Icom PW1 Installation guide

Care and Feeding an Icom PW1
W6DE
Page 1
Copyright 2017, All rights reserved.
Care and Feeding of Icom PW1 1,000 Watt Solid State Power Amplifiers
W6DE, November 2017
Use the following information at your own risk. No warranty is offered, implied
or expressed. I make no warranty as to correctness or completeness of the
following information. I am not associated with Icom, nor has the information
contained herein been approved by Icom. Modifying, repairing and/or
following these procedures may void Icom’s original Manufacturer’s warranty.
If you undertake any repairs and/or adjustments to your PW1 amplifier based
on this information you do so at your own risk.
This is a compilation of replies I have made to the Yahoo! PW1 on-line forum. This is loosely organized
around the causes of why PW1s fail, how to protect PW1s and how to repair some PW1 failures.
Setting up a PW1 with an Icom Radio:
Some folks find the ALC Level adjustment confusing. I drive my PW1 with an Icom 7600 radio which I’ll
refer to as exciter and/or radio. I adjust my ALC level on 20 or 40 meters. I use the Icom supplied cable
to connect the radio ACC2 connector to the PW1 ACC1 connector. The Icom supplied cable routes the
ALC and PTT signals between the radio and amplifier.
The following advice about setting the ALC level is not the Icom recommended method. While I believe
this is a safer method to adjust the PW1 ALC, you follow this advice at your own risk. Here is how I
adjust the ALC:
--#1 rule: Never use the radio/exciter’s antenna tuner when operating into a PW1!
--#2 rule: Everybody should have a dummy load. If you don’t have one, borrow or buy one—tuning and
adjusting into an antenna is just looking for trouble. A good dummy load is always on the right
frequency and always has low SWR.
For the following steps do not engage the PW1’s “TUNER” you should be operating into a matched load
of 1:1 SWR!
--PW1 should be connected to the mains power. The PW1 power can be on, but the “TUNER” and
“AMP/PROTECT” LEDs should be off. That is; the amp should not be amplifying and is in “by-pass”
mode.
--When setting ALC, set the PW1 meters to read PO (on the left meter), and ALC (on the right meter).
--Set your radio’s meter on Power Out. Set your exciter power out to its lowest position. Set your
exciter to CW mode and use a hand key to transmit; a second way to generate the correct amount of RF
is to select FM and the press TRANSMIT key on the radio front panel. DO NOT use or connect the hand
mic to the radio, the mic may pick up sounds and effect the readings.
--In contrast to Icom directions: start setting ALC with lowest exciter power and then slowly turn up the
exciter’s drive.
--When you get to around 100 Watts out of the exciter (remember the amp is off), Stop raising the
exciter’s power, stop transmitting.

Care and Feeding an Icom PW1
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--On the PW1 meter, switch the right meter from ALC to SWR, transmit again. Look at SWR. If it isn’t
below 1.2 or 1.3, stop and find out why it isn’t closer to 1:1. Do not continue until you fix the SWR.
--If your SWR is ok, stop transmitting, return the PW1 right meter to read ALC.
--On the exciter turn the power down to its lowest level.
--Power up the PW1 and depress “AMP/PROTECT” once and the “AMP/PROTECT” light is on and green.
The PW1 is now on and will amplify the RF fed to it.
--With the exciter’s power at its lowest level, resume setting the ALC level. Start transmitting again.
Increase the exciter power out until: 1) the PW1 Power out shows 1000 Watts, OR 2) you reach 35-50
Watts output from your exciter, OR 3) ALC level reaches mid-scale (where the red band starts).
--If your PW1 power gets to 1000 Watts before the ALC meter gets to midscale—turn down the ALC
adjustment on the back of the PW1.
--If you get to midscale ALC before you get 1000 Watts of PW1 power, then turn up the ALC adjustment
on the back of the PW1.
