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Author Topic: problem 10m rig...  (Read 512 times)
KDUV7462
Member

Posts: 32




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« on: April 17, 2010, 10:49:44 PM »

KB3OYZ here...

I have, amongst other things, a president lincoln 10m rig. Several years back, it started acting up, then it started acting up more, and finally was unusable for xmit (receive was always good, still seems to be...)

Last time, I went thru the tech ref alignment procedure, but everything ws spot on, or just a HAIR adjustment of the coil can to get the reading perfect, most were freq measurements.

That was on the main board, all was well. On one of the last steps, this time on the PLL and CPU board... one DC V measurement was seriously low by several volts... I had to almopst max out adjustment on the coil can to bring it back into spec. I finished the aignment procedure, and went BACK thru tyh alignment again, and all was perfect. Closed the lid, and it worked fine after that.

It acted up again a couple years ago, and I put it away. Had gotten a ICOM 718, but it kind of shat the bed, so... now i drag this sick cat back out of the woods. I anticipated going thru the alignment procedure again, to the same effect. Surprise, surprise... I started at the PLL bard again, as that was the problem last time. NONE of the freq readings are good. And worse yet, I cant drag them back into alignment by coil can adjustments!!

Heck, that voltage reading that was the problem last time, is the ONLY thing in spec on that board, LMAO. ANyhoo, my freq counter says 27.100 Mhz when I key up AM unmodulated carrier on 28.000 Mhz.

Staring at the block diagram of the PLL board for divine inspiration, I cannot for the LIFE of me figure out whats connected to all those cans, much less what could be spreading like a virus thru th PLL bard, LMAO. I am watching my patient get progressively worse, lol.

I wrap a test lead around the antenna on a handheld freq counter to take readings, I know thats not lab spec, but, its what I have, you know? inductive readings like that have always worked in the past for me... anyways, I alligator clamp on onto the can thats around the 10.2xx Xtal, and my counter gets a FIRM lock on 10.2xx, like dead nuts.

When I do the same thing on the 22Mh Xtal... I get 21.xxx, and its not a firm lock, its hopping and dancing around like a, well, its just dancing around all thru the 21's, never hitting 22 Mhz.

I was noticing that the 22Mhz Xtal is dancing around about 1Mhz low, AND the 28.000 Mhz AM unmodulated carrier is about 27.1 Mhz...

... and I dont believe in coincidences, eh? I cant flip the PLL board up while its runnign to get a real reading on the suspect Xtal, but, is inductively sniffing it like I am doing good enough to suspect its the problem? The OTHER Xtal gives a firm lock with teh same test.

ANyone who knows more than me care to comment on my hypothesis that resoldering the suspect 22Mhz Xtal will fix it?

I just cant figure why Rx seems okay when the Tx is that far off frew... unless that Xtal only gets mixed for Tx and not Rx...
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KB9JXZ
Member

Posts: 36




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« Reply #1 on: April 18, 2010, 07:14:46 AM »

I am not exactally sure what the problem is but I can tell you that the 22.000 Mhz crystal is used on both the TX and RX. It is the main L.O.
 If you frequency counter is not getting enough RF it will hop around and not give you a good frequency reading. There is test points on the CPU pcb and the main board for frequency measurements.

73,
KB9JXZ
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