PDF Version - The American Watchmakers-Clockmakers Institute

L&R tempo 400 watch cleaning machine
Repair & Modification of the Start Switch
by karel ebenstreit, cmw, cc21
1. Description of Problem and Parts:
L&R Tempo 400 watch cleaning machines came on
the market some 30-40 years ago and were proven
to be made very robust and have been doing an
excellent job for decades. They are still working
in many shops, but if they fail, spare parts and the
shops that perform the repair are hard to find. The
machine I have now has worked flawlessly for some
28 years, except for a start switch that has failed
twice. The first time was about four years ago when
the parts inside the switch broke lose, shorted and
caused severe burning damage to the body of the
switch. I managed to get the replacement switch
from L&R, but it failed again in exactly four years.
This time the switch was not making any contact
inside. When
I pressed the
start switch,
nothing was
happening and
there was no
way to fix the
inside of the
start switch.
An ohmmeter
test confirmed
the contacts
were not doing
their job.
There are four
yellow push
button (PB)
switches on
the front of
this machine. Three of them are simple ON/OFF
switches, but the start switch is a double switch, a
combination of “normally open (NO)” and “normally
closed (NC)” contacts that must operate at the
same time. All push buttons are illuminated inside
by a small light bulb. These are separately fed and
rarely fail, but bulbs are still available.
The L&R shop in Kearney, New Jersey no longer
supports this machine and parts are no longer available.
In the U.S., this service has been passed on to
the shop in San Rafael, California called Electronics
Instruments Service (Contact: Richard, 415-479-
8960). In Canada, similar help for this equipment
and ultrasonic work is available from Crystal Electronics
in Newmarket, Ontario (905-953-9129).
When I talked with both of them I found they would
be able to repair the start switch, but not with original
parts. Additionally, they would need to search
for the replacement to do the job at a cost of at
least $400 plus shipping. Considering the cost of
shipping this heavy machine, the risk of equipment
damage during shipping, and the time lost being
without the machine, I decided to find replacement
parts myself. I thought this would not be too difficult,
and it should work far better with new, more
robust parts, if done correctly.
Figure 1
I was lucky to find the replacement switch parts. Although
they were a bit larger than the original, they
still fit nicely and feel great to the touch. The complete
switch consisted of four parts: the push button,
main body, plus two contact blocks (one NO,
the other NC contacts). The main body has three
insert locations for a maximum of three contact
blocks. Since I used only two, I chose the locations
that best fit my case to ensure they were away from
the transformer on the printed circuit board inside
the machine (Figure 1).
The assembly of these parts can be done simply by
clicking them together or unclicking them apart. To
get the push button out, pull on the L-shaped lever
at the corner of the switch. To unclick the NO or NC
contact block, pull on the metal part on the top of
the body at the center on the opposite side of the
setting screw. These parts are very robust mechanically
and should last much longer than the rest of
the machine. I obtained new parts from a regular
electrical distribution parts supplier (Grey Bruce
Electric Supply Inc., Owen Sound, Ontario,
Horological Times November 2010 10