# Radar Exam mishaps



## Corky (Feb 25, 2008)

Anyone want to recall any bloopers when taking the Radar Maintenance Pratical exam?
My claim to fame was blowing the main fuses for the entire top floor of South Shields Marine College, when the HT cap flew off the CRT after I'd checked the HT. I thought that was the end of the exam, but the examiner put everything back together (after eventually getting the mains power back on), and told me to continue..
I put the set back on, and after the warmup period, switched it to the "run" position. The examiner was peering over my shoulder, when "BANG" the HT flew off the CRT and again blew all the fuses!
This I think proved the HT lead clip to the CRT was goosed... After muttering about "electrostatics" - the rest of the exam proceeded with the offending plug securely taped on with half a roll of insulation tape.
And yes, I did actually pass! I think I was the last person to work on that Radar, a Marconi ?, the college switched over to Decca radars the next term.


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## sparkie2182 (May 12, 2007)

I recall the D.T.I. Radar written paper in the mid'70s when one of the questions wasn't even on the syllabus............. We all had to re-sit it.


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## rknibbs (Mar 11, 2006)

When took my practical exam at Norwood Tech the radar developed a whole series of other faults. I found many of them but not all. I was sent away to wait for the instructors to check my log against the faults they had set. I had found all of them. They asked me to rewrite my log but take out the errant faults. I did this but was rebuked for a `too neat' and ` too well-written' log. I was given 98% for the practical and a scraped through theory paper. But I passed.


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## Larry Bennett (Aug 28, 2005)

During my exam I was supposed to find 4 faults but I amazed the examiner by finding 5....however he got his own back by writing "guidance given" on my notes whilst I was logically following the circuit diagram. I was not best pleased, the more so as he told me I would have found the relevant fault anyway.....however, it mattered not as I duly passed.

However during the mock exam a week previously I managed to produce a firework display of awesome proportions whilst checking a component for resistance with my Avo 8 - and forgetting to switch the HT to the PCB off. The lecturer leapt across the room and I learnt some nice new swear words. 

Both mock and real exams were on the Radiolocator II, a fine piece of kit - we were all afraid we would have to take the exam on the 'new' Decca Radar with those funny "integrated circuit" things on. This was in 1979, just when the new generation of radars were becoming the norm.

Larry +


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## Vital Sparks (Sep 19, 2007)

I remember most of that exam like it was yesterday, the hardest I ever did, MSc included. The first two faults were easy and then it started.

My problem was that the examiner hadn't checked that the induced fault actually resulted in the symptoms one would predict from having read the circuit diagram. He had faulted one of a pair of final stage output transistors in the scan coil driver with the expectation that the collector voltage would fall to zero. It didn't, (as I worked out later) due to the working half of the push pull circuit inducing an apparently correct signal onto the non working half via a parastic circuit formed from the floating half of the scan coil. 

All the voltage and scope waveforms around final stage appeared correct and so there was no reason to justify the removal of either transistor but the solder spatter, unscratched transistor can and missing sleeving on the leads clearly indicated which component had actually been changed. It was then that I remembered an overheard conversation from months previously about a weird DOT fault that hadn't produced the correct symptoms, maybe it was this fault. 

I was then in a crazy situation of knowing what the fault was but not why it was, and with my log already written I couldn't afford to backtrack and 
"frame" the affected component so I had to come up with a convincing reason for it's replacement based solely on my recorded readings. Decided to go for the "spurious voltage" explanation, one which could only be isolated to a single component by testing by substitution both of the output transistors. Not surprisingly the fault cleared after the first candidate was replaced. I don't remember the last fault or performing the re-cal but I must have done them becuause I passed.


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## sparkie2182 (May 12, 2007)

"spurious"

A lovely word which says so much..........

I never heard an engineer use it, come to think of it.


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## Gareth Jones (Jul 13, 2007)

sparkie2182 said:


> "spurious"
> 
> A lovely word which says so much..........
> 
> I never heard an engineer use it, come to think of it.


I used it a lot when i didnt know what was wrong !!


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## Graham P Powell (Jun 2, 2007)

We were doing "manual" faultfinding. i.e. given a faults symptoms and working out what it was purely by using the manual. "Fuse blows". My friend Charley says put in a bigger one. "that blows". Put in an even bigger one..
eventually we reached the point where Charley had put in a nail as a fuse and the instructor well, he just blew a fuse!.
rgds
Graham Powell


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## King Ratt (Aug 23, 2005)

Bigger fuse syndrome sometimes known as "Tune for maximum smoke".


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