Hi,
I have a HAMEG HM 103 Oscilloscope, which has been working fine for years.
However, when I turn it on now, I only get a single dot - no horizontal line.

Does anyone have any suggestions on how to diagnose of fix this problem ?

Regards,
Martyn

 

Your trigger in auto mode ? AT/NORM position.

Regards, Dana.

 

Your trigger in auto mode ? AT/NORM position.

Regards, Dana.

Hi Dana,
Thanks for your response.
Yes, the trigger was in auto mode. AT/NORM position.
I tried all the push switches in and out and rotated all the knobs to check for bad contacts but with no success.
Martyn

 

No timebase or not set to correct mode...

Service manual.. ..

https://www.allaboutcircuits.com/test-measurement/oscilloscopes/hm-hm-103/service-guide/

 

If you can't move the dot with the horizontal position control, the horizontal deflection amplifier or the power supply for it has probably died. If you can't move the dot vertically either, then the power supply is almost certainly the problem. It depends on the design if the horizontal and vertical power supplies are the same.

Be sure to keep the brightness turned down to a low level while you are testing. You can damage the phosphor if you leave the beam in one position at high brightness.

 

If you can't move the dot with the horizontal position control, the horizontal deflection amplifier or the power supply for it has probably died. If you can't move the dot vertically either, then the power supply is almost certainly the problem. It depends on the design if the horizontal and vertical power supplies are the same.

Be sure to keep the brightness turned down to a low level while you are testing. You can damage the phosphor if you leave the beam in one position at high brightness.

Hi, ebp,
Thanks for your response.
I can move the dot, both horizontally using the X-POS knob and vertically using the Y-POS knob, but it does not produce the horizontal line, nor does it show the square-wave when probing the 'cal' post.

Martyn

 

But you get a vertical line of the right height when using cal? (it will appear as two dots connected by a faint line)

It sounds like the sweep generator may be the problem. This is rather tricky to diagnose without another oscilloscope. Sweep generator circuits usually aren't terribly complicated for that sort of oscilloscope.

I still recommend checking all the power supply voltages with a meter. Be careful, some of the voltages will be fairly high and accidentally shorting anything could cause damage.

If the scope can be set to X-Y mode where you input a signal to the horizontal deflection the same way you normally would to vertical, you can check performance of a large part of the circuit that way, even with just a variable DC power supply. That is, you should be able to move the dot a certain number of divisions by applying a known DC voltage to the X input, then reverse polarity to move it the other direction.

Have a look at the manual the Dave mentioned. It may have some useful troubleshooting information.

 

No timebase or not set to correct mode...

Service manual.. ..

https://www.allaboutcircuits.com/test-measurement/oscilloscopes/hm-hm-103/service-guide/

Thanks DodgyDave and ebp, I have downloaded the manual and will have a read.