weltradio
Newbie level 1
RF output Frequency jitter at a Marconi 2955R
Folks,
I have a very special fail at a 2955R(German) which is very hard for me to find. At least its any fail at the AA4 board which I could swap from an older A version.
The output frequency is jittering/jumping about 30Hz, sometimes bigger, somtimes just a few Hz.
I verified it with an HP3588A. At the HF outside I can see this >FM< frequency jumping with an scope and also at very light gain variance.
Removing the bottom cover and slighly pressing the aa4 section shows a very instable frequency, but is alway running home to the old frequency
when depressed. Some copper stripes near the 3 RF generators seems to be a factory change issue, because one of the old AA4 boards got it not.
Actually the unit is open and the selftest is ok. Two of the OM345 Hybrid were renewed at at the bottom board(was it AA1?), right side, have got some fails at part1.xx.No ripples at the power unit, output voltage levels are ok, stable sources.Very stable 10Mhz reference oszillator at the CRT board checked.
Has anybody an idea about that ? How can I get a very stable output frequency ?
This fails can never be heard with an simple AM receiver but of course it popped up with a CW reception and testing a radio with RF without modulation.
It is a noise like a chirping bird...
Best regards
Thomas
Folks,
I have a very special fail at a 2955R(German) which is very hard for me to find. At least its any fail at the AA4 board which I could swap from an older A version.
The output frequency is jittering/jumping about 30Hz, sometimes bigger, somtimes just a few Hz.
I verified it with an HP3588A. At the HF outside I can see this >FM< frequency jumping with an scope and also at very light gain variance.
Removing the bottom cover and slighly pressing the aa4 section shows a very instable frequency, but is alway running home to the old frequency
when depressed. Some copper stripes near the 3 RF generators seems to be a factory change issue, because one of the old AA4 boards got it not.
Actually the unit is open and the selftest is ok. Two of the OM345 Hybrid were renewed at at the bottom board(was it AA1?), right side, have got some fails at part1.xx.No ripples at the power unit, output voltage levels are ok, stable sources.Very stable 10Mhz reference oszillator at the CRT board checked.
Has anybody an idea about that ? How can I get a very stable output frequency ?
This fails can never be heard with an simple AM receiver but of course it popped up with a CW reception and testing a radio with RF without modulation.
It is a noise like a chirping bird...
Best regards
Thomas
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