Alpha Technologies Spectra Series - Manual (Page 48)

Preliminary Operating Instructions 48 of 62 AIP SERVICE NUMBER 1-800-863-3364
15.2 TESTING SCRs
While troubleshooting, it may be necessary to determine if you have a defective SCR1 in the charger.
The following sections assist in this task.
15.2.1 SCR1 SHORTED OR LEAKY
If an SCR1 is suspected of being faulty, it may be checked for a shorted or leakage condition with
an ohmmeter. With the AC and DC voltages removed and properly de-energized and locked out
from the charger, remove the secondary (SEC) transformer leads and disconnect the “G: or gate
wires from the SCR1s on the charger.
On the SCR1s, as in FIGURE 15.2.2-1, you can remove the wire on the terminal labeled “A” for
anode. The “K” or cathodes of the two SCR1s then go to the shunt. The “G” or Gate is the
smaller terminal with brown wires going to it. These are electrically isolated TO-239 package
SCRs with quick disconnect connections.
On the SCR1s, as in FIGURE 15.2.2-2, you will remove the wire attached to the heat sink plate
and disconnect the gate wires. These are electrically non-isolated TO-94 package SCRs with a,
½-20 STUD for mounting. The mounting stud is the “A” or anode of the SCR, which is mounted
to the heat sink plate. The “K” or cathodes of the two SCR1s are hooked together and then
mounted on the shunt with a red wire.
An ohmmeter reading between each SCR anode and cathode (which is connected to the shunt)
should show an open circuit for both polarities of the meter. If continuity is shown, the SCR is
shorted or leaky and should be replaced.
An ohmmeter reading between each SCR anode and gate should show an open circuit for both
polarities of the meter. If continuity is shown and the anode to gate is shorted, the SCR should
be replaced. If SCR is replaced, the SCR Driver board may also need to be replaced.
15.2.2 SCR1 OPEN
If the ohmmeter indicates an “OPEN” circuit, the SCR may have to be checked on some type of
SCR tester to determine if it is OK or an “OPEN” circuit.
Another way to determine if the SCR1 is open, is to use a clamp-on ammeter on either the wire
going to the anode or cathode while the charger is running with a small load on it. This needs to
be done using caution as to not touch anything that has voltage on it. On the SCR1s, as in
FIGURE 15.2.2-2, the heat sinks will have a dangerous voltage on them when the charger is
running. Both SCR1s should have about the same current reading. If one has no current flow,
then it may be open. Before replacing the SCR1, switch the two brown “G” or gate wires to see if
the working and non-working SCRs switch.
If not able to use another method to find out if the SCR1 is working, the SCR temperatures may
help determine which SCR is working and which is not. Make sure to disconnect all power before
touching anything.