Powerboard - Ikegami HTM-1550R Service Manual

3-2 POWER BOARD
(1) Outline
lhis board inputs AC power supplied lo the monitor and outputs
current voltage used by each board of the deflection and video
blocks.
(2)
Circuit description
(a)AC voltage switching circuit
The AC input voltage is switched manually by disconnecting and
connecting connectors.
Insert CNJ02 and CN104 when using lheACIOOV block.
Jnsen CN!03 and CNI05 when using lheAC200V block.
(b) DEGAUSS circuit
The power of lhe degauss coil is supplied from lhe AC. And
ON/OFFperfonned al RL!03 and lhe drive circuit (IRJ06).
(c) Main power circuit
This cirruit outputs current power supply other than that for hori-
zontal defleclion output. Switching is contro11ed
by
IC101.
(j) Start Up
When the input voltage is input
10
the slarting vo1tage input termi-
nal (Pin 5 of!C!O!) via lhe staning resistor (R!07), the output
Iran·
sistor lRI (MOS FEI) lhal is inclusion to lC!Ol turns ON and
drain current flows via the coils between Pins 4 and 3 of 1102.
Following Ibis, vollage is induced in the coils between Pins 2 and 1
ofT102. As these coils are wound so that this voltage turns ON
the output transistor 1Rl oontinuously, drain amen! continues to
flow lo increase the voltage at two ends of the current detection re-
sistor (RllO).
The vo]lage generated lo the resistance (RHO) for C:UITent detection
supplies the voltage that was inlegraled with the time conslant of
RI and C114 to lhe base o!TR2.
When the TR2 base JXllential exceeds about 0.6V. 1R2 turns ON lo
tum OFF the output transistor TR 1.
When the output transistor TRI goes OFF, power is supplied to the
secondary side. Al the same lime, as the ib current (see the fol-
lowing figure) is supplied to the TR2 base, a negative voltage is
supplied, lhus making ii difficult lo tum ON TR2.
By repeating the above operations for several times, the load volt-
age at both ends of secondary duty rises. While the output tran-
sistor TRI is OFT; power is supplied to the secondary side, after
lhe oscillation outpul transislor TRI, comes lo tum on with lhe
back swing and slabilizerl.
Vi
-- 5 ·-··••-,
ICI02:
,--- -
PCM'ef :
Sv.ildi :
•
I CT!tuil:
'Li----,-,-n_._,,,,-11-~4!>-t<l2!J--ill
I;. '.
WI
~
I
~
R2
wl..t.J
RI-;---,.-
k
--- 2 ............... :
Cl14
- 39 -
@ Output stabilization circuit (Constant voHage operations)
This amplifiesthechangesin lhe+ 120 V output by!CI06,inpuls ft
lo
the
amplification circuit control tenninal(Pinlof!CIOI) via lhe photo
COLI·
pler(ICI03) to impose lhenegativefeedback
and
stabilize lhe output
voltage.
@ Over current protection circuit
This is composed o!RllO, RI, TR2, C114, R2 and ZD2. The TR2
base potential in lhe nonnal stale is obtained by smoolhingwilh C114
the ia and ic potentials generaled when the output transistor 1RI is
turned ON and ib generated when the output transistor TRI is turned
OFF.
As
the output voJlage
increases,
the source current of the output
transislor 1RI increases. Consequently, the potential at the two
ends of R 110 increases lo decrease the generalion frequency.
When the base potentia1 of TR2 becomes about 0.6V, the gate
voltage of the output transistor TR I is pulled.
The output transislor1RI source current flows in biangular waves.
Therefore when lhe output current increases, lheON timeof lheoutpul
transislorlRI becomes a:mstant, the OFF time increases, and the
outpul amenl decreases, and the over-current protection circuit
operate.
(d) DEF+ B power supply circuit
The variable DC power supply for horizonlal deflection output
is
being output in this circuil. The witching in th.is circuil is con-
trolled by IC102.
<D
Start Up
After a certain time from lhe start of lhis power supply. the resel
signal from lhe DEF BOARD passes through lhe focus coupler
(IC!05), added to lhe ON/OFF lenninal (Pin 5 of 1C!02), and
when the potential beromes GND. IC102 slarts witching opera-
tions.
The operations of lhe transformer (fl03) can
be
turned ON/OFF.
®
Output stabilization circuit
Titls amplifies the fluctuations of the DEF+ B output at IC107 and
1C108, feeds back lhe output lo lhe F/B lenninal (Pin 8 oflC102)
via the photo coupler (IC104) to stabilize the output voltage.
@
Over-current protection circuit
By feeding back the vollage of the resis(or (Rl25) for over-current
protection lo the CI.M lenninal (Pin 15 of!C102), the limiter lo
operate when over-currenl is output.
(3)
Adjustment procedure
(a)VRJOJ: +BADJ
Q)
Connect an accurale digilal vo]tmeler to 1Pl02.
!Note
I :
As
the secondary power supply circuit is used, connect the
minus side to TP!07 (GND).
@ Adju~ lhe DC voltage to
+
120V using VRIOI.
,,,,,mm1,1
• The section marked as !PRIMARY
I
in the schematic diagram is the
primary side of the power supply. Be sure not to shor1 with the secon-
dary side.
• Titls control is not for field servicing and is fixed with glue after setting
to avoid X-ray radiation, which may cause one component failure in
the circuit and touch not of this control.
The sealing method is shovm in the diagram.
lltls adjustment is required when re-
placement of lhe parts marked wilh
*•
@in the schemalic diagram of
lhe POWER BOARD is done.