Fellow Listers,
Maybe someone on the list may be in a position to assist with the
following query. Some time ago I posted a message concerning battery life
associated with my Infra-Red remote control single button keyfob. At the
time it seemed as if I had purchased dud coin cell batteries. Two sets
depleted in very short order, a couple of operations and phut. Or even phut
phut : ) The unit continued to operate properly with a 9V PP3 battery
strapped to it for a number of weeks. I then fitted a set of cells which
were unused but lying about the house for over three years (Brothers’ Merc.
Keyfob spare batteries) These, though physically thinner than the CR2032’s,
worked fine when spaced with an aluminium disc to make up the difference in
size. However they gave up the ghost after about a fortnight. I put this
down to the age of the cells. I fitted a further set of three new CR2032
cells and — nothing.
The new cells were by a different manufacturer to the earlier sets of
suspect cells. I didn’t get a chance to immediately check the Voltage on
the new cells, following initial operation. After a period of some days,
when I did so I found them to be depleted. I connected another 9V source to
the keyfob and checked for current draw. When the device was in the
quiescent mode the current was in the 2.9mA region. When the button was
pressed no additional current was drawn by the unit. The high quiescent
current draw explains why the cells depleted. I think it should be in the
region of 4.5 micro Amps or so.
The remote control unit has worked nearly perfectly since 1989. It was
manufactured in Germany, by Kiekert I think.
The dealer advises that I must purchase both the Transmitters and Receiver
because the transmitter can not be purchased as a separate unit. They
advise that the transmitter is not programmable. The cost of the
replacement system is IR?260.00 / US$ 243.00. I know that I can purchase a
keyless entry system for much less than that, at around IR?50.00 / US$
48.00. Also I can interface the less expensive system with the central
locking module in the car. However the original keyfob unit is smaller and
neater than any others I have seen. I may not be able to repair the
original, but I would like to give it a try.
I checked one component which I thought might be suspect, a 220 micro Farad
capacitor. The value had certainly reduced, to 50 uF. However on
replacement with a new one - no joy.
There is an adjacent component on the Printed Circuit Board, which is
identified by the capital letter Q, on the PCB. A colleague advised me that
he thinks that such marking may be associated with a protective device. The
component has a blue plastic casing, 8mm x 8mm x3mm. It has two connections
in ‘Radial’ format. The marking on the top of the casing is: 485B y , The
‘y’ is in lower case script. When checking the impedance (Ohms) with a
Digital Multimeter, I get what is in effect an open circuit across the two
connections. It is difficult to tell exactly what is connected to what as
the PCB is coated in a dark Shellac or Conformal or some such protective
coating. Also the PCB is double sided, with component identifiers printed
on one side. It appears that one of the two connections on the mystery
component is connected to the 220uF cap. and the second seems to be
connected to one of the ‘legs’ of the main chip.
On opening a number of TV remote control units, I have observed similar,
but not absolutely identical, components in these devices. They are similar
in colour and connections but are physically a little smaller and with
different markings. They are also identified on the relevant PCB’s with the
letter Q. I wonder are they some kind of ‘potted’ RC Filter or some kind of
crystal or the protective device indicated by my colleague. I think that
crystals are usually encapsulated in a metal case.
In any catalogue of electronic components I have looked at, I can not find
a similar looking device. I have also searched a number of websites and so
far no success.
If anyone can identify this device and it’s function or point me in a
direction which might help identify the component, I would be grateful.
Kind Regards,
John Tarrant.