“The FT-897D went suddenly deaf on 2m!” At least that was the report from a good friend of mine that borrowed my rig for a few months to operate it.
Back in my lab I went through every band and mode with the rig and tested its performance. Indeed, in FM mode only, it was deaf to the point that 9+10dB signals where not even registering on the S-meter.
The first thing I did was to study the block diagram and the schematics. It is a good thing that the rig’s service manual has always been available on the net. My initial suspicion was that the ceramic IF filters may be the problem once again. I was right. These filters are famous for their failure in those rigs. I am showing a portion of the block diagram to focus on the signal path for different modes. The signal path has CF1005 filter for AM mode, and CF1003,CF1002 for FM and NFM modes. The SSB/CW uses the CF1004 filter which is marked with green line in the diagram. This filter is a metalic can type near the TOKO ceramic filters.
To connect the block diagram with reality, I am attaching a picture of the main board. The three ceramic filters are (from left to right) CF1002, CF1003, CF1005.
When I visually inspected the ceramic filters I was quite sure that they are the root of the problem. There were tiny flakes of crystal salts on their surface together with a residue that looked like moisture on their plastic bodies. A lot has been said on the internet about the reliability of those filters so I will not go into further discussion about this issue.
I order a replacement for all three filters to have piece of mind.
Removing the old filters proved to be quite challenging due to tiny 0402 smd components placed very close to the pads of the filter pins. They only way to do this professionally in my opinion is to use a de-soldering station. I couldn’t have done it without one. Once the new filters were soldered in place I cleaned my rework flux and visually inspected the board once again.
The problem was addressed. The rig’s FM reception/sensitivity is within specs once again.
Just before I put the whole thing back together, I though it was a good idea to check the rig for proper alignment. Following the Alignment procedures in the Service manual, I checked the LO frequency, and found it within specs, (I’ve got the TCXO option installed). I then proceeded checking the PLL subsystem for proper VCO steering voltages at every band. Everything was within spec. That was good news. When I finally checked the Idling Current, I realized that the pre-driver/driver stage idling current was lower than spec and the driver stage idling current very low compared to the specs. For the later, the ideal value is 200mA (combined) and my reading was about 80mA. I found a few articles on the web regarding the issue of FT897 rigs without proper factory alignment on this stage and on the PA stage. Anyway, I carefully adjusted the stages to values within specs. For the PA adjustment, there is a two pin header which is closed with ta soldered jumper from the factory. You need to un-solder the jumper, place the ammeter and carefully make adjustments to achieve a current of 300mA (+-10mA) at this stage. Note that the current indication rises the first seconds after pressing the PTT, so you need to wait for a few seconds before adjusting the value. And finally the jumper must be soldered back in place.
In the end, I put the rig back together and after going through all the modes and bands and testing the receiver with an RF signal generator and the transmitter with the help of a FT-817, I operated my fresh FT-897D on the bands. A couple of QSOs and the nice reports was the reward for this successful repair.