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I own an Hameg 204 analog oscilloscope.

Unfortunately the x-axis oscillation on the CRT screen is broken. I am looking for advice on how to fix this.

My background: I have fixed several little electronics devices. Examples include networks switch with burnt capacitors. This oscilloscope is much more complicated and a little above my level to handle it myself.

Precise description of the issue

  • Expected behavior: the CRT ray moves from the far left to the far right of the CRT screen.
  • Actual behavior: the CRT ray is stuck at 60% of the x-axis of the screen (y-axis works fine). The x-pos button does nothing from 100 down to 50% and move the line start further right when turned from 50% to 0%.

    When I activate the "x magn x10" button, the ray moves from 60% to the far right.

    Basically, with the "x magn x10" trick, I have a working oscilloscope with only 40% of the original screen width. These "40%" do not depend on the time resolution.

What I already did

The following was made with "x magn x10" always activated.

First thing I did what to get the schematics: http://www.sky-messtechnik.de/images/PDFs/HM204-1.pdf .

I made the hypothesis the issue comes from a faulty component in the 'x-final amplifier' (page 37 reproduced below). x-final amplifier

I then used a working (digital) oscilloscope to check "from S281" point (it is not only 'from CT' as stated in the manual but also 'from timebase'). Here I see the x-oscillation I expected to see, with 0V in the middle (see image below). I can also confirm that x-pos (bottom left) works as intended (-12V to 0V).

"Inside" the x-final amplifier though, the situation is very different. I always see the same pattern (at both 'W2-6 CRT', Chp12, ...) but obviously with different voltages. depending on the location in the amplifier (see image below; minimum value is very close to 0V).

Pattern seen on the working oscilloscope

I do not see any weird-looking component (see picture). PCB picture of the x-final amplifier

EDIT: I also checked all power rails and all are at their expected voltage.

Where you can help

As the board is quite difficult to take apart (so I would like to do it only once), I am looking for some advice on how to precisely locate the faulty component so I can order a replacement.

I am hoping that for an experienced eye, the pattern would be typical of a specific component failure.

If needed, I can make further measurements.

EDIT: new measurement:

T2101, base (to R2101):

T2101

T2101, collector (to R2110):

T2101

T2101, emitter (to R2100/R2101/R2108):

T2101

T2102, base (to R2103):

T2102

T2102, collector (to R2112):

enter image description here

T2102, emitter (to R2109, VR2100, VR2101):

enter image description here

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closed as off-topic by Ale..chenski, Voltage Spike, Sparky256, Bruce Abbott, Lior Bilia Mar 31 '18 at 15:49

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "Questions on the repair of consumer electronics, appliances, or other devices must involve specific troubleshooting steps and demonstrate a good understanding of the underlying design of the device being repaired. See also: Is asking on how to fix a faulty circuit on topic?" – Ale..chenski, Voltage Spike, Sparky256, Bruce Abbott, Lior Bilia
If this question can be reworded to fit the rules in the help center, please edit the question.

  • 1
    \$\begingroup\$ Did you verify all Vdc , incl. 220Vdc? \$\endgroup\$ – Sunnyskyguy EE75 Mar 25 '18 at 21:20
  • \$\begingroup\$ Yes I did. +220,+12 and both -12V Vdc show no anomaly. \$\endgroup\$ – user135781 Mar 26 '18 at 7:07
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    \$\begingroup\$ Compare Vb,Vc,Ve on T2101 and T2102. This is a differential output with single input with Xadj DC-offset and x10 gain and notice collector is inverted T2101 and non inverted on T2102 otherwise fault. The next stages are just differential buffers \$\endgroup\$ – Sunnyskyguy EE75 Mar 26 '18 at 7:39
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    \$\begingroup\$ Moving parts fail more often. Spray cleaner on variable resistors, switches & plugs and cycle them several times. If you must remove the board, reflow solder connections. \$\endgroup\$ – Optionparty Mar 26 '18 at 20:45
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    \$\begingroup\$ Seems to be saturated on 2102 and not getting bias from -12V via R2133 bottom left. \$\endgroup\$ – Sunnyskyguy EE75 Mar 27 '18 at 23:50