Tokyo Hy-Power HL-550FX User manual

Users Manual
Solid-State HF/50MHz Band
550W Linear Power Amplifier
Model HL-550 F

1
1. Introduction
Thank you for purchasing the HL-550 FX .
This compact and light eight desktop HF linear po er amplifier has a maximum input
po er of 1.2kW. Our solid-state broadband po er amp technology makes it the smallest
and lightest in the industry in its class.
Typical output po er is 550W (SSB, CW) ith the drive po er of 65-90W.
It is best suited for the DX-pedition use due to its light and compact design.
2. Cautions
2-1 The amplifier is cooled by forced airflo . Several inches of clearance on the top
and the rear all are necessary to allo for smooth air intake into the fan. Do not
block the air vents on the top cover.
2-2 Keep the amplifier out of direct sunlight, in a cool dry environment.
2-3 Internal high voltages (AC, DC and RF), are present at all times, ON AIR or OFF.
Internal access should be limited to avoid injury.
2-4 Turn off the AC main po er immediately upon any unusual sounds, sights, or
odors. Check the multimeter readings of Vd and Id, the fuses and all cable
connections around the amplifier. Please notify the dealer or the factory of any
problems.
2-5 For your safety, do not operate the amplifier ithout adequate grounding. A
proper ground connection ill result in peak performance and stability, in
addition to reduced RF strays or noises.
2-6 To eliminate the RF interference to such home appliances as TV, FM radio,
telephone sets, and etc., it is recommended that clamp-on ferrite cores be
inserted at both ends of the remote control cable, ALC cable, coaxial jumper cable,
and antenna cables, as needed. Also, a common mode AC line filter (near the AC
outlet), and in-line lo pass filters on the antenna coaxial cable (as necessary),
are recommended.

2
2-7 The amplifier has fast acting sophisticated protection circuits. Please note,
ho ever, any such actions that cause the same fault to occur repeatedly, ill lead
to failure of the valuable final po er FET transistors.
2-8 Before checking inside the amplifier, be sure to ait a fe minutes for the high
DC voltage to discharge (monitor Vd meter reading). The potentiometers for RF
po er detector, protection circuits, FET bias voltage circuit, etc., are precisely
adjusted at the factory, and should not be altered. Doing so, ould require
readjustment ith precision measuring instruments.
2-9 The DC po er supply section consists of most efficient and sophisticated
s itching mode circuit. It accepts the ide AC line voltages ranging from AC
100V up to 260V. Since the line voltage is detected and selected automatically,
you do not have to orry about the tap change of internal po er transformer
hichever country you ill travel. Be sure to verify capacity of AC line fuse
before you plug the AC po er cord into the outlet.
2-10 Before starting the amplifier, be sure to connect a dummy load (50 ohms, 550W
min.) or a ell-adjusted antenna to the output terminal. Operating ithout any
load ill cause extreme stress to the RF po er FET’s, although protection
circuits should ork under critical conditions.
2-11 Required drive po er is slightly less than 100W to obtain the full 550W output.
Do not attempt to operate ith excessive drive from a high po er transceiver.
2-12 Keep the aluminum heat sink and air openings free from dust and blockages.
Periodic cleaning ill prevent degraded cooling efficiency.
2-13 For long continuous operation in RTTY/FM modes, it is recommended that you
reduce the RF drive levels by 20% to 30% lo er output than CW/SSB modes.
2-14 To prevent damage to the precision electronic components, avoid extreme
physical shock to the amplifier. If factory service is required, the amplifier should
be shipped using the original box and packing materials.

