To test SCRs construct the circuit outlined above. Resistor values are plus or minus
ten percent. The voltmeter scale should be low, approximately 0-5 or 0-10 volts DC.

6 VOLT
LANTERN
BATTERY

SW1

SW2

SCR
UNDER
TEST

R1= 4 ohms/10 watts
R2= 3 ohms/10 watts

7. To test SCRs, construct the circuit outlined

in Figure F.13. Use one 6V lantern battery.
Resistor values are in ohms +/- 10%, The
voltmeter scale should be low, approxi-
mately 0-5 or 0-10 volts.

BATTERY TEST

Check the battery by shorting leads (A) and
(C) and then close switch SW1. Replace bat-
tery if voltage is less than 4.5 volts.

A. Connect SCR into the test circuit as

shown (A) lead to anode (C) lead to cath-
ode and (G) lead to the gate.

B. Close switch SW1 (switch SW2 should

open), voltmeter should read zero. If the
voltmeter reads higher than zero than the
SCR is shorted.

NOTE: Do not disassemble the heat sinks.

8. With switch SW1 closed, close switch

SW2 for two seconds and release. The

voltmeter should read 3 to 6 volts before
and after switch SW2 is released. If the
voltmeter does not read, or reads only
while SW2 is depressed, the SCR or bat-
tery is defective (repeat battery Test
Procedure).

9. Open switch SW1, disconnect the gate

lead (G) and reverse the (A) and (C) leads
on the SCR. Close switch SW2. The volt-
meter should read zero. If the voltage is
higher than zero, the SCR is shorted.

10. Replace any SCR assembly that does

not pass test.

11. When test is completed, reconnect the

positive bridge leads to the shunt.

12. Reconnect Plug J4 into the Firing Board.

13. Replace the case top, sides and control

panel.

FIGURE F.13. SCR Test Setup