[Elecraft] RE: OT: Cyclocomputer repair help

[John Clifford]

Never mind... I fixed it!

After sending the previous email, I stared at the internal circuit board a
little more and pondered.  I couldn't see any other reason than mechanical
to cause this thing to fail after being dropped.

As noted in my previous email, I couldn't see any mechanical way that the
LCD module was secured to the PCB besides the crimped bezel... no pins came
thru the reverse side of the PCB and I couldn't figure out how they could
solder it if the component completely covered the board.  I hypothesized
that perhaps the display was attached solely by the bezel, and perhaps being
dropped caused it to get out of alignment with the contacts on the PCB.
So... gathering my courage (because such hypothesizing and the further
exploration that comes from it usually results in permanent damage), I
grabbed a pair of needlenose pliers and a small jeweler's screwdriver and
pried off the aluminum bezel, and it and the LCD came off in my hand.

The LCD module covered up a large portion of the PCB.  Underneath it were
several SMT capacitor chips and evidently a small IC... lots of traces
leading to a square covered with black goop.  Hmmm... how does the LCD
connect to all of these?  There were two rows of pads at the top and bottom
of the PCB, but no clear contacts on the LCD... angling it this way and that
to catch the light from the ceiling fixture in different ways showed slight
marks on the top and bottom 'edges' of the LCD where the pads had made
contact.  There was also some crud stuck to the leads where the larger
electrolytic cap was mounted (on the reverse side).  I removed the crud
(thinking that perhaps it was shorting out the cap/traces somehow), then
carefully repositioned the LCD module so that the marks on it lined up with
the pads, and recrimped the bezel.  I put everything back in the plastic
case and hit the reset button... and VOILA!

So... I guess the diagnosis was either/both 1) the LCD module became
misaligned due to the shock caused by the dropping, or 2) there was some
conductive crud left during assembly that moved and shorted out a trace due
to the dropping.

(Is it just me, or does it seem like a dumb idea to secure a large
multi-contact component, like an LCD display module, to a PCB solely via a
mechanical crimp, especially when the product/circuit will be mounted on the
handlebars of a bicycle and subject to a lifetime of severe jarring?  I'm
sure that this facilitates manufacturing... but how many warranty claims
must be made because this thing gets slightly out of alignment and stops
working?)

I'd tell you all how smart I am... but the newly-repaired cyclocomputer is
sitting on my desk ticking away, with one of its two buttons missing,
because I misplaced the darn thing (even after repeatedly reminding myself
to carefully remove them each time I dissassembled the unit, and place them
in the same spot on the desk) and now I can't find it.  (Fount it... 10
minutes later!).

 - jgc

John Clifford KD7KGX

Heathkit HW-9 WARC/HFT-9/HM-9
Elecraft K2 #1678 /KSB2/KIO2/KBT2/KAT2/KNB2/KAF2
                  ...waiting _eagerly_ for KPA2!
Ten-Tec Omni VI/Opt1

email: kd7kgx@arrl.net