3
3. Features
3-1 Our solid-state broadband design engineers orked to make the HL-550FX, the
lightest and most compact 550W out portable HF/50MHz amplifier in the
industry. This orld-class compact 550W HF amplifier is the easiest to handle
and operate any here in the orld.
3-2 The amplifier’s main PA section includes 4 high po er MOS FET VRF150,
resulting in 550W (SSB/CW max.) on HF and 500W on 50MHz bands. The
amplifier’s broadband characteristics require no further tuning once the
operating band is selected.
3-3 The amplifier allo s operation in full break-in CW mode due to the use of the
amplifier’s high-speed antenna relays (made by Panasonic).
3-4 With the unique duct structure design and the po erful blo er fan, the
aluminum heat sink block for RF PA module (and other components), are
effectively cooled. The fan’s quiet operation allo s for even the eakest DX
signals to be heard.
3-5 The amp utilizes a sophisticated circuit to run the various high speed protection
circuits such as overdrive, high antenna SWR, DC overvoltage, band miss-set etc.
3-6 This amplifier is compatible ith ide AC line voltage ranging from AC 100V to
260V. Although AC line voltage is automatically selected, be sure to install proper
fuse into AC line fuse holder.
3-7 For the safety of the operator, an Interlock system is employed. The AC po er is
shut do n if the top cover is removed, and the automated safety interlock is
activated.
3-8 An analog multimeter allo s the operator to monitor Pf (For ard output po er),
Pr (Reflected po er), Vd (Drain voltage of po er FET), Id (Drain current) etc.

4
4. Specifications
Frequency Band 1.8~50 MHz all amateur bands including WARC bands
Mode SSB, CW (RTTY)
RF Drive 65~90W typ. (100W max.)
Output Po er HF: 550W typ., 50MHz: 500W (RTTY, SSTV, FM 250W max.)
(When set to AC100V-120V, 500W on both HF and 50MHz)
Drain Voltage 44V
Drain Current 30A max.
Input Impedance 50Ω (unbalanced)
Output Impedance 50Ω (unbalanced)
Final Transistor VRF150 x 4
Circuit Class AB parallel push-pull
Cooling Method Forced Air Cooling
Output Po er Pf 1kW
Reflected Po er Pr 100W
Drain Voltage Vd 60V
Multi-meter (F.S.)
Drain Current Id 50A
Input/Output Connectors
UHF SO-239 (Type M-J)
AC 200~260V, 50/60Hz 7.5A max. AC Po er
AC 100~130V, 50/60Hz 15A max.
AC Consumption 1.3kVA max. hen TX
Dimension 232 x 145 x 392 mm, 9.1 x 5.7 x 15.4 inches (WxHxD)
Weight Approx. 9.2kgs. or 20.9lbs.
Accessories AC Po er Cord x 1
Coax Jumper Cable ( ith PL259 at both ends) x 1
RCA Plug x 2
Spare Fuse 8A x 2 (for AC200V line)
Spare Fuse 15A x 2 (for AC100V line)
Spare Fuse 15A x 2 (for F202, F203 of PC1662V po er amp board)
Spare Fuse 1A x 1 (for PC1662V po er amp board) (miniature fuse)
Spare Fuse 3.2A x 1 (for PC1819 sub AC control board) (miniature fuse)
Users Manual

5
5. AC Line Voltage
5-1 Although the amplifier is designed to ork ith both AC 115V (100-130V) and
AC 230V (200-260V), for stability e recommend operation from AC 230V.
5-2 The correct AC plug (not included in the package) must be obtained locally due
to the AC plug variations orld ide.
5-3 The AC line fuse has been factory preset for 115V use (or as requested by the
customer at the time of order). If you ish to change to AC 230V, change the fuse
to 8A. For your safety, before making this change, be sure to pull the AC plug
from the AC outlet to avoid injury.
NOTICE
Please note the followings when you are using
AC100V line (AC100V~120V).
NEVER EXCEED OUTPUT POWER OF 500W,
WHEN RUNNING THE A P FRO AC100~120V LINE.
Otherwise, over-current protection completely shuts down the drain voltage power
supply for five minutes before it gets resettable.
When this protection works, O.DR VE lamp lights and HL-550FX will enter the through
state, the reset of the amp being disabled for five minutes.
To restart the amp, turn the POWER switch OFF, and wait for 5 (five) minutes. Then
turn the power ON.
f the protection works too often, please take one or all of the following measures.
① Lower the drive power of the transceiver.
② Connect the ALC line. Adjust the ALC Output Adjustment Knob on the rear panel
so that the drain current ( D) will never exceed 26.0A on any frequency.
③ Change to AC200~240V line.

