Author Topic: RCI2950 (1st gen) No PLL adjustment at VC1?  (Read 3234 times)

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Offline KK4MSA

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RCI2950 (1st gen) No PLL adjustment at VC1?
« on: November 14, 2016, 11:53:10 PM »
Hello everyone, i have a old 2950 here, works, but had a few problems, so was going to go thru the alignment. started with the PLL, and got to step 3 adjusting for 10.240mhz. the adjustment is VC1, it makes no change in the freq sampled from L61 as instructed. I took VC1 out, and checked it on my lcr meter, print says its a 20pf, and it will adjust a little beyond that, so its working. now the counter is showing 10.240-10.250, what makes it change is turning the radio over or touching the case, i have checked all the grounds on the radio and there all soldered and all screws are tight. but there seems to be something up with the grounding i think, i can not clip ground lead to chassis as it will not settle, meaning it fluctuates quite a bit, i ground it to the incoming 13.8 line and its fine. the coil that comes off the positive and negative to pcb, looks like it has been hot once or twice, there is a little black on it, could that be an issue, if so what can i replace it with, i have quite a few old radios here with similar components from incoming power to pcb.
akso i can touch the case of the radio and the 10.240 will change when i touch the case. i have never had one have an issue with the alignment on the PLL. has anyone else had this issue? I assume the crystal is good as im am seeing 10.240 up to 10.250, i just have no adjustment on vc1.
any ideas?

Justin

Offline KK4MSA

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Re: RCI2950 (1st gen) No PLL adjustment at VC1?
« Reply #1 on: November 15, 2016, 03:03:40 AM »
figured this out, there are several small caps to ground off of ic7, there were 2 disc caps that were bad from vc1 and the xtal to grnd, 22pf and 33pf replaced and now i have adjustment..  :)

Offline The Radio Shop

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Re: RCI2950 (1st gen) No PLL adjustment at VC1?
« Reply #2 on: November 15, 2016, 05:00:07 AM »
Great Deal,
Don't you love it when you ask a question then find the answer to it? I do that a lot in my repairs.
Also welcome to the forums.
Buddy kc4umo

Offline KK4MSA

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Re: RCI2950 (1st gen) No PLL adjustment at VC1?
« Reply #3 on: November 15, 2016, 11:23:14 PM »
Yes  lol i get frustrated when i cant fix things. i have a little trouble reading schematics, meaning, i always end up chasing in the wrong direction, i cant seem to follow in the right direction for some reason, and some of those things are a little difficult to read to say the least. lol 
and yes, i didnt know you had this forum, so i signed up as soon as i found out, i hope to catch you on 40 soon, tower came down a couple years ago, so i dont have height, but i did put the 1/2 wave up at about 20' apex, so should be good enough for our distance. i did have up an NVIS for local that i got out of a early 70's 73 mag, it was called a " a super-gain antenna for 40m" was only 7' off the ground and boy did it work, had 3 80' reflectors, one under the driven and 1 6' on each side, man did that thing work, was good for about 700m in the day and out about 1100 or so at night and cut out all that shortwave junk in the am section. anyway, im sure ill have more questions as im always screwing up something over here lol  hope all is well with you Bud...73
KK4MSA

Offline The Radio Shop

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Re: RCI2950 (1st gen) No PLL adjustment at VC1?
« Reply #4 on: November 16, 2016, 07:12:05 AM »
don't worry Justin, that schematic is a bit of a mess. Some can be hard to follow along.  But keep at it and soon you will learn the steps through them. This is where the block diagram helps to keep you in the right direction.

I lost my ButterNut during Mathew. Still have the HyGain DXX6 up. And of course all the wire dipoles. We need to set up a time and give it a try on 40 meters sometimes. I am in the shop on Saturday mornings quite a bit.
Buddy kc4umo