"robb" wrote in news:13j1fghd5a5t9d7
@corp.supernews.com:

"John Tserkezis" wrote in
message u...
robb wrote:

Currently the only diagnostic tools at my immediate disposal
are

Fluke 177 DMM, a Tek 2236 oscope and a usb/PC based all
purpose
logic anal/spectrum anal/oscope

i am hopeing these will be sufficient to solve / track this
fault(s)
if low ohm meter is not terribly expensive then i'll try to
get
one if it helps more than my current tools

You're missing a hammer.


well i purposefully left the hammers out because i did not
realize their usefull ness in this situation.

Since you have an "anal" scopes,
Google for RCA curve tracer. There are several different versions and plans
for building one.

There is a simple device that I have used for years for checking ICs,
transistors and diodes---
in circuit!

Basically, it consists of a transformer that gives some ac voltage (12 or
so will do fine), current limited with a resistor.
The voltages goes across the part to be tested and the scope monitors the
voltage across the resistor on the vertical axis
The scope uses the voltage across the leads that go to the part to drive
the horizontal trace.

You get a nice sharp knee for a good diode.
You get a slanted line for a resistor.
You get an oval for a capacitor.
You get multiple knees for some of the good ic gates.

After a while you will recognize a bad gate by the rounding of the knee.

A dead short is a vertical line
An open is a horizontal line.

You can often see reverse breakdown (zenering) for good ic junctions.

You want your series current limiting resistor large enough so that your
peak voltage from the transformer will not damage a good junction.

















--
bz 73 de N5BZ k

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

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