6
6-A. Front Panel Description
P
PP
PO
OO
OW
WW
WE
EE
ER
RR
R
O
OO
OF
FF
FF
FF
FS SS
ST
TT
TB
BB
BY
YY
Y
O
OO
OP
PP
PE
EE
ER
RR
R.
..
. O
OO
ON
NN
N A
AA
AI
II
IR
RR
R O
OO
O.
..
.D
DD
DR
RR
RI
II
IV
VV
VE
EE
EO
OO
O.
..
.V
VV
VO
OO
OL
LL
LT
TT
TF
FF
FU
UU
US
SS
SE
EE
E O
OO
O.
..
.H
HH
HE
EE
EA
AA
AT
TT
TP
PP
PR
RR
R
B
BB
BA
AA
AN
NN
ND
DD
DM
MM
ME
EE
ET
TT
TE
EE
ER
RR
R
P
PP
PR
RR
RO
OO
OT
TT
TE
EE
EC
CC
CT
TT
T
F
FF
FX
XX
X
M
MM
MO
OO
OD
DD
DE
EE
EL
LL
L
T
TT
TO
OO
OK
KK
KY
YY
YO
OO
O H
HH
HY
YY
Y-
--
-P
PP
PO
OO
OW
WW
WE
EE
ER
RR
R
S
SS
SO
OO
OL
LL
LI
II
ID
DD
D S
SS
ST
TT
TA
AA
AT
TT
TE
EE
E L
LL
LI
II
IN
NN
NE
EE
EA
AA
AR
RR
R A
AA
AM
MM
MP
PP
PL
LL
LI
II
IF
FF
FI
II
IE
EE
ER
RR
R
1
11
12
22
2 3
33
3 4
44
45
55
5 6
66
6 7
77
7 8
88
89
99
9
1
11
10
00
01
11
11
11
1
1
11
14
44
4
H
HH
HL
LL
L5
55
55
55
50
00
0
F
FF
FA
AA
AN
NN
N
I
II
ID
DD
D
1
11
12
22
21
11
13
33
3
①
①①
①POWER
POWERPOWER
POWER : Main po er s itch to turn AC po er on and off.
②
②②
②POWER
POWER POWER
POWER (LED)
(LED)(LED)
(LED) : Green LED lights hen po er is turned on.
③
③③
③OPER
OPEROPER
OPER.
..
. : OPERATE/STAND-BY s itch. At OPERATE, the amplifier is ready to
go into ON AIR (TX) mode and at STBY, it is on STAND-BY mode.
④
④④
④ON AIR
ON AIRON AIR
ON AIR (LED)
(LED)(LED)
(LED) : Green LED lights hen the amplifier is in transmit (TX) mode.
⑤
⑤⑤
⑤O.DRIVE
O.DRIVEO.DRIVE
O.DRIVE (LED)
(LED)(LED)
(LED) : When overdrive or band miss-set is detected, LED lights to indicate
the protection circuit has orked. When this lamp is on, the amp is in a
through state. (When over-current protection of s itching po er supply
has orked, this LED also lights for approx. 5 minutes.)
To reset protection, turn POWER off and turn on again.
⑥
⑥⑥
⑥PR
PRPR
PR (LED)
(LED)(LED)
(LED) : LED lights hen reflected po er from antenna exceeds 70W to
indicate protection circuit has orked.
⑦
⑦⑦
⑦O.VOLT
O.VOLTO.VOLT
O.VOLT
(LED)
(LED)(LED)
(LED) : When the DC drain voltage of the FET (Vd) is too high, the LED lights
to indicate the protection circuit has orked.

