Repairing Maggiore R1 Repeater

The SOARA 224.100 Repeater became intermittent and stopped transmitting a few months ago. I finally made an appointment with the Laguna Beach water district to visit the site on May 28th.

Once on site, I quickly determined that the repeater had no power output. Keying the repeater did engage the transmitter, but nothing was heard even at close proximity to the repeater. I disconnected and removed the repeater radio from the shelf and took it home to troubleshoot the problem.

Once on the bench, I took the cover off, a time consuming task given it has so many screws that hold the top cover on!

The receiver and transmitter are in separate shielded sections with the center section of the cabinet available for a repeater controller, PL encoder/decoders and cabling. The transmit side consists of a Maggiore Hi Pro EV1 Rev F. transmitter/exciter and Hi Pro PAV-1 Power Amplifier.

My first thought was that the PA output transistor might have failed since it’s a part that is put through a lot of stress from heat and high current. I disconnected the exciter from the PA and wired a test transmitter to the input of the PA. It worked fine. I followed the alignment procedure and was able to obtain a clean 20 watts of output power into my service monitor.

The output of the exciter was only a few milliwatts when it should be about 3.3 watts. Measuring voltages through the filter stages, I found the voltage on the base of a transistor in the first buffer stage was very low. I removed the exciter board to make it easier to perform further testing and repair.

When removed from the chassis, I had to apply 13.8 volts to both the oscillator and subsequent buffer/multiplier/amplifier (PTT keying) stages. Once I did this, I noticed a large increase in power into the service monitor.

Once I went through the alignment procedure described in the service manual, I was able to obtain about 4 watts output from the EV1 transmitter.

Now that I had a working exciter/transmitter and PA, I reassembled everything back into the chassis.

Measuring the power output, it was back down to a few milliwatts output. Measuring the two 13.8 volt supply lines to the transmitter while grounding the PTT line, I found that the oscillator voltage was fine, but the PTT keying line was only 3volts! The obvious problem was the PTT relay. For some reason, Maggiore had used a 28VDC relay instead of a 12 volt relay.

I fabricated a small PCB with a relay and flyback diode. Luckily I had just purchased some automotive quality relays to fix a problem with the central locking system in my Toyota and I had a spare Fujitsu 52ND12-W relay.

Fujitsu 52ND12-W automotive relay used for PTT keying

Grounding the supply side of the relay energizes the relay and passes 13.8volts onto the keying line of the transmitter.

The output power was now 20 watts. I hooked the R1 up to a repeater controller and adjusted the audio levels. Lastly, I grounded the transmit PL enable line and adjusted the deviation of the PL encoder.

A few days later, I re-installed the repeater at Temple Hill. I added an RCA “Y” cable to connect the PL decoder logic output to the PL encoder enable input. This causes the transmit PL encoder to be activated any time a user’s input PL is received and decoded. The purpose is to allow listeners with CTCSS / PL Decode enabled to only hear users and not courtesy tones or repeater IDs.

TM-742AD no TX audio

I noticed an old TM-742AD in a friends garage recently. It had been disassembled and had a label on it that read “Defective Unit” – that piqued my interest!

I brought the radio home and put it on the bench. The radio powered up but all of the memories were reset to default frequencies so I suspected the backup battery was dead. I programmed a simplex frequency and transmitted into my service monitor. The PTT switch on the microphone was stuck. I fixed that by replacing the heavy foam bumper inside the microphone. Transmitting again, I noticed there was no TX audio. Since this radio uses an electret microphone, my first question was – is there power to the microphone? I measured 0 volts on the “8C” line to the microphone. Tracing through the schematic, I found a bad fuse. Replacing the fuse restored mic audio.

I disassembled the radio’s controller section which consists of two circuit boards fixed to a metal frame and connected together via a SIP connector and a ribbon cable. I measured the backup battery and found that it was flat. I have replaced many of these batteries in the TM-742 model radios and had brand new ones in stock. I bought direct replacement backup batteries from Mouser. Replacing the battery solved the memory issue.

When turning off the radio, I noticed the sound of a DTMF digit over the speaker and that the speaker was still making a rushing noise when it should be silent.

Power to the audio amplifier is controlled by two transistors, one a high power switching transistor that provides the source voltage for an 8 volt voltage regulator. With the power off, there was still 12.6 volts on the input side of the voltage regulator. I immediately suspected Q102, the larger switching transistor. Testing it confirmed that it was internally shorted which provided power to the audio circuits even when the logic circuits were shut down.

I replaced the 2SA1641(S) with a new one that I had in stock. I’ve seen this switching transistor fail in other units I’ve worked on.

The radio had been worked on before and the trace from the base of the transistor to the collector of the previous stage switching transistor through a current limiting resistor had been replaced with a short length of bare wire.

After I replaced the transistor, I cleaned up the wire that replaced the burned out PCB trace.

Upon further testing, I found that the output audio was intermittent! I installed a plug in the mixed audio output jack to plug into my test amplifier and while inserting the plug, I noticed the audio was restored. So, I reflowed the solder on the 3.5mm stereo mixed audio jack, sprayed contact cleaner into it, and the output audio is back to normal.

