Re: Hameg HM208 Oscilloscope Timebase fault
Normally the horizontal signal should be DC coupled all the way from the ramp generator to the deflection plates. It looks like something (a switch, connecting lead, transistor ...) has gone open circuit leaving a weak capacitive coupling that passes the sweep signal only at high speeds. You should be able to track this down using the Hameg's vertical amplifier, and the length of the displayed vertical line, to show the amplitude of the timebase signal as you progress from the ramp generator through the stages of the horizontal amplifier. If the height of the signal on the scope changes when you change sweep speed then you are probing after the fault.
Begin by finding the ramp generator circuitry in the manual and checking the output signal. The amplitude should be the same at all sweep speeds, if not then the fault is in the ramp generator and you need to look closely at that. If the ramp generator is OK then work your way forwards looking especially either side of switches and plug-in connectors.
Quick check - if the timebase has a 5x or 10x magnifier then select that and see if it stretches the horizontal display as you would expect. If that works then stages after the gain switching are probably OK.
Roger
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