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Old 11th Sep 2005, 9:13 pm   #1
Sean Williams
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Default Ferguson 951T - Where to start......

Ok, it had to happen didnt it... I have finally succumbed to owning a small 405 TV....

It was cheap, looks diabolical, and apart from some obvious 1950s repairs seems to be untouched.

The tube has seen replacement with a mw22-18, and a seperate crt heater tranny has been employed.

I have located a circuit in the Radio and TV handbooks, and am just about to wander into the shack for an play with it.

So, being my first attempt at a tv repair/resurrection some pointers would be useful (I am quite happy and conversant with high voltages, along with live chassis design )

So over to the TV buffs......

Cheers
Sean
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Old 11th Sep 2005, 10:54 pm   #2
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Default Re: Ferguson 951T - Where to start......

Ok, some preliminary info.

I have found the original HT smoother to be completely shorted (no suprises there then), so first question would have to be can I still get a replacement 100+200uf@275v?

In the meantime I subbed a fairly gruesome NOS RS multisection in there for the purposes of testing.

The heater chain was o/c, but a fuse sorted that problem out.

I applied power to the set, and after an agonising wait was rewarded with a noise I have not heard for a long time, followed by a half inch wide "picture" (or white stripe) across the centre of the tube..... I hasten to add the noise was a fairly sickly whistle.....

I guess its armageddon for the waxies now is it?, or should I try a spot of proper fault finding and replace only what is faulty?

Some encouraging progress I think?

Cheers
Sean
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Old 11th Sep 2005, 11:15 pm   #3
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Default Re: Ferguson 951T - Where to start......

Hi
If you have lots of time and like a challenge then do it the hard way, but if you want a reliable set then its got to be out with the waxies !
You have a good start in that the line timebase is running and the LOPTseems to be OK.
The wirewound pots on these sets give trouble and could be causing the frame collapse; worth checking as I had to replace all the ones in my set.
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Old 11th Sep 2005, 11:18 pm   #4
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Default Re: Ferguson 951T - Where to start......

I know nowt about fixing vintage tellies but it sounds like you have the basis of a good set there. At least the LOPT and the tube are servicable. A good set for a first TV repair.

I tend to replace all the caps in just about any piece of valve equipment I repair, but I guess you need to assess how many are looking suspect and how big a job it'd be (plus how much the replacements would cost). If it's 2 or 3 dozen I'd probably do the lot, if it's nearer 100 I'd be tempted to leave some of the less critical ones.

Of course while mass recaping may get the set working, you don't actually learn anything from it. There is also the risk of connecting a replacement incorrectly and making things worse. So it may be worth spending the time working through the suspect stages (frame output would be a good place to start) with a combination of fault-finding and changing caps that are likely suspects. Higher value resistors in that area are worth checking too, as one that's gone high may well cause the lack of height problem you have.

Anyway that's my £0.02p worth. Now wait for a reply from someone that knows what they are talking about!
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Old 12th Sep 2005, 8:28 am   #5
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Default Re: Ferguson 951T - Where to start......

Whilst initially getting a set up and running, I'd be real tempted to at least test/replace all caps in the timebases before applying any power where failure of such caps might cause further damage (ditto waxies across HT rails). Whilst waving the iron in there I'd check the resistor values too - no, not OTT, cos 1) having soldered the most perfect ever joint on a valve socket when replacing a cap then you aint going to like it if you subsequently find a resistor on the same pin is faulty, 2) a resistor say 50% out probably won't stop the circuit running but may give an "odd" fault you then spend ages looking for, and 3) if you aren't familiar with the chassis you at least get to learn your way around the thing.

Once running and happy that the tube is a good 'un, the LOPT holds up for a while, and all the other difficult bits are OK then as Danny says it really is a case of out with all the waxies (or Hunts!) if you want it reliable.

When replacing caps in the RF section try to position the cap and it's leads as close to the original as you can (same with radios really).

TTFN,
Jon
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Old 12th Sep 2005, 3:42 pm   #6
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Default Re: Ferguson 951T - Where to start......

