I am very interested in electronics and especially electronics applied to ham radio. I have been in ham radio for more than 25 years and many more as DIY(do it yourself) and repairing electronic equipment. I am currently teaching electronics and computer science. I have several Yaesu FT-817's at home.
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| My FT-817 collection |
The Yaesu rig is an interesting equipment to make radio "on the go", something that I really like to do but that I haven't practiced for a long time because of a lack of free time. The fact is that several years ago I got a damaged FT-817. I had already repaired several ones and modified others, for example, to incorporate a lithium ion battery inside the rig. This was one more FT-817 to repair. I have several spare parts and main boards for repairing these old model rigs, so in this case the first thing I did was to simply change the main board.
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| Main boards to repair others |
Once changed, I managed to get it working and receive some AM broadcasting, however the mode change, band and other settings did not work correctly. The microcontroller has a multiplexed SPI bus for these functions. It also has several control signals for each SPI peripheral that controls these functions on the main board. Although the SPI bus was operational, these control signals were not present. Since there is nothing between these signals and the microcontroller, it must be most likely a fault in the microcontroller outputs, perhaps due to applying overvoltage or reversed polarity to the rig.
We can say at this time that the rig can no longer be fixed, since obtaining a new control board or a replacement microcontroller is not possible.
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| First Try |
The first thing I did was to try to generate the control signals independently by means of a C program inside a small ATTINY85 microcontroller. However, this is not an easy task since there is a bus multiplexer and several control signals that take place almost simultaneously and it isn't possible to differentiate which signals are from each device. After doing some tests I managed to get the tuning and mode change to work, but other functions were not operational.
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| Signal generated from SPI clock |
The rig can't be repaired. How wrong I was, because after asking for help in the EEVBLOG forum they advised me to ask a technical service in Italy: CSY & SON. This service is very famous and hopefully they quickly answered me by email and confirmed that they had the microcontroller in stock. I could finally repair the rig after so long!!
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| Microcontroler Received |
Once the microcontroller is received, the first thing is to remove the old microcontroller. Due to the large number of microcontroller pins, it is a very delicate process that can end up lifting some copper track and causing problems.
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| Microcontroler retired with low melting point tin |
To avoid this, I use a low melting point tin, so that by adding tin and heating the entire chip, it can be easily removed without risk of damaging the delicate copper tracks. I used the solder from Chip Kit SMDIN100, which although it does not have such a low melting temperature it turned out to be adequate.
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| Board clean, ready to get the chip |
Once the defective chip has been removed and the PCB has been thoroughly cleaned with alcohol, the new component is precisely placed on it. For this operation I use a microscope with a 7-inch screen from AliExpress. With this microscope you can see the placement of the pins very well. It is also used to review the work afterwards.
When the work was finished, I tested the rig. But it does not turn on. It failed miserably on the first try. The issue was obviously pins unconnected and not properly welded. There is no other option but to check the soldering of all 100 pins one by one. So with patience I realized that there were many pins that were not well welded and it took me a while to check them all one by one.
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| Second try. It works!! |
Hopefully, on the second try the rig turns on and works perfectly. At least the band selection and the frequency control, since I don't have the power output board connected.
The ribbon cable that connects this board to the main board is broken and I don't have a replacement (really all the spares I have were broken too). There is no other choice but to order the spare part and wait for it to arrive.
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| Spare flat cable received |
A few weeks later the part arrives and it looks good. We move on to connecting the final board and testing all. Once connected, I lose the tuning of the rig and the relays of the LPF filters neither are working. Possibly the chip that controls these relays is defective. It is a JRC NJU3714G that has broken down.
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| JRC NJU3714G with LPF relays |
This component is obsolete and not easy to get. Fortunately, in the box of scrapping boards I found an output board with this component. Very carefully, I desolder it and solder it again on the board. Once turned on and tested it seems to work perfectly. We are getting lucky.
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| Chip fitted |
Finally, it seems that the meter measures a very high SWR and I cannot adjust the rig using the service menu. However there is no SWR, nor does the SWR circuit measure anything, it seems to be a problem with the flat cable that connects the control board with the main board.
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| Repair testing |
Once I replaced the flat cable, I have my 5W output and I can now finish the service menu settings.
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| Testing with Service Monitor |
Now it's time to make the modification of the lithium battery. In this modification I installed a 2.5Ah lipo battery and a BMS. The BMS must be modified by changing the sensing resistance so that it does not power off when supplying 2.5A at high power. In addition, I use greater section cables to connect it. Another part of the modification is to use the HP/SP switch to disconnect the battery. The FT817 draws about 16mA at idle, so the battery must be unplugged when not in use or it will be drained. Also, the modification replaced a diode with a 2.3A SMD fuse (only for the old FT-817 models that do not have it) and eliminated a transistor so that the equipment thinks that it is always battery powered. The battery is charged with an external charger by connecting it to the rear power input.
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| 2.5Ah Battery |
Once the modification is done, only stereo headphones will be used in the headphone jack. In addition, 13.8V cannot be inserted into the rear power input because it is directly connected to the BMS and can cause problems. If it is connected to 13.8V through a resistor that dissipates the voltage difference (12.8 vs 13.8), there will be no problem and the battery will be charged.
Therefore, this modification is not for everyone, it has worked very well for me, but you have to know what you are doing.
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| New rubber buttons ready to change |
Once the modification was made and the equipment tested, we finally got it working. However the "F" rubber button is broken. We are going to replace it, I already ordered a spare "gummy" a long time ago, so I have it ready to change.
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| Changing rubber |
Finally, the equipment is ready for use. Congratulations!!
