Hameg HM 303-4, Service Manual

Subject to change without notice

37

(25) R663: ADDition/Offset.

Press DUAL pushbutton (in!).
Locate and identify R663 (25) on YPA-Board.
Set input coupling CH I and II to GD.
Move both baselines with Y-POS. I and II controls to the horizontal center line of the graticule.
Release DUAL pushbutton (out!).
Press ADD pushbutton (in!).
Adjust R663 (25) for the same signal position as before in DUAL mode.

(26) RV2417 (A), RV2418 (B): Overscan.

Locate and identify RV2417 (26A) and RV2418 (26B)on XY-Board.
Press channel I and channel II GD pushbuttons (in!).
Press DUAL pushbutton (in!).
Set baseline with Y-POS.I control to the top line of the  graticule.
Set baseline with Y-POS.II control to the bottom line of the graticule.
Adjust RV2417 (26A) for just lighting up of the upper LED.
Adjust RV2418 (26B) for just lighting up of the lower LED.
Repeat both procedures until both adjustments are correct.

(27) RV3519: Sweep start voltage.

Locate and identify RV3519 (27) on TB-Board.
Set time base to .2ms/div.
Locate and identify pin 7 of test socket on XY-Board.
Use a control oscilloscope with a x10 (10:1) probe and measure under DC input coupling

conditions the sawtooth voltage at pin 7.

Adjust RV3519 (27) for 0 volts DC at the sawtooth start (end of the hold off time).

(28) RV2225: X-Magnification x1.

Locate and identify RV2225 (28) on XY-Board.
Set time base to .2ms/div.
Adjust RV2225 (28) for 10.2 div sweep length.

(29) RV2260: X-Symmetry.

Locate and identify RV2260 (29) on XY-Board.
Set the X-POS. knob to the mechanical center position.
Adjust RV2260 (29) for a symmetrical trace position in respect to the graticule.

(30) RV3591 (A)/3589 (C), CV3511 (B): Time base.

a) Locate and identify RV3591 (A) on TB-Board.

Set time mark generator to f= 20kHz and connect signal to CH I  input.
Set time base to 50µs/div.
Move trace with X-Pos. control so that the first time mark  coincides with the first left

graticule line of the screen.

Adjust RV3591 (30A) so that the 11th time mark coincides with the last right graticule line.
Rotate time base variable control to fully left position.
Now more than 2.5 time marks per division should be  displayed.

b) Locate and identify CV3511 (30B) on TB-Board.

Set time base to 0.5µs/div. and time base variable control to   CAL position.
Set time mark generator to f= 2MHz.
Move trace with X-POS. control so that the first time mark  coincides with the first left

graticule line of the screen.

Adjust CV3511 (30B) so that the 11th time mark coincides with the  last right graticule line.

c) Locate and identify RV3589 (30C) on TB-Board.

Set time base to 5ms/div. and time base variable control to CAL position.
Set time mark generator to f= 200Hz.
Move trace with X-POS. control so that the first time mark  coincides with the first left

graticule line of the screen.

Adjust RV3589 (30C) so that the 11th time mark coincides with the  last right graticule line.

Check all time base settings with suitable time mark signals.