Amada Miyachi Unitek STA-100A, Operation Manual, Page: 66 / 154

CHAPTER 5: MAINTENANCE
STA SERIES AC CONTROLS
5-2 990-351
Fuse Replacement
The Control contains a fuse, mounted on the load side of the Valve Transformer. Before replacing the
fuse, determine what caused it to fail and make appropriate repairs. The fuse size will depend on which
transformer has been ordered. See table 4-1 for appropriate fuse selection.
Valve Transformer Fuse Selection
Transformer Rating Fuse Size Amada Miyachi America Part Number
115VAC, 150 VA 2A FNM-2
115VAC, 250 VA 3A FNM-3
115VAC, 500 VA 6A FNM-6
24VAC, 150 VA 10A FNM-10
24VAC, 250 VA 15A FNM-150
24VAC, 500 VA 30A FNM-30
Principles of Operation
Input power (L1 and L2) enters the Control. L1 is applied through the (optional) circuit breaker and
(optional) primary current sensor to the SCRs and the valve transformer.
Simplified Block Diagram
SCR
Snubber
Weld
Transformer
Common
Gnd Gnd
Primary Current
Sensor Optional),
L2
L1
Circuit B
reaker (Optional)
Weld
Transformer 2
Transformer
shown wired
for 460V
Control Panel
Assembly
AC Timer
Main Board
Input for
Secondary
Current
Sensor(s)
(Optional)
Key
Lock
SCR
Drive
Board
NOTE:
Current Sensors are
optional. Unit may
have Primary,
Secondary, or no
Current Sensor
SCR
SCR
Drive
Board
Snubber
Cascade
Board
Surge
Resistors Surge
Resistors
Weld
Transformer 1
Power
Transformers
Valve
Expansion
Card
(Optional)