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HELP! Service Manual For Cobra 2000GTL??

Discussion in 'General CB Services Discussion' started by Robb, Jul 8, 2009.

  1. Robb

    Robb
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    I'm a'workin on a Cobra 2000GTL for a neighbor. I can't seem to find the service manual so I can adjust the meters and check some test points.

    Anyone know where one may be found? Not the schematic - the service manual - pleez!
    :headbang


     

  2. Quiksilver

    Quiksilver
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    Hopefully these help! You probably already know about these though. Is it the same as the owners manual? If so, I have one to scan.
    Cobra 2000GTL
     
    #2 Quiksilver, Jul 8, 2009
    Last edited: Jul 8, 2009
  3. Robb

    Robb
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    I appreciate that link - Quicksilver.

    But CBTricks doesn't have the service manual.
    I can't find the service manual still.
    Anyone know a link that has it?

    Thanks!
     
  4. Cotton Mouth

    Cotton Mouth
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    I have on here in the shack but that don't do you any good. If you can hold out tell tomorrow I can scan the copies you need and email them to you. I also thought I had it in PDF Form where I could send the file to you but wasn't where I thought it was. I will look for that as well in the mean time. Let me know if tomorrow will work and if so PM me with your email and exactly what your needing out of the service Manual.

    Cotton Mouth.
     
  5. loosecannon

    loosecannon
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    i wrote this out a few years ago on another forum, and i dont have time tonight to proofread it, but i will post it here, and re-read it tomorrow evening to make sure it is right.

    this is from the factory service manual for the 2000GTL, but it should work with the 148gtl, the new grant, the new madison, and the tramD300 among others.if your radio has an MB8719 or MB8734 chip in it and a dual conversion receiver, then this alignment procedure should work for you.

    for any other radio, you will have to find the specific service info for that radio. DO NOT USE THE NUMBERS IN THIS ALIGNMENT TO ALIGN OTHER RADIOS. YOU WILL SEVERELY DAMAGE THE RADIO!
    when looking for sevice info, the internet is your best friend. you can often find the manuals on the auction site for a fair price.
    if the radio is older than say, 10 years, then you should be able to find a SAMS PHOTOFACT for your radio. these were made by the Howard W. sams company. they are no longer made but you can find them around if you look. YOU MUST HAVE THE SERVICE INFO FOR THE RADIO YOU WISH TO ALIGN. DO NOT ATTEMPT THE ALIGNMENT WITHOUT THE SERVICE INFO AND THE TEST EQUIPMENT!

    here we go:
    1. input of frequency counter to TP13 (test point 13) IC1 pin 8.

    radio on ch.19 am. clarifier in center pos. NB and ANL off.

    check for 10.240mhz.
    this means that you will hook the alligator clip rom the shield (-) or the freq. counter and clip it to PC ground. i like to use the tuning cans as they are all grounded. just clip right to the can, or if there is a wire soldered to it, clip to that. make sure the place you clip to is true ground. (connected to the big foil trace) and also make sure you dont use the metal case of the radio or "chassis ground" this is not the same as the PC board ground and will not work.
    now take the probe from the freq. counter and touch the tip to pin 8 of IC 1. look at the freq. counter, it should read 10.240mhz. (if you get no reading and the radio seems to work correctly, then you have either hooked something up wrong or your freq. counter is set wrong or doesnt work.

    2. input of RF voltmeter to TP10

    radio on ch. 19am. clarifier centered.

    adjust L21 for maximum RF out.

    this means that you will clip the negative lead of your RF probe to where you had the freq. counter hooked to and the positive tip will go to TP10 (location found in service manual)
    adjust the can SLOWLY for the maximum voltage. you will notice the volts rise to a point and then start to fall again, go back and forth until you find the peak point and leave the can set there.

    3. input of DC voltmeter to TP9

    radio set on ch. 40am

    adjust L19 for 3.20 volts. check channel 1 for 2.45 volts.

    this means set up the same way as before except dont use the RFprobe and set the can for 3.2 volts and leave it there.

    4.input of RF probe to TP1.

    radio set on ch.19am

    adjust L20 for maximum voltage. (you may have to use the mV setting on the voltmeter for this one.

    this is done the same way as in step 2.

    5. input of freq. counter to TP1.

    radio at ch.1 am

    adjust L23 for 34.7650mhz + or - 20hz (try to get it exact)

    6.input of freq.counter to TP1

    radio at ch.1 USB

    adjust L59 for 34.7665mhz.

    7. input of freq. counter to TP1

    radio at ch.1 LSB

    adjust L22 for 34.7635mhz.

    8. input of freq. counter to TP10

    radio at ch.1am

    check for .790mhz

    9.input of freq. counter to TP3

    radio at ch.19USB

    adjust CT2 for 7.8015mhz

    10. input of freq. counter to TP3

    radio at ch.19LSB

    adjust L30 for 7.798mhz

    11.input of freq. counter to TP14 (IC3 pin 7)

    radio at ch.19 AM TRANSMIT (key mic with no modulation)

    adjust L31 for 7.800mhz.