Hello,
A different approach from me with this little FERGUSON 951T but here goes. [Well I never was one to 'conform']
This is the Sutton Coldfield version of the London 941T an example of which was the very first set I repaired. I would not tackle a complete capcitor replacement until you have something on the screen to guide you. A couple of incorrect connections will give you hours of frustration.
The R.F. section is TRF and you should be able to get some sort of signal through it even if the stages are somewhat below what is expected of them. Replace all the wax condensers in the frame generator and output stage. This should sort out you height problem. Work from that point dealing with each stage in turn, testing the set after EACH REPLACEMENT. Snip off the capacitor across the mains switch or replace it with a 250v AC type to prevent heart attacks when it explodes! The set will work without it if you do not have a suitable replacement. These sets work VERY well and are a simple straightforward circuit as all FERGUSON sets were. Ideal for a first repair for the inexperienced. Remember you will need a channel 4 modulator for this model. It was FERGUSON's first set with flyback EHT. [1949] I have attached a pic of mine together with its external type 'C' I.T.A. converter. Regards JOHN.
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Old 12th Sep 2005, 5:53 pm   #7
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Default Re: Ferguson 951T - Where to start......

Hi All,

Well, the waxie armageddon is going well, and each one I replace makes things a little better.

The vertical hold control does not appear to be working too well, but the bright line is now nearly a full screen of what I guess to be "rolling snow"

The PL38 screen is getting a bit warm though (orange hot infact.....) surely this is not too good!

Just waxies left in the rf stages now.

Audio amp works better with the correct anode feed resistor in there

Lots more to do!

Sean

Oh, a simple (cheap) method of line conversion would be useful!!

As would a 405 line pattern generator........
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Old 12th Sep 2005, 6:19 pm   #8
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Default Re: Ferguson 951T - Where to start......

A wrinkle from an old hand (of 941 days, too).

I know there's not a Test Card C scrunched up in your thin white line, but if you waggle a flat hand-mirror back and forth (think "mirror drum" action) you can fake the vertical scan, and may be rewarded with a vision of "real" snow. Not much, I know, but it might just give you a psychological lift, and more heart to carry on.
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Old 12th Sep 2005, 8:45 pm   #9
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Default Re: Ferguson 951T - Where to start......

hello Shan,
Good to know you are working your way through the wax capacitors.......Great fun and what a pong! Your PL38 screen glowing orange should not be. When you get around to the line timebase waxygoo you may find it clears up. The line coupling cap to pin 5 of the PL38 is probably the reason. [Leaking] If the problem persists but the crt screen has good brightness you may find that removing the H.T. connection to pin 3 screen grid connection from the PL38 and fitting a 5watt wire wound resisitor around 2.2K in series will cure this. The line output transformer may have a shorting turn. [ Sorry] These sets were on the knife edge of technology for the times and were working on the limit of their capabilities. Remember ONE component at a time and switch it on after every replacement. The original tube fitted was a MW22-14C. A MW 22-16/18 will replace this without the need for a transformer. It may be a 'booster' transformer. Check the output to the CRT heater. It should be 6.3V approx. If much over this the tube may be a bit low but knowing the Mullard CRT's will still give a good picture.
Regards. JOHN.
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Old 12th Sep 2005, 11:44 pm   #10
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Default Re: Ferguson 951T - Where to start......

Hi John,

Ok, all the waxies have been replaced around the chassis with the exception of the RF stages.

I measured the cathode voltage on the PL38, and was shocked to see 50 volts!

I also have a query regarding the potential divider used in the cathode circuit - the book states that the cathode resistor should be 33 ohms, in series with a control pot for picture width (300 ohms), followed by a resistor listed as 3.9? this resistor in the set is actually 3.9k, which sounds a bit high for that sort of application - is this about right?

I have found waving a signal generator near the RF stages, at somewhere near 50 megs causes the "picture" to change contrast, so I guess something is getting through.....

Such fun, lots more challenging than midget radios.......

Cheers
Sean
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Old 13th Sep 2005, 7:48 am   #11
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Talking Re: Ferguson 951T - Where to start......

"Oh, a simple (cheap) method of line conversion would be useful!!"

Hi Sean,
I can make you a 405 VHS tape and you give me your waxies.

Kind regards
Darius
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Old 13th Sep 2005, 8:19 am   #12
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Default Re: Ferguson 951T - Where to start......