--Perfect ALC adjustment is when you reach 1000 Watts of PW1 power out, the ALC meter will be at
midscale and your exciter power lever is around 35 to 40 watts out (ok, maybe 50+ watts on six meters).
--If you can’t get 1000 Watts out of your PW1 with 35 to 40 Watts drive, something is misadjusted or
broken.
--There is absolutely no reason you should ever turn the exciter drive level to more than approximately
halfway up when driving a PW1. Reason defined as: safe from errors that will blow up your PW1.
--Now that you have the ALC set correctly; when adjusting the exciter’s power knob, you will find lowest
exciter power when the knob is pointing to a 7:00 o’clock position; then normal PW1 driver level setting
should be around 11:00 o’clock on 40 and 20 meters. For 6-meters the driver power level setting will be
around 1:00 o’clock. And when the PW1 is OFF, you will find 100 watts of maximum power is at 5:00
o’clock.
I leave my 7600 power level set at 11:00 o’clock. I almost always transmit through the PW1. When I
want to run 100 Watts I turn the drive level down to somewhere between 7:00 and 8:00 o’clock. That
way, I never have the exciter running full power and when I walk away from the radio, there is no
chance of forgetting to turn down the power at the next operating session. The only time I turn off the
PW1, when operating, is when I run WSJT. That way the power level is a somewhat comfortable power
of 35 watts if I forget to turn power down to the WSJT HF recommended 15 to 20 watts.

Care and Feeding an Icom PW1
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What causes PW1s to blow up?
I have found no inherent failure modes in the PW1. It is my opinion that some of the PW1’s protection
circuitry may not act fast enough for self-protection from some common operator errors.
PW1 amplifiers blow up because of these operator errors:
You use a computer to control your radio and PW1 without CI-V arbitration,
The ALC is set wrong,
The PW1 is set to the wrong band,
The PW1 is operated into the wrong antenna,
The PW1 is intentionally operated into a high SWR antenna,
Also, the PW1 ‘Antenna Tuner’ is operated at high power in an attempt to tune out a high SWR,
The operator forgot to turn off Split when he/she change bands,
The operator failed to disconnect the PW1 from the mains during a lightning storm.
Here are some details on operator errors that can cause your PW1 to FAIL.
One: CI-V control collisions:
This is the noted CI-V collision problem that leaves the PW1 on the wrong band. See: K8UT’s “Riding the
CI-V Bus” at:
http://www.k8ut.com/download/documents/Riding%20the%20CI-V%20Bus%20by%20K8UT.pdf
K8UT describes the problem and several cures. I use the k9jm solution.
If you have a computer, PW1 and Icom radio connected to each other, all on the CI-V buss, you are just
marking time until you have a PW1 failure. Icom specifically states in their documentation NOT TO DO
THIS. Please note: this is when will the failure occur not an IF the problem can occur! Yes, this means if
you have a (1) PW1, (2) an Icom radio and (3) a computer on the CI-V buss you are just waiting for the
problem to happen! This is how an “Automatic” system transmits into the wrong band or antenna!
HOWEVER, Icom has implemented a solution for this problem in the Icom 7850 and 7851 (that
have the latest Firmware installed) and it appears this fix is also in the IC-7610. These radios
have built in mitigation for the PW1 CI-V collisions and are thus PW1 friendly.
The basis of the 7850/7851 solution are two electrically separate CI-V data paths:, 1) a miniature
phono jack and 2) one of the USB ports on the radio’s back panel. The logical connection can be
separate or combined by menu software selection. If a PW1 connection is desired:
In the 7850/7851 Menu Option: CI-V USB Port, select Unlink [default is linked]. Then the
miniature phono jack (aka the Remote jack) on the rear panel can be connected to a PW1 and
the USB port on the rear panel can be connected to your computer for control. I.e., the “Unlink”
selection disconnects miniature phono from the computer control path, making possible a safe
PW1 control connection. And, a separate firmware section in the 7850/7851 keeps the PW1
informed of the radio’s status. Also, see the menu selection for: CI-V USB/LAN-> REMOTE
Transceive Address for additional instruction.

