by Woody AK2F 11/25/12
The Icom IC-PW1 amplifier is a great amplifier until thepower supply fails. This is a fear of most PW1 owners since replacements run$3122 plus shipping. The good news is that this 2250 watt (45V @ 50A) switchmode power supply can be repaired and made stronger than new. Alternatively,an external 48V power supply can be controlled by the amplifier.
*** WARNING ***
THIS ARTICLE DISCUSSES CIRCUITREPAIR AROUND LETHAL VOLTAGES. DO NOT PERFORM THIS WORK UNLESS YOU AREFAMILIAR WITH HIGH VOLTAGE SAFETY PRACTICES. PERFORM AT YOUR OWN RISK.
THE AUTHOR IS NOT RESPONSIBLE FORDAMAGE OR INJURY.
AC power from the 220 VAC outlet goes through RFI filterboard, fuses, and then to a relay board. So far, there are no semiconductorsthat are susceptible to power line surges. For 45V main power, the AC goes toACTFIL board where it sees a 600V 25A full wave bridge rectifier, and a FETcircuit to boost the voltage when running off 110V. These semiconductors failin a voltage surge. For the bridge, replace original D25XB60 with D25XB80(available from Mouser.com). This is an 800V exact replacement. Remove 320N50 power FETS from ACTFIL board, since these are only rated for 560V. Thislegal limit amplifier will now be wired for 220 VAC only, but can withstandsurges up to 800V.
Second alternative is to disconnect the 45V supply, and powerthe PW1 from an external power supply. The +12V for amplifier main boardcontroller is separate and located on SUBREG board. Many surplus 45-50V high currentpower supplies are available on eBay from telecomm/cellular, server, and other-48V backup battery systems. Another option is a new Ameritron/MFJ ALS-1300SPSfor < $1000. This modification will bring the switched AC external, andbring in the 45V back for RF boards. Yet another choice is a Meanwell RPS-3000-48which is a 48V 62.5A modular OEM SMPS. The Meanwell RPS-2400-48 (48V 50A) is also suitable. (www.meanwell.com)
Figure 1 - AC flow
Figure 2 - Power Supply removed from Amp
Disconnect blue and brown wires going to relay board onright side of Figure 3 below. Tape these wires well since they are input for internal45V supply and will no longer be used.
On front of power supply remove red and black wires fromterminal strip and DC filter board. These can be reused with external supply.
Run well insulated power cable through front grommet torelay board, keeping Line, Neutral, and Ground consistency. Use ring terminalsfor internal connections and proper receptacle for external power supply plug.
External power supply will be switched on/off by PW-1. Voltage to external power supply will be that of the PW-1 plug (220 or 110)
DC output from external power supply comes back to terminalstrip on front of power supply. Make sure polarity is correct (red = +45V)
Figure 3 - AC switched to ACTFIL (45V) Board
This modification retains internal switching regulators, upgradesbridge rectifier and removes vulnerable 110V boost converter. It is notcompatible with modification #1. Blue and brown input wires remain connectedto relay board.
Order diode bridge D25XB80 (available from
For full access to ACTFIL board, where D1 bridge and FETsare located, remove 4 screws holding heat sink to assembly, and 8 screwsholding relay and DC filter boards. This allows electronics to be pulled out.
Figure 4 - Heat Sink screws
Replace original D1 with new higher voltage part. See D1location in Figure 3.
Three high power FETs 20N50, are located under coppershield. Remove them. This makes this amp 220V only at higher reliability.
Check circuit for other opens and shorts according toschematic diagram in figure 5.
Re-assemble heat sink and circuit boards securely usingoriginal screws.
I used a variac to slowly bring the voltage back up. DCoutput voltage was approximately 28V with 110V input. After final assembly, DCout was 45V from 220 V AC.
Perform any additional power supply adjustments (likevoltage adjustments, current limiting).
Re-assemble and check DC output voltage before connection RFamplifier power wires (red and black) to terminal strip.
Figure 5 - Schematic of high surge 220V only modifications
Last updated: 09/25/2019