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Cobra 138xlr alignment
- Thread starter zinger827
- Start date
B
BOOTY MONSTER
Guest
you need a lot of high dollar equipment to do an alignment . a lot of the "techs" that work on radios dont have the equipment to do it or even have the knowledge to operate the equipment even if they did . id suggest sending to a competent tech with the correct equipment and knowledge to operate it . heres some suggestions......
http://www.firecommunications.com/
http://www.dtbradio.com/
http://www.sparkyscbshack.com/home.html
http://www.firecommunications.com/
http://www.dtbradio.com/
http://www.sparkyscbshack.com/home.html
you will need a frequency counter that has a BNC connector on the front, and a set of clip leads that have a male BNC on one end.
you also need to know that the counter is accurate, otherwise whats the point!
if you plan on doing this type of stuff in the future, go ahead and buy one; they can be had for about 120.00 on ebay. buy a new one.
ok, so you have a frequency counter and some clip leads.
first turn the radio on, and let it sit for about 30 minutes to make sure it is good and warmed up. (also let the freq. counter warm up)
set the radio to channel 19, AM mode, and make sure the clarifier knob is directly in the center position. (do not bump or move it during the alignment)
clip the negative lead to PC board ground. there are usually a few jumper wires running between two tuning cans that make a convenient place to clip this lead.
if not, just find a place to clip it that is connected to PC board ground. (by PC board ground, i mean that big circuit trace on the green side of the PC board that seems to run all over the board; NOT the metal chassis of the radio)
now, clip the positive lead to TP8 which is a piece of wire sticking up from the board with a white insulator on it. the top is looped to provide an easy place to clip the test lead.
looking at the radio with the component side up, and the knobs facing you; look inside the area where the PLL chip is and the channel selector connects to. find L16 which is one of the tuning cans. TP8 is just in front of L16 and to the right.
looking at the crystals just to the right of L16, you can see tiny trimmer capacitors next to each crystal. the crystals are for each mode, and the trimmers are what tunes them to freq.
using a plastic tool, adjust CT6 for 34.9850 mhz.
switch to USB mode, and adjust CT4 for 34.9875 mhz.
switch to LSB mode and adjust CT5 for 34.9825 mhz.
while still in LSB mode, key the mic and adjust VR9 for 34.9825 mhz.
there are other things that will put the radio off freq. like that pesky transistor mounted near the front crystal. it gets hot and changes the freq. of the crystal.
it really should be replaced with an NTE152 (along with all the other 2SC1419's in the radio) and mounted to the side chassis wall near the mic connector.
then replace that big resistor behind it with a 56 ohm 5 watt resistor.
for now, just do the alignment, im only telling you this, so you'll have something to try if the alignment doesnt work.
good luck,
LC
you also need to know that the counter is accurate, otherwise whats the point!
if you plan on doing this type of stuff in the future, go ahead and buy one; they can be had for about 120.00 on ebay. buy a new one.
ok, so you have a frequency counter and some clip leads.
first turn the radio on, and let it sit for about 30 minutes to make sure it is good and warmed up. (also let the freq. counter warm up)
set the radio to channel 19, AM mode, and make sure the clarifier knob is directly in the center position. (do not bump or move it during the alignment)
clip the negative lead to PC board ground. there are usually a few jumper wires running between two tuning cans that make a convenient place to clip this lead.
if not, just find a place to clip it that is connected to PC board ground. (by PC board ground, i mean that big circuit trace on the green side of the PC board that seems to run all over the board; NOT the metal chassis of the radio)
now, clip the positive lead to TP8 which is a piece of wire sticking up from the board with a white insulator on it. the top is looped to provide an easy place to clip the test lead.
looking at the radio with the component side up, and the knobs facing you; look inside the area where the PLL chip is and the channel selector connects to. find L16 which is one of the tuning cans. TP8 is just in front of L16 and to the right.
looking at the crystals just to the right of L16, you can see tiny trimmer capacitors next to each crystal. the crystals are for each mode, and the trimmers are what tunes them to freq.
using a plastic tool, adjust CT6 for 34.9850 mhz.
switch to USB mode, and adjust CT4 for 34.9875 mhz.
switch to LSB mode and adjust CT5 for 34.9825 mhz.
while still in LSB mode, key the mic and adjust VR9 for 34.9825 mhz.
there are other things that will put the radio off freq. like that pesky transistor mounted near the front crystal. it gets hot and changes the freq. of the crystal.