    12. input of freq. counter to TP15 (FET 1 gate1)

    radio at ch.19am

    check for 7.345mhz.

    13.input of freq counter to antenna input (so-239)

    radio at ch.1 AM TRANSMIT

    adjust VR5 for 26.965mhz.


    thats it for the PLL section.


    so here is the reciever alignment procedure.

    for this you will be using your signal generator.
    make sure you have a .01uf cap in series with the positive test lead.

    to set the s-meter and the squelch; you will need a voltmeter that measures microvolts. i do not have one of these, and therefore, i cannot do an accurate adjustment on these two pots.
    this is where the bench radio comes in handy.
    the bench radio i have has an analog meter on it, and after performing a tune up on a radio, i will find a local with a steady carrier, and match the radio im tuning to the S-meter on the bench set.
    same with the squelch. (you wont need to adjust this ever, unless someone has turned the pot by mistake, and then, its not the most critical adjustment on the radio)
    for this radio, the squelch range is VR3, the AM s meter is VR1, and the SSB meter is VR2.
    YES, i realize that this is not entirely accurate, and i do not claim it to be. if you want it completely perfect, you will have to take it to a tech with a higher quality signal generator.
    you could buy a better one yourself, but i dont feel the need for it, and can always find something else to buy with that ammount of money.(more radios!)

    here we go:
    FOR ALL RECEIVER ADJUSTMENTS: RF GAIN MAX. CLARIFIER AT CENTER, SQUELCH AT MINIMUM, NB OFF, ANL OFF, TONE MAXIMUM CLOCKWISE.
    1. output of signal generator to TP16 (TR15 emitter)
    7.8mhz

    radio at ch.19USB

    adjust L14,12,10,9,8,7 in that order for maximum s meter reading.

    so, set your sig gen at 7.8mhz, clip the negative lead to PC ground, and the positive lead to TP16.
    adjust the output of the sig gen so that the S meter on the radio reads about S-3. (no more)
    slowly turn the coils, starting at L14 and working down. you will notice that they cause the S meter to move up or down as they are turned. turn the coils SLOWLY until you find the peak reading. leave the coil in that position and move on to the next.

    2.output of sig. gen. to TP15 (FET 1 gate 1)
    455khz.

    radio at ch.19AM

    adjust L15,13,3 for max. s-meter reading.
    same as last step.

    3.output of sig. gen. to antenna input
    27.185mhz.

    radio at ch.19AM

    adjust L6,5,4 for max. s-meter reading. readjust L7,8,9,10 for max. in that order.

    i also adjust L1,and L2 at this time. these are the NB coils, and should be adjusted using an oscilloscope and very high quality signal generator.
    at this point, its up to you whether or not to mess with them. if you are doing a tune up on a radio that you know the history of, then there is no need to adjust them. if, however, you happen to be working on a garage sale special that you want to get working; then adjust them for max. s-meter reading using the set up from the previous step. this is how i do it on my radios, and my ear cant tell the difference.

    and finally, the transmitter alignment.

    you should use a dummy load for these tests, if you dont, you will be causing malicious interference, and generally being a jerk. and your results wont be as accurate. dont do it!

    hook up a wattmeter between the radio and the dummy load.
    radio should be on ch.19
    1.radio at ch.19 AM

    key the mic, and say "aaahhhhh" in a steady natural voice tone. using a two tone generator here can be very helpful. there are numerous designs around on the net, and they are simple to build. i use one. do not tune the coils for max. deadkey, as this will weaken the modulation to a great extent, sometimes making the output power actually DECREASE when you are speaking. (downward modulation)
    while speaking into the mic, adjust L47,48,46,45, and L38 in that order for max. peak (modulated) power. on one or more of these coils, you will notice that there is a waxy substance covering the opening. carefully pick this away, and then, right before you make your adjustment, put your soldering iron on the ferrite core for just two seconds. be careful not to melt the plastic threads on the edges. this will allow the core to turn easily. if you dont do this, you can break the core, and then you'll have to scrounge another one from a different radio which may or may not work as well. be careful, dont turn anything fast, and never force anything.

    2.ch.19USB mike gain at minimum.
    adjust VR4 for 0 watts. (no carrier)

    3. ch.19USB mike gain at minimum.
    insert DC ammeter at TP8. (driver bias)
    this means that you need your DC volmeter set to milliamps on a scale that can read 200ma (milliamps).
    this hook up is not the same as voltage testing! when you test for current, you hook the voltmeter in series with the lead under test.
    so, pull the wire off of TP8, and clip the negative lead to the end. touch the positive lead to TP8. key the mic and adjust VR9 for 30ma.
    reconnect the wire to TP8.

    4. ch.19USB mike gain at minimum
    pull wire off of TP7 and clip negative lead of voltmeter to it.
    touch positive lead to TP7.
    key the mic and adjust VR8 for 60ma.
    reconnect the wire to TP7.

    VR11 is your SSB power out. set it wherever you want it. if you are running an amp after the radio, you should set it for no more than 15 watts.
    i set mine at 12 watts.