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In the 7610 Menu Option: CI-V USB Port, selects the internal connection type between
the[USB] and [REMOTE] CI-V ports. ]. The Default is already: Unlink from [REMOTE])
So, the miniature phono jack (aka the Remote jack) on the rear panel can be connected to a
PW1 and the USB port on the rear panel can be connected to your computer for control. I.e., the
“Unlink” selection disconnects miniature phono from the computer control path, making
possible a safe PW1 control connection. And, a separate firmware section in the 7610 keeps the
PW1 informed of the radio’s status. Also, see the menu selection for: CI-V USB/LAN->
REMOTE Transceive Address for additional instruction. Please note: As of this writing, in early
November 2017, the IC-7610 has not been released in the USA and I have not been able to
test/verify the IC-7610 CI-V commands for this functionality.
With the above menu selections made you then connect the PW1 to the radio with the
miniature phono cable and connect the radio to the computer via the USB connection (between
the radio and computer). This isolates the PW1 from the computer CI-V traffic.
Two: The next possible source of problem is you were operating your radio split (Listening on VFO-A
and transmitting on VFO-B) and you requested/made a band change and you did not cancel split. On
the new band your VFO-A and the PW1 went to the new frequency, but your radio was still in split and
transmitted on VFO-B, which remained on the previous band. There is a 50/50 chance you will then
transmit into a band pass filter that will try to eliminate your 1 KW signal all by itself. On occasion the
protection circuits don’t operate fast enough and the High SWR reflected voltage will arc across the
isolation relay contacts and blow out a clamp diode and the driver chip.
Note: DXLab suite logging and control software has a solution that I use. DXLab’s Commander, the radio
control module, has an option in its Configuration | General tab | General panel | select: Switch to
simplex on 1 MHz QSY. With this option selected Commander will cancel split when you change bands.
Three: Mismatched antennas. The PW1 antenna “tuner” will not match your wire antennas for all
bands. At best, the built-in “tuner” can be used to help you extend the bandwidth of an antenna. E.g., if
your antenna is resonant on the bottom of a band (CW/Digital) and you want to operate higher in the
band (Phone). For these cases the PW1 “Tuner” will successfully force a match a SWR of no more than
1.5 for down to SWR limit of no more than 1.2.
The PW1 Instruction (operator’s) manual on page 13 states:
“The built-in antenna tuner automatically tunes the
antenna.
- SWR reading on meter-2 should be less than 1.2:1.”
And later in the manual on page 14 it says:
“When the tuner cannot tune the antenna (SWR 1.5:1 or
greater), the tuning circuit is bypassed automatically after 20 sec..”
If you intend to use a non-resonant, multi-band antenna, e.g., G5RV, buy a heavy-duty antenna tuner
advertised to handle SWR ratios of greater than 10.
Automatic antenna tuner failure: To prevent tuner run-away, you should only make the automatic tuner
adjustments at reduced power—100 watts or less. Use exciter power only or turn down the power on
the exciter. I have not had to repair a tuner, but accidentally using full a KW into a miss-matched
antenna caused my auto tune function to go wild as described above and take out a PA board. Arced
tuner capacitors in the tuner and failed tuners are also a result of allowing the tune function to be
performed at High Power with the PW1.

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If you are trying to use a multiband antenna anyway, allow the tuner to find a match at low power and
then slowly increase the exciter’s power and watch the PW1 SWR meter. If the SWR starts creeping up
or the tuner starts to initiate another tune—tuner light blinks—immediately roll the power back and
start the process all over again. It may be that you can find a match at a lower PW1 power level that still
works without a tuner run-away.
Four: PW1s do not always survive an Electric Company/Utility power failure and subsequent power
restoration. Sometimes upon power restoration the power surge overwhelms the power supply’s
power input protection circuitry.
