INSTRUCTIONS for
SCR CONTROL P.C. BOARD RETROFIT KIT
F-15-002-A
May, 1995
P/N 31236
This retrofit kit contains a modified SCR control p.c.
board, P/N 31545, which is provided as an equivalent
replacement for older-style SCR control boards, P/N
675405 w/integral CCP pot, used in Heliarc 250 HF/pf
units.
The retrofit kit’s p.c. board has been redesigned to provide more secure and reliable wiring termination at the
board (using plug connectors), and to improve low output stability in low ampere applications.
The retrofit kit, P/N 31236 consists of the following:
Qty. P/N Description
1 31454 SCR Control P.C. Board Assy.
1 31066 P1, 6-Pin Plug/Lead Assy.
1 31067 P6, 5-Pin Plug/Lead Assy.
1 953916 CCP Pot, Front-Panel Decal
1 31065 CCP Pot
To install the kits SCR control Board do the following:
Electric shock can kill. Precautionary measures
should be taken to provide maximum protection
against electrical shock. Be sure that all primary
power to the machine has been externally disconnected. Open wall disconnect switch or circuit
breaker before attempting inspection or work inside
the power supply.
a. All 250’s manufactured “after” serial number
B87B72400 incorporating an Arc Force control
feature on the front panel, the SW2 dip switches
must be set (or repositioned) to the OFF or OPEN
position.
b. All 250’s manufactured “prior” to serial num-
ber B87B72400 “do not” contain the Arc Force
control and SW2 dip switches must be set (or repositioned) to the ON or CLOSED position.
NOTE: Some “dip” switches may be marked with “O”
or “I” to identify the OFF and ON modes respectively.
3. Before physically removing the old SCR Control
board, it is suggested that the two plug/lead assem-
blies (P1 and P6 provided in the kit) be connected to
the existing wire terminations, of the old SCR board,
as shown in Figure 2.
1. Remove the top and side panels of the power supply
to gain access to the internal components.
2. Unpack SCR control board and inspect the setting of
the SW2 “dip” switches located on the lower left-hand
side of the p.c. board as shown in Figure 1. Depending on the “vintage (age)” of the power supply being
repaired, make sure the SW2 “dip” switches are set
(or repositioned) as follows.
Be sure this information reaches the operator.
You can get extra copies through your supplier.
Fig. 1- SCR Control Board # 31545
(Part of Retrofit Kit P/N 31236)
You may also notice that an additional wire (orange)
attached to the kit’s P6 plug (at terminal B) will need
to be connected in your machine because of the modified circuitry on the new p.c. board. This is also clearly
shown on the appropriate diagrams in Fig. 2.
After all of the new plug/lead reconnections have been
properly made, you can install the new p.c. board and
insert the P1 and P6 plugs into the board receptacle
headers.
Tape any exposed connections in the new plug/leads
(to prevent any possible short circuiting), and secure
all loose wires to the existing wire harness(es).
4. Please not that the kit also contains a new current
control (CCP) decal. Place it directly over the existing silk-screen markings for this potentiometer on the
front panel.
5. This completed the retrofit installation and you can
replace the covers and test the unit.
Fig 2 - Heliarc 250 HF/HFpf SCR Control P.C. Board Retrofit Wiring
F-15-002-A 5/95 1C Printed in U.S.A.
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