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Author Topic: kenwood 520 dies after 15-20 minutes  (Read 1334 times)
KC9VZB
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Posts: 45




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« on: December 24, 2012, 06:03:34 AM »

thanks for all your help,I got a dummy load and got antenna matching very close.replaced all 3 tubes,and neutralized finals.Replaced hv cap feeding finals.set now puts out 100+ watts and getting good reports yea!After a good while of listening and butting in all output dies,didn't think to look at high voltage.I'll do that next.    my suspicion is out put transistor on rf board I think it was #10.thought I might find a glue on heat sink for fun,but then will that act like an antenna?  Just what is the bad thing that happens when transmitter is keyed with no antenna .set came from ebay.
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KC9VZB
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« Reply #1 on: December 24, 2012, 07:31:18 AM »

Ok,I warmed it up and hv is ok when dead.another clue,it shows power in tune and cw. dead in sideband only,time for more reading.
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N4NYY
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« Reply #2 on: December 24, 2012, 07:33:23 AM »

Can that mode switch be Deoxit-ed?
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KC9VZB
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Posts: 45




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« Reply #3 on: December 24, 2012, 07:56:44 AM »

easy enough to look I got some,and all the screws are out.
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AC2EU
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« Reply #4 on: December 24, 2012, 08:46:52 AM »

If you get full power in CW key down, then your PA is fine. Your problems may be back in the balanced modulator/SSB circuits.
Are both upper and lower sideband affected?

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KC9VZB
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« Reply #5 on: December 24, 2012, 09:00:38 AM »

yup both upper and lower
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G3RZP
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Posts: 4497




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« Reply #6 on: December 24, 2012, 09:36:50 AM »

Check the carrier oscillator - some rigs have one osc for CW and one for the two sidebands. It's possible that the crystal or oscillator has died. Or there's a bad joint or component.
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WA1RNE
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Posts: 825




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« Reply #7 on: December 24, 2012, 09:59:36 AM »

Quote
another clue,it shows power in tune and cw. dead in sideband only

Could be a lot of things, including audio starting from the mic.
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G3RZP
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Posts: 4497




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« Reply #8 on: December 24, 2012, 11:02:48 AM »

I got caught out with my FT102 CW crystal osc. Very slow starting so I would actually send RQ CQ CQ........I increased the current in the FET and that cured it. But solder sealed xtals do lose activity over the years as well as drifting in frequency.
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