The “Power” button on the PW1 is a misnomer. The PW1 is on whenever the mains power is
connected. The “Power” button more or less acts like a standby/operate button.
Because the PW1 is always powered, folks living in areas of lightning activity with the accompanying
power spikes and failures, it is wise to unplug the power cord—if you have a weather forecast predicting
a Storm with Lightning and Thunder, disconnect your PW1 from the power mains until the storm is over.
One way to increase the survivability of a PW1 through a power fail and restoration is to remove the
capability of the amplifier to operate on 120 Volts. This will make the PW1 always require a 240 Volt
power connection. Removing the 120 Volt capabilities allows the amp to survive higher voltage surges.
See this nice write up from AK2F: http://www.ab4oj.com/icom/pw1/psu_repair.html for more
information.

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Care and Feeding an Icom PW1
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Repairing your PW1:
Use the following information at your own risk. I make no warrantee as to correctness or completeness
of the following information. If you undertake any repairs and/or adjustments to your PW1 amplifier
based on this information, you do so at your own risk.
Not all problems have the same source. So while I’ve may have seen the same symptoms, it doesn’t
mean you have the same problem and the same fix.
First, do a Google search to find and then down-load the PW1 Service Manual.
If you have the technician skills you can repair a PW1 yourself. However, one extremely important and
needed skill is soldering. Soldering will require judgement about what size and type of tip on your
controlled temperature soldering iron to use. And, if you have to replace the MRF-150 finals you need
to know what type/size of soldering gun/iron to use. If you do not have significant electronics soldering
skills—this is not a project for you.
The daunting part is the disassembly. Take pictures of the unit before disassembly and at stages as you
disassemble the PW1. Take pictures of screw locations, cable routing and general layout. I’ve probably
got about 30 or so pictures and even then I missed a few screw locations. First time disassembly for
either the PA/RF side or the Tuner/Controller/Power supply side will take about 6 to 8 hours per side.
With experience it goes a lot faster.
A repair will take about a week or two as you figure out: what to do, what to fix, order parts and repair.
Be sure to work in a static free area. Don’t do the repair in a house where you are standing on a carpet,
a synthetic floor, or a plastic carpet protector. I have a shop with a concrete floor and a wood table to
work on; i.e., low static. Put cotton towels (NO synthetic material!) under the amp to help slide it
around. In the end, you will scratch whatever you have the PW1 sitting on—don’t use the dining room
table. Have a space with about an extra 12” to 18” around all sides of the amp while you work on it.
You’ll need another similar amount of space to safely place the assemblies/parts as you remove them
from the chassis.
Icom did a really good, sturdy, mechanical design on the PW1. A complete disassembly will have you
dealing with 40 to 50 small parts and fasteners. To keep from having left over parts, have several small
containers to separately place fasteners and small parts in as you disassemble the PW1 in stages. That
is: put all the fasteners in one container for the cabinet disassembly, then another container for the first
part of the left side (filter/combiner) then another container for the PA if you have to take that out too.
And so on. . . . You get the idea.
Any project is an excuse for another tool.
--Any PA work will require a good quality multimeter that can read milliamps to set the idle current—I
used the 300 ma scale on my multimeter.
--A clamp-on ammeter will be nice to compare the individual idle draw of all four power modules
without disconnecting the power leads. A suspected PA problem may require this to determine which
of the four PA boards is bad.

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--Hemostats (6” and 8”) will be needed to pick up the screws that will fall into impossible to get to
places.
-- To get to some screws, a long blade 6” Phillips screwdriver will also be needed. Always use the largest
size Phillips screwdriver blade that will fit into the screw head slots.
Symptom: The Tuning Light changes from Steady On to Flashing when increasing the power level in
the PW1
The tuning light flashes when the tuner is trying to find a match. In the PW1 Instruction (operator’s)
manual on page 13 it says:
“The built-in antenna tuner automatically tunes the
antenna.
