Paragon PLL Out of Lock Fix

From the Ten-Tec Reflector April 15, 1999

This is a common problem with the Paragon I. The cure is to remove the topside shield cover (where the FM adapter goes), take out the major loop PLL board and resolder all of the connections. The problem is usually caused by cold solder joints. There are 4 VCO's on the board, so if you can localize the porblem to one range of frequencies you might be able to resolder the connections in that area only. However, I ended up resoldering everything.

Pressing on the board or flexing it can sometimes cause the problem. Other symptoms are distorted received SSB signals or warbly CW tones.

Also check the VCO for each band. There is a test point at the junction of Q1-C and Q3-C. The test point voltage will range from about 2.8 V to 7.6 V DC from the low to the high end of the VCO range. You can tweak the slugs in the VCO cans to align them. Count the VCO shield cans from left to right when loooking at the board with the rigs front panel facing you. The VCO ranges are a follows:

  1. 22-30 MHz
  2. 14-22 MHz
  3. 7.0-14 MHz
  4. .1-7.0 MHz

VCo's are selected by voltages on connector 90 (left to right 1,2,3,4). Each connector pin will go to 0 V when that VCO is selected. The pins corresponding to the unselected VCO will remain at 5 V.

In some cases you may need to resolder the connections on the minor loop board. This is tedious, because the shield on the bottom of the board has to be unsoldered and removed to get at the connections. If you do this, save yourself a repeat operation by resoldering the entire board.

I found that some of the little transformers, the ones with the ferrite cores and colored wire wound through them, were microphonic when I poked at them. The cure was to flow some clear nail polish into them. Q-dope or epoxy should also work well, provided it can flow into the holes in the core. Some of the aluminum electrolytic capacitors were also microphonic. I replaced them with tantalum types.

Lastly, and maybe you should try this first, some Paragons had a tiny trim pot on U3 on the major loop board. THis pot is sensitive and a small rotation will cause the PLL to go in and out of lock. Adjust the pot for a voltage of 3.2 V at the wiper, or set it to the middle of its lock range. The second thing to try is VCO alignment, but don't be surprised if you have to resolder all of the connections on the board anyway.

I know this sounds like a lot of work, but I had to do it all (I like tinkering anyway). I was rewarded, though. After putting in all of these fixes, my Paragon has been reliably playing sweet tunes again, and I'm keepin' it!

73, Bob WB2VUF


September 4, 2007

Having owned several Paragon {original version} radios and experienced the PLL UNLOCK problems and having repaired several others including my own radio, I have always found that the soldering on the PLL board is thought to be the source of the problems. In actuality, the PC board lands are bare copper and were not tinned immediately after etching. The result is oxidation forming on the lands and pads. Subsequently, the manufacturing process did not include adequate cleaning and thus the solder flow was inadequate, often leaving etching agents and oxidation below the solder. This surfaced as a bad solder connection after a few years.

While many say "touch up" the solder on the PLL boards, this usually is only a temporary fix. The contaminated etching agent and oxidation still remains. The solution is to remove the solder with a vacuum system or solder wick system. Clean and polish the pads with a Dremel buffing wheel and immediately solder tin the pads. Once done, this results in a satisfactory and long term solution to the problem.

73
Bob, K4TAX


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