how to get a scope from your bench - RF Cafe Forums

 Post subject: how to get a scope from your bench

Posted: Mon Aug 15, 2005 11:48 am 

Long ago I was the youngest member of an electronics design group. An older collegue had a bench opposite to mine. He was a wise and experienced guy, but also rather proud of this experience. Above all he marvelled in his ability to operate a very special Tectronics scope. For its time a very fast one, with dual trace, delayed timebase, memory screen and a lot of funtionality thanks to various plug-in units.

OK, no problem so far. However, the scope was so large that it stood partially on my bench. OK, not a real problem, BUT, it was also blowing a LOT of hot air into my face and my experiments. Polite suggestions for other arrangements, a cart for instance, so that others could use this wondermachine too, were stubbornly negledted (very bad for the tubes, no one else can work it, etc).

I was once tought that every problem has one or more stupid solutions and sometimes also a smart solution. Making a row might cost me my job in this really good group, so a smart solution was desperately needed.

After some days of staring into the back of the monster, I discovered some plugs. One of them was labeled 'Z'. A smart idea was coming up!
I (secretly) consulted the manual, and indeed, this input directly controlled the beam intensity.

I quickly arranged some other equipment, including a power supply, on my bench and hidden behind this I slipped a cable loosely on the Z-plug. The rest was simple. In the middle of an experiment my esteemed collegue would suddenly loose his trace. After some juggeling with the triggering, it suddenly reappeared. But after a week, he decided that the scope needed repair. It took two man to lift the monster and I agreed to help, so nobody noticed my little cable.

After a day of testing, we decided that a minor adjustment in the trigger circuit and a new tube had solved the problem. But the next day the problem was there again....

After a month, several replaced tubes and a lot of contact cleaning it was decided that the beast was tired of life and was put aside. We both got a 7000 scope that fitted neatly on our benches.

The monster was later donated to a very happy collectioner. Smart solutions make everybody happy, but not everybody has to know everything.

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Posted: Mon Aug 15, 2005 7:47 pm 

That is one of the best lab stories I've ever heard told. Bravo!

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Posted: Sun Aug 21, 2005 4:27 pm 

It must have been the 549...

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Posted: Sun Sep 04, 2005 2:31 pm 

Ulf, you can tell that, just from the description of its weight and all?

As I read it, I get a shudder. One of those little flat blue-case scopes that you can fit in a briefcase, screen about 8 x 3 cm. Only used for trace diagnosis, and because I was the lowliest in the place, I was expected to get on with it. The batteries would not hold up for long, and had their life shortened by being on more or less permanent charge from the mains connect anyway.

Next is a shared sync signal from a rack generator amp. Commonly guys would come to it, and finding it full, would disconnect one of the BNCs, and pause awhile.
If major strife did not ensue, then they would quietly "lose" it into the big untidy bundles on the floor, and plug in their own. I used pink nail varnish painted into the knurling of my BNC so I could tell if I was being relegated.

When I came to plug the BNC into the little scope, I grabbed onto it to stop it sliding about, and slid my hand along the cable to get at the BNC. I was floored by the 240V mains leak from the faulty PSU/charger in the scope to the grounded BNC. Easily one of the most painful things I remember.

Scary bit was when fellas picked me up from the floor, and I thought "OK, I made it - I survive", I was then subject to about 2 minutes of variable and missed heartbeats, so I went back onto the floor! I can tell all that when your heart misses a beat or messes about, you know instantly!
Feeling nausea, and freezing cold, I could hardly take in the stuff about how I "broke" their scope, and "ruined" the distribution amplifier. There was much disaproval about how all this was to be "reported" and logged, and all the paperwork that would result.

OK - sure, my mates helped me, and I would be OK. But it set the atmosphere for me. I could not work up the enthusiasm anymore. I eventually left the place for better, with some regrets because I also found that it is mostly your true friends that always swipe your video cable!

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Posted: Mon Oct 24, 2005 11:16 am 

Well - It was an old tek scope. I guessed it was a tube type instrument. The only one with memory screen (bistable) and dual time base was the old 549. It also had a BNC-connector at the rear for Z-modulation.

I have one such instrument in a closet next to my RF-lab on the 2nd floor. When a friend decided to threw it out, I got it. The only sad thing is that I do not have Tek's original square type graticule cover which was special for the CRT of the 549....

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Posted: Fri Feb 10, 2006 1:49 am 

I don't kown what happened.because my English is poor...
I find no funny from this article.
I am sorry.

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Posted: Sun Mar 05, 2006 5:11 am 

Hugo,

I got unconcentrated and did not properly read the rest of the anecdote.

Not very nice at all.


As a ham-radio operator I have of course experienced a few shocks. Now older I can not understand how I could be so careless. Nowadays I always approach high voltage devices with extreme care. 1kV plate voltage of a 2C39 amplifier for 23cm also hurts even if it is only a short path between the pointer finger to the palm of the hand. Human flesh does not smell very nice when it gets burned....

One collegue had an experience which he will always remember. Having an old Weller 230V solder iron he had to replace the tip. It was stuck, so he drilled it out of the tool and replaced it not realizing that the drill had penetrated the metal and short circuited the 230V winding with the metal of the tool.

One day he was sitting in his home. Bare feet. Soldering something and then needing a third hand to hold the solder. He used his mouth and then went on with the soldering. For some reason he touched the electric radiator under the window with one bare foot.

You can imagine the rest....