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Old 29th Jun 2019, 8:06 pm   #1
bionicmerlin
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Default Marconi 1400

I bought this set last year as I been after one for a long time.
Not putting any blame on the seller as he may not of known but it was sold as working.
I can’t believe how bodged up it was and still working reasonably well.
It had a nice dropper bodge but then more all electrolitics replaced most of them totally the wrong value and one round the wrong way round. The clip on the cover for the control pots at the rear was lost so that was soldered on but , the tripler was wrong but best of all the tuner shaft was cut off then the knobs had plastic glued on them to extend them.
I had a doner set exactly the same full of woodworm so I could swap a few bits.
I got the set working very well apart from a couple niggles .its better than it looks in the picture
If I could have some help .
I got some over scan. On 625 only I can get rid of most of it but the horizontal hold is on full travel. I have checked I couple near by resistors and replaced one but still about the same.
The other thing the system switch wants cleaning as it’s abit iffy . Any tips on the best way to do this without spray getting everywhere. Andy
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Old 30th Jun 2019, 10:01 pm   #2
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Default Re: Marconi 1400

One more little problem . On 405 lines when I turn down the contrast if also turns down the volume . The contrast is good having replaced a 3.3M resistor adjacent to the contrast pot.
Any help appreciated Andy
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Old 30th Jun 2019, 10:52 pm   #3
Restoration73
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Default Re: Marconi 1400

Hi Andy
Check R143 for the width, although the vdr Z4 can be suspect. Best to underscan a bit.
I would tend to replace the entire dropper as they can be found. If you have access to
the switch contacts you can iso alcohol or meths, but they need a lubricant. See;
https://www.americanradiohistory.com...UK-1976-08.pdf
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Old 30th Jun 2019, 11:44 pm   #4
bionicmerlin
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Default Re: Marconi 1400

Tony .
Thanks for the info . The system switch is well dirty so I will go along with what you say.
I have a few new droppers so I have replaced it.
The width is ok I replaced R143 .

It’s just the 625 line hold is at the end of its travel. Picture is pretty good though.
And on 405 contrast is at the end of travel. If I turn it back as well as adjusting the contrast it turns the volume down.
I can live with these minor faults but it would be nice to improve it . Andy
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Old 1st Jul 2019, 8:58 am   #5
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Default Re: Marconi 1400

You mentioned the tripler was incorrect. The third harmonic tuning capacitor mounted on the LOPT has to match the tripler. It's usually 220pf with a five stick tripler and 160pf with the three stick. Just a thought. This will give excessive width if a three stick tripler is used with a 220pf cap. Regards, John.
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Old 1st Jul 2019, 9:49 am   #6
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Default Re: Marconi 1400

Sounds like you have quite a challenge on your hands, but you are getting there. The picture of the mains dropper bodge was amazing lol.
The condition of the cabinet and the tube do look good making this a very worthwhile project.
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Old 1st Jul 2019, 1:54 pm   #7
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Default Re: Marconi 1400

I have a picture of a 1400 with the wire from a firebar element drooping over the chassis.
Check the correction capacitor in the line stage, and the resistors in the width circuit that I think were the subject of a mod.
I'm baffled by the contrast/sound interaction though.
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Old 2nd Jul 2019, 2:57 am   #8
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Default Re: Marconi 1400

Thanks for the messages everyone. I will check the capacitor John .
I didn’t realise but infact the 405 line contrast control is controling the 625 as well also reducing the sound but not so bad.
The proper 625 line contrast is doing nothing. I did check the system switch that’s in circuit and that appears to be ok so more testing tomorrow Andy
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Old 12th Jul 2019, 12:46 pm   #9
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Default Re: Marconi 1400

i think i have sorted most of the problems. There is a link on the board that gives the option of 625 on VHF that was on the wrong position . what through me was my doner set also had the link in the wrong position. This is sorted out the contrast problems. The pictures on here from my camera are not good the quality of the picture and sound is good .I have had the set running for a few evenings but its only yesterday i notices a very faint hum bar. About 4 inches wide and travels up . its so faint its very hard to see unless you know its there . its only on 625 line.i would of thought if it was a component it would be worse . i might leave it unless anyone has any ideas Andy
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Old 12th Jul 2019, 1:22 pm   #10
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Default Re: Marconi 1400

It's probably a capacitor in the power supply. More than likely it's in the main smoothing can, though there might be a couple of those black electrolytics that will need changing even if they aren't causing this fault. If it's in the main can bridging each section in turn with an appropriate value will point to the faulty section.
A more remote possibility is one of the rectifiers or an earthing problem.
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Old 21st Jul 2019, 2:05 am   #11
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Default Re: Marconi 1400

Glyn. Thanks for your advice .its abit of a late reply but I think I got it sorted. I found by tapping on the cabinet I could stop the hum bar. Traced it to a bad earth connection on the vhf tuner Andy
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