7
To reset protection, turn POWER off and turn on again.
⑧
⑧⑧
⑧FUSE
FUSEFUSE
FUSE (LED)
(LED)(LED)
(LED) : LED lights hen the 15A glass fuse (F202,203) has blo n from
excessive Id. (T o fuses are on the PC1622V PA board.)
⑨
⑨⑨
⑨O.HEAT
O.HEATO.HEAT
O.HEAT (LED)
(LED)(LED)
(LED) : When the PA module temperature reaches 80 deg.C, the LED lights to
indicate the protection circuit has orked, and the amp ill enter the
through state. (It is necessary for the cooling fan to operate for several
minutes to cool the PA module.)
(Turn the main POWER s itch to off, and then on again to reset the Protection Circuits.)
(Turn the main POWER s itch to off, and then on again to reset the Protection Circuits.)(Turn the main POWER s itch to off, and then on again to reset the Protection Circuits.)
(Turn the main POWER s itch to off, and then on again to reset the Protection Circuits.)
⑩
⑩⑩
⑩BAND
BANDBAND
BAND : Select the desired operating frequency band.
⑪
⑪⑪
⑪METER
METERMETER
METER : To change the multi-meter scales. Meter reads Pf, Pr, Vd, and Id.
⑫
⑫⑫
⑫FAN
FAN FAN
FAN (LED)
(LED)(LED)
(LED) : LED lights brighter hen fan is running at high speed. When the
heatsink reaches 50℃ the cooling fan ill s itch to high-speed mode to
cool the heatsink.
⑬
⑬⑬
⑬I
II
I D
DD
D (LED)
(LED)(LED)
(LED) : LED lights hen the input drain current is over 20A. This does not
mean that any damage occurred to the amplifier, but is useful for the
user to notice any stress influencing the final FET caused by high drain
current, load impedance trouble, etc. We recommend that you note the
usual condition of the lighting. When any unusual symptoms are
noticed, the user may lo er the drive po er from the transceiver, check
the antenna SWR, etc.
⑭
⑭⑭
⑭ MULTIMETER
MULTIMETERMULTIMETER
MULTIMETER : Pf (For ard output po er), Pr (Reflected po er from antenna), Vd
(FET drain voltage), and Id (FET drain current) are sho n on the scale
as selected by ⑪METER select s itch.

8
6-B. Rear Panel Description
A
AA
AL
LL
LC
CC
C
A
AA
AL
LL
LC
CC
C A
AA
AD
DD
DJ
JJ
J
S
SS
ST
TT
TB
BB
BY
YY
Y
G
GG
GN
NN
ND
DD
D
A
AA
AN
NN
NT
TT
T
A
AA
AC
CC
C
F
FF
FU
UU
US
SS
SE
EE
E
I
II
IN
NN
NP
PP
PU
UU
UT
TT
T
⑮
⑮⑮
⑮AC POWER
AC POWERAC POWER
AC POWER : AC Mains Socket. Socket for the AC po er cord. (Socket is EMI
filtered.)
⑯
⑯⑯
⑯STBY
STBYSTBY
STBY : RCA Jack. Connect the control cable from the ACC terminal (or SEND,
TX GND etc.) of the transceiver. The center pin is to be shorted to
ground through the relay circuit of the transceiver.
⑰
⑰⑰
⑰ALC
ALCALC
ALC : RCA Jack for ALC Voltage Output. Negative DC voltage appears at the
center pin, hich is fed back to the ALC terminal of the transceiver.
ALC is used to keep the amplifier output po er at certain limits. Also it
is useful hen the transceiver output po er is higher than 100W.
(See page 12, 8.ALC Connection). Also consult your HF/50MHz
transceiver’s user manual.
⑱
⑱⑱
⑱GND
GNDGND
GND : Ground Terminal
⑲
⑲⑲
⑲ALC ADJ
ALC ADJALC ADJ
ALC ADJ : Potentiometer to adjust ALC voltage level.
Negative DC10V is available at maximum, hen turned full
counter-clock ise.
Factory setting is 0 volts, ith the pot turned full clock ise.
⑳
⑳⑳
⑳FUSE
FUSEFUSE
FUSE : A pair of fuses for AC mains. 15A glass pre-installed fuse.
(Change to 8A fuses if 200V~230V line is used.)
○
○○
○
21
2121
21
IN
ININ
IN PUT (TX)
PUT (TX)PUT (TX)
PUT (TX) : RF Input Connector. Connect the coax jumper cable from the
transceiver.
○
○○
○
22
2222
22
ANT
ANT ANT
ANT (OUTPUT)
(OUTPUT)(OUTPUT)
(OUTPUT) : RF Output Connector. Connect the coax cable to the antenna.