- SWR reading on meter-2 should be less than 1.2:1.”
And later in the manual on page 14 it says:
“When the tuner cannot tune the antenna (SWR 1.5:1 or
greater), the tuning circuit is bypassed automatically after 20 sec..”
The first comment is telling you the amplifier wants less than a 1.2 SWR in order to operate.
The second comment is telling you that the tuner may not be able match an antenna if the starting point
is greater than 1.5 SWR.
I can attest that continued operation with the Tuning Light flashing can cause damage to the PW1 long
before the 20 seconds is up. If you continue operation long enough (not recommended) with the
blinking tuning light you will see the SWR meter vary up and down and eventually peg at full scale as the
tuner hunts for and fails to find a match. The PW1 tuner is really only intended for slight mismatches. I
now only operate with matched antennas (under 1.5:1 SWR). If your only antennas are so-called
multiple band, non-resonant, antennas, then my recommendation is to buy an external high
power/heavy duty antenna “tuner” that is advertised to handle 10:1 SWR.
Automatic antenna tuner failure: To prevent tuner run-away, you should only make the automatic tuner
adjustments at reduced power—100 watts or less. Use exciter power only or turn down the power on
the exciter. I have not had to repair a tuner, but accidentally using full a KW into a miss-matched
antenna caused my auto tune function to go wild as described above and take out a PA board. Arced
tuner capacitors in the tuner and failed tuners are also a result of allowing the tune function to be
performed at High Power with the PW1.
If you are trying to use a multiband antenna anyway, allow the tuner to find a match at low power and
then slowly increase the exciter’s power and watch the PW1 SWR meter. If the SWR starts creeping up
or the tuner starts to initiate another tune—tuner light blinks—immediately roll the power back and
start the process all over again. It may be that you can find a match at a lower PW1 power level that still
works without a tuner run-away.
.

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Symptom: On the PW1’s Control Panel, the AUTO indicator is Flashing and the protection circuit
cutting in.
In the PW1 Operator manual, page page 14, “Protection circuit”, “Linear amplifier protection circuit” is a
description of the various fault indications and faults. It says AUTO flashing means PA Boards have
become unbalanced. This means one of the four PA boards may be bad.
There are four PA boards; two boards on each side of the heat sink and the two PA boards on each side
of the heat sink are paired together. Then each side of the heat sink is paired in the Combiner Board.
Icom service centers do not repair boards, they replace them. The reason they might recommend to
replace all four of the PA boards is that there at least three versions of the PA board. The difference
between the boards that I’ve seen is the value and quantity of the power source swamping resistors
feeding the pair of MRF-150s. If you replace a board it is likely the new board will have different resistor
values. Thus, you also have to replace the mate board on that side of the heat sink. To be comfortable
you should also replace the pair of boards on the other side of the heat sink. If you repair your own PA
board(s), then you don’t need to replace all the PA boards.
The PA boards are sold by Icom for about $250 to $300. They are listed as a single item, but they come
as pairs—thus, for a purchase of the Icom PA board item you get two identical boards. However, the PA
boards do NOT come with the MRF-150 devices. Two MRF-150 devices are needed per PA board.
If you smelled a component cooking it could be on one of the PA boards and/or on the Combiner Board.
--The failure point on the PA boards is likely the power source swamping resistors R11 & R12. If they are
cooked, you’ll probably have to replace the MRF-150 devices on that board. Be careful replacing R11 &
R12, it is very easy to lift the PCB trace on the bottom of the card.
--If you need to repair a PA board it is also likely that you will have to replace or repair the Combiner
Board. The power imbalance that occurred when the PA board failed is likely to have cooked the
balance resistor R6 on the Combiner Board. If R6 has cooked, it will likely char the PCB under the
resistor. You must remove all this char, doing so will also remove several layers of the Fiberglas PCB
itself—reseal the PCB with MG Chemicals Super Corona Dope. When installing a new R6, I elevated the
resistor slightly above the PCB (between 1/8 and ¼ inch). The Combiner Board is around $150 from
Icom.