This is a really great radio and is still serviceable after 28+ years! Parts are becoming a little more scarce but you can still find these radios and optional modules and accessories on ebay for reasonable prices.

FT-911 low-audio repair

My Brother recently took his old FT-911 23cm handie talkie out of storage and powered it up. The radio worked, but the output audio was very low.

Tracing the audio path, I found sufficient audio at the output of the LM386 audio amplifier and the only component between the speaker and that was an electrolytic capacitor.

Naturally, that capacitor was buried deep in the circuit boards under lots of RF shielding. After some work, I was able to liberate the circuit board assembly from the transmit side. I couldn’t find a 100uF/10v capacitor – I only had a much larger 100uF/25V cap. It fit rather snugly but should do the job.

Once replaced, the radio now has sufficient audio. The output audio is not perfect in that there are some strange audio artifacts that can be heard from time time, but the radio works now.

Alpha Delta Coax Switches

I have one primary HF antenna, a Hustler 6BTV (6 band trap vertical). I was using an Alpha Delta 4-port coax switch to switch the antenna between my K3, K2, and coax that I use on the workbench. This morning when I listened for the SOARA 40 meter net, signals were very weak. SWR was very high when I tried to transmit. I removed the switch and replaced the K3 position with a SO239 barrel connector and that resolved the problem.

I used a digital VOM to test the ports on the switch and found ports 3 and 4 (K3 and K2) to be shorted out while activated! After opening up the switch, I found out why.

The busbar that provides grounding for ports that are not activated was higher on the port 3&4 side than the port 1&2 side. This was caused by the screw and washer that were supposed to hold the bar down being located too far away to engage the bar. A manufacturing defect.

I attempted to email the company but both of the email addresses they list on their web site are no longer valid.

Buyer beware! If you have a Delta4, you might want to take a look inside to see how it is constructed and make sure it doesn’t have this defect.

Tivo Power Supply Repair

I’ve got a very old Tivo, an HRI-250. Last week we had a major power outage that lasted 12 hours. When the power came back on, my Tivo did not. It had been having some over-heating problems, so I wasn’t surprised.

Investigating further, I found that I was missing some of the supply voltages. The Tivo supply provides 12V, 5V, 3.3V, and 32V I believe.

There were several capacitors that were puffed out on top – a sign of failure. So, I set out to replace those.

There were pairs of 470uF, 2200uF, and 3300uF caps that looked to be bad. I removed them in pairs and tested them. All of them measured very high ESRs and low capacitance.

I ordered replacements through my primary electronics parts dealer, Amazon.com and they arrived the next day.

Hopefully the replacement capacitors are able to withstand the high frequencies in the switching power supply. If not, I’ll have to order more specialized caps from Digi-Key.

Here are some photos of the repair. I had to remove the heat sink with power transistors and diodes attached in order to remove the caps. They caps were fixed to the board with a nonconductive fixating compound which I left alone as much as possible.

So far the Tivo is working great and running cool at 39C

Arduino KISS TNC

Mobilinkd (http://www.mobilinkd.com) is the producer of very compact and capable bluetooth enabled KISS mode TNCs that are used with APRS applications on Android, iOS, Windows, and Linux, and Mac OS.

Their original prototype was built using the Arduino platform.

On their website, they provide breadboard descriptions of various TNC designs including an Arduino based KISS TNC: http://www.mobilinkd.com/2014/09/11/arduino-kiss-tnc/

Having a few spare Arduino boards lying around, I though it would be fun to build one.

First I drew a schematic based on their breadboard design using iCircuit:

Then I built the simple circuit on a Radio Shack prototype DIP IC circuit board that I had on hand:

Mobilinkd provides the firmware for the project in the form of a HEX file that can be uploaded to the Arduino using “avrdude”. I used a Raspberry Pi 3 to flash the firmware onto the Arduino board.

I connected the finished KISS TNC to an Icom IC-91AD via the Speaker/Mic jack (RX/TX+PTT). I used the same Raspberry Pi 3 to test the KISS mode TNC using the AX25 utilities kissattach and axlisten:

It worked right off the bat! Next, I configured the Java based “Yet Another APRS Client” (YAAC) software on the Raspberry Pi computer to use the new KISS mode TNC. That worked right off the bat also.

To build a more permanent interface board, I drew up a PCB design using OmniGraffle Pro. I saved that as a JPEG and then used my Cricut (pronounced “Cricket”) die cut machine to cut the design out of vinyl. I wasn’t sure the vinyl would hold up to the PCB etching process, but it did! I used a Dremel drill press to drill the circuit board holes.

Lastly, I designed a custom 3D enclosure. I wanted it to be as small as possible, so instead of building in circuit board stand-offs, I simply used hot glue to fix the boards to the case.

Later I’ll try to figure out a clever snap-in design for the Arduino board and will probably use stand-offs for the interface board. The interface board can be scaled down to make it smaller. I’m also thinking about adding solder pads for my standard TX+PTT/RX 3.5mm stereo jack to the PCB.