Hi Darius,

No problem - I will start a box for dead waxies.......

Many thanks
Sean
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Old 13th Sep 2005, 8:56 am   #13
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Default Re: Ferguson 951T - Where to start......

"I measured the cathode voltage on the PL38, and was shocked to see 50 volts!

I also have a query regarding the potential divider used in the cathode circuit - the book states that the cathode resistor should be 33 ohms, in series with a control pot for picture width (300 ohms), followed by a resistor listed as 3.9? this resistor in the set is actually 3.9k, which sounds a bit high for that sort of application - is this about right?"

Yes!!!
Hi Sean

This set generates a negative booster voltage. Look at your instrument
it is -50V (!).
This voltage is added to the plate and screen voltage to get a better
effeciency. Please read this:
https://www.vintage-radio.net/forum/...ead.php?t=1549

R34 is a load resistor for the booster voltage. It makes sure that the
electrolytic C26 (tradersheet 937) is not charged with wrong polarity
during the first seconds when the set is switched on. And it stabilizes
the EHT at brightness changes.

If you sent me a DVD or something I can make a standard converted
vhs copy of it for you.

Kind regards
Darius

Last edited by oldeurope; 13th Sep 2005 at 9:02 am.
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Old 13th Sep 2005, 11:43 am   #14
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Default Re: Ferguson 951T - Where to start......

Hi Darius,

Thanks for the reply - I went and rechecked the measurement on the Cathode of the PL38, and I found two interesting facts......

1 - The voltage is positive with respect to chassis ( now approximatley 18volts)

2 - C26 on the trader sheet is missing, when I install one the "picture" dissapears, and the cathode volts rise to +40volts.

I was a bit bemused to find no eht reservoir on the chassis, nor could I find any trace of one being there originally - surely this will not make the PL38 happy having no reservoir to charge?

Any ideas?

Thanks
Sean
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Old 13th Sep 2005, 12:21 pm   #15
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Default Re: Ferguson 951T - Where to start......

Hi,
no C26? strange. Maybe I took the wrong trader sheet.
The V11 must generate the negativ booster voltage.

Maybe you are at the wrong measuring points.

Darius
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Old 13th Sep 2005, 1:34 pm   #16
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Default Re: Ferguson 951T - Where to start......

Hi Darius,

The sheet you used is correct, the phantom set wrecker has been in there and removed several components, and added a few others in the wrong place......

I am sure that C26 should be there.

I am still puzzeled as to why the cathode of the PL38 reads positive?

Cheers
Sean
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Old 13th Sep 2005, 2:35 pm   #17
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Question Re: Ferguson 951T - Where to start......

Hi,
what about V11? Is the katode on ground? Do you have negativ H pulses
at the plate? How much is the DC level at the plate?

Darius
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Old 13th Sep 2005, 3:12 pm   #18
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Default Re: Ferguson 951T - Where to start......

OK, V11 Cathode is tied to ground., there are negative going pulses on the anode of the PY31 of considerable amplitude, however according to my avo we have a negative voltage of 4.7 volts - Trader sheet is looking for a positive voltage around 24?

Hmm, now I know why there are professional people repairing these things

Cheers
Sean
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Old 13th Sep 2005, 6:24 pm   #19
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Default Re: Ferguson 951T - Where to start......

Good evening Sean,
RMS, average, peak...
The long pulse must be a little bit positive, the average must be
negative. You can add a RGP30M in parallel to the V11 with alligator clips.
Then you must get a negative DC voltage at R34 C26.

Kind regards
Darius
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Old 13th Sep 2005, 6:32 pm   #20
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Default Re: Ferguson 951T - Where to start......

Hi Darius,

Ok, I have found some more interesting things.

I measured volts all around the PL38, anode, screen both read around 240vdc, however the grid reads positive, which im sure it shouldnt, so I tried shorting the grid to chassis - this gave me three effects.

1, the picture brightened considerably, and I could see some form of scanning lines

2, The positive volts on the cathode reduced

3, the line whistle reappeared as a pure tone when the picture width control was avanced.

I guess this points to secondary emmission on the PL38?

Do I try to find another PL38 ?

Cheers
Sean
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