9
① RF Po er Detector and Send-Receive S itching Relay
② Inter-lock S itch
③ LPF Board
④ Main Po er Source Unit (S itching Mode Po er Supply)
⑤ Sub-Po er Source Unit
⑥ Control Board
⑦ Po er Amp Unit (PA board/heatsink)
⑧ Frequency Detector Board
⑨ Cooling Fan
⑩ AC Fuse

10
7. Connection and Operation
This section explains a one-antenna system connected to the transceiver and an external
SWR/POWER meter.
A
AA
AL
LL
LC
CC
C A
AA
AN
NN
NT
TT
T
(
((
(S
SS
SE
EE
EN
NN
ND
DD
D,
,,
,T
TT
TX
XX
X G
GG
GN
NN
ND
DD
D)
))
)
A
AA
AC
CC
CC
CC
C
I
II
IN
NN
NP
PP
PU
UU
UT
TT
T
A
AA
AN
NN
NT
TT
T
S
SS
ST
TT
TB
BB
BY
YY
YA AA
AL
LL
LC
CC
C
A
AA
AC
CC
C
T
TT
TX
XX
XA
AA
AN
NN
NT
TT
T
T
TT
T R
RR
R A
AA
A N
NN
N S
SS
S C
CC
C E
EE
E I
II
I V
VV
V E
EE
E R
RR
RA
AA
A N
NN
N T
TT
T E
EE
E N
NN
N N
NN
N A
AA
A
S
SS
S W
WW
W R
RR
R /
//
/ P
PP
P O
OO
O W
WW
W E
EE
E R
RR
R M
MM
M E
EE
E T
TT
T E
EE
E R
RR
R
7-1 Connect AC cord and coax cables as illustrated above. Connect the cable from
“SEND” to ACC or the remote terminals of transceiver, here it is marked
“SEND” or “TX GND”. These terminal pins are shorted to the ground hen the
transceiver is in TX/ON AIR mode. If these connections are not made, the
amplifier ill not go into TX (amplification) mode. For a temporary check to the
amp, ground the STBY center pin by inserting an RCA plug hose center pin has
been soldered to the outer case of the plug ith a small piece of ire.
7-2 At first, turn the ALC knob full clock ise to avoid ALC voltage being fed to the
transceiver. Application of ALC ill be covered in the follo ing Section 8. ALC
CONNECTION.
7-3 Keeping the POWER (AC mains) s itch off, check the SWR of your antenna by
keying the transceiver to TX mode (CW or RTTY mode). Monitor the SWR ith
an external SWR/Po er meter. If SWR is 1.5 or higher at band center, the
antenna has to be adjusted for lo er SWR. As an alternative, an antenna tuner
may be inserted.
HL
HLHL
HL-
--
-550FX REAR
550FX REAR550FX REAR
550FX REAR

