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Old 20th Aug 2018, 11:55 am   #1
hamsterman
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Default Yaesu FT480R faulty

My trusty FT480R of many years has suddenly stopped working. Although the display lights up and the digits change as you tune and there is noise out the speaker, it won't receive any signals or produce any power output.

This really smacks of the LO not functioning confirmed by lack of any ~133Mhz present when I "sniff" with my scanner. The LO is a complex 3 VCO system and as far as I can tell perhaps 2 of the 3 are functioning.

Perhaps someone has seen this fault and can short circuit my fault finding for me?

Regards
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Old 20th Aug 2018, 1:27 pm   #2
orbanp1
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Default Re: Yaesu FT480R faulty

You can download the service manual from here:
https://www.manualslib.com/download/...u-Ft-480r.html
It has a detailed "fault tree", a troubleshooting flow chart.
I guess you need to go through that.

Good luck, Peter
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Old 20th Aug 2018, 1:33 pm   #3
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Default Re: Yaesu FT480R faulty

Japanese rigs of this period had problems with trimmer capacitors being rotted by the gunge they poured around to stop microphony.

A complex synthesiser is just a lot of simple circuits flying in close formation. Your approach of finding which loops are running and on frequency with a receiver is a very good starting point. You'll likely come to the point where a scope is needed.

My old FT480's kicking around in the shack. I don't think it's seen power in 10 years. Must give it a try. Quite nice radios.

David
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Old 20th Aug 2018, 5:22 pm   #4
hamsterman
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Default Re: Yaesu FT480R faulty

Quote:
Originally Posted by orbanp1 View Post
You can download the service manual from here:
https://www.manualslib.com/download/...u-Ft-480r.html
It has a detailed "fault tree", a troubleshooting flow chart.
I guess you need to go through that.
I have the manual etc Peter so no troubles there thanks. It seems the LO buffer stage has no power to it maybe because the out of lock ccts are faulty. But the preceding stage should still be heard on my scanner unless it really is out of lock!!
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Old 20th Aug 2018, 9:46 pm   #5
Steve G4WCS
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Default Re: Yaesu FT480R faulty

I’d check all the voltage rails round the circuitry are in tolerance. If it's anything like the Kenwood I've just brought back to life there is a lot of electrolytic cap decoupling and they go out of spec.
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Old 23rd Aug 2018, 10:00 am   #6
hamsterman
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Default Re: Yaesu FT480R faulty

I checked the 3 PLL voltages against the manual and they were quite far out so I have reset them all to the values stated and it all seems to be 100% again. Quite why they were all so far out though remains a mystery.
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Old 3rd Nov 2018, 6:16 pm   #7
hamsterman
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Default Re: Yaesu FT480R faulty

Quote:
Originally Posted by Radio Wrangler View Post
Japanese rigs of this period had problems with trimmer capacitors being rotted by the gunge they poured around to stop microphony.

A complex synthesiser is just a lot of simple circuits flying in close formation. Your approach of finding which loops are running and on frequency with a receiver is a very good starting point. You'll likely come to the point where a scope is needed.

My old FT480's kicking around in the shack. I don't think it's seen power in 10 years. Must give it a try. Quite nice radios.

David
I reset all the PLL voltages as they were far out and it then it came to life but its failed again after a couple of months. This time the VCO tuning voltage is sitting at 7.12 volts and nothing I do seems to cure that. I have had a poke about with the scope on the PLL chip which drives this voltage and although it has inputs from the other synths. which are all okay it seems to produce little or no output.
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