Marconi 2022E some freq bands not working.. - UK Vintage Radio Repair and Restoration Discussion Forum

jpdesroc · 7th Feb 2018, 3:12 am

I just bought a Marconi 2022E frequency generator and I just tested it with my reliable HP frequency counter and my Tektronix oscilloscope to verify the possible frequencies of the generator..

Well here are my measurements: Some frequency bands are dead and not generated at all

0hz to 16.49Mhz dead no signal..
then

62.50Mhz to 88.24Mhz dead no signal..
125.0Mhz to 176.4Mhz dead no signal..
250.0Mhz to 352.9Mhz dead no signal..
500.0Mhz to 705.9Mhz dead no signal..

All the other frequencies worked.

I checked all the OEM345 modules (IC1,2,3,8,9,10,14)
They have all around 6vdc at their collector outputs at rest when their 12vdc supplies are switched on by relays.
The only OEM345 I did not check was IC7 (hidden Inside shielded case).
The only clue I have so far is that most of the non working freq bands are multiple of 2's...
Any ideas where to look at ?
Thanks.

jpdesroc · 7th Feb 2018, 4:15 am

I just found that their are 2 VCO's that are the cores of this generator.
The first VCO goes from 250Mhz to 353Mhz and the second goes from 353Mhz to 500Mhz.
All other frequencies are derivated from these 2 VCO's.

My problem is that the first VCO 250Mhz to 353Mhz is not oscillating and it's because of a short I just found in his 12vdc supply. Probably a short electrolytic capacitor. Each VCO's have a separate 100R supply series resistor. The bad VCO resistor gets hot.

I'll dig deeper tomorrow cause it's getting late now..

dave cox · 7th Feb 2018, 3:34 pm

I think I had a similar fault. There are a LOT of screws to remove to get at it and its a bit a swine to get back togeather, especially the little adjuster whatsits

Enjoy !

dc

EDIT:

Here https://www.vintage-radio.net/forum/...ad.php?t=77468

jpdesroc · 7th Feb 2018, 3:54 pm

According to my latest calculus The actual suspect VCO
could be the cause of ALL the lost frequencies
including those from 0.0 to 16.49Mhz since those
are derivated from the not working 250Mhz-500Mhz VCO shopped
to 160.01-222.5Mhz by a divider and then substracted with a standard 160Mhz VCO. giving normally .01Mhz - 62.5Mhz but with the trouble
only gives 0.0 - 16.49Mhz..

jpdesroc · 8th Feb 2018, 5:17 pm

After some work I finally found and replaced
one offending electrolytic capacitors (220uf/16v) that
were keeping the first VCO from working properly
on the synthesis board generator.
Now all the frequency ranges work like a charm.

I tested with my HP Spectrum Analyzer and the spectrum readings

All matched the 2022E’s. Glorius !

7th Feb 2018, 3:12 am	#1
jpdesroc Retired Dormant Member Join Date: Feb 2013 Location: Québec City, Québec, Canada Posts: 42	Marconi 2022E some freq bands not working.. I just bought a Marconi 2022E frequency generator and I just tested it with my reliable HP frequency counter and my Tektronix oscilloscope to verify the possible frequencies of the generator.. Well here are my measurements: Some frequency bands are dead and not generated at all 0hz to 16.49Mhz dead no signal.. then 62.50Mhz to 88.24Mhz dead no signal.. 125.0Mhz to 176.4Mhz dead no signal.. 250.0Mhz to 352.9Mhz dead no signal.. 500.0Mhz to 705.9Mhz dead no signal.. All the other frequencies worked. I checked all the OEM345 modules (IC1,2,3,8,9,10,14) They have all around 6vdc at their collector outputs at rest when their 12vdc supplies are switched on by relays. The only OEM345 I did not check was IC7 (hidden Inside shielded case). The only clue I have so far is that most of the non working freq bands are multiple of 2's... Any ideas where to look at ? Thanks.

7th Feb 2018, 4:15 am	#2
jpdesroc Retired Dormant Member Join Date: Feb 2013 Location: Québec City, Québec, Canada Posts: 42	Re: Marconi 2022E some freq bands not working.. I just found that their are 2 VCO's that are the cores of this generator. The first VCO goes from 250Mhz to 353Mhz and the second goes from 353Mhz to 500Mhz. All other frequencies are derivated from these 2 VCO's. My problem is that the first VCO 250Mhz to 353Mhz is not oscillating and it's because of a short I just found in his 12vdc supply. Probably a short electrolytic capacitor. Each VCO's have a separate 100R supply series resistor. The bad VCO resistor gets hot. I'll dig deeper tomorrow cause it's getting late now..

7th Feb 2018, 3:34 pm	#3
dave cox Nonode Join Date: Jan 2009 Location: Bristol, UK. Posts: 2,061	Re: Marconi 2022E some freq bands not working.. I think I had a similar fault. There are a LOT of screws to remove to get at it and its a bit a swine to get back togeather, especially the little adjuster whatsits Enjoy ! dc EDIT: Here https://www.vintage-radio.net/forum/...ad.php?t=77468 Last edited by dave cox; 7th Feb 2018 at 3:41 pm.

7th Feb 2018, 3:54 pm	#4
jpdesroc Retired Dormant Member Join Date: Feb 2013 Location: Québec City, Québec, Canada Posts: 42	Re: Marconi 2022E some freq bands not working.. According to my latest calculus The actual suspect VCO could be the cause of ALL the lost frequencies including those from 0.0 to 16.49Mhz since those are derivated from the not working 250Mhz-500Mhz VCO shopped to 160.01-222.5Mhz by a divider and then substracted with a standard 160Mhz VCO. giving normally .01Mhz - 62.5Mhz but with the trouble only gives 0.0 - 16.49Mhz..

8th Feb 2018, 5:17 pm	#5
jpdesroc Retired Dormant Member Join Date: Feb 2013 Location: Québec City, Québec, Canada Posts: 42	Re: Marconi 2022E some freq bands not working.. After some work I finally found and replaced one offending electrolytic capacitors (220uf/16v) that were keeping the first VCO from working properly on the synthesis board generator. Now all the frequency ranges work like a charm. I tested with my HP Spectrum Analyzer and the spectrum readings All matched the 2022E’s. Glorius !