11
7-4 Turn the POWER s itch on. Turn the BAND s itch to a desired operating
frequency band. Turn the STAND-BY s itch to OPER (operate) position and the
amplifier is ready to go. If you key the transceiver ith the carrier level set
relatively lo (such as 20-30W), you ill achieve an amplified output signal of a
fe hundred atts. Monitor this output ith the multimeter (at the Pf position)
or ith an external po er meter. Increase drive level to roughly 50W and see if
the antenna SWR stays constant. (As higher RF currents flo , some antennas
may sho a changed SWR value due to heated connector junctions and trap
coils.)
7-5 You can no increase the drive level to nearly 80-90W to achieve maximum
carrier output po er of 550W (CW) from the amplifier. If you change to SSB
mode, average voice po er of a fe hundred atts ill be observed on the panel
meter, Pf scale, hile peak voice po er reaching a little over 550W. For high duty
cycle transmissions like RTTY mode, it is recommended that you reduce the drive
po er by some 30%.
7-6 With a high po er transceiver in SSB mode, you can overdrive the amplifier
resulting in a distorted output signal. This can occur if you speak too loud or if
you set the microphone gain too high. Speak into the microphone properly to
reduce the possibilities of splattering into the neighborhood. The ALC is effective
in preventing the output signal from being distorted or to limit the carrier level to
ithin rated output levels. It is strongly recommended to make ALC connection,
especially hen 200W out high po er radio is used to drive.
7-7 Protection circuits may ork during operation depending on the conditions. If the
protection circuit has shut do n the amplifier, check the antenna SWR, Vd, AC
line voltage, or try to reduce the drive level. To reset, turn off the POWER s itch
once, then back on again. The po er transformer has an overheat protection in
the coil layer. If this temperature s itch activates, the amplifier ill put you in
receive mode ith the cooling fan operating until the transformer has cooled off.
It may take ten to fifteen minutes to cool, depending upon room temperature. For
more details on this protection circuit, see Section 9. PROTECTION CIRCUITS.

12
8. ALC Connection
ALC voltage is available at the terminal marked ALC (RCA phono jack) on the right lo er
corner of the rear panel. Negative maximum DC voltage of ten volts (-10V) is produced at
this terminal hen the amplifier is fully driven. This voltage is adjustable ith the ALC
ADJ. knob located above the ALC jack. Setting ALC voltage properly fed back to the
transceiver, e recommend you to keep the maximum output po er constant or hold the
po er at a certain level. Also ALC is useful in avoiding your SSB signal from being
distorted hen overdriven. Depending upon the manufacturer of the transceiver, the
suitable ALC voltage differs. ICOM may need 0~-4V, and Yaesu may need 0~-5V range.
Ken ood may need -6~-8V maximum. Check your transceiver manual.
8-1 Prepare an ALC control cable using RCA plug supplied in the package. Solder a
single ire or (more preferably) a shielded single ire to the center pin of RCA
plug and solder the shield braid to the outer side of the plug. Connect the control
cable to the “ALC (or EXTERNAL ALC)” jack of the transceiver. External ALC
input is sometimes available at one of the pins of the “ACC” socket of the
transceiver as ell.
8-2 At first, turn ALC ADJ full clock ise. Drive the amplifier in CW/RTTY mode to
full output po er. Then turn the ALC ADJ counter-clock ise. Observe the
SWR/Po er meter at the output, (or Pf of the multimeter). Stop turning the ALC
ADJ at the point the po er starts to decrease. Or if you ish to further reduce
the po er, keep turning ALC ADJ until the desired level is achieved. If you
further try to increase the drive po er you ill no see the output po er become
rather saturated, from these adjustments.
(Maximum ALC voltage produced is -10V hen the amplifier output po er is
over 200W.)
REAR PANEL ALC POT.
S
SS
ST
TT
TB
BB
BY
YY
YA
AA
AL
LL
LC
CC
C
A
AA
AL
LL
LC
CC
C
A
AA
AD
DD
DJ
JJ
J
A
AA
AC
CC
C
MAX MIN
T
TT
To
oo
o T
TT
Tr
rr
ra
aa
an
nn
ns
ss
sc
cc
ce
ee
ei
ii
iv
vv
ve
ee
er
rr
r

