SB-614 Monitor has trace - but not pattern

Discussion in '"Boat Anchor" & Classic Equipment' started by VE7GPG, Jan 14, 2019.

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  1. VE7GPG

    VE7GPG XML Subscriber QRZ Page

    So I got this second hand - fired it up - nice bright trace, horz and vert move ok, hook it up to monitor the SSB - and no pattern, sweep slows trace down to almost a static postion.

    Looking for ideas

  2. WB5WPA

    WB5WPA Ham Member QRZ Page

    The SB-614 will display just plain old "audio" besides the RF envelope - how do you have yours hooked up?
  3. VE7GPG

    VE7GPG XML Subscriber QRZ Page

    Ant in and out
    Mode SSB
  4. WA2CWA

    WA2CWA Ham Member QRZ Page

    In order to see the transmitted audio, rig needs to be modulated.
    If no response, RF attenuator components may have problems.
    Or, on the Demodulator circuit board, diodes and/or transistors may have a problem.
    Trouble shooting may be required.
  5. K7TRF

    K7TRF Premium Subscriber QRZ Page

    It sounds like your mode switch is in Trap mode or perhaps external horizontal sweep mode. If the switch position is correct, the switch itself may be miswired. It's either that or something is wrong with your sweep oscillator but you said it swept normally until you connected a signal, that's very strange. Do you see any vertical deflection as in a vertical line when you transmit carrier or modulated SSB? If it's just a problem with your horizontal sweep you'd still expect to see vertical deflection when you transmit with your rig connected properly to the ANT terminals, it would just be a vertical line on the display without horizontal sweep but you should see something.

    Do you know the history of this unit? Since these are kits do you know if it ever worked properly? If not, I'd spend some time with the Heathkit assembly manual to make sure it's all wired correctly and perform the tests described in the manual: Manuals/Heathkkit/Heathkit SB614 Monitor Scope .pdf
    AI3V likes this.
  6. KL7AJ

    KL7AJ Ham Member QRZ Page

    The RF input goes right to the vertical deflection plates, no demodulation involved
  7. WA2CWA

    WA2CWA Ham Member QRZ Page

    If you're monitoring your transmitted RF signal, output of transmitter connects to one SB-614 antenna jack and the antenna gets connected to the other SB-614 antenna jack. Antenna jacks of SB-614 are connected to the Demodulator circuit board.

    If you just want to see a receive waveform, you can connect the audio output of the receiver to the SB-614 vertical input. But personally, this is worthless and its only virtue is eye candy.
  8. VE7GPG

    VE7GPG XML Subscriber QRZ Page

    Thanks, I'll check that board next

    Appreciate the help !

  9. VE7GPG

    VE7GPG XML Subscriber QRZ Page

    In Trap mode the trace is a dot
    For the sweep control, counter clockwise slows the sweep down so that it is a series of traces - as in a horizontal line with a bright spot travelling along it, but it never stops completely. Transmitting in SSB Mode does not affect the displayed trace in any manner I can see. The horizontal and vertical controls do move the trace around as expected. So it appears to me that it is not receiving the required signal to move the trace at all from the TX.

    This is a new to me piece of equipment, I'll tear it down and see what I can find out. I do have a spare with what I suspect is a bad tube so I can swap in the modulation board from that and se if it makes any difference.

    Thanks for the help.
  10. WB5WPA

    WB5WPA Ham Member QRZ Page

    TRAP stands for TRAPEZOIDAL display mode.

    Its really a cool way of observing an AM transmitter's performance.

    As a matter of fact, it will look like this:

    ZERO percent modulation is on the left, and anything near/over 100% is on the right.

    Easy to see clipping this way.

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