    VR7 is the mod control in the 148 chassis. in the 2000 chassis its VR12.
    i just set this at max and use the front panel mic again to adjust the modulation. (you wont have to run the mike gain all the way up anymore)
    VR10 is the AM carrier power. this is where people blow up their radios. they say, "wow! how cool! the manufacturer put in an easy adjustment for more power out!" dont be fooled! most radios cant handle the increased wattage for very long when this is turned up.
    if you are running an amp; set this control for 2-3 watts and NO MORE! otherwise you will sound very quiet coming out of your amp, and you may just smoke it!
    if you are running barefoot, then set it for about 5 watts. this is safe, and no one can tell the difference between 5 and 8 watts anyway. your radio will last for a very long time if you keep this control under control. if you get the power bug, you will be buying transistors that are getting more expensive every day.

    finally, adjust VR6 so that the S meter on the radio agrees with the wattmeter.

    well, thats pretty much it, except for the 50 flaming posts ive got coming my way for condoning such cheap and dirty tricks.
    make no bones about it. this is not as accurate as sending your radio to a good tech shop, but if you wanted to do that, you wouldnt have read this far would you!
    good luck, and please feel free to point out any mistakes or bad advice that you see. all quesitons are good questions.


    i will correct any mistakes tomorrow, gotta go for now.
    LC
     
  6. Robb

    Robb
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    wow!

    That's a nice piece of work there - loosecannon!

    Thank U Very much!
     
  7. loosecannon

    loosecannon
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    thanks for the compliment rob.

    a few years ago i had a job that required me to be at a desk for long periods of time with not much to do. (oh how i long for those days now LOL)

    i spent a LOT of time on cb forums and was always getting asked about how to align an 8719 radio, so i just decided to type it up somewhere where i could always get to it.
    i have it as a .doc file on my computer but for some reason i could not open it last night.

    there are a couple of typos, and i forgot my SAMS for the madison that i meant to bring to work with me tonight so i cant correct them yet.

    i will bring it tomorrow for sure.

    the typo im thinking of has to do with the IF (7.8mhz) tuning procedure.
    i think the USB and LSB numbers are off a bit.

    otherwise it should be correct.

    also there is a procedure for tuning the noise blanker coils using just a sig gen and a voltmeter that was shown to me by a galaxy tech that is not in this procedure.

    if you want, just join the yahoo group "the_mod" and look in the files section.

    bunch of great stuff for the 8719 radios in there. also check out the photos section!
    i am a mod there, and if you let me know here that you tried to join, i will go to my email and approve you right away so you can get started.

    good luck,
    let me know what you find on that 2000GTL.
    is there a specific problem it is exhibiting?
    LC
     
  8. Robb

    Robb
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    I appreciate all of the help, guys.

    With the info, I was able to check some of the radios inner settings. Most of them were OK. Someone had previously clipped R131 and turned the deadkey down to 2 watts - I left it alone because he has a 100 watt modulator that he will also hook up to it. I usually re-solder the resistors when I find this mod in any radio I get - but I left it alone in this instance. The squelch needed to be adjusted, and the radio needed a couple of meter lights. The modulation meter and the S/RF meter also needed some adjustment, got that done - too. I think that a couple of the pots may need to be replaced in the future - the clarifier(s) and the squelch. I also had to replace the plug on his external speaker and re-glue the faceplate of his Cobra desk/power mic.
    All done...

    I took it back to the guy, didn't charge anything, I had a couple of lamps laying around anyway. SO - he is happy with it. He needs to get a new piece of coax and put the Antron A99 another 20 feet up. So, I will probably help him do that as well. He also said he was going to give me some stuff that he doesn't use any more. He also said that he needed a few more things fixed as well. So I will give it a shot. He is an older guy, and was raised only thirty miles from my families home in NW Iowa. I think he is in his late 70's and still enjoys talking on the radio.

    I thank you all, and so does my neighbor.
    Thanks LooseCannon, Cotton Mouth, and Quicksilver..

    This thread has also provided what is lacking on the internet. LooseCannon, I appreciate your lengthy dissertation on the Cobra 2000GTL - it was most helpful. If you are going to update the info here, you will be providing the WWRF as the ONLY resource for this radio that I seen on the internet. We should do this more often!

    Great Tech Stuff!!!
     
    #8 Robb, Jul 9, 2009
    Last edited: Jul 9, 2009
  9. Quiksilver

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    Maybe we should sticky that post somehow.
    JMO...
     
  10. loosecannon

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    i will correct the mistakes in the next few days. (i couldnt find my SAMS book today LOL)

    if the mods want to make this a sticky, that is fine with me.

    glad to help,
    LC
     
  11. KB1TPX

    KB1TPX
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    Try this:

    Cobra 2000GTL
     
  12. loosecannon

    loosecannon
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    great downloads buttfuzz!

    that alignment is from volume 28 if im not mistaken.

    just to put it out there for anyone who uses it; the voltage on the VCO adjustment is wrong. adjust the VCO for 3.5 volts on channel 40 and you should be good to go.
    LC
     
  13. 1speeDemon

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    Thanks to one and all from a new member on the help on my Corbra 2000 GTL project.



    1speeDemon
     
  14. Klondike Mike

    Klondike Mike
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