CTV [Sticky] 1974 20" Ferguson 3C03; Thorn 4000 ; Super Rare

OK, Martin, I'll make a start on it.

A few questions:

1. Can you get suitable metalwork, including a suitably large heatsink, made up?

2. Can you get the two connectors?

3. What PCB software do you use? I use Altium but if you don't I may be able to export to yours.

4. The circuits and waveforms have been helpful. I've been able to confirm the LM1875 can do the job - it needs to source just under 3A peak, it's rated for 4A.

Time to test the Fergy CRT A51 152X to see where its at.

Unlike the HMV whose CRT was a picture of good health, see here, the Ferguson was decidedly sickly. Maybe due to it being asleep for many years. With that in mind, I left it running on the B&K for 40+mins or so, only a marginal improvement was forthcoming. Oh dear!

Rasing the heater by a couple of volts to 8.4V and all three guns came up good, that's encouraging. Therefore, I decided to leave the heater at this level for a further 30-mins in the hope it might boil off some cathode crud and thus gain some improvement. After 30-mins returning the heater back to 6.3V showed only a marginal improvement, not enough to make this a valid repair. Double Oh Dear!

I decided next to try the B&K's legendary 'clean & balance'. Upon selecting this option, it became apparent there was a G1-k short, interesting this didn't show up on the first test. Anyway, running the clear shorts, cleared this fault. Next, each gun was cleaned as per the user manual. As ever, the B&K does a fantastic job of cleaning the cathodes. Fantastic!

These testers are in my opinion an invaluable addition to the workshop. This makes the Fergy a valid candidate for restoration.

All looking very good and no signs of corrosion which is rare for your usual acquisitions, the dust is a comforting sign. That focus control is similar if not identical to the one used in the 9000/9900 series, even if it is faulty I'm sure one from an 8500 could be used with suitable adaptions to mounting.

Time to get the capacitor reformer powered up?

Posted by: @jayceebee

no signs of corrosion which is rare for your usual acquisitions,

Yes, it does make a nice change to most of my recent finds of the last couple, coming out of barns.

Posted by: @jayceebee

Time to get the capacitor reformer powered up?

If past experience is anything to go by, those German electros on the field and PSU might be problematic, we shall have to see.

Lots of tants too. Might be worth powering up the signal stages with an external 30v supply to be sure all is well here.

@crustytv looks very interesting , I think if I was going to build another frame panel I would be inclined to use discreet components rather than try and replicate those thick film units 

I think I have a couple of parts for this chassis somewhere I know one is a transformer it not a 100% what part of the circuit it’s from might be horizontal output when I can put my hand on them you can have them .

chris

Posted by: @the_teleman

I think I have a couple of parts for this chassis somewhere I know one is a transformer it not a 100% what part of the circuit it’s from might be horizontal output when I can put my hand on them you can have them .

Thanks Chris, that's very kind of you. As you might expect, I've zero 4000 specific spares in stock, so anything folk have that they can offer, is greatly appreciated.

I only just found today that I have one part in stock, a new focus unit.

@crustytv Isn't a focus unit something you were concerned about on one of the sets?

I've made a start on the replacement vertical module circuit.

Using the Pye T29 circuit as a basis, the only part that might not be available is L501, the Vertical Tilt control tapped inductor that forms part of the N-S pincushion correction.

Without knowing its inductance that would be a problem. Easy enough to wind one when you do.

So I ran a quick simulation of the N-S pincushion circuit, since I really didn't understand how it works.

The sim is set up at the top of scan with +4v on the current sense resistor. Points A and B are in series with the current feedback path. V2 is the line pulse that triggers the parabola at line rate.

I was a bit disappointed initially, not being able to get the parabola voltage that I expected to see on the collector of the transistor.

Then it all became clear. This is CURRENT feedback.

So, the green trace shows the voltage and the blue trace shows the current through the inductor.

A 7.8mH centre-tapped inductor gave the best results.

Note I mistakenly labelled it "EW mod" in the screendump.

Does my reasoning look OK?

Here's the singular Vertical Deflection I have to share between the two, 4000's.

After a gentle clean, it appears to be in good condition, but looks are deceiving, so proof will be when powered. I've added dimensions to one photo. Measured to the millimetre, checked and double-checked, as I know John was after these figures.

It still has the original, special BRC output transistors fitted. I'd go as far to say it looks like no work has ever been carried out on it, looking on the print side.

p.s.

Trivial observation, but I've pretty much all the early Thorn colour TV chassis', this one's screen print has a distinct “Philips” look about it compared to all their others before and after.

Aaaargh! Kill those orange moulded electrolytics NOW!! 

I've had too many run-in with those: but the red ones are even worse... 

That scrubbed up well!

I see what you mean about the Philips similarity

That board does look to be in good untouched condition. 

Posted by: @crustytv

I'd go as far to say it looks like no work has ever been carried out on it, looking on the print side

I retract that.

With the benefit of putting it under the inspection scope, there appears to be one past repair. From evidence of flux residue, I would say TF402 has been replaced. Neat soldering but flux not cleaned off. Nonetheless, a very good condition board.

Posted by: @cathovisor

Aaaargh! Kill those orange moulded electrolytics NOW!! 

I've had too many run-in with those: but the red ones are even worse... 

When they go bang, they bang. In style !

Naturally, this excitement is to be avoided if possible.

There's no doubt from the underside it's Thorn but never seen those print markings on the component side. Thanks for the dimensions, I've got a rough and ready print layout done and resized it. I might see if I can borrow a laser printer and try doing a toner transfer copy. Not tried it before so no guarantees and still leaves the problem of obtaining the two TFs.

Posted by: @jayceebee

Not tried it before so no guarantees and still leaves the problem of obtaining the two TFs.

Does anybody know what the circuit of the thick film units is? I'm sure it could be replicated with SMDs on a small PCB. At this point I am thinking of the encapsulated resistor packs used in some Regentone transistor radios of the 60s.

All the data is in the library 👍 

If no other choice is open other than to try and build a board, I didn't see the Thick-Films as a problem. I had a mind to  replicate them with through-hole on a matrix board, more in keeping and there's not that many components. I'd want to avoid smd, I'm hopeless with things that small, and they are far too modern a solution for my liking.

The main concern I have is, I've no idea to do about L401, I guess one would need to be wound.

Finally, some serious thought into providing a suitable heat-sink for those output transistors

Regardless, there are a number of people looking into helping me with a solution to my single vertical board issue. For that, I am eternally grateful and humbled by folks' kindness.

Keith on the Oz forum was in the thick of the 4KA project back in the day. He just posted a very relevant comment here:

https://vintage-radio.com.au/default.asp?f=6&th=313

Sounds like this is going to be a very interesting project.

I'm prepared to take the vertical design to a ready-to-stuff PCB. Anyone offering to take on the metalwork side? Source compatible connectors?

Posted by: @irob2345

Source compatible connectors?

PL16 is the same type as used on the 3500 convergence, I have one of those in stock (see below). The other socket connector that connects to the yoke is going to be tricky to find. John reckons it might be the same as used somewhere on the TX10.