Using the Cricut cutter software, it was easy to scale the PCB etch pattern down. Since I’m using through-hole parts without critical dimensions like resistors and transistors, I don’t have to worry too much about the parts fitting the new spacing.

I made a smaller version of the interface PCB. However, I forgot that I had the larger PCB drill installed in my Dremel drill press that I used for a PowerPole circuit board project, so some of the through-holes were drilled too large.

Here’s a comparison of my original board (right) and my new scaled-down board (left)

The new board is much closer to the size of the Arduino Nano board that runs the KISS firmware. The first enclosure was 70 x 70mm square. The new one is 60mm x 52mm.

PowerPole Power Panel

SOARA has “battery box” building events every so often. The idea is that you build a portable container with a battery, cigar lighter socket, power switch, volt meters, and Anderson PowerPole connectors that you can use during an emergency. I have designed and/or printed and built several such breakout boxes. I built a Pelican case with a 9AH AGM battery and single PowerPole connector. That provides power to two breakout boxes that I designed and/or printed:

I use 12V DC power on a daily basis and need ready access to power plugs. I have connectorized at least 500 radios and other equipment with PowerPole connectors over the years.

I designed and printed a simple under-the-shelf voltmeter as one of my first 3D projects. I thought it might be nice to have some powerpole connectors in the same under-the-shelf design.

I designed a 90 degree bracket with integrated voltmeter and 4 powerpole outlets copying the design of the 1 1/8″ round PowerPole receptacle to hold a PowerPole plug captive such that it can easily be connected to.

To interconnect the PowerPole connectors, I etched an FR4 copper clad circuit board in Ferric Chloride. My printed circuit board (PCB) drafting supplies are over 33 years old and most have dried up so I ended up using electrical tape and some round etch resist press-on film that was still good to do the job.

I drilled the holes too large for my 16 AWG wire. The problem with that is that solder ends up running down into your connectors. I had to smack the assembly on the bench to eject the excess molten solder from the jacks.

Update – Not being satisfied with the first PCB I etched, I tried a new method. I used my Cricut die cutter to print the PCB layout onto vinyl. I transferred the vinyl to a blank PCB and used it an etch-resist. It worked very well.

I used a smaller drill bit. I have a PCB drill however, the motor attaches to a Weller rechargeable soldering iron and the batteries on that died many years ago.

I used the smallest bit I had for the voltmeter traces, and the second to smallest for the 16 AWG wire.

I redesigned the panel to not carry the grooves for the Power Pole connectors through to the front and designed a cover for the circuit board on the back.

YAdmHS – Yet another digital mode hot spot …

I got to thinking about how I could make a thinner MMDVM based multi-mode hotspot with a Nextion display.

I decided to try mounting the boards next to each other instead of plugging the MMDVM board into the Pi ZeroW board.

I also wanted the case to have rounded corners. Here is what I came up with.

Unfortunately, it did not turn out to be much thinner at all. I was able to center the display in the front of the case though.

I also designed a desk and wall mount bracket for it. I left room inside the case for a battery option in the future.

To make the unit more portable, I added a battery charger/boost regulator, battery, and power switch.

APRS on Raspberry Pi

About a decade ago I bought a TNC-X from Coastal Chipworks. I used it for a fill in digi for Laguna Niguel for a while. I bought the X-Track and X-Digi add-on boards for the TNC-X as well. Unfortunately, when I tried to add a larger 5V regulator to power an external GPS, my dyslexia got the better of me and I ended up letting the smoke out of most of the ICs on the board. I have since bought a new TNC-X to replace this one! And, I am still planning on repairing the one that I blew up!

Always looking for a good Raspberry Pi project, when I saw that John Hansen from Coastal Chipworks had a new Raspberry Pi based TNC product in 2013, I bought one of his kits and put it together. The TNC-Pi board was designed with a stacking header that allows it to mount on the 26-pin GPIO header of an early Raspberry Pi. Using I2C, you could stack multiple TNC-Pi boards on top of each other if you needed multiple radio interfaces.

I used an instrument case for the project and it made a nice portable full featured APRS setup using Xastir software. The older Raspberry PI had reasonable performance, but not great.

In 2017 when John introduced the updated TNC-Pi2, I bought a couple of those. In 2019, I assembled one and built a custom 3D printed case for it. It uses a much faster Raspberry Pi single board computer and has excellent performance. Using the Yet Another APRS Client (YAAC) software, the functionality is excellent also.

Instead of stacking the boards, I designed a case that allowed me to mount them side-by-side with only a few pins needed for the TTL UART wiring, power and status LEDs to the GPIO pins.

For the radio transceiver, I’ve built cables for a Kenwood TM-261 mobile radio and Icom-style Handie Talkie with integrated PTT/Mic-audio connections. Both work great.

In early 2020, when I heard that Coastal Chipworks was closing down, I bought a couple more TNC-Pi2’s and built a few more of them.

For more information about my various APRS projects, and a presentation on APRS I gave at SOARA Saturday, visit my web site