Monday, November 12, 2007

THE (UN)COMMON SENSE


About 6 years ago I had to set up servers for my colleague at
a laboratory inside ALTTC (Advanced Level Telecom Training Centre),
Ghaziabad,Near Delhi. I hooked up the server, monitor, keyboard,
mouse and the works! I first switched on the monitor and next I
tried switching on the server but it refused to do so.

Based on my years of “on-the-job” experience, the first thing
I suspected was the SMPS. SMPS seemed to be order because the
power ‘ON’ LED on motherboard was on. Next, as a standard procedure, I pulled out all the peripheral cards, disconnected keyboard, mouse and all other
connections except the power cable and tried again.
 Still NO SIGN of server switching ON! 
   Due to non-availability of CRO or such other testing equipment,
I could not test the motherboard and called up the supplier and
told all the symptoms, who advised me to bring it to Delhi, as he
did not have service centre at Ghaziabad. Meanwhile, I called up
our Delhi office to borrow another server and after some initial
reservation they agreed but asked me bring along the ‘faulty’ server.
 We confidently connected power to the new server! But, still no sign
of life!
 NOW I was really at my wit’s end! My whole confidence was at the
lowest ebb! By now it was late in the evening. Completely exhausted,
on an impulse I checked the supply voltage. It was 110V AC instead of
normal 220V AC, which one would normally expect. (We later found that
a special supply network of 110 V AC had been created for these
equipment supplied by Fujitsu, Japan.)
   But why did the monitor switch on at 110 V AC? Well it turned out
that the monitor had higher voltage tolerance range.
  Even today the remark of my boss keeps ringing in my ears “ Gana, 
sometimes you need to stop using too much of brain!”

 ---------   R. GANAPATHI RAO
Research Associate,CENTRE FOR DEVELOPMENT OF TELEMATICS,
ELECTRONICS CITY,BANGALORE.

Saturday, January 06, 2007

Drilling Machine Drills

Drilling machine mystery

Our ½ hp, 3ph, drilling-tapping machine is 10 years old. Recently, the 6A HRC fuse in the R phase blew, followed by tripping of the upstream ELCB.

Could it be an earth fault? Ohm-meter did not indicate any visible earthing. I tried hard but could not trace the fault physically. I just replaced the fuse. The machine operated without problems for few weeks.

Wonderful!

And then the fuse blew again. Well, I reckoned it could be just a transient phenomenon.

Cleaned up the electrical panel. Replaced the fuse. No problem.

After about 10 days the fuse blew again, followed by tripping of the ELCB.

Now I was getting really mad. Opened up the incoming R-phase cable terminals at both ends (about 4 meters). Checked with a “Neon tester’ and it glowed gracefully. Cable must have got shorted inside. Changed the cable. Replaced the fuse. Now the machine was running perfectly. But strangely there was no tell-tell sign of burn mark in the old cable.


After about a week the drama was repeated. This time, without much ado, I replaced the R phase fuse with a 16A HRC fuse.


After about a week, there was a flash at the incoming terminal box of the drilling machine.

The Fuse blew, ELCB tripped.

But I was more than happy. I had found the culprit. The incoming screw holding the Terminal Block had fouled with the terminal of the R phase.


Another lesson. Neon tester had been showing capacitive voltage.

--- P. K. Ray ----

raynar.industries@gmail.com