Home Yaesu ham radio transceiver fault finding
This is an article on faultfinding and repairing Yaesu ham radio transceivers. We describe common faults with the Yaesu FT8100 amateur radio transceiver, which has very poor reliability especially if used for lengthy periods on high transmit power.
Trying to squeeze a relatively high power VHF/UHF transmitter into a small sized ham radio transceiver, with a combination of poor heat-sinking, inadequate cooling and poor internal design results in very poor reliability.
Most of the common problems relate to poor PCB design practices and quality. The designers of this ham radio transceiver stupidly routed the final amplifier DC supply voltage (high current draw) through small inadequate plated through holes on the board and this caused many of the faults. It's not unusual to get arcing at these (and other) plated through holes on the FT8100R and some people have even suffered severe circuit board damage due to plated through hole and track burn-out, in some cases so bad that the transceiver has been scrapped.
I also had the VHF receiver front end MOSFET die on my transceiver due to nearby lightning. Getting hold of a spare device is very difficult and is best done through Yaesu USA, even if you're in the UK (see address at the bottom of this page). See below for tips on fixing this problem.
More on this topic (including details on a number of other ham radio faults) can be found at http://www.mods.dk.
Symptoms of the FT8100R circuit board power track problem are:-
If the above symptoms match the problem you are seeing then solder a wire onto the top board as shown in the repair picture below. Click here to see the full size image (needed to carry out the repair). You don't need to remove the circuit board to do this repair (although I did originally to find the fault!). To start the repair, you'll need to scratch off the varnish on the tracks shown in the picture to get a good solder connection.
Be careful not to short anything else out when doing this! The tracks between which I placed the bridging wire should have already been connected together by an underside board track (and plated through holes). You can't see this unless you take the whole radio apart. Unfortunately, plated-through hole failure due to the high current draw of the 70cm PA burns out the plated through holes between these tracks and there is no longer a reliable connection (hence the need to fit the wire).
My FT8100R amateur radio transceiver is 100% working now. However, I can't take any responsibility if anything goes wrong when you attempt to carry out this repair and accidentally damage anything. Do this repair at your own risk. If you follow the instructions you won't have any problems. A local dealer wanted 90 pounds to repair the radio. Considering it's actually 5 minute fix that's an awful lot of money!!
The FT8100R has a ten layer circuit board, so try not to heat it up for too long with the soldering iron and this is another reason why I recommend not taking the radio apart. You'll only need to take the top cover off and disconnect the speaker connector to do this repair - NOTHING ELSE. All you need to do then is solder a wire across the circuit board tracks as shown in the picture below. If you take the board out (not necessary) and bend the circuit board you can cause other inner layer fractures. These problems are also common. If the symptoms you are seeing do not match those described - then you may have another track fracture somewhere - bad luck as this can be an expensive repair. The FT8100 is also known for these faults.
I include these instructions for people who have to take the VHF (upper) board
out of the FT8100 chassis. Remember that you don't need to do this if the
UHF transmitter power output has failed due to the plated through power track
going open circuit (see above article), as you can repair that problem by just
soldering wires on the top of the PCB. However, if you do need to take the upper
board out of the chassis for some reason, you will need patience and a reasonable
soldering iron and de-soldering tools or you could wreck the board. Follow the
procedure below to minimise chances of damage.
You'll will need to remove the top PCB if the VHF receiver front end device fails. Symptoms include S-meter readings of half what they were previously (with added noise) and much worse sensitivity. Weaker signals will now (most likely) be inaudible!
Another fault that the Yaesu FT8100R develops is the optical tuning knob (on the radio's removable front panel) develops some play causing the transceiver tuning to jump erratically up and down in irregular and uncontrolled movements.
The replacement part can be ordered from Vertex Standard, 10900 Walker Street, Cypress CA 90630 - 5013 USA. Tel: +1 (714) 827 7600. E-mail: .
In case you need them, here are the Vertex order code details for the Yaesu FT8100R optical tuning knob replacement part:-
Cost: approx $30 USD including International Shipping (correct as of October 2004)