E R V I C E; Troubleshooting And Fault Isolation; Power-Up Self-Test; Subassembly Diagnosis - Facit 4431 Service Instruction

Adjustments:
• Focus
• Vertical Amplitude
Linearity
Frequency
• Horizontal Frequency
Phase
Amplitude
Linearity
• Brightness (black level adjustment)
8.3 POWER SUPPLY
Electrical design
• The circuit operates with a SMPS at 25kHz
(approx)
• The switch processor is from SIEMENS
(TOA4600)
Performance
• Input voltages
(Jumper select)
• Regulation range
220V 49-61Hz
117V 49-61Hz
187V --- 264V
100V --- 135V
• Output voltages and currents:
+5V
+12V
+12V
+17V
-12V
-23V
+/-0.3V
+/-0.2V
+/-0.6V
+/-1.5V
+/-0.6V
+/-1.5V
2.5A (for the Logic)
0.3A (for the Logic)
1.0A (for the Monitor)
0.25A (for the Keyboard)
0.10A (for the Logic)
10mA (for the EAROM)
• All outputs are overload and short circuit
protected
• Operating frequency is 20kHz --- 70kHz de-
pending on the load
• Output power 35W max.
• Efficiency approx 70%
• Mains current 0.3A RMS
8.0 during on
Adjustments:
• The output voltages are adjusted on the +12V
0.3A line by a potentiometer. See Chapter 9
Troubleshooting and Repair for details
Mains Voltage conversion
• In order to convert between 117 and 220V AC
operation, a jumper on the power supply cir-
cuit board is provided. See power supply as-
sembly drawing for visual aid
25
9
S E R V I C E _ _ _ _ _ _ _ _ _ _ _
9.1 TROUBLESHOOTING ANO FAULT ISOLATION
This section suggests methods for determining
which circuit is faulty in a malfunctioning u-
nit. The primary objective is to determine
which subassembly (Main Logic Board, Keyboard,
Power Supply or Monitor) is faulty.
9.1.1 POWER-UP SELF-TEST
Upon Power-Up, the 4431 tests the program EPROM
's EAROM, processor scratchpad RAM, and the
display refresh memory. If the terminal halts
with the LEDs on, then the processor has deter-
mine that the scratchpad RAM 072 is defective
and no further tests are attempted. If any oth-
er error is detected, the bell will ring 5
times and an error code will be displayed in
the upper left portion of the screen.
ERROR CODES:
1
2
4
DISPLAY MEMORY FAILURE
EAROM parity error
EPROM checksum error
9.2 SUBASSEMBLY DIAGNOSIS
If the Bell rings (beeps two times) when the
terminal is turned on then the main logic board
is in fairly good shape, for in order to sound
the bell the entire processor section must be
functional and the +5V logic supply must be op-
erating. If the bell does not sound on powerup
then either the keyboard, the power supply or
the main logic board is at fault. Also note if
the keyboard communication is at fault the Bell
will beep four times, this will result in, (af-
ter approx. 6 sec. delay) two times two beeps
as the keyboard internal test sequence will be
turned on.
Should the Monitor fail, one of the following
symptoms may be observed:
• no picture, regardless of brightness setting
• a bright horizontal line in the middle of
the screen
• a raster at high brightness, but no cursor
or characters
9.3 KEYBOARD FAULT DIAGNOSIS
The keyboard perform the following self-diag-
nostic sequence upon power-up:
If a suspected hardware fault is detected the
bell will "quack" five times, the appropriate
error code (see table below) will flash at ap-