Tweco PAK 10 - Manual (Page 34)

Service 22 Manual No. 0-0515
Tests requiring voltage measurements are marked with
the warning symbol:
All other tests are to be made with the primary power
to the machine turned off.
NOTE
A. The two time delay relays, TD1 and TD2, are inter-
changeable and can normally be checked by swap-
ping them. They are the “delay on operate” type
with a fixed 2 second delay.
B. The 24 volt transformer and switch circuit can be
checked with an AC voltmeter. The meter probes
should be on J1-2 and J1-6 which are pin connec-
tions on the printed circuit card that holds the re-
lays. These pin connections can be located by find-
ing J-1 and counting from the four corner pins which
are numbered as shown.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Harness Connector
J1
Pin 2 Pin 6
A-01899
Measure 24 volts AC here when torch switch is closed.
C. Relay 1CR has a 24 volt AC coil. The coil resistance
should be approximately 80 ohms measured from
pin A to pin B (on bottom of relay).
1 2 3
4 5 6
7 8
A B
9
A-01900
Pin A Pin B
Bottom Of
Relay 1CR
D. To check the main contactor remove the left side
panel of the machine. The contactor should close
when 115 volt AC is applied to lines 1 and 15 (when
the torch switch is closed). At this time, 150 volt 3
phase power should be present at lines 33, 34, and
35. (150 volt 3 phase power should always be
present at lines 38, 39, and 40 when the primary
power is turned on).
E. A “quick check” can be made on the main diodes
without removing them from the circuit as follows:
Using an ohmmeter with the RX1 or RX10 scale,
measure the resistance of each diode in both direc-
tions. The readings should differ by at least a factor
of 10. If they do not differ (both high or both low)
the diode has failed and must be replaced. If a di-
ode fails it is important to check several things to
make sure that the replacement diode will not fail.
There are four potential causes of diode failures:
1. An in-rush current surge is the most probable
cause of main diode failure. The in-rush surge
is absorbed by capacitor C-5 and resistor R-1 in
series with each other across the output of the
bridge rectifier. The capacitor and resistor, as
well as the wires connecting them to the circuit,
should be completely checked in any case of
diode problems. The capacitor is a polarized
capacitor, and it is important to be sure that the
side marked + is connected to the positive side
of the circuit.