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Electronics => Repair => Topic started by: Armando1989 on January 26, 2022, 10:11:54 am

Title: Marconi 2955b wrong AF output level
Post by: Armando1989 on January 26, 2022, 10:11:54 am

Hi
I have marconi 2955b test set. Passes all selftests.
Problem is that output AF level does not correspond with setting... Level is much higher than set.. ie: set 400mv but output is 2.7v
I tried follow service manual adjust Ab6 card R1 potentiometer till get correct voltage, however selftest fails on modulation 3.x selftests as the level is too low. I have to go back to the previous level to get selftests fine again
Furthermore, manual states u can set af level to 1v while my 2955 cannot go so high in menu.
Any ideas?
Thanks
Br

Title: Re: Marconi 2955b wrong AF output level
Post by: Armando1989 on January 26, 2022, 10:43:05 am

Solved, my fault
In "change parameters" menu it was configured as 20dB attenuator installed for bf (not the case) thus instrument was applying higher output accounting for the attenuation... Removing this setting allows select up to 1V and now output voltage is correct