Hameg HM 303-4, Service Manual

Subject to change without notice

29

(1)

 R1008: +141 Volt supply.

WARNING:

To avoid damage use a fully insulated screwdriver!

Locate and identify R1008 (1) on PS-Board (screened section).
Locate 8 pole checkpoint socket on XY-Board and identify pin 2.
Adjust R1008 (1) for e141Volts (± 0.1 Volt).

(2)

R1016: +12 Volt supply.

Locate and identify R1016 (2) on PS-Board.
Locate 8 pole checkpoint socket on XY-Board and identify pin 4.
Adjust R1016 (2) for e12Volts (± 10mV). All other vo185V (pin 1), -12V (pin 5)

and -1950V on cathode of CRT depend on the c12 Volt adjustment. All these
voltages must be checked and verified.

(3)

VR7000: Trace Rotation Check.

Locate and identify VR703 (3) „TR“ on the front panel.
Using Y-Pos.I and X-Pos. controls, move baseline to the center of the graticule.
Press channel I GD pushbutton (in!).
When turning VR703 (3), check that the range of inclination of the baseline is at least 1mm at both
horizontal limits of the graticule.
Readjust baseline exactly parallel to the horizontal center  line of the graticule.

(4)

 R1004 : CRT minimum intensity.

Locate and identify R1004 (4) on PS-Board.
Set INTENS. control to fully left position.
Press XY pushbutton (in!).
Adjust R1004 (4) so that the dot just disappears.
Release XY pushbutton.

(5)

R1003 : CRT maximum intensity.

Locate and identify R1003 (5) on PS-Board.
Set INTENS. control to fully right position.
Set FOCUS knob on the front panel for optimum sharpness.
Adjust R1004 (5) so that the beam diameter is 1.5mm.

Repeat adjustment 4 and 5 until optimum is obtained!

(6)

R712: Mean Y-plate Potential Channel I.

Locate and identify R712 (6) on YPA-Board.
Press DUAL pushbutton (in!).
Set both beams to the horizontal center line of the graticule by using Y-position I and II knobs

on the front panel. The Y-position knob settings must not be changed during the following
procedure until item 7) is finished.

Release DUAL pushbutton (out!).
Switch the oscilloscope OFF.
Locate and identify both lines from the Y-final amplifier to the Y-plates of the CRT.
Connect both lines (short)galvanically.
Switch the oscilloscope ON.
Measure the DC voltage at the Y-plates in respect to ground.
Adjust R712 (6) for +85Volt Y-plate voltage.

Note:

Do not remove the short at the Y-plates until item 7) is finished.

(7) 

R714: Mean Y-plate Potential Channel II.

Note:

Do not start item 7) until item 6) is finished.

Locate and identify R714 (7) on YPA-Board.
Press CHI/II pushbutton (in!) for channel II mode.
Measure the DC voltage at the Y-plates in respect to ground.
Adjust R714 (7) for +85Volt Y-plate voltage.
Switch the oscilloscope OFF.
Remove the connection between both Y-plates.
Switch the oscilloscope ON.