CTV [Sticky] 1974 20" Ferguson 3C03; Thorn 4000 ; Super Rare
That other plug was certainly used as the mains input from the on/off switch to the main chassis on the TX100, not sure about the TX10 ?
I would need to drag the manual out for that chassis as I don't have it to hand.
Edit: Yes, it was also used on the TX10 for the same purpose as well, I just looked at the manual on this PC 👍
Not sure if this is useful or helps in any way. The 8-pin 10-pin socket PL16 is 25mm X 15mm, here are the pin spacings for PL16, as taken from the 4K board, including the locating pin coordinate.
I could be wrong, but I seem to recall that 2-pin plug was also used on the 9800
edited: reason PL16 pin
Could very well have been used on a few earlier Thorn chassis, it was so long ago now I just can't recall with absolute certainty.
I knew it was definitely used on the TX100, I thought it might have been used on the TX10 as well but was not a 100% certain, it was all just so long ago now added to the fact that that particular plug never really gave any trouble and was probably the least noticed part of the sets in question, it was just there.
Hi Baz, forgot about the TX100. The plug was certainly used on other chassis such as the 9600 and 9800 but plugged into a filter unit.
Great you have a spare for the 10(?) way connector. Will need accurate dimensions or a mech. drawing of it. I wonder if Farnell stock it, or something similar?
The yoke socket could be implemented with a couple of PCB pins (wrong polarisation = upside-down picture), we just need to know the size and spacing.
A dimensioned sketch of the aluminium casting would allow a suitable substitute to be made in sheet aluminium. I could draw that up in Fusion360.
Replied before I saw the dimensions. That's good enough to create a footprint for it.
Usually 0.1 inch spacing (2.54mm) for the PCB artwork grid reference. Although stating that I find the pitch on the BRC 2000 edge connectors is 4mm.
Here are the 'Real-World' measurements, taken from the board.
I've superimposed the socket not as it would appear from below, but does reflect the correct key-way orientation. This is just for reference and includes its body dimensions. I will put out a wanted request in the forum, should anyone have a scrap TX10/TX100 chassis. Sods-law I have all manner of PCB's for all manner of sets, but virtually zero TX spares.
A dimensioned sketch of the aluminium casting would allow a suitable substitute to be made in sheet aluminium
Here it is exactly duplicated. I didn't map the transistor output pair's mounting holes. Precision here does not matter, a close approximation will suffice, as there are flying leads from the PCB to the transistor legs.
The taper on the last 65 mm of the vanes, toward the rear is essential, this ensures adequate clearance from the CRT
Jim @jcdaze has kindly donated an actual Thorn 4000 Vertical Deflection metalwork, which is the heat-sink/frame that holds the PCB, not the PCB as he understandably needs that for his.
Not only that, Jim will include the coil L401, and the 2-pin grey connector. Wow! Cheers Jim, you're a star.👍
That's a few of the major hurdles, now tackled. Leaving the tricky task of the actual PCB to fit the frame. Both Ian and John are working on this, pursuing from different perspectives, interesting times to come.
As I've said before, humbled by the generosity and spirit within the great VRAT community.
That's something I already have Chris, see here. Thanks for taking the time to offer though, very much appreciated. Indeed the socket was used on lots of Thorn TV's, got mine off a scrapper 3500.
Just for clarity, this will be the currently gathered 4k deflection parts, Jim's posted them to me, just missing the PCB.
Edit: Posted on Weds for next day delivery. Nothing Thurs, Fri or Sat. Not looking good, really hoping RM have not again excelled themselves at losing rare items for me.
The Vertical Deflection PCB mount/heat-sink, coil and 2-pin plug have finally turned up Jim, many thanks, I reckon RM don't like snow and wind. 👍
So here we have it, I've all the rare bits needed, to try to replicate the 4K Vertical Deflection board.
John (jayceebee) is working on etching a replica Vert Def PCB, so dedicated to the task, John has taken the kit with him whilst he works in Ireland this week. Something to do in the hotel, in the evenings I guess, either way I'm so very grateful. Hopefully in a couple of weeks or so I should have something, and then be able to start populating the main PCB.
Which then leads on to the other hurdle we face, TF401 & TF402, the vertical deflection 'Thick Films'.
Remember, we know the resistor and caps values used, as the TF's are detailed in the service manual. However, the same is not true for the diodes and transistors, they are unknown. John, using his Thorn knowledge, is making an educated guess as to what these might be. Once he has simulated this in Kicad and proven the replica TF cct works, I'll set about building the replica 'Thick films' on matrix boards. I will then encapsulate in Silcoset 101, the same I used when I rebuilt the Thorn 2K tripler, which should make them look identical to the originals.
I suppose if the etching of the main PCB fails to produce something useable, I can always revert to building on Matrix. OK, the back will not be pretty, but I guess it would work and a fallback option.
I've just noticed the frame mount Jim sent (on the right) has an extra vertical fin on the opposite side, whereas mine does not. What's that all about? 1st gen, 2nd gen, perhaps.
I think that extra fin may may have been to help protect the slighty flimsy thick film vertical shift control. Field engineers would have had these boards knocking about in their cars/vans.
Did a dry fit on my Matrix board, mainly to find out if I had all in stock that is required, for the main Vertical Def PCB.
I've everything, bar three components, C417 75pF @ 500V 5%. All I've got is 68pF & 100pF at 500V. As the cct calls for 5% they are no good. The other cap is C411 0.27 @ 250V 10%, again none in stock. Both of these have now been ordered, and should be here sometime this week.
The third is R411 a 0.68R 6W 5%. I've boxes of Hi-watt resistors, but no idea if I've that value, I suspect not. What on earth were Thorn thinking when designing that value into the cct. Anyway, to save the pain of sorting through loads of boxes, I've ordered these from Farnell, they do 0.68R 7W
For the output pair, VT402 & VT403, these are BRC specials, BRC R84 (RCA) & BRC R83 (RCA). These I will not be able to find. Having a chat with John earlier today, as the toroidal scan coils need high current he recommends TIP41/42C, these are good for 6A, I have these in stock.
My next problem is TF403, this is another thick-film unit used for vertical shift. This unit consists of high-wattage resistor elements that are selected by a make-before-break switch. They have to be very high wattage due to the high current required to shift the 110 toroidal scan coils. TF403 is connected between the 30V rail and R411, that's the large .68R 6W resistor I had to purchase from Farnell. Adjustments to TF403 results in current flowing through the scan coils L402/L403 to or from the centre-point of VT402/VT403.
Starts to become clear why the massive heat-sink, the 6W output pair, the 6W R411 and the High watt, thick film for vertical shift. A lot of heat generated here, not so much a concern for the HMV, must be a nightmare on the 3C03.
Anyway, I had though about implementing a Decca Bradford style solution to vertical shift, a tag board with a few resistors and a flying lead to select pairings. Not sure now, and I've no idea what the 3 resistors should be other than 6W. Nothing in the manual or on the cct.
Anyone, any ideas how to solve this?
Looking at the thick film it looks just like a fancy pot, the wiper is free flowing, meaning no click positions. How important is the Make-before-break in its operation? The reason I ask is, I had a mind to use a high current pot, I still have that surplus 5K 4W from the G6 project. However, testing TF403 shows it to have a range of 55R - 8.9K.
It is more to do with the ratio in a potential divider rather than absolute values, however the current source will probably be important.
The AC current in the coils will be around 6 Amp but I don’t think the DC requirement will be as much. For the testing stage I would recommend this, set the TF to around its mid point then check the resistance between the slider and each leg making a note of the resistance. Fit fixed resistors for now and work out a suitable pot later.