7000 series readout system/Repairs

Zeroes in display shrinking after some minutes

Symptom: The digits zero in the display are getting smaller after some minutes

Root cause: Resistor R224 in emitter circuit of Q2240 (zeroes logic) cracked and high value

Solution: Replace resistor

Source: www.amplifier.cd repair report (in German)

Display jitter

Vertical jitter of the readout characters is typically caused by under- or overshoot in the step response of the vertical amplifier. When the vertical amplifier is being overdriven (signals outside the graticule area), the effect is strongest, and largely unavoidable.

It may be possible to reduce jitter under non-overdrive conditions by adjusting the vertical amplifier high-frequency compensation, see e.g. Table 4-3 in the 7704A manual, page 4-11. For horizontal jitter, look for a horizontal amplifier thermal balance calibration step.