| Author |
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Haymaker
| | Posted on Wednesday, April 30, 2003 - 9:53 pm: | 
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PLL IS UNLOCKED WHAT SHOULD I LOOK FOR? PLUS THE RECIVE IS NOT WORKING.P.S THE RADIO HAS BEEN LIGNED UP TO SPECS,ANY ADVISE WOULD DE HELPFULL. |
307
| | Posted on Thursday, May 01, 2003 - 7:20 am: |
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If the PLL is unlocked , you can only tell with a scope because of the "pulsing" , you may check to see if the 10.240 Reference Crystal is working...Common problem...
307 |
2600
| | Posted on Friday, May 02, 2003 - 2:35 am: |
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The 10.240 MHz crystal used in dozens of RCI-made radios that use the MC145106 PLL is not terribly reliable. Some time in the last 5 or 6 years I think RCI bought a large batch of these crystals from a super-low bidder. It got me in the habit of buying them 50 at a time (elsewhere, not from RCI).
It tends to be an "on again, off again" failure. Touching the soldering iron to the crystal's leads under the board will sometimes "shock" the thing into running again, but only for a while.
The only real way to check this is with a scope. Even then, I have seen an entirely WRONG frequency right there on pins 3 and 4 of the PLL. Looked okay on the scope screen, though. Just wouln't lock-in onto a channel.
Swapping it for a new one is more cost-effective than a lot of squinting at a scope screen or head-scratching. Pulling a used part from a derelict radio may be a bad risk if the derelict has the same markings as the crystal in the 99. If the derelict radio was made by Uniden, the part is probably good.
Yeah, there are lots of other possible causes, but this one keeps popping up. Odds alone favor it. A peek with a scope would tell you more.
73 |
Tech671
| | Posted on Friday, May 02, 2003 - 5:30 am: |
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Commonly too is cold joint in the area of the PLL, more commonly around the 10.240. On the solder side radio facing you look to the right edge. There's a ground plate soldered to the board. Lifting that plate and touching up joints in that area can be a common fix. |
Haymaker
| | Posted on Friday, May 02, 2003 - 11:55 pm: |
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2600&671 thanks for the info.i tryed a new 10.240 & touched up the board. the radio will change channels 1-22,and then drops off freq.I ALSO PUT A NEW PLL IN THE RADIO&STILL THE SAME.I CANNOT GET ANY ADJ.ON L17 NOR CAN I GET ANY ADJ ON THE 10.695 OFFSETS VERRY LITTEL.WHAT KIND OF SCOPE DO I NEED OSCILLOSCOPE? OR A AF VTVM ? |
2600
| | Posted on Saturday, May 03, 2003 - 1:47 am: |
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The PLL chip used in this radio ALMOST never fails. They have made so many of them, defects are truly rare. The list of things to check when a radio just "drops out" at one frequency is long enough, I'm gonna dodge it for now.
Nearly any DC-coupled scope will tell you a lot about what is going on in this kind of PLL. A scope rated for 20 MHz or higher is better, but not absolutely necessary. A "Times ten" or "attenuator" or "Ten to one" probe really IS a necessity, regardless of the scope you use. A direct probe will disturb many of the circuits in a radio like this when you touch it to a test point.
Sounds like a copy of Lou Franklin's "Understanding and Repairing CB Radios" would be a good place to start. He explains this stuff pretty well. He sells that book and another good one called "The Screwdriver Expert's Guide" at www.cbcintl.com
Speaking of screwdriver experts, how many of them were in this radio before you saw it? If three of them left one small boo-boo apiece in the radio, that's not the same as "It ran fine until one day it quit".
If someone else would like to describe checking/setting the VCO tuning coil/tuning voltage, please jump right in. I've got customers coming in the morning, so I won't right now.
I'll check back in later in the weekend. PLL problems can frustrate an experienced tech. When any one part of a PLL is disturbed, the whole thing unlocks and shuts down, giving you very little to measure and analyze.
73 |
Haymaker
| | Posted on Saturday, May 03, 2003 - 10:57 am: |
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2600 I GOT THIS AND A COUPLE MORE RADIOS FROM A FRIEND ON THE RADIO AND HAD NO PROBLEM,S REPAIRING THIEM,EXCEPT THIS ONE. THIS RADIO WAS NOT WORKING AT ALL WHEN IT CAME IN.THE GUY THAT WORKED ON IT LAST HAD DONE SOME THINGS TO THE RADIO I COULD NOT BELEIVE.I HAVE HAD THE RADIO LINED UP TO SPECS BUT IT JUST WOULD NOT WORK RIGHT.IVE HAVE WORKED ON 5 OF THIS SCREWDRIVER EXPERT,S MESSUP,S I WILL .NOT MESS WITH A NOTHER ONE THAT HE HAS TINKERED WITH TOO MUCH HASSEL THANKS FOR THE REPLY. |
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