it really should be replaced with an NTE152 (along with all the other 2SC1419's in the radio) and mounted to the side chassis wall near the mic connector.
then replace that big resistor behind it with a 56 ohm 5 watt resistor.
for now, just do the alignment, im only telling you this, so you'll have something to try if the alignment doesnt work.
good luck,
LC
B
BOOTY MONSTER
Guest
my bad apparently....... i thought you needed ocoilloscopes tone generators and other stuff for an alignment . thanks for correcting my bad info LC .
booty monster,
your info is not bad info at all.
it is wise, prudent advice.
any tech who runs a business fixing radios should have the things you mentioned.
aligning a cb radio on one's own can be done with a freq. counter, and RF signal generator, a voltmeter, a wattmeter, and some other odds and ends, but thats only for your own equipment.
zinger,
i hope it works for you.
you probably only need to adjust VR9.LOL
LC
your info is not bad info at all.
it is wise, prudent advice.
any tech who runs a business fixing radios should have the things you mentioned.
aligning a cb radio on one's own can be done with a freq. counter, and RF signal generator, a voltmeter, a wattmeter, and some other odds and ends, but thats only for your own equipment.
zinger,
i hope it works for you.
you probably only need to adjust VR9.LOL
LC
is that reading from an external freq. counter?i agree with loosecanoon
vr9 probaly got acidently moved.if it were me think id try that first,remembering
were the orignal position was.but thats just me.is your recieve off freq. also
RX side was great just TX side off. I did that alignment did not help the TX side must need them transistors? I sold radio locally as is and the person said they woud just run on AM since they dont use SSB. Thanks for the help guys.
Old post I know any know how to hook up a galaxy counter to one of these for use with the extra channels the points all the wires get soldered too in this case I know thare are instructions around for the newer 148 and Washington but haven't seen any for this or older 858 based Washington
Biggest reason you won't see this hookup for the 858 SSB radios is the way that radio's PLL jumps around from receive to transmit in AM mode.
Once you have the Galaxy-style counter modified to work with the radio's 7.8 MHz offset frequency you will find that the reading jumps about 3 kHz when you key the mike.
Oops.
The wires that connect to the USB and LSB wires inside the radio won't properly correct the reading when you choose SSB mode. This radio uses a different 'jump' from upper to lower sideband than the newer radios with the 8719-type chip. That's what those counters are programmed to work with properly.
Short answer is you could hook it up to this radio, but the display will usually be wrong.
73
Once you have the Galaxy-style counter modified to work with the radio's 7.8 MHz offset frequency you will find that the reading jumps about 3 kHz when you key the mike.
Oops.
The wires that connect to the USB and LSB wires inside the radio won't properly correct the reading when you choose SSB mode. This radio uses a different 'jump' from upper to lower sideband than the newer radios with the 8719-type chip. That's what those counters are programmed to work with properly.
Short answer is you could hook it up to this radio, but the display will usually be wrong.
73
Well thanks again for a great explanation nomad as I've come to expect from you and our days at CB tricks speaking if that did they bring the forum back up yet? And on the radio mostly wanted to use the counter to quickly navigate the extras we use am mostly here. 26.05.50 to 28.04.50 is a lot of ground to cover with out one but I'd much prefer to not use a coax pass through.
For now you're stuck with the counter that goes inline with the coax.
The only guy I have seen to sell a frequency display for this type radio was Ralph of Backwoods RF. His Fleabay seller name was fasttrack*09, if memory serves.
He figured out a clever way around the frequency-jump problem. But it had two drawbacks. First, it only had five digits. Second, it would not change when you turn the clarifier. As a result, it wasn't really a true frequency display, but more like a five-digit version of the channel display.
Just the same, nobody else has worked out that trick but Ralph, far as I know.
He stopped selling that one a while back. Just checked, and he has nothing listed for sale.
Dern!
73
The only guy I have seen to sell a frequency display for this type radio was Ralph of Backwoods RF. His Fleabay seller name was fasttrack*09, if memory serves.
He figured out a clever way around the frequency-jump problem. But it had two drawbacks. First, it only had five digits. Second, it would not change when you turn the clarifier. As a result, it wasn't really a true frequency display, but more like a five-digit version of the channel display.
Just the same, nobody else has worked out that trick but Ralph, far as I know.
He stopped selling that one a while back. Just checked, and he has nothing listed for sale.
Dern!
73
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