Tweco PAK 10 - Manual (Page 33)

Manual No. 0-0515 21 Service
4. Current control circuit inoperative (A cutting arc can
be established on very thin material if the torch is
held very close)
a. See next section (Problem M).
Once the cutting arc is established, the cutting current
should be equal to the setting of the CURRENT adjust
knob (unless the remote current control is in use). If it
is not, there is a problem in the current regulating cir-
cuit as follows:
M. Unit only puts out minimum current
1. Fuse 1FU blown
a. Replace.
2. Fuse blows again
a. Check diodes, varistor and SCR’s in control
bridge (See N & V, Test Procedures).
3. Reactor disconnected
a. Check (See P, Test Procedures).
4. Printed circuit card failed
a. Check (See Q, Test Procedures).
5. Potentiometer failed
a. Check (See 0, Test Procedures).
6. T5 transformer failed.
a. Check for 12VAC at each sec. coil.
N. Unit only puts out max. current-100+ A
1. Pilot arc remains on during cut
a. Check CSR circuit (See R, Test Procedures).
2. Shunt disconnected
a. Check (See T, Test Procedures).
3. Printed circuit card failed
a. Check P.C. card (See Q, Test Procedures).
O. Unit can only put out about 70 amps maximum
1. P.C. card failed
a. Check P.C. Card.
2. One SCR failed
a. Check SCR’s (See U, Test Procedures).
P. Unit output does not match potentiometer
setting
1. Remote Control resistance open
a. Check circuit (See S, Test Procedures).
Q. Short torch parts life
1. Pilot arc remains on during cut
a. Check CSR circuit (See R, Test Procedures).
2. No pre-purge gas flow
a. Check time delay TD2.
3. No post purge gas flow
a. Check time delay TD1.
4. Misuse of torch
a. Use torch within ratings for current and work
thickness.
R. Arcing in collet area
1. Back cap not tight
a. Replace collet and tighten cap securely.
2. Dirt in collet area
a. Clean electrode, collet and collet seating area.
S. Discolored electrode
1. Gas hoses switched
a. Check.
2. Contaminated gas
a. Check plasma gas system for leaks.
3. No pre/post purge
a. Check TD1 and TD2.
4.6 TEST PROCEDURES
The following tests are suggested for specific problems
listed in the preceding trouble shooting chart. The let-
ter designations correspond to those listed in the “Rem-
edy” section of the trouble shooting chart.
WARNING
Several of these tests involve voltage measure-
ments that must be made with power on. In or-
der to make these measurements, the leads ac-
cess door interlock switch must be propped closed
or by-passed. Use extreme care when making
these tests and be sure to return the interlock
switch to proper operation after work is com-
pleted.