HF transceiver – Yaesu FT-990

Yaesu FT-990
This HF rig is over ten years old and the little brother of the FT-1000D with many of the same features and same quality of build. Inside, you find the circuit boards are cards connected to a motherboard and have excellent shielding. It is an excellent transceiver and I was lucky enough to buy it from someone who has looked after it well.

The rig has good s/n and is armed with wide and narrow SSB filters, IF shift, and DSP on receive. The transmitted audio can also be frequency tailored to enhance base or treble.

 

Lights on but no-one at home
Unfortunately soon after buying the rig, it developed a problem which is best described as ‘lights on but no-one at home!’. On switching on, the s-meter backlight is lit but nothing shows on the LCD panel or any of the LEDs. The only sign of life is the degree of hiss from the speaker when turning the AF gain.

Investigation
Harry Leeming G3LLL, told me that he’d had very few FT-990s to see as they had a reputation for being well built and very reliable. He did think he had seen one case of these symptoms before however and thought he had to replace the voltage regulator.

Turn the transceiver upside down (resting on its head!) and remove the base panel – there are about 8 or more screws. You might need to loosen the side screws too (including the carrying handle screws) otherwise it is quite difficult to get the base off.

With the transceiver front facing you, you will see the motherboard to the left and two-thirds along its right edge you will find connector JP9111 which is the power supply from the voltage regulator board.

From front to back you will find connections:-
6. white ALC
5. white Ground
4. white +5v
3. black +13.8v
2. white +12v
1. white -12v

Unplug this connector and switch the transceiver on. Check the DC voltages pin by pin. In my case, I found no +5v present.

Following the power supply leads you will find the voltage regulator is mounted on the internal facing side of the power supply and rather difficult to get at! The 5v regulator is seen on the bottom edge of the voltage supply board and is the IC on the right. It should be marked HA17805P and is a positive fixed 5v regulator with a max load of 1A and 15w power dissipation. I found by nudging it with a plastic stick, the transceiver burst into life!

After a few of these incidents I decided it was time to replace the regulator. I found a direct replacement was unavailable and replaced it with a cheap L7805 with the same spec.

5v Regulator Replacement
Remove the 4 securing screws for the power supply/voltage regulator block. There are two screws fixing to the front chassis and one screw on each side also fixing to the chassis. There are another 2 screws on each side which can be left in place, they keep the sides of the power supply box on. Having done this, the ‘block’ should lift out vertically but with lots of connections to move first!
Yaesu FT-990 viewed from base

1) You will see a group on wires going to the front panel area which are taped to the right hand corner. Remove the cable tie and carefully move these out of the way. You will find that most of them (4 one of which is blue) plug into the voltage board itself. Ease this connector out from the board and remember the blue wire is the one furthest away.

2) Unscrew the thick red and black cables going to the edge of the voltage regulator board. Note which way around red and black are and which are marked “input” from inside the power supply and the other ones which shoot off behind the motherboard. From the left it should be (input) black – red, (other) red – black. Also disconnect the large plastic connector from the left hand side of the thick cables.

3) You will see two more cable ties to the back of the voltage regulator which need to be removed to provide enough room for the ‘block’ to be pulled out.

4) In the photo above, I have shown which cable ties I removed by using green replacement cable ties.

Once the ‘block’ can move freely, it is possible to remove the 4 side screws which secure the regulator board to the ‘block’. Having done this, I let the block back into position and was able to unsolder the regulator and unclip it from the metal screen side which forms a heatsink for it.

The new regulator was put in place with fresh heatsink paste and reclipped to the screen before resoldering.
Voltage regulator board solder side

Everything was put back in place in reverse order.

I have documented this fix in case anyone finds they are in a similar position and hope this is of some help. Please be aware that I accept no responsibility for the accuracy of my notes so please take all the usual sensible precautions and good luck!

Last updated: 30th August 2008