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8562EC A14 U429B wrong ref voltage

Question asked by marc1 on Mar 26, 2015
Latest reply on Aug 25, 2016 by minolta1

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This 8562EC had err 334, 356, 317, 319. I tracked down to U429B on the A14 board and found the inputs of the op amp are at -3mV and -8mV and the output is at 0.5V. According to the attached diagram the ref voltage at the input should be at -0.1 to -0.25V on pin 5 of U429B. I was wondering if anyone knows how to debug this issue. Which DAC to look for and etc..?

Also, where could I get the schematic for this spec?

Thank you!

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LODA.tiff143.8 KB

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hedgehog Mar 26, 2015 3:21 PM
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It might be the case that YTO has failed. You might want to measure the YTO output (set spectrum analyzer to zero-span).
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- marc1 @ hedgehog on Mar 26, 2015 8:30 PM
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  I haven't measured the YTO output yet. However, I sort of verified the output of the LODA is present. What I did was connecting a 680k resistor between -10v to pin 5 of U429B. This brought pin 5 to -0.14v. Pin 6 was measured to be -0.14v as well and this is the peak detector output of LODA. Therefore, YTO and LODA should be working if above observed.
  
  It seems that it is either a fail DAC or something along that path is problematic.
  
  Your input will be appreciated.
  
  Thanks!
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  - hedgehog @ marc1 on Mar 27, 2015 6:08 PM
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    It seems that the LO amplitude sensing segment is problematic. Do you have the complete schematic/service documentation available?
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    - marc1 @ hedgehog on Mar 27, 2015 6:17 PM
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      I only have the service guide and I can't find the schematic anywhere online. If you have one, it would be great if you can share with me.
      
      I also measured the 600MHz ref and it looks right.
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      - hedgehog @ marc1 on Mar 27, 2015 9:08 PM
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        I found a schematic of A14 board on this forum. I would still recommend you to monitor the YTO output with another spectrum analyzer, to see if intermittent problem exists.
        Attachments
        08564-60014.pdf4.0 MB
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        marc1 @ hedgehog on Mar 28, 2015 11:17 PM
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        Thanks for sharing. This CLIP seems to be the 8564 A14. It's kinda different from 8562EC. But thanks anyways. I am going to measure the YTO next week. Is it easier to remove the SMA at LODA LO IN for the measurement?
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        hedgehog @ marc1 on Mar 29, 2015 2:03 AM
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        The schematic doesn't exactly match the A14 board in my 8563E either, but it is helpful in terms of studying the circuit topology. Yes, that's what I did to measure the YTO output. Don't forget to set the jumper on A14 board to "TEST" position to open the YTO PLL. Good luck!
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PA0ALV Mar 29, 2015 12:44 PM
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Hi Marc1,

Hereby a .jpg from A14 is this the same as yours ??

Ary
pa0alv
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- P2220003.JPG1.2 MB
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- marc1 @ PA0ALV on Mar 29, 2015 10:03 PM
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  Hi PA0ALV,
  
  Yes, it looks exactly the same!
  
  Thanks!
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  - PA0ALV @ marc1 on Mar 30, 2015 1:36 AM
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    Hi Marc1
    
    I do have once the same problems.
    Check the both diodes VR1 and VR5. VR5 have a brown shade of colour (overheathed).
    Unsolder the diode, forward normal value but the oposite way an odd one.
    May be it's the solution.
    gl
    Ary
    
    Edited by: PA0ALV on Mar 30, 2015 2:36 AM
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    - marc1 @ PA0ALV on Mar 30, 2015 3:47 PM
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      Thanks a lot, PA0ALV. I will take a look of these diodes. So, VR5 is not regulating the voltage if reverse measured abnormal, correct? They seem to be in the main coil drive circuits.
      
