Knowing my new interest in Amateur Radio, my father-in-law, or the "Old Man from California" as he likes to call himself, offered me his old ham radio equipment that he no longer used. I readily agreed. In the next couple months, my father-in-law shipped me the following from his collection:
- Kenwood TS-520 SSB Tranceiver
- Azden PCS-3000 2M FM Transceiver
- Ten-Tec Century 21 CW Transceiver
- Yaesu FRG-7700 All Mode Transceiver
- MFJ 949C Antenna Tuner
This encouraged me to obtain my Amateur Radio Technician license. As soon as I passed I immediately started fiddling with the Azden PCS-3000 2M Transceiver. I installed a J-Pole antenna, made by Arrow Antenna, in the attic and routed the coax transmission line through the closet on the first floor and to my Radio Shack in the basement. I knew that the J-Pole antenna was closely impedance matched to the RF output of the Azden PCS-3000 so that no Antenna Tuner was required. I set the frequency offset and enabled the PL Tone switch on the top of the transceiver and was ready to make contacts!
Despite repeated attempts I was unable to trigger the local repeater. I then decided to put my MFJ 949C Antenna Tuner in series with the PCS-3000 and the J-Pole antenna. I set the Antenna Tuner to direct mode bypassing the internal LC circuit. The issue became evident. Keying the microphone produced no RF output to the antenna! The cross needle meter on the Antenna Tuner did not indicated any forward or reflected power. Time to take apart to the PCS-3000 to determine the issue!
Disassembly - Loosen Control Unit Knobs
Time to figure out what's "broke", first you must remove the detachable control unit. This is done by loosening the knobs on each side of the radio.
Disassembly Tip - Organization is important!
When disassembling a radio, I carefully place the parts into two bins, one bin for the larger parts and a smaller bin for the screws.
Disassembly - Remove the control unit
Pull the control unit strait forward, the control unit attaches electrically to the body of the radio by an edge connector.
Dissaembly - Remove the mounting rails
There are two mounting rails, one on each side of the radio. Two counter sunk Philips screws hold them in place. Remove the screws then pull the rails off.
Disassembly - Top cover Removal
The bottom cover is held in place with four screws, one at each corner of the cover. Remove the four screws and pull the cover off. The speaker is attached to the bottom cover, you will need to disconnect the speaker from the printer circuit board.
The RF Amplifier Module
The Taiyo VP-15E13LF RF Module is circled in red, I believe that this is the failed component but need to do some checks first.
Voltage and Signal Checks
All voltage and signal measurements are taken with reference to the metal chassis. I attached the negative lead of my Multimeter and ground lead of my Oscilloscope to the internal metal chassis when making measurements. Signal measurement is in Volts Peak to Peak.
PA Board Input Checks
Measurements taken on connector circled in red. PIN5 12 Volts DC, PIN9 9 Volts DC, PIN4 9 Volts DC when MIC keyed. PIN1 9 Volts DC when MIC NOT keyed.
PA Board Input Checks (Continued)
You should see a small FM signal (under 1 Volt) on the IN pin circled in red when the MIC is keyed.
RF Amplifier Module Checks
IN, VC, VD, OUT are marked on the PA printed circuit board. IN should be a small FM (under 1 Volt) signal when MIC is keyed. VD should be around 9 Volts DC, VC should be 12 Volts DC. OUT should be an FM signal of several volts when MIC is keyed.
My Troubleshooting Results
I have determined that all the proper voltages and signals were present going into the PA Circuit Board. I have also determined that the proper voltages where present on the pins of the Taiyo VP-15E13LF RF Amplifier and the proper FM signal was present on the IN pin of the RF Amplifier Module but that no signal was present on the OUT pin of the RF Amplifier Module. This leads me to believe that the RF Amplifier Module is defective.
The RF Module is made of Unobtainium
The Taiyo VP-15E13LF RF Amplifier Module part has been discontinued. I like to say is that it is now made of "Un-obtainium". I cracked the RF Module open to see if there was any serviceable parts. The RF transistors that are in the Taiyo VP-15E13LF RF Amplifier Module are available but our expensive as they have been discontinued as well. The RF transistors were too expensive to justify the repair of this aged 2M Transceiver that is worth under $100 in working conditions. Time to look for alternatives.
Inside the Taiyo RF Amplifier Module
What's inside the Taiyo VP-15E13LF RF Amplifier Module
The M57737 RF Amplifier Module
Pinout and package dimentions of the Mitsubishi M57737 RF Amplifier Module
Source for replacement Mitsubishi M57737 RF Amplifier Module
As mentioned, the pin layout of the the M57737 is slightly different. The M57737 does not have any ground pins but instead the metal base of the module is ground.
Make sure you apply heat sink compound to the back of the RF Amplifier Module before mounting.
Here are the connections of the M57737 to the PA Board:
M57737 Pin | PA Board Connection
Pin1 ============ IN
Pin2 ============ VD
PIN3 ============ VC
PIN4 ============ Anode of D30 which is connected directly to OUT
Metal Case ======= Any connection designated as G
The Transplanted M57737 RF Amplifier Module
The M57737 mounted and soldered in place. Notice the ground connection between the M57737 metal case and G on the PA printed circuit board.
A Leap of Faith
I had no idea if the replacement Mitsubishi M57737 RF Module was going to work. It was a $50 gamble! That was the cost of the replacement part. I could easily power it on an smoke the new RF Amplifier module.
I moved the Azden PCS-3000, with the newly installed RF Amplifier module, over to the desk in my Radio Shack, connected power and attached the antenna output to my MFC 949C Antenna Tuner. I then set the Antenna Tuner to use the built in dummy load.
Upon power up there was no smoke....whew....the PCS-3000 was working correctly in receive mode. I checked voltages at VC and VD points on the PA printed circuit board, they look correct.
Time to key up the MIC and transmit into the Dummy Load. Success! I was reading about 100 Watts Peak to Peak as forward Wattage on the cross-hair meter on my Antenna Tuner.
Once connected to my J-Pole antenna, I was able to trigger our local repeater and establish contact with a fellow Ham on the 2 Meter band.
Bench testing my Azden PCS-3000 after the RF Amplifier module implant.
The Down Side
As part of my testing, I decided to try low power mode which is accomplished by pulling the Squelch control out. Low power mode effectively cuts the RF output power in half. I heard a "pop" as soon as I keyed the MIC in low power mode. It blew the inline fuse in the power cable. I immediately turned off my 12 Volt bench power supply. My first concern was, did it blow the newly installed RF Power Amplifier module? I replaced the inline fuse with a suitable size, pushed the Squelch control back in, putting the PCS-3000 back into high power mode, and turned the 12 Volt bench power supply back on. The PCS-3000 sprang back to life and when I keyed the MIC I was still able to contact our local repeater.....whew.
My solution to this problem was to not use the low power mode and to place a sticker on the top of the rig warning to not use this function.
Back in Service
My Azden PCS-3000 back in service in my Radio Shack!
My transplant of a similar Mitsubishi RF Amplifier module into my vintage Azden PCS-3000 2M Transceiver was a success! I am hoping that this Hub will help you in diagnosing and fixing a "no RF output" problem with your PCS-3000 was well.
Who Writes This Blog?
John is an IT professional from Cleveland, OH who enjoys amateur radio, ham radio, metal detecting,
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