Hi,

I wonder if you can make any suggestions on my problem.

I have a high frequency gate opener key fob issued by work.
Unfortunately it was left in a jacket that went in the washing machine
and afterwards the keyfob no longer worked.

I took it apart and cleaned up the circuit board with alcohol (tape
head cleaner) and let it dry for a day. On testing it it didn't work
so I decided to clean it again and through a complete slip of the mind
I put it together and tried it while still wet and it showed signs of
life. I thought the second clean had done the trick. I let it dry and
tried it again but it didn't work. I applied some alcohol to it to wet
it (component side) and it showed signs of life.

Therefore when the board/components are wet it shows signs of life but
nothing when dry. The unit is pretty straight forward, a single
surface mount I, surface mount resistors and a couple of transistors,
a pot, a crystal, one component which I don't recognise and two 3v CR
batteries. The pcb is double sided and a visual check shows all tracks
look complete and ok and not corroded by the water.

I'm an enthusiast who has built circuits before but I don't have in
depth knowledge or test equipment.

Can anyone shed any light on this? Why it works when wet?

Thanks,

Mark.

"Mark" wrote in message
...

snip

Can anyone shed any light on this? Why it works when wet?

Thanks,


It probably needs a bath in isopropyl alcohol or, at a pinch, methylated
spirits. Give it a good soak, put it on its side in a warm place to dry for
a hour or two, and finish it off with gentle hair drying.

If that doesn't work, perhaps the variable capacitor or pot has water
contamination inside, or maybe there's some corrosion.

BTW, is the component you don't recognise in a round metal can? It could be
the 'SAW' resonator. If there's any dampness under that then perhaps it
could shift the frequency enough to stop it working correctly.

Dave

As has been suggested a bath in i.p.a. would be a good idea, with a
gentle scrub with a brush. With the batteries out you could bake it at
80Deg.C to dry out any water.
Water and detergent won't damage modern electronics as long as it's not
powered up.
Unfortunately your fob was.
Are there any blue-green deposits anywhere. pth holes and via's can be a
problem especially under chips as any conformal coating tends to miss
those areas.
--
Neil J. Harris

"Neil J. Harris" writes:

As has been suggested a bath in i.p.a. would be a good idea, with a
gentle scrub with a brush. With the batteries out you could bake it at
80Deg.C to dry out any water.
Water and detergent won't damage modern electronics as long as it's
not powered up.
Unfortunately your fob was.
Are there any blue-green deposits anywhere. pth holes and via's can be
a problem especially under chips as any conformal coating tends to
miss those areas.

If there were blue-green deposits or evidence of corrosion, even if you can
get it to work, I'd never trust it for anything critical.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.