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Author Topic: Sick FT-840 -- blink, blink, blink display?  (Read 5446 times)
W1CEW
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« on: August 20, 2005, 07:26:48 AM »

Just got it today, and I knew it had problems.  I don't see anywhere in the documentation what it means when the entire display goes in blink blink mode and stops receiving...?  

Seems I can "reset" it by pulling the power and letting it sit for a while, so it is perhaps a CPU seizure of some sort?

Thanks for any suggestions,

Chuck
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N3ZKP
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Posts: 2008




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« Reply #1 on: August 21, 2005, 05:55:09 PM »

Have you done a master CPU reset? The manual should have the instructions.

73,

Lon - N3ZKP
Baltimore, Maryland
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M1FRH
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« Reply #2 on: August 23, 2005, 03:01:13 AM »

hi  i had the same problem with my ft-840 recently...turn radio on and after about a minute the display would flash then loose audio then come back again then flash and go off again....itried the full reset but this didnt cure the problem....after taking it apart and doing some tests i found that the tcxo board that pushes onto the main bourd via 4 pins was the problem...the tcxo board was fine when tried in another ft-840....but when investigating the 4 pins i found that there were 2 that had worked loose....after taking all the plugs from the board and releasing about 5 screws that hold the board down to the chassis i was able to resolder these joints on the pins....taken me about an hour in total to do..after reassemble of the rig switched on and everything worked fine.....hope this helps    cheers from frank M1FRH
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N4ZAW
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« Reply #3 on: November 26, 2012, 10:19:32 AM »

I know this thread is ancient, but because this is a common fault with the 840, I thought I would add my two cents, Just in case anyone else has had this problem;
The blinking display would indicate it has no data supply to the VCO or DDS circuits. These radios have two voltage regulator IC's mounted on a small PC board, which plugs into the local board near the audio output ic. They are Q2901 (a 5V regulator ic ) and Q2902, (a 9volt regulator ic).

The 9Volt ic can outright FAIL, but this board is 'free-floating' -- simply "plugged-into" the local pcb much like the option boards are, pin-n-socket style while the IC's themselves are heat-sunk to the base of the chassis. Vibration can provide a lot of "fun" little quirks here. The main problem is that the soldered pads on the PC are subject to break if the rig was banged-around a lot, or causing this sub-board's pins to lose contact... And to think, they actually made (and sold a boat load of) mobile mounting kits for the 840.. LOL.
IC replacement tip: Mount the new ic's WITHOUT soldering them to the pc board. Mount the ic board into the local board, then mount the IC's to the chassis using heatsink compound -- THEN solder the ic legs to their board. This way, no "pre-stress" is placed on the connections when it is buttoned-down....... Found this out the hard way.

Happy hunting.
 
« Last Edit: November 26, 2012, 10:31:33 AM by N4ZAW » Logged
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