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Thread: Looking for a VCO for an R 2600 B

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    KootComm No Longer Registered

    Default Looking for a VCO for an R 2600 B

    Hi,
    I am desperately looking for a VCO for a Moto R 2600B service monitor. It has a tracking generator and the VCO has failed. Any suggestions for repair or replacement would be greatly appreciated. Thank you in advance!


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    I have them, Please PM me.

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    KootComm No Longer Registered

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    Great Thanks

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    Quote Originally Posted by KootComm View Post
    Hi,
    I am desperately looking for a VCO for a Moto R 2600B service monitor. It has a tracking generator and the VCO has failed. Any suggestions for repair or replacement would be greatly appreciated. Thank you in advance!

    All of the R2600 and r2550 have the tracking gen hardware installed.

    Which VCO failed ? The Spectrum Analyzer just used discrete components for the VCO on that board.

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    I am also having weird problems with the tracking gen function on an R-2670. It shows a drop-off in level at about every 10 MHz. For example, a 10 MHz window shows the level fine at 0db on the left half of the display, then at the 0 point (center) it starts dropping off in level until the right side of the screen where the level drops off to nothing. Bottom line is what should be a flat-line display at 0 db instead gets a repeating pattern of drop-offs to -80 or whatever the bottom of the scale is, repeating every 1 or 10 MHz.

    I have service manual, but of course they are completely useless.

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    Quote Originally Posted by Alpha View Post
    I am also having weird problems with the tracking gen function on an R-2670. It shows a drop-off in level at about every 10 MHz. For example, a 10 MHz window shows the level fine at 0db on the left half of the display, then at the 0 point (center) it starts dropping off in level until the right side of the screen where the level drops off to nothing. Bottom line is what should be a flat-line display at 0 db instead gets a repeating pattern of drop-offs to -80 or whatever the bottom of the scale is, repeating every 1 or 10 MHz.

    I have service manual, but of course they are completely useless.
    The R2600 series "stitched" together the spectrum and tracking generator screens on scan widths needing more than the 10Mhz from what I can tell.

    This is why you get a sawtooth effect on greater than 10mhz tracking widths into a jumper.

    Sounds like you want to check the SA module track output to see if you have a consistent level from 284 to 294 with and external spectrum analyzer. Problem may be further into the generator area but that would be where I would start. You could also substitute the SA track output with an external 284-294 generator and see if the level drops off.

    The 2670 should be using the later version C or D version boards which has some components updates but still the same basic design in the RF section.

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    Quote Originally Posted by jry View Post
    The R2600 series "stitched" together the spectrum and tracking generator screens on scan widths needing more than the 10Mhz from what I can tell.

    This is why you get a sawtooth effect on greater than 10mhz tracking widths into a jumper.

    Sounds like you want to check the SA module track output to see if you have a consistent level from 284 to 294 with and external spectrum analyzer. Problem may be further into the generator area but that would be where I would start. You could also substitute the SA track output with an external 284-294 generator and see if the level drops off.

    The 2670 should be using the later version C or D version boards which has some components updates but still the same basic design in the RF section.
    OK, that makes sense, I kind of figured the repeating effect was due to re-use of a converting frequency block, and that it was contained into something that repeatedly sweeps 10 MHz segments.

    Where would I pick up the measurement for the 284-294, can you refer a jack, jumper or test point? I have plenty of SMA "T" and attenuators, and a 7L14 with Tracking gen (TR502) to test with. Since the one in the R2670 is busted, I have been using that setup for my tracking gen needs but I'd like to get the service monitor fixed.

    I guess the crux of troubleshooting this depends on whether the fault lies with the genertor or the recevier.

    Also is there any service documentation around that has schematics or anything actually useful in it?

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    Quote Originally Posted by Alpha View Post
    OK, that makes sense, I kind of figured the repeating effect was due to re-use of a converting frequency block, and that it was contained into something that repeatedly sweeps 10 MHz segments.

    Where would I pick up the measurement for the 284-294, can you refer a jack, jumper or test point? I have plenty of SMA "T" and attenuators, and a 7L14 with Tracking gen (TR502) to test with. Since the one in the R2670 is busted, I have been using that setup for my tracking gen needs but I'd like to get the service monitor fixed.

    I guess the crux of troubleshooting this depends on whether the fault lies with the genertor or the recevier.

    Also is there any service documentation around that has schematics or anything actually useful in it?

    The SA LO out to the generator for tracking is on the SA module J2,

    A quick test would be to just verify that the SA level is consistent across the 10Mhz scan ...use an external signal at say 100Mhz -20dbm or a radio station and vary the center frequency from 95 to 105Mhz and make sure the level stays at -20dbm + or - 2 db at most. If the level is consistent across the 10Mhz than the issue is in the generator section and not the SA module. To be absolutely sure you would still want to measure the output at J2 since a bad connection could be causing the problem internally

    The same VCO is used for both the tracking gen and SA internally.

    The manuals for the 2600 series are around and have full schematics.

    Believe General Dynamics has the D version available ...display and display interface were updated/ changed from the "C" vintage EGA CRT to TFT panel and VGA

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    Just a quick update.
    There is one active stage different between the VCO and the tracking gen output on the SA moudule.
    Just a MAR-3 broadband and it's associated current limiter.
    So the short version is verify that the SA response is flat across a 10Mhz scan on standard receive and if that is correct verify the output at J2 is flat as well.
    The SA module J2 tracking output is always there ...tracking gen output feature is switched on later in the gen path