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Author Topic: Yaesu FT 840  (Read 2255 times)
KC2SPU
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Posts: 9




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« on: September 20, 2017, 04:02:30 PM »

Suddenly...my radio is messing up.
The front display starts flashing, and I lose audio and sometimes my S-meter goes to zero.
After about 30 seconds.....it will stop flashing and everything goes to normal function.
I am thinking that there is a component crapping out on the front end of the receiver.
Any ideas on this radio and what could be causing this to happen  Huh
Thanks
Tom
KC2SPU
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N4ATS
Member

Posts: 1192




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« Reply #1 on: September 21, 2017, 03:29:43 AM »

Display flashing is an unlocked condition with the VCO. When the VCO is unlocked your receive will go to zero or way off is a better term
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KC2SPU
Member

Posts: 9




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« Reply #2 on: September 21, 2017, 05:20:57 AM »

So.....what can I do to fix this problem?
Funny, I worked the radio for an hour last night with no problems.
It seems to be an intermittent thing. Huh
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KC2SPU
Member

Posts: 9




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« Reply #3 on: September 21, 2017, 05:36:41 AM »

I am going to check the solder joints on the VCO-PLL card edge.
 
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N4ATS
Member

Posts: 1192




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« Reply #4 on: September 21, 2017, 06:09:41 AM »

Do an alignment on it. Download the service manual which is free all over the place and complete the PLL alignment procedure for the Local BPF and VCV. Its typical for the 4 trimmer capacitors to become flakey over time from tin issues
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KC2SPU
Member

Posts: 9




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« Reply #5 on: September 21, 2017, 03:10:24 PM »

Thanks
I downloaded the manual.......hope I can figure this out....
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KC2SPU
Member

Posts: 9




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« Reply #6 on: October 27, 2017, 06:14:29 AM »

Well,
I replaced the R2213 resistor and replaced a few caps around the hot spot on the board.
the radio runs a little better but still will do the flashing display crap.
I dont know what to do now......?
any help?
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K4JJL
Member

Posts: 820




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« Reply #7 on: October 27, 2017, 08:23:46 AM »

Well,
I replaced the R2213 resistor and replaced a few caps around the hot spot on the board.
the radio runs a little better but still will do the flashing display crap.
I dont know what to do now......?
any help?

Did you fiddle with the trimmer caps as mentioned earlier?  Corrosion on the wipers can make it act flaky.
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KC2SPU
Member

Posts: 9




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« Reply #8 on: October 29, 2017, 04:44:11 AM »

Well,
I think I will try that next......
Thanks
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KC2SPU
Member

Posts: 9




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« Reply #9 on: November 04, 2017, 02:31:42 PM »

I t is beyond adjustments.......
There must be another component failing.  What to look for in the PLL circuit?
It seems to loose frequency...then recovers, runs fine for a bit...then fails again.
The display does not always flash on and off when it happens.   Huh
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