N_Cook wrote:
On 14/12/2015 18:02, Cydrome Leader wrote:
N_Cook wrote:
On 14/12/2015 14:05, Cursitor Doom wrote:
Anyone care to share their experience on the correct approach to
troubleshooting? I'll kick off by suggesting:

1. Assume nothing.

Perhaps we can assemble a list of golden rules....


First analysis instrument to use on removing the case cover - your nose

smell test is good.

check power, fuses, probe around for expected voltages. For example if
there's any sort of linear regulator check output, input, check voltages
on ICs. I deal with old stuff so there's always some 7400 series logic so
+5 is expected to be all over the place.

Look for burned parts, puffy caps, probe anything in areas with
heat-discolored circit boards, check and resolder and suspect joints by
parts that warms up. Diode check is a great feature on DMMS.

If you're dealing with suspect dried up caps, just solder a new one on
the solder side of the board and see if that helps at all. I like to add
parts on the bottom of the board, get things working then position parts
where they belong if all good.

If these things appear OK, then you have to narrow the problem down and
dig around into what the circuit should do vs. what's happening.

For intermittent problems tap the hell of boards, cable assemblies etc.
Check power supply voltages with the device cold AND after it warms up.

Just came across a machine that would crash fairly often, The problem
appears to be a mix of loose sensor and power connectors, a power supply
that drops voltage as it warms up, plus a dead cooling fan in the
electronics section. Just to keep things interesting, nothing warms up
that much with the service panels removed.









There is problem with "twizzling" for intermittant soder joint failure,
if it is a PbF board. Its too easy to temporarily "fix" a failed joint.
I start with light touching stuff with a bird feather, while switched
on. Then firmer twizzling.
Then hot air or freezer spray.
Then if I auapect a PbF failure ,an adapted engraver tool with a shaped
nylon bolt in place of the engraving tip, to rattle the board, listening
on headphones , if an audio amp.

I'm pleased to say I don't really deal with PbF stuff. How often do you
find bad joints that looked OK (well, as good as PbF looks) and did have
weird cracking or separating from the part lead?

Do you do repairs with real solder or that fake tin stuff?