How to fix the frequency drift of the Yaesu FT-890 / FT-840

Update 2018-03-19 - I don't own the FT-890 any more, neither do I have any of the circuit diagrams or the service manual, so I probably cannot help with any questions that go beyond what is covered here.

Update 2006-07-20 - The same problem exists with the Yaesu FT-840 and it can be fixed in the same manner. TNX info KU5B.

I am using the FT-890 for several years now and I have always been very pleased with this small but well performing radio except for one problem: heavy QRH sometimes occurs a few minutes after switching the RIG on. At the beginning it only drifted away a few Hz and jumped back to the correct frequency, later it got worse and the RX even switched off and the display started to blink.

After some trouble-shooting I found out that a trimmer cap (TC 1002) which is in series to the reference-frequency-oscillator XTAL was faulty. Since my abilities in SMD-soldering are very limited, I tried to 'repair' the trimmer by just turning it around a few times and succeeded. For several months I experienced no more trouble with frequency-stability.

The "repair" is very easy, only takes 10 minutes and all you need is a screwdriver. Upon several requests I quickly put this page together to show the whole process in detail. All pictures can be enlarged by clicking on the thumbnails.

See text Step 1

Disconnect all cables (power supply, keyer ..) from the transceiver and place it on a plane and clean surface.

See text Step 2

Place the transceiver upside down, with the frontpanel showing into your direction. Remove the eight screws of the lower part of the chassis.

See text Step 3

Remove the lower part of the chassis.

See text Step 4

Locate the blue coaxial connector (with grey coaxial cable) in the upper right corner of the board and pull it out.

See text Step 5

Now turn the transceiver around, with the backside of the transceiver pointing towards to you and remove the 4 screws of the chassis.

See text Step 6

After you have removed the screws, turn the transceiver on it's right side (as seen from the backside).

See text Step 7

After pulling the two parts of the radio ca. 2cm apart, you can fold over the right side as shown in the picture. Take care that the coaxial-cable that you removed earlier doesn't get stuck anywhere.

See text Step 8

After you have 'unfolded' the transceiver, remove the yellow tape which is fixing the bunch of cables running across the shielding ..

See text Step 9

Then remove the 4 screws of the shielding ...

See text Step 10

.. and remove it carefully without damaging any wires.

See text Step 11

You now see the LOCAL UNIT which contains the reference oscillator in the box shown.

See text Step 12

After opening the box you will see a the XTAL, a few resistors and capacitors and the trimmer TC1002.

See text Step 13

Now simply turn around the trimmer a few times. Remember in which position it was before you started turning it and turn it to the same position in the end!

See text Step 14

That's it. Now reasseble the box containing the reference osc, then replace the shielding with 4 screws.

See text Step 15

'Fold' the two parts of the transceiver together again, be careful not to damage any wires. Don't forget to put the coaxial cable which you disconnected earlier in place!

See text Step 16

Mount the upper part of the chassis with 4 screws.

See text Step 17

Turn the transceiver around and put the coaxial cable back into it's original position....

See text Step 18

Mount the last part of the chassis. Be carefull not to damage the white ribbon cable.

See text Step 19

That's it! Enjoy your FT-890.

After this 'repair' no more QRH occured on my FT-890. I have heard from several other HAMs who could solve the problem in the same way. Of course it would be better to replace the faulty trimmer (update 2005: I did it, because after 3 years the drift came back), but this works just as fine.

Fabian KurzHam RadioFT-890
Created: 18-Sept-2002 - last changed Monday, 19-Mar-2018 12:45:47 CET - Author: Fabian Kurz, DJ1YFK <<,