Safety Related Adjustments - Dell P780 - 17" CRT Display Service Manual

P780
When replacing parts shown in the table below, the
following operational checks must be performed as a
safety precaution against X-ray emissions from the unit.
HV ADJ
HV Regulator
D board T501, IC501, RV501, R540,
Circuit
HV HOLD D board T501, R510, R543, R547, R549,
DOWN Circuit
Beam Current
D board T501, R545, R546, R548, R550,
Protector Circuit
* Allow the unit to warm up for one minute prior to
checking the following conditions:
a
) HV Regulator Check
1) Input white cross hatch signal. (fH = 80 kHz)
2) CONT maximum and BRT center
3) Cut off Screen VR (G2).
4) Input voltage: 120
5) Confirm that the voltage is within the voltage range
shown below.
Standard voltage: 26.9 KV
6) When replacing components identified by ] , make
sure to recheck the High Voltage.

SAFETY RELATED ADJUSTMENTS

Part Replaced ( [ )
RV501
Part Replaced ( ] )
R541, R542, R544, R564, R567,
R568, C532, C534, C539, C553,
C554, C555, C556, C558, C561
R552, R595, D515, D517, C540,
C542, C544, IC607, IC901
R596, R934, C535, C541,
IC605, IC607, IC901
2 VAC
0.4 KV
RV501
SECTION 3
7) Verify the High Voltage as shown above (26.9 KV
0.4 KV) is within specification. If not, set H. SIZE
data at minimum (-127) and then adjust RV501 on
"D" Board.
8) After adjusting the High Voltage within specification,
put the RV cover on RV501 as shown below and apply
sufficient amount of RTV around RV501.
b) HV Protector Circuit Check
1) Confirm that the voltage between cathode of D517 an
GND is more than 27.5 VDC.
2) Using an external DC Power supply, apply the voltage
shown below between cathode of D517 on "D" and
GND, and confirm that the HV Hold-Down circuit
works. (Raster disappears) Apply DC Voltage: Less than
35.5 VDC
Check Condition
• Input voltage
• Input signal
• Controls
• B+ Voltage
c) Beam Protector Check (Software logic)
1) Using an external current source, apply < 1.55mA
between pin
that the raster fades out.
Check Condition
• Input voltage
• Input signal
• Controls
d) B+ Voltage Check
1) Input white cross hatch (fH = 80 kHz) signal.
2) CONT (max) & BRT (center)
3) Input voltage: 120
Note: Use NF power supply or make sure that
distortion factor is 3% or less.
4) Confirm that the voltage is within the voltage
range shown below.
Standard voltage: 180
— 12 —
: 120 2 VAC
: (fH = 80 kHz), White Cross Hatch
: CONT (max) & BRT (center)
: 180 3.0 VDC
of FBT (T501) and GND, and confirm
: 120 2 VAC
: (fH = 80 kHz), White Cross Hatch
: CONT (max) & BRT (min)
2 VAC
3.0 VDC