13
9. Protection Circuits
There are five major protection functions in this amplifier. If the amplifier has shut do n
for some reason, before re-setting, correct the possible cause of the shut do n. Turn off
the POWER once and back on to reset.
9-1 O. DRIVE (Over Drive / Band Miss-set)
When the drive po er exceeds the 100W level, the amplifier ill shut do n to
STAND-BY mode (or receive) in order to protect the input side of the po er FET’s.
This protection might also activate if the band is set rong. This usually occurs,
hen the amplifier band setting is lo er than that of the transceiver.
Note that O.DRIVE LED ill also light hen Over Current protection of s itching
po er supply orks hen operating AC100V line.
9-2 O. HEAT (Over Heat)
When the temperature of the aluminum heat sink in the po er amplifier reaches
80 degrees C, the amplifier defaults to RECEIVE mode to protect the po er FET’s.
9-3 O. VOLT (Over Voltage)
If there is a sudden AC line voltage spike, the FET drain voltage may rise above
acceptable levels, and O. VOLT protection may trip.
9-4 FUSE (Fuse Blo n)
If either of the glass fuses (15A) on PC1662V fails, “FUSE” lamp lights. Under
normal usage of the amplifier, this failure should rarely (if ever) occur. If it occurs,
there is a possibility that the po er FET’s have failed together. If the amplifier
cannot be reset, consult ith the dealer or the service center.
9-5 PR (Reflected Po er Protection)
If reflected po er from the antenna reaches approximately 80W, the PR protection
may trip. If it does, one solution is to reduce the drive po er from the transceiver.
Or you may need to check that your antenna match (SWR) is still OK. If the match
cannot be corrected and the antenna system isn’t faulty, use an antenna tuner.
As noted above, the amplifier is equipped ith several kinds of fast acting protection
circuits using the latest analog technology. Ho ever, if the amplifier is operated in such a
manner that multiple protections ork repeatedly over a long period of time, the
amplifier can be seriously damaged.

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*O.Current protection of Po er Supply
Note that you need to reset in a different ay from the above 5 protections hen
O.Current protection orks on the po er supply. See NOTICE on page 5.
When this protection orks, the meter display of Vd ill be 0V.
Turn the POWER s itch OFF, and ait for more than 5 minute before turning it ON
again to reset.

15
10. Explanation of Major Circuits
Six major circuit blocks are explained in their basic form and using signal flo s.
Refer to the Block Diagram on the final page.
10-1 RF Po er Detector / TX-RX S itch (PC1821)
10-2 Frequency Detector Unit
10-3 PA Unit
10-4 LPF Unit
10-5 Control Unit
10-6 Po er Supply
10-1 RF Po er Detector / TX-RX S itch (PC1821)
As illustrated in the block diagram, there are t o RF po er detectors on this
board. One detects the drive signal level from the radio and the other monitors the
outgoing po er and the reflected po er from the load (antenna).
The TX-RX s itch (Send-Receive s itching) ill s itch the flo of drive
po er/output po er and the incoming signal from the antenna ith t o
high-speed relays mounted at the input and output sides of the PA.
The drive signal level of for ard po er and reflected po er is sent to the control
circuit.
10-2 Frequency Detector Unit
This unit detects the frequency of the drive po er from the transceiver. When
frequency beyond the 26-28MHz amateur bands is detected, the amp ill stop
operating.
10-3 Po er Amp (PC1662V)
The RF PA is the heart of this amplifier and is composed of four VRF150 MOS
FET’s made by Microsemi of USA, gaining 550W max. output. The amplifier is a
parallel push-pull, class AB amplifier. The gate bias supply circuit is regulated for
the best stability and is thermally compensated.
The PA has a 6dB attenuator on the input for gain reduction and to enhance the
stability of the ide band po er PA. The heat sink has t o different thermal
sensors to detect temperatures of 50 deg.C, and 80 deg.C, respectively. At 50 deg.C,
the cooling fan shifts into high-speed mode. At 80 deg.C, the amplifier ill lock the
amplifier into RECEIVE mode to protect the po er FET’s.