      hedgehog, thanks for the tips as well. I did some measurement on YTO output today (jumper on test position), and found no output signal there.
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      - hedgehog @ marc1 on Mar 30, 2015 4:07 PM
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        Did you set the span to zero to "park" the LO signal at a certain frequency? The actual LO frequency can be acquired from "Cal" menu.
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        marc1 @ hedgehog on Mar 30, 2015 4:10 PM
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        Yes, I set zero span and checked center frequency at 0Hz and 300Mhz and etc. No output from YTO.
        I was wondering if main coil drive fail will also lead to no output at YTO. I am not sure and I am studying the circuits now.
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        hedgehog @ marc1 on Apr 3, 2015 12:07 AM
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        Yes. Without the tuning current in the main coil, YTO will not generate RF output. However, this issue can fairly easy to identify by measuring the current fed into the mail coil.
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        marc1 @ hedgehog on Apr 6, 2015 6:39 PM
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        Thanks all for the information.
        
        The voltage between main coil + and main coil - is +3.5 for most of the frequency with zero span. Is that a reasonable reading?
        
        I un-soldered the two zener diode, 5V and 10V and verified they are good.
        
        Any suggestions would be appreciated.
        
        Thanks!
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        hedgehog @ marc1 on Apr 6, 2015 7:58 PM
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        The current into the mail coil is linearly proportional to output frequency. Since I don't know the tuning sensitivity or main coil resistance of this particular YTO, I can't tell if the voltage you measured makes sense. However, the voltage should change if you vary the center frequency (within the same band), as the mail coil at DC is equivalent to a resistor.
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        MikeM @ hedgehog on Apr 7, 2015 8:12 AM
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        Attached is information on the main coil from the specifications for the YTO used in the 8560 series so that you can see the sensitivity. However, you would do better to measure the voltage across the resistors in the main coil drive path on the A14 Frequency Control board and calculate the current through the coil.
        
        Mike
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        8560 Series YTO.png21.4 KB
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        PA0ALV @ marc1 on Apr 9, 2015 3:40 AM
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        Hi Marc1,
        
        sri fo the delayed response.
        
        An other possibilty is by using a sweep- or rf generator in CW mode. !
        It is a lot of work! Disconnect the spa's YTO output rigid cable. (You have to take out the YTO)
        Connect the sweep- or rf generator to the rigid cable.
        Connect the 300 MHz "Cal signal" to the spa input connector.
        Set analyser band "0" Freq 300 MHZ, center freq 300Mhz. "zero span"
        Set generator appr. to 3,62 GHz +10 dBm (or calculate the frequency) and tune carefully back and forward
        and look at the crt when the line goes up.
        
        There's no sweep action so it can be difficult to see something.
        When there is some movement during tuning it is sure the original YTO is malfunction.
        
        The main- and fm coil are never defect, its "only" the oscillator transistor.
        Measuring main coil current, it must change by turning the RPG. If so and no output from YTO, 2e conclusion YTO defect.
        If main coil current did not change, driver or circuit not ok
        
        Ary
        pa0alv
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    - PA0ALV @ PA0ALV on Apr 9, 2015 3:17 AM
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      Hi Marc1,
      
      sri fo the delayed response.
      
      An other possibilty is by using a sweep- or rf generator in CW mode. !
      It is a lot of work! Disconnect the spa's YTO output rigid cable. (You have to take out the YTO)
      Connect the sweep- or rf generator to the rigid cable.
      Connect the 300 MHz "Cal signal" to the spa input connector.
      Set analyser band "0" Freq 300 MHZ, center freq 300Mhz. "zero span"
      Set generator appr. to 3,62 GHz +10 dBm (or calculate the frequency) and tune carefully back and forward
      and look at the crt when the line goes up.
      
      There's no sweep action so it can be difficult to see something.
      When there is some movement during tuning it is sure the original YTO is malfunction.
      
      The main- and fm coil are never defect, its "only" the oscillator transistor.
      Measuring main coil current, it must change by turning the RPG. If so and no output from YTO, 2e conclusion YTO defect.
      If main coil current did not change, driver or circuit not ok
      
      Ary
      pa0alv
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      - minolta1 @ PA0ALV on Aug 25, 2016 3:44 AM
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        Dear PA0ALV ,
        write me please to email minolta1 at cninet point cz I need your help about 8591A . Thanks!
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8562EC A14 U429B wrong ref voltage

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