Yaesu FT-411 2M Transceiver Modification Gone Bad!

The Story

My father-in-law, AKA "The old man from California" loves hunting for bargains at flea markets and garage sales in his so-cal neighborhood. If he finds something interesting and Amateur Radio related, he'll ship it back east to me so I can take a look at. My father-in-law knows I enjoy the challenge in getting vintage radio equipment working again. He couldn't resist purchasing this Yaesu FT-411 2M Transceiver for a couple dollars at a garage sale and shipping it to me to see if I could repair it.

The Problem

The Yaesu FT-411 was a popular 2M FM Transceiver from the late 1980s and early 90s. It boasted up to 5 Watt RF Power Output with the 12Volt 600mAh ni-cd battery pack installed! The one my father-in-law sent me had the mobile PA-6 DC-Adapter/Charger installed but not the required "Wall-Wart" AC Adapter. I was, however, able to power the FT-411 up using my variable DC bench power supply. Surprisedly, the FT-411 powered up but some of the indicators in the LCD screen did not display as they are supposed to in receive mode. In addition, the FT-411 would not transmit and it would "forget" the frequency I was on turned off and back on. 

Remove Bottom Plate

Time to disassemble the FT-411 in order to troubleshoot the issue. Slide the PA-6 DC-Adapter/Charger or battery pack sideways to remove, this will expose four screws on the bottom of the radio. There are a lot of small screws holding the FT-411 Transceiver together so I recommend keeping a set of jeweler's screwdrivers handy. Remove the four screws, circled in red, then remove the bottom plate. 

Remove Top Cover

Disconnect the antenna, then remove the four screws that hold the top cover in place. Remove the waterproof membrane, shown in the picture below, after the top cover has been removed. 

Opening the Case

The sides of the case are held in place with one screw on each site (circled in red in the picture below). Once removed the FT-411 opens up in clam-shell fashion. The printed circuit board on the left is the RF board and handles the sending/receiving  of radio signals. The printed circuit board on the right is the microprocessor board that handles display functions and controls the RF board. 

I desoldered one side of the copper shield, used to protect the processor from RF energy, and pulled it back so I could get a closer look at the processor board.

Possible Fix

While examining the processor board, I noticed some sloppy soldering work across several semi-circle solder pads (circled in red in the picture below). This was unlike the neat solder work across the rest of the board. Through some Internet research I found a site containing information about modifying the FT-411. I have determined that bridging these pads with solder alters the behavior of FT-411 Transceiver. The processor determines the state, open or close, upon power up and uses this information to determine operability. It looks like the previous owner of this FT-411 tried to modify the operation of this transceiver by soldering/unsoldering the pads but he/she did not do in a pattern that this transceiver would recognize. It was my hypothesis that this botched modification job prevented the FT-411 from working properly. I de-soldered all bridges but across terminal 3, this is the factory default setup. 

Website Containing FT-411 Modification Info

Testing

It is a good idea to test a fix, before completely assembling a transceiver. I connected the battery terminals leads, observing the polarity, via alligator leads to my DC bench power supply and raised the power up to 7.2volts. In addition, I used another alligator lead as an antenna. SUCCESS! Indicators on the LCD panel display properly in receive mode and I was able to transmit! Although, I still had the issue where the FT-411 would not remember my frequency setting when turned off then back on.

3V Lithium Battery replacement

The FT-411 uses a 3V Lithium Battery (circled in the picture below), in order to retain configuration settings in it's volatile  memory, when not powered on. Most likely, this battery is already marginal or dead after 25 years of service. Having your FT-411 "forget" the frequency you were on with each power cycle is a good indication that this battery has failed! You will need to remove the processor board from the case in order to replace this coined shaped battery. I circled the locations of the screws for processor board removal below. 

3V Lithium Battery replaced!

Amazon had a suitable replacement 3V Lithium Battery with solder tabs. The battery was intended as a replacement for the first generation Nintendo Gameboy but suits my purpose just fine. Do not try to purchase a 3V Lithium Coin battery without solder tabs then try to solder leads to it. The heat will ruin the battery.  Below is a picture of new 3V Lithium Battery install on the processor board.

Reassembly

To reassemble, follow the disassembly steps in reverse order, make sure you reattach the insulator using a dab of hot glue to ensure that the battery does not short out on the metal shielding of the RF board. See are circled in the picture below.

Conclusion

Sometimes the fix to a complex transceiver system can be as simple as a dab of solder in the wrong place, as in the case of this Yaesu FT-411 repair.  One of the most important troubleshooting tools a Amateur Radio Enthusiast has is his/her eyes, ears, and sense of smell. In this case the only tool I needed were my eyes. It was a real joy to get this old Yaesu FT-411 functional again!