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Old 4th January 2012, 04:32 AM   #41
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Quote:
Originally Posted by wrenchone View Post
That senior chap had the right idea. Sometimes you just need to lay aside whatever project is frustrating you for a while and work on something else. This is a luxury usually not available except to us DIY types, as bosses want things done to schedule (or before).
Yup. Sometimes you just get too close to see something simple. Walking away and getting a cup of coffee (or tea) helps shift your perspective.
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Old 4th January 2012, 10:32 AM   #42
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My supervisor had great confidence in me after my first two digital design projects and assigned me, a physicist, to design a 10 mhz data logging memory address calculation board. This was to analyze data coming in on the NASCOM network. (Internet was not yet ) It was 1976 and Schottky 74S logic was new and hot. I calculated and drew out time charts. I settled in an AMD bit slice 2901 ALU set to calculate the next address and figure when to circulate back to the beginning of the buffer, etc. It was built up on wirewrap board. When I got the prototype, I hooked up the HP logic analyzer to the output to check my "microprogram" was running through the addresses as planned. I was getting doubles of some instructions, kind of randomly occuring. Not the expected sequence. I postulated the clock line was ringing, and terminated it with suitable ohm resistors as the line driver application book suggested. Same result. I changed the clock line driver IC to something else. Same result. I doubled up the number of clock driver IC's and halved the length of the clock wire run, with terminating resistors. Same result. I had the entire clock line pulled up and re-wrapped with twisted pair, with one end of each dead half grounded. Same result.
I pulled the government audited calibration stickers off the logic analyzer pod (horrors) and opened the pod up. I intended to look at the clock in there with a scope, but the ground wires were burned in two inside. The whole thing had been an artifact of defective test equipment. eight days of checkout down, three weeks to go. The system eventually tested out at 13 mhz, when my calculations had said it would go to 16. Darn! Met spec, though.
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Last edited by indianajo; 4th January 2012 at 10:53 AM.
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Old 4th January 2012, 06:11 PM   #43
macboy is offline macboy  Canada
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This one is a little tame compared to some of the stories here. I am not a repair tech, just a DIY nut and an EE by trade (but that itself means nothing; most of my EE classmates and coworkers would not know which end of the soldering iron to hold).

My automatic garage door opener would open the door but would not close it. It would start down, then bounce back up and the lights would flash. This usually happens when something interrupts the optical sensor across the bottom of the door. I checked the connections to no avail, then replaced all of the solid (!?) 18 ga zip cord wiring with new stuff, also without success. Then I took the optical modules down to my workbench and pried them open. Tested the electrolytics and one was in fact bad so I replaced the lot. Re-installed the modules and it seemed to work. After a few days, the problem returned. Opened up the modules again. Inspected very carefully ... eventually I found the problem. There was a missing solder joint on one leg of an SMT transistor connected to the output of the module. Not a cracked or cold joint; no solder joint whatsover. The thing had worked for years on nothing but incidental contact between PCB and component. Eventually, vibration and/or corrosion made that connection go bad. One touch of the soldering iron later and it has worked for years since.

A friend gave me an older surround receiver that was going into protect mode. He said that it had worked intermittently but was now going into protect immediately every time. I opened it up and saw that several grounds on the PCB (and RCAs) connected to the common ground (i.e. the chassis) only via mounting screws. So I backed off every screw I could see about a 1/4 turn, then re-tightened them. Fixed.
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Old 4th January 2012, 08:09 PM   #44
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Quote:
Originally Posted by macboy View Post
This one is a little tame compared to some of the stories here. I am not a repair tech, just a DIY nut and an EE by trade (but that itself means nothing; most of my EE classmates and coworkers would not know which end of the soldering iron to hold).
I started this thread and so far every story has been most welcome, and enjoyed. A long time friend and I have remarked many times about conversations we had that not only our fathers, but danged few people on earth would have a clue of understanding about. Just knowing that there are others on earth who know some of the same things is a comfort at times.
That applies to Audio, electronics in general, physics and even computer programming.

One of the joys of working in Silicon Valley in the eighties was the sheer diversity of technical people that you encountered. At the local bar I played foosball with a doctor of chemistry. One of the guys worked at the hypersonic wind tunnel at Moffet field. A contingent of the Norwegian Air Force would drop in (on assignment to Moffet, got a scar on my chin from the Screaming Nazis drink that they introduced me to.... involved a ten speed and a dog...afterward.) One night I was talking to someone about lasers and remarked the only ones I didn't as yet comprehend was Ring Dye... lo and behold he's one of the worlds leading authorities about Ring Dye lasers and proceeds to explain them to me on a bunch of bar napkins. One of the treasured mementos of the valley was a distributor cup that had a Db / SWR chart printed on the side. Like the sands of time these are the days of our lives.....


Moving on with stories.....

