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Old 13th Oct 2019, 2:27 pm   #41
deliverance
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Default Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver

Checked The L1 coil that's fine C1 reads 0.003 uf the 680 ohm resistor is fine still the same .
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Old 14th Oct 2019, 9:02 am   #42
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Default Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver

Running out of ideas with this issue anyone have any more thoughts on it cheers Chris.
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Old 14th Oct 2019, 10:43 am   #43
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Default Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver

I would first confirm that the local osc is working properly as has been suggested.

Lawrence.
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Old 14th Oct 2019, 11:48 am   #44
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Default Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver

Hi I presumed with the other nine bands working the oscillator was okay I have a scope but no leads only just bought it also no small radios only boat anchors so no room on the bench to put another on . Is it worth checking components around L35 in the oscillator ?.
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Old 14th Oct 2019, 11:55 am   #45
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Default Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver

Check the osc anode voltage, if that's ok try measuring the voltage on the oscillator's control grid, normally it should be a few volts -ve.

Remember that the first ECH81 is the mixer only, not the oscillator....

Lawrence.
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Old 14th Oct 2019, 2:24 pm   #46
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Default Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver

On band 6 the anode on V4 EF85 reads 42 volts . On L35 pin 1 reads - 1.9 volts . Pin 3 no volts. Pin 6 34 volts. Pin 5 34 volts .
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Old 14th Oct 2019, 3:17 pm   #47
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Default Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver

Have you checked the anode voltage on V1, have you tried a sig gen for inputs or as a substitute osc, various things you can check, first is always the work you've already done.

Also the anode of the 2nd mixer is switched via the band change switch, is that voltage ok?

Lawrence.

Last edited by ms660; 14th Oct 2019 at 3:35 pm. Reason: additional circuit info
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Old 14th Oct 2019, 4:49 pm   #48
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Default Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver

Hi , I don't have a sig gen I have checked and double checked my work so far it's fine I'm going no where now with it thanks for your help .
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Old 14th Oct 2019, 4:57 pm   #49
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Default Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver

What frequency does Band 6 cover?
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Old 14th Oct 2019, 4:58 pm   #50
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Default Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver

Medium wave .
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Old 14th Oct 2019, 5:49 pm   #51
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Default Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver

Right,that should not take much sorting with the circuit.There is a sig gen sat here ,bring the set across.
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Old 14th Oct 2019, 6:18 pm   #52
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Default Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver

Thanks for your kind offer I will have another try on resolving this if I fail I will take you up on your offer . It seems sorting one band that doesn't work when the other nine do would be easier !
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Old 14th Oct 2019, 7:11 pm   #53
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Default Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver

It could be anything from an o/c coil caused by the dreaded green spot etc to the band switch o/c even,though normally you would be able to see the damage.

I am not the best at remote diagnosis,I do much better when the item is in front of me on the bench.

PS what ever you do,do not twiddle any cores/coils etc
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Old 14th Oct 2019, 7:31 pm   #54
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Default Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver

No coils have been twiddled with or micas touched. I removed the AGC can to replace some components which resolved other issues but there are no coils in there .
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Old 7th Nov 2019, 11:02 am   #55
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Default Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver

I changed the function switch to a 6way switch, added a small PCB with two reed relays and two behive trimmers, set the BFO to 86.5khz and the relays bring the BFO to 86.0 for CW and 83.5 giving LSB, USB and CW mode on the function switch.

Has anyone tried the IF mods in Practical Wireless from March 1983 adding in an additional EF85 in the 700kHZ IF and an additional W77 in the 85kHz IF?

"Modifying the Marconi Atalanta by W.Titmuss" pages 37,38 and 39.
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