Re: Marconi 1400 birthday present
Your set looks to be a model 4623.
Here is the final supplement to the 1400 service manual, listing modifications in production.
You will see that R135 was changed from 1.5kOhms to 1.7kOhms, to eliminate frame cramping.
There are several mods listed that are well worth carrying out.
You will almost certainly find that many of the paper capacitors (Hunts, Dubilier and TCC/Plessey-TCC) and those black cylindrical "Callins" (and any TCC in colourful plastic cases with radial leadouts) electrolytics are faulty, in addition to numerous printed circuit type carbon composition resistors.
I would certainly check the values of the high value resistors in the boost HT stabilisation circuit: R143 (fit a 680k), R142 (fit a 2,2Meg), R141 and R140.
I'd also replace R132 (3.9Meg) - the boost HT feed to the CRTs 1st anode and check the values of R130 and R131 (preset pot) in the focus circuit.
Check the values of R133 (220k) and R103 (330k) in the Boost HT feed to the frame timebase.
Sorting out these ought to allow a full sized picture/raster.
I'd get VHF/405 working first, before worrying about UHF/625.
Last edited by dazzlevision; 28th May 2020 at 8:47 pm.
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