Doc
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Old 4th January 2012, 10:36 PM   #45
benc is offline benc  United Kingdom
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Off topic I guess. But I once spent a very (VERY) drunk evening (thanks to an unplanned weather event at JFK) with two fellow travelers (I met in the line at the AA desk) - one was a Norwegian fish magnate (on his way to Alaska) and a guided-missile salesman (on his way home from the Paris Airshow). Those stories were toe-curling.
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Old 4th January 2012, 11:07 PM   #46
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Default The Wang Incident

Back in the day we had a RF transmitter of sorts, where the resonator had to sit a very high vacuum due to the large amounts of power we were pumping.

Once in a great while the vacuum would burp and things would go very bad, very quickly, lots of melted copper and glass Jennings caps, scorched wave guides. The residual gas annie would always show a clear water signature.

Only glitch is we couldn't find nary a water leak with 100's of hours of He leak checking.

Fast forward 20 years into the Past. One night in that distant past a grad student (Mr. Wang) was manning the controls. Automatic controls shut everything off due to vacuum issues.

Mr. Wang sat by the hour forcing things to run..... till they wouldn't. Next morning the day crew came in and heard the story.

Looking into the RF tank through video or sight glass showed none of the tell tail signs.... just clean copper, SS and glass. Maybe a little too much sparkle!

Opening inspection hatches let out ohhhh 600 - 1000 gal of polished water.... the RF tank was full to the top, ditto the vacuum pumps, roughing pumps, chases, catch basins.

Everything came apart got cleaned, dried and put back together, 3 months of double shifts...... everything but one capscrew.... one hidden out of the way capscrew.

Twenty years later that one capscrew was still burping water, from what we called a virtual leak... which is why it never showed in the normal leak testing.

Most of the time that water just sat nice and polite in the bottom of a threaded hole as ice. Institutional memory through change of site managers had all but forgotten Mr. Wang.

Cyclotronguy

Last edited by cyclotronguy; 4th January 2012 at 11:12 PM.
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Old 4th January 2012, 11:09 PM   #47
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Benc: Yes, airports used to be a fact of life for me. Had a tag line that read "If you are too good at your job they put you on airplanes". Got a message back from one guy who said he read it at 30,000 feet and stewardess was wondering why he busted out laughing.

Met a guy in the bar at the San Francisco airport from a south American country -which shall remain nameless- who got REAL INTERESTED when he learned I was working for a used test equipment place. He was actually a minister of technology procurement for x-country. Wanted me to sell him stuff on the export restricted list. I said we'd be happy to sell him anything it was LEGAL to sell him... conversation wained.


More stories:
Basic rules forgot.
Working in the late seventies as a job shopper in cal lab at Sperry Univac. Had these ATE (automatic test equipment) power supply testers that were pretty simple. A switch selected ROM output would turn on X transistors leading to load banks to verify that the PS boards were doing their job. A whole bunch of these things kept eating the switch transistors for seemingly no reason. The devices were well heat sinked and well within current and voltage specs. One day I walked up to this one engineer with a masters degree and told him he could cure the problem if he just put some back emf protection diodes on the switch transistors. Yup, he hadn't taken into account the load banks were big wire wound resistors. The back emf spike was punching the switch transistors. Diodes got put on each device and I don't think they lost another transistor. He started bringing me coffee in the morning in exchange for learning electronics.

Doc

Seems I was posting at same time as last message.
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Last edited by thaumaturge; 4th January 2012 at 11:17 PM.
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Old 4th January 2012, 11:23 PM   #48
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Cyclotronguy. Once got a private tour of SLAC. Pretty impressive. At the time they had one 15KW klystron ever fifty feet or so pumping more RF umph into the line (phased push to the accellerated particles.) They were upping that to 45KW every fifty feet. The guy giving the tour told a story about the beam taking an unexpected turn one day and started boring a hole into the adjacent mountain at 20 feet per second.

Doc
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Old 4th January 2012, 11:30 PM   #49
poynton is offline poynton  United Kingdom
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The story above
Quote:
.......this one engineer with a masters degree.........
reminded me of an incident in the land of the pharoahs.

It was a requirement that the company hired one local for every expat employed.
The only problem was that the "graduates" only wanted to drive a desk and not do any field work.

One day, we had to make up some new lighting cables, -- plug, 20m twin flex, light socket -- nothing difficult.

So we set the local guy the task and went for our lunch (it was Ramadan).

We came back 2hrs later and found him still sat at the workbench with not one complete cable.

In front of him was a pile of white insulation pieces and another pile of copper wire cuttings.

"This reel of wire is no good !"
"Why"
"It doesn't matter how much I cut it back, it's still rusty!"

Closer questioning revealed he had done no practical electronics in getting his degree and also had never seen flex with bare copper wire only tinned!

He didn't last much longer.


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Last edited by poynton; 4th January 2012 at 11:33 PM.
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Old 4th January 2012, 11:49 PM   #50
benc is offline benc  United Kingdom
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I once tasked an 'engineer' with a 2:1 in Electronics from a good university with building a simple PSU (toroidal, bridge, electrolytic) - gave him the contents of that mornings delivery from RS Components.

Came back later on to find him unwrapping the clear plastic insulation around the toroidal, it didn't occur to him as *odd* that the *packaging* was so difficult to unwind..

Last edited by benc; 4th January 2012 at 11:50 PM. Reason: speeling
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