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10-4 LPF Unit (PC1817)
In the L.P.F. (output lo pass filter) circuit, there are seven band filters that are
selected by the manual band s itch. Each L.P.F. is used to reject harmonics so that
the amplifier meets international telecommunication equipment standards,
including FCC rule.
10-5 Control Unit (PC1818)
This is the heart of the control signal processing for the HL-550FX. It judges the
operating condition of the amplifier, as ell as issuing the commands to the
peripheral circuits. Various analog signals are processed such as RF drive from the
transceiver, RF po er signals at various points, DC po er supply information, etc.
There are ope-amps, various three terminal voltage regulators, GAL logic device
etc. Warning signals are processed by the logic IC for Over Heat, Over Voltage, Pr,
Band Miss-set etc. Ope-amps produce the necessary DC signals to drive the Pf, Pr
meters. Also there is a control circuit that issues the drive shut do n command in
case of the over drive, band miss-set and high antenna SWR conditions.
10-6 Po er Supply
The main DC po er supply feeds the 44V DC po er to the final PA stage. It is a
state of art, s itching po er supply ith high efficiency.
Sub AC po er supply, feeding ±15V is also installed to consist a high quality
po er circuit, along ith the LPF circuit.

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11. Trouble Shooting
Failure Possible Cause Solution
AC mains not
operating
① AC fuses blo n
② AC cord not plugged in
③ Interlock s itch lifting
④ Wrong tap used on
po er transformer
primary
① Replace ith ne ones.
② Plug in securely.
③ Scre bolts tightly on the top cover.
④ Correct primary iring.
Can’t enter
Transmit
mode
① Remote control cable
not connected
② Protection circuits ON
① Check the cable and connect properly.
② Check the drive po er, antenna SWR.
Reset ith AC POWER s itch.
O.Drive lights
① RF overdrive
② Band miss-set
③ O.Current orks (High
Id hen using AC100V)
① Decrease drive.
② Select the BAND correctly.
③ Same as ①. Wait for more than 5
minutes, and turn po er ON.
PR lights ① Reflected po er high,
Antenna SWR high
② Poor connection to coax
cables
① Check/adjust antenna
(Or decrease drive.).
② Check the coax cable connectors.
O. Volt lights ① Drain voltage of po er
amp extremely high
① Check AC line stability.
FUSE lights ① Fuse blo n
② Antenna SWR high
③ Short circuit
① Replace F202 and F203 (15A) on the
PA board (PC1662V).
② Adjust the antenna.
③ Contact the distributor, or service
center.
O.Heat lights ① Internal Temperature
above 80 deg.C
① Cool off until LED turns off. Check for
air intake blockages. Also check air vent
on top cover.
Vd appears
normal, but no
po er
① 1A fuse of PA unit is
blo n
① Replace 1A mini fuse (F203). Confirm
input po er.
Vd is 0V ① O. Current protection
circuit of po er supply
unit has orked.
① Turn off po er, and ait for 5 minutes
before turning it on again.

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TVI, FMI ① Overdrive
② RF leakage from coax
cable, grounding ire,
AC po er cord etc.
① Decrease the drive. Check ALC
setting.
② Insert common mode filters on
antenna cable or AC line. Add
clamp-on ferrite cores (TDK, Amidon,
Palomar) on various cables.

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12. Parts Layout
12-1 Top Vie (Detailed)
12-2 Top Vie & Side Vie
12-3 PA Unit (PC1662V)
12-4 LPF Unit (PC1817), Sub AC Unit (PC1819)
12-5 Frequency Detector Unit (PCS1733), RF Po er Detector Unit (PC1821)
12-6 Control Unit (PC1818)
13. Schematic Diagrams
13-1 PC1662V PA (Po er Amplifier) Unit
13-2 PC1821 RF Po er Detector Unit
13-3 PC1817 LPF (Lo Pass Filter) Unit
13-4 PCS1733 Frequency Detector Unit
13-5 PC1818 Control Unit
13-6 Overall Block Diagram