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3) INSTRUMENTS AND CONVENTIONS FOR PERFOR-
MING DIAGNOSIS AND REPAIR
3.1) Instruments for basic diagnosis
The following are required:
- a multimeter with the following scales:
Ohm: from 0 to a few Mohm
Diode testing
Direct voltage (Vdc): from mVdc to 1000 Vdc
Alternating voltage (Vac): from 10 Vac to 700 Vac
NOTE: Y ou are advised to use an instrument with
automatic scale since it is not theoretically possible to
predict the electrical quantity to be measured when
the machine has broken down.
- an AC/DC ammeter clamp at least in class 2.5 with e.o.s. 400A pk
- alternatively to the ammeter clamp, a shunt can be used with
value 60 mV @ 400 A.
NOTES:
* remember that other types of shunts can also be used,
but accuracy is reduced with higher capacities, whe-
reas with lower capacities the measurement must be
taken quickly to avoid overheating of the shunt
* once fitted, the shunt is at welding potential (be
careful especially with discharges during arc stri-
king in TIG HF)
* the ammeter clamp is preferable as it is more practi-
cal
3.2) Repair tools
- complete set of fork spanners
- complete set of pipe spanners for hexagonal nuts
- complete set of blade screwdrivers
- complete set of Phillips screwdrivers
- complete set of Allen keys
- Phillips torque screwdriver for M3 screws with tigh-
tening torque adjustable range from 1 to 3 Nxm,
accuracy 0.1 Nxm
- crimper for insulated wire terminals (blue, red and
yellow)
- pliers for AMP contacts
- tweezers and cutting nippers - type commonly used
for electronic components
- tongs (dimensions suitable for closing gas pipe
clamps)
- welder for electronic components, minimum power
50 W
- portable electric drill
Instruments and conventions for performing diagnosis and repair
3.3) Grid load
Use of grid load can speed up fault tracing and machine testing.
J ust remember that a fixed power resistor applied to machine's
output is somewhat equivalent to a welding arc, but only inside
of a narrow output voltage range, whose center value can be
determined by the formula:
TIG DC WELDING:
V
10 + 0.04 x I
OUT
OUT
Es.:
12Vdc @ 50A
14Vdc @ 100A
18Vdc @ 200A
STICK WELDING::
V
20 + 0.04 x I
OUT
OUT
Es.:
22Vdc @ 50A
24Vdc @ 100A
28Vdc @ 200A
If output voltage goes too much above or below the rated value,
the generator could either saturate or go into arc force or other
special features could be performed (such as anti-flashing): in
both cases real output current could be much different from
expected value and the generator could even show an intermit-
tent output power (output power led blinking, see also sec.7.1
in the following).
Grid load resistor's rated power is also important, 'cos a 24Vdc
@ 100A grid load produces 2400W to be dissipated by air
cooling.
So, when using grid load, pay attention to both out-
put current & output voltage and use correct resistan-
ce value & power!
etc.
etc.
5
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