IBM 655743N - P 92 - 19" CRT Display, Service Manual

Page: 19 / 46

6557-03N/03S/43N/43S
SECTION 3
SAFETY RELATED ADJUSTMENT
3-1
Part Replaced (
[
)
RV901 HV ADJ
When replacing or repairing the shown below table, the follow-
ing operational checks must be performed as a safety precaution
against X-rays emissions from the unit.
•
Beam Current Protector Circuite Check
(1) Hardware logic circuit
•
Turn the POWER SW on, and check that the RAS-
TER fades in.
•
Connect a variable resistor (20 k
Ω
or more) and an
ammeter in series between FBT pin
!¡
and – 15 V
line (– side of C637). Decrease gradually the resis-
tance of the variable resistor from maximum to mini-
mum, and confirm that the Beam Current Protector
Circuite works (TV Raster disappears). The current
must be within the range shown below.
Standard current: Less than 1.09 mA
(2) Software logic circuit
•
Turn the POWER SW on, and check that the RAS-
TER fades in.
•
Short b of C639 and GND.
•
Connect a variable resistor (20 k
Ω
or more) and an
ammeter in series between FBT pin
!¡
and – 15 V
line (– side of C637). Decrease gradually the resis-
tance of the variable resistor form maximum to mini-
mum, and confirm that the Beam Current Protector
Circuite works (TV Raster disappears). The current
must be within the range shown below.
Standard current: Less than 1.14 mA
HV Regulator
Circuit
HV HOLD
DOWN Circuit
Beam Current
Protector Circuit
Part Replaced (
]
)
D board IC901, R903, R922,
T901, RV901
• Mounted D board
D board D913, D916, C923,
R920, R927, R935,
R936, T901
• Mounted D board
D board IC901, D901, D902,
D918, R053, R918,
R923, R928, R932,
R933, R934, R939,
T901
• Mounted D board
* Confirm one minute later turning on the power.
•
HV Protector Circuit Check
(1) Confirm that the voltage between cathode of D913
and GND is more than 17.5 V DC.
(2) Using external DC Power Supply, apply the voltage
shown below between cathode of D913 and GND,
and confirm that the HV HOLD DOWN circuite
works. (TV Raster disappears)
Standard voltage: Less than 23.40 V DC