobias

Mon Oct 05 2009, 02:35PM

Registered Member #1956 Joined: Wed Feb 04 2009, 01:22PM
Location: Jersey City
Posts: 172

There are Icel scopes (they are made by Witting Technologies and branded Icel). They are around $700.

But then the fear of paying much for a scope that I don't know if it is reliable got me. Any one knows about it?

Steve wrote ...
I refuse to believe there are no cheap oscilloscopes in Brazil.

We have cheap stuff here but most of them are bring from Asia by the black market. As I said before, the tax for importation is around 100 % in Brazil. Sum to that the costs of shipping, the profits of the seller and you will have a idea of how expensive things are around here. Even the crappiest things are. Even good caps are hard to find (I didnt found yet) if you dont work in a big company. And the way it is today is a improvement. Two decades ago or so we lived in a closed market: no importation at all and a huge lack of local knowhow.

To have any warranty the importation must be legal so... I'm searching for a branded good used and cheap scope for a while now. Just saw this thread as a good second opinion =)

teravolt

Mon Oct 05 2009, 03:53PM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

tobias could anybody send a scope say from the USA to you with out terifs. I just bought an old tektronix for 100$

tobias

Wed Oct 07 2009, 08:31PM

Registered Member #1956 Joined: Wed Feb 04 2009, 01:22PM
Location: Jersey City
Posts: 172

teravolt

That's actually a great idea! I know that if the box and documents contains "GIFT" wrote in it, by the law the contents don't pay taxes.. I'll search how it works in detail to know if it is possible to bring a scope from US without taxes that way! A good used scope for a hundred bucks would be reachable!

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