Operating Instructions
2
01004C
the ammeter tests as an open circuit, until a complete
circuit is established to the battery pack and correct
battery pack voltage is measured across these
terminals.
Unplug the connector from the electronic timer
assembly. Inspect the plug contacts for distortion,
corrosion or any condition that would prevent
electrical contact with the pads on the electronic timer
assembly. Test all of the leads of the control cable
assembly to verify that none test as an open circuit.
Repair or replace the control cable assembly to
correct any deficiencies.
If all of the above test in good condition and the
charger still has not had output, then the only two
components remaining are the thyristor assembly and
the electronic timer assembly.
The complexity of the electronic timer assembly
prohibits field service and replacement with a known
good unit for test purposes is the only alternative. For
this reason, it is essential to have a spare electronic
timer assembly on hand when performing diagnosis
and repair.
The feedback control design of the charger makes it
possible for one of the thyristors in the thyristor
assembly to not function and the charger to still have
some output. This condition can be detected by
noting the temperature of the separate thyristors and
replacing the complete assembly if one of the
thyristors feels cold and the other hot. This condition
may also suggest its presence by continual melting of
the DC fuse.
The thyristors may be turned on one at a time to test
for failure. Use a 1.5 volt "AA" (Double A) penlight
battery. DO NOT USE A HIGHER VOLTAGE OR
LARGER BATTERY TO PERFORM THIS TEST OR
YOU CAN DESTROY THE THYRISTOR. Connect
the AC cord to a live outlet, set the power switch to
AUTO, unplug the electronic timer, and connect the
charging plug to a fully charged battery pack.
Connect a lead from the NEGATIVE (-) end of the AA
penlight to contact #9, or #7 or #3 of the electronic
timer plug. Momentarily touch a lead from the
POSITIVE (+) end of the AA penlight to contact #1
and then to contact #2. Do not continue this for more
than a few seconds as it is possible to damage the
thyristors and charger.
If the ammeter does not indicate current flow for each
thyristor, then one of the thyristors has failed and the
complete assembly must be replaced.
SERVICE NOTICE – JANUARY, 1987
There has been a change in the AC power fuse used in
some Type 24EL8 dual mode wheelchair battery
chargers. This change affects the models listed below
designed to operate on 120 VAC, 60 Hertz power.
Models affected:
12090
12160
12395
12620
12425
12630
The 5 amp, fast blow single element AC power fuse
(Lester Part No. 14359S, Buss MDX-5), used in these
charger models, was replaced by a 5 amp slow blow
dual element AC power fuse (Lester Part No. 16208S,
Buss MDX-5).
False blowing of the fast blow AC power fuse (Lester
Park No. 14359S, Buss MTH-5) has been reported.
Replacing this fuse with its slow blow equivalent
(Lester Part No. 16208S, Buss MDX-5) is intended to
eliminate this.
The replacement fuse is a round cartridge fuse, ¼"
diameter by 1¼" long. It is rated at 5 amps, is designed
for use in circuits with a maximum operating voltage of
125 volts, and is a slow blow dual element design.
Locally available replacement fuses with these
specifications may be used if you encounter a situation
where false blowing of the AC fuse is determined.
