Mark Wendt mark.wendt.ctr@... [TekScopes] wrote:
On 12/16/2014 09:18 PM, 'Michael A. Terrell' mike.terrell@...
[TekScopes] wrote:
My troubleshooting is to always inspect & test the power supply,
then break the problem down into blocks. A quick signal tracing narrows
down the problem stage, then you look for defective components. Today,
ESR testing is a must on any modern equipment. In the past, I could
repair some common items in two minutes with nothing more than a VTVM,
1/4" nut driver and a soldering iron.
I later worked at Microdyne (Now L3-Com), troubleshooting new VXI
based cards for an $80,000 telemetry system that we manufactured. That
required a lot of other techniques, including locating hairline shorts,
and shorted components without damaging a board with over $8000 worth of
components. I used a HP 651, and a transformer to give a very low
impedance 1 KHz sinewave, and followed the signal along traces with a
Fluke 8920 True RMS Voltmeter. (The transformer was from a junked
Commodore 1541 floppy drive power supply and they could be had for free
at the time.) The 10:1 turns ratio took the output impedance of the 651B
down from 50 Ohms to .5 ohms. By using a 100 mV output, the level was
low enough to not turn on any semiconductors, or protection diodes.
Follow the trace while watching the voltage drops. The steps are large,
until you reach the short. Once they level off, go back one point and
start looking. That saved me hours of time on the bench. When I combined
all the little tricks I knew, It made me more than twice as productive
as anyone else in the department. :)
I had a Tek 2465B scope, and about 30 other pieces of test
equipment, with many connected to the in house GPS derived 10 MHz
standard. Each repair is different, but start with the basics before
deciding what you need to do next. Also, it doesn't hurt to keep a
notebook and a good digital camera with Macro capability on the
bench(es) to make notes and keep a photo record of how something was
assembled.
The camera on the workbench is a must. It's saved my bacon more than a
few times, especially with complicated cabling. I now have one
dedicated strictly to the workbench so it's always there when I need it.
Mark
I recently bought a cheap Borescope camera to be able to look under harnesses, and boards or other places. It can be used to read part numbers, if you have steady hands. :)
Michael A. Terrell