Repairing a Hameg HM1008 oscilloscope

Discussion in 'Technical Repair' started by Yami, Jan 8, 2019.

  1. Yami

    Thread Starter Member

    Jan 18, 2016
    154
    1
    Hi, I have done some recapping on the power supply on couple of HM1008 scopes. There is this one unit which when powered up all the lights on the front panel flashes and there is nothing displayed on the screen. What could be the possible cause for this, I haven't done any intensive troubleshooting yet. But I did check supply voltages at the other boards and it showed the correct voltages. I was able to get the service manual today but I couldn't find this error stated.

    I have attached some pictures and I was hoping that you could help me identify the circled parts.
    1. Photo 1
    Photo 1.JPG
    2. Photo 2 - there are two wires which one end of it doesn't seem to be connected to anything, what could these be? Referring to the manual the board is MB board, and the function of the board is to generate sweep(sawtooth)signals.
    Photo 2.JPG


    I also have a calibration question, I checked all the units (both channels) using a 1kHz square wave from a function generator. One unit displayed a trace similar to the picture attached (photo 3). Whats the name of the calibration which corrects this issue? For the probe I used a one with a bnc connector and alligator clips on the other end.
    Photo 3.jpg
     
  2. MrChips

    Moderator

    Oct 2, 2009
    17,595
    5,470
    Don't worry about the trace waveform calibration at this point.
    This has nothing to do with the scope. The calibration is done on a x10 scope probe.
    Your BNC cable does not a scope probe make.
     
  3. AlbertHall

    AAC Fanatic!

    Jun 4, 2014
    6,832
    1,626
    The red circled thing looks like 2 resistors - 470Ω?
    The wires only connected at one just might be very low value variable capacitors - guess?

    My standard procedure for locating the area responsible for no trace:
    1. Low voltage supplies. Fix any deficiency.
    2. High voltage supply (usually circa 1000V - don't know what it is on this scope. Fix if wrong.
    3. Connect a voltmeter between the Y plates and adjust the Y controls to get 0V on the meter. Fix if 0V not attainable.
    4. As 3 but for the X plates. Fix if 0V not attainable.
    5. Short the grid cathode of the CRT - careful high voltage here. If trace now appears, problem is in brightness control circuit.
     
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