If you can’t find a cooked resistor, a clamp-on ammeter will tell you which pa board is bad by its idle
current being different than the others. Separate the four DC power lines at the front of the cabinet just
after you remove the case sheet metal and measure there. The red power lines loop left down behind
sheet metal [Where, if I recall correctly, the wires go through a toroid] then up, right and then pass
toward the back between brackets and then to the four PA boards. The four red wires are B+ for the PA
units. Note carefully how your wiring gets from the front to the back, I had to disassemble and
reassemble this several times to get the wires routed without pinching them or pulling on sharp corners.
NOTE: the black two wire (red and black wires inside a black casing) termination on the Combiner Board
looks likes it is a connector on the Combiner Board. That is NOT a connector attached to the Combiner
board—it won’t remove.
To remove the PA assembly you have to take out the Filter assembly and Combiner Board assembly out
first. On the left side, you also have to remove both the center and bottom cross bars and a lateral bar

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across the PA assembly (when assembled this bar is partially hidden by the combiner cables). In
addition there a lot of screws on the back panel. You also have to remove the back left corner foot to
slide the PA assembly forward (required in order to slide the PA forward because the foot’s screw
protrudes through the cabinet floor).
Make sure you mark every cable and take lots of cable routing and placement pictures first. Also note
where the shouldered screws go to hold the Filter assembly on the left side (a picture will help here).

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Regarding: The MRF-150s on one of My PW1 final boards are bad. Should I buy a matched pair of
MRF-150 devices or just buy two from stock?
You can replace a set of finals on one board of the four PA boards in a PW1. That is, you only have to
replace the finals on the bad board. You should replace both finals on a board as a set.
A matched pair of MRF-150 devices is cheaper than two non-matched devices. Get the matched pair at
mouser.com (part number: 937-MRF150MP). When shopping at Mouser get some Thermal Paste. You
can use some computer CPU chip thermal paste if you have it. It is also available at a computer
shop/store. Or, go ahead and order some white thermal paste when you order the MRF-150 devices. I
had some white Wakefield thermal paste lying around.
Without specialized equipment it is difficult to separate the MRF-150 devices from the PC board without
damaging the PC board.
1) While the board is still mounted on the PA heat sink, with an X-ACTO knife carefully cut all the fins on
both MRF-150 devices in order to protect the board.
2) Remove the board from the heat sink and
3) Then remove the remnants of the two MRF-150 devices from the heat sink.
4) Remove all traces of thermal paste from the heat sink.
5) With the now removed PA board clean up the board by unsoldering and removing the fin remnants.
6) one-at-a-time, apply a very thin paste of thermal conducting material to the base of each MRF-150
device and test fit it to the heat sink. Gently and firmly push the MRF-150 onto the heat sink. Remove
the MRF-150 device and inspect both the device and heatsink. If you see peaks in the thermal paste,
you have used too much. Wipe off the MRF-150 device, leave the paste on the heat sink. Then repeat
the mounting process and removal again. When you have a slight wave like appearance on the device
and heat sink, you have the correct amount of paste—do not mount the device yet! Carefully set aside
the devices, protect them from dust.
6) Re-install the board onto the heat sink. Mounting the board before the MRF-150 will allow the MRF-
150 fins to lie on top of the board where they are supposed to be.
7) Then install the MRF-150 devices.
8) Finally solder the MRF-150 fins to the pc board.
There are two potentiometers to set the bias on each board, one for each MRF-150. These pots are
used to balance the pair of devices on each board.
I’ve found the Icom factory settings for the MRF-150 bias settings to be different from what the Service
Manual calls for. You must make a choice to either: 1) measure what the other PA boards have their
idle current set to and then match the replaced MRF-150 to be the same value; or 2) to set all four of
the PA boards as per the Service Manual. I found enough variance between all the boards to cause me
to set the bias on all four boards, eight MRF-150 devices, to the 100ma per MRF-150 (which equals
200ma per board) as stated in the service manual. Note: There are four PA boards total, two boards on
each side of the heat sink.
