Hameg HM 303-4, Service Manual

Subject to change without notice

35

(21) RV2005 (A), RV2006 (C), CV2000 (D) and CV2001 (B):

Y-Final Amplifier.

Connect a 1MHz squarewave signal of 25mV via 50

Ω

 cable  and 50

Ω

 through termination

to input CH I.

Check that DC input coupling is selected.
Set time base to 0.2µs/div.
Locate and identify the adjustment points RV2005 (21A), RV2006 (21B), CV2000 (21C) and

CV2001 (21D) on XY-Board.

As the capacitive influence of the cabinet is of importance, a metal sheet above the Y-final

amplifier section is required.

Adjust RV2005 (21A) and CV2001 (21B) for flat top, RV2006 (21C) and CV2000 (21D) for fast

 leading edge with minimum  overshoot.

Repeat until optimum is obtained.
Check channel II under the same conditions.

(22) Y-Amplifier Bandwidth Check.

Connect a 40mVpp/50kHz sinewave signal from a constant amplitude generator via

a 50

Ω

 throughtermination to the input of channel I.

Adjust the generator amplitude for 8 div. display height on the screen.
Increase the generator frequency until the signal is displayed with 5.6 div. height ( -3dB).
Repeat the adjustment under item 21), if the frequency reading on the generator shows a value

less than 30MHz.

Press CHI/II-TRIGI/II pushbutton (in!).
Connect a 40mVpp/50kHz sinewave signal from a constant amplitude generator via

a 50

Ω

 throughtermination to the input of channel II.

Adjust the generator amplitude for 8 div. signal height displayed on the screen.
Increase the generator frequency until the signal is displayed with 5.6 div. height ( -3dB).
Repeat the adjustments under item 21), if the frequency reading on the generator shows

a value less than 30MHz.

(23) C113/111/102/105: Attenuator Compensation CH I.

Locate and identify trimmers VC102-113 for CH I on YPA-Board.
Check that DC input coupling is selected.
Check that input attenuator CH I is in 5mV/div setting.
Set time base switch to 0.5ms/div.
Set amplitude calibrator to 1kHz and connect a 2:1 pre-attenuator via 50

Ω

 cable to input of  CH I.

Set calibrator output voltage to 80mVpp (40mVpp at the 2:1 pre-attenuator output,

if terminated with 1M

Ω

).

Adjust trimmer in pre-attenuator for flat squarewave top. This adjustment must not be changed

during the following procedure.

Adjust compensation as listed in the table below:

Scope

Input

Adjustment

Input

Atten.

CH I

250mVpp

50mV/div

A (VC111) flat top + B (VC113) leading edge

2.5Vpp

0.5V/div

C (VC102) flat top + D (VC105) leading edge

(24) C413/411/402/405: Attenuator Compensation CH II.

Locate and identify trimmers VC402-413 for CH II on YPA-Board.
Check that DC input coupling is selected.
Check that input attenuator CH II is in 5mV/div setting.
Set time base switch to 0.5ms/div.
Set amplitude calibrator to 1kHz and connect a 2:1 pre-attenuator via 50

Ω

 cable to input of  CH II.

Set calibrator output voltage to 80mVpp (40mVpp at the 2:1 pre-attenuator output,

if terminated with 1M

Ω

).

Adjust trimmer in pre-attenuator for flat squarewave top. This adjustment must not be

changed during the following procedure.

Adjust compensation as listed in the table below:

Scope

Input

Adjustment

Input

Atten.

CH II

250mVpp

50mV/div

A (VC411) flat top + B (VC413) leading edge

2.5Vpp

0.5V/div

C (VC402) flat top + D (VC405) leading edge