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Success Stories If you have successfully repaired or restored a piece of equipment, why not write up what you did and post details here. Particularly if it was interesting, unusual or challenging. PLEASE DO NOT POST REQUESTS FOR HELP HERE! |
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20th Jun 2020, 2:00 pm | #1 |
Pentode
Join Date: Nov 2005
Location: Crewe, Cheshire, UK.
Posts: 138
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Marconi TF2002B signal generator
I've just completed repairs to my TF2002B and thought some notes might help others who in the future have any of the problems I encountered.
There were 3 faults: no RF output on range F, no indication on modulation meter at all and crystal calibrator only audible very faintly in headphones. Range F problem was the oscillator fet (BF246 - TR2 on PCB A14). This had failed for some reason. Swapped the source follower TR3 into its position and oscillation was fine - fitted a 2N3819 (it was to hand and has the right pinouts) as TR3. Modulation meter problem was due to a failed 714 opamp that drives the meter (IC2 on PCB A3) - replaced with an MC1741 and now works fine. Crystal calibrator fault was due to two things: open circuit loudspeaker voice coil - replaced the faulty unit with a small 64 ohm speaker from the junk box - and an open circuit inductor in the filter unit (L4 on PCB A7 - this feeds the signals from the calibrator rf section into the audio amplifier). This inductor suffered from what is I think a common problem - the insulating sleeves that cover the winding wires where they emerge from the pot core bobbin disintegrate and the residue corrodes the (very fine) winding wire. I managed to unwind some of the wire from the bobbin, locate the break and take out some wire to form a new connection. This is extremely fiddley - a magnifier and lots of patience is essential! All working again fine now. The TF2002B is quite easy to work on, all screws are BA threads and the manual (thanks VMARS) is comprehensive. It will now become my workshop RF signal source and will displace a TF144H (itself a nice sig gen) that I will put in the "offered" section in case anyone is interested. Stay safe everyone. Regards, Roger G4BZI |
20th Jun 2020, 2:32 pm | #2 |
Octode
Join Date: May 2016
Location: Oxfordshire/Bucks borders, UK.
Posts: 1,604
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Re: Marconi TF2002B signal generator
Good write up. I've a TF2002B on the list of jobs to sort, so may well ask your advice some time in the future.
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Avometer, vintage Fluke and Marconi collector. Also interested in vintage Yaesu and KW. |
20th Jun 2020, 5:22 pm | #3 |
Dekatron
Join Date: Nov 2011
Location: Surrey, UK.
Posts: 4,398
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Re: Marconi TF2002B signal generator
They are really nice bits of kit, and correspond well with that old jibe about Marconi being a metalwork company that also dabbled in electronics. They are knocking half-a-century old now though, so a bit of diligence may be needed to clear out all the gremlins. My current one had a good list to work through that included 5 open circuit filter chokes, though three of the other faults really ought to be considered as one plus consequences- the two secondary side rectifiers had gone short circuit, the reservoir capacitor had ballooned and blown its guts all over the lower rear section including regulator board and ancilliaries, and the voltage selector was badly corroded as a result and determinedly open circuit all ways. Nice and easy to find and cure, though, and an open circuit voltage selector had stopped power from being applied any more!
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24th Jun 2020, 5:31 pm | #4 |
Nonode
Join Date: Nov 2015
Location: Welwyn Garden City, Hertfordshire, UK.
Posts: 2,015
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Re: Marconi TF2002B signal generator
I miss my one, nice generator. Made in St Albans no doubt...
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24th Jun 2020, 5:51 pm | #5 |
Dekatron
Join Date: Nov 2011
Location: Surrey, UK.
Posts: 4,398
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Re: Marconi TF2002B signal generator
I still find it difficult to persuade myself that something that uses this many active devices only consumes around 9-10W! (The rating plate claims 15W, but I think this is playing it safe). It sits all day cool as a cucumber, contrasting with the preceding thermionic era and succeeding digital era. Well worth keeping going even if it involves ploughing through a list of faults. It taught me a new word, too- boustrophedon, from the back'n'forth tuning slugs and scale approach adopted by Marconi.
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