The instructions in the service manual seem incomplete to me. Icom has you set bias on one side first
by biasing the 2nd side to cut off and then set the 2nd side by turning both of them on and doubling the
value you set the first one to. I found this didn’t always get each side to a close match. So, I did my bias

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adjustments by adjusting each side separately with the other side biased off and then checked the
current draw for both.
The balance potentiometer is very, very touchy, only about 2% or 3% of the entire range of the pot is
used to actually adjust the bias. And, the pots have high friction, so it’s difficult to set. I tried using a
plastic “tuning” wand/screw-driver and it would wind up and snapped the adjustments too far when the
friction broke. I gave up and used a small blade metal screwdriver--much better than the plastic but still
very difficult to adjust to the desired value.

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Regarding: My PW1 won't tune up on 6 meters even into a dummy load. All other bands will put out
1000 watts but not on 6 meters. Note: This is symptom can also apply to other bands not working.
To diagnose, on the Main Unit board at connector J8 measure the voltage for each band filter selection
as you manually go through each band. There is not a filter for each band, some bands are combined—
check the service manual. When engaged each the voltage for each band filter will be ~13 Volts.
You will likely find one of the band filter voltages to be significantly lower than the others. I don’t
remember exactly what it was, but it wasn’t zero. If you find filter select voltage too low, then you need
to repair two separate boards in the PW1!
Required Fix 1: Filter Unit, remove the filter unit. It is in the left front side of the chassis assembly. The
combiner assembly is attached to the filter and they will come out together. NOTE: the black two wire
(red and black wires inside a black casing) termination on the Combiner Board looks likes it is a
connector on the Combiner Board. That is NOT a connector attached to the Combiner board—it won’t
remove! After removal of the Filter/Combiner, separate the combiner from the filter assembly. Then
remove the circuit board from the filter assembly sheet metal.
Then (for 6 meters) replace diode D18. Other bands will have a corresponding diode across the relay
coil—see next paragraph.
You won’t find this diode in any standard catalog. It is a general purpose diode being used as a clamp
diode. I used a fast recovery diode P/N 1N5602. Mouser Electronics P/N 610-1N5062.
It is not always the 50MHz filter relay clamp diode that fails, other band relay clamp diodes fail. On
other band fail to select problems, there is a corresponding clamp diode for each band filter relay. The
failed bands have been indicated by reading the band filter select voltages on the Main Board connector
J8.
Note: it is likely you won’t be able to detect a failed clamp diode while it is in place on the circuit board.
Furthermore, this is a 50 cent device protecting a $300 board and it took you 2 to 3 hours to get to it—
just replace it. Be sure to observe polarity markings.
Required Fix 2: On the Main Unit, replace Integrated Circuit IC19. It is a Display driver used as a relay
driver. Toshiba P/N TD62783AFG(O,S,EL), Mouser Electronics part number 757-TD62783AFGOSEL.
Replacing the SMT driver chip is a delicate operation but doable using a CHIPQUIK SMD Removal Kit. Do
a Google search and watch a video or two.
However, if you don’t want to mess with the SMT chip removal you can buy, from ICOM Service Center
Parts, a 98415169 “Main Unit New Version circuit board”. As I recall it is in the $200 to $300 range.
“New Version” means it is for later versions of the PW1s that can still select bands with the PW1 power
off. It can probably be used to upgrade and repair your original PW1 too—I haven’t done this upgrade,
so you are on your own. CAUTION you still have to repair the appropriate blown Clamp diode on the
filter board or you are going to blow up the new board too!!!!!
For additional information on diagnosing and repairing PW1s; ZS6KR provides this excellent advice:
http://www.ab4oj.com/icom/pw1/zs6kr_pw1_repair.pdf