Project [Sticky] 1969 Philips G22K511 Missing I/F & LOPT, Conversion

Now that is spiteful of it. A double shame now that the +ve pulse is no longer playing ball. I had an idea last night on how to get the -ve pulse a bit higher using the old G6 desaturation choke. My idea was to fasten it close to the unused limb hoping there was enough close coupling to get to a couple of hundred volts from it. 

Posted by: @crustytv

my nice new 200MHz probe now as a gash burnt into it as I'd not noticed its casing was slightly resting against one end of R4072. Not happy! Pesky G6🤬 

 

You should see the state of the case of my LeCroy after it got too close to an "Anglepoise" whilst trying to help fix the Philips 210 I mentioned elsewhere...!

Posted by: @crustytv

R4072 is sited right next to X4141, my nice new 200MHz probe now as a gash burnt into it as I'd not noticed its casing was slightly resting against one end of R4072. Not happy! Pesky G6🤬

That's just a friendly little love bite! - Like the ones cats give you when they're just playing around. I told you it loves you really! When it starts getting a bit darker it'll come running in and curl up by the fireplace, they always do! 😻🔥😽

If that telly was really in a malicious mood it would easily sever a two inch section clean off the end of a three sixteenth inch diameter screw driver. That didn't happen to me, oh no, that was one of Jerry's 'moments'. Now, "Mr Nelson" was a very highly regarded chap in our locality, and rarely made mistakes, so if it could happen to him, it could happen to anyone, and he brushed it off with the quip "Oh well, it was a 12" screwdriver. Now I'll take it home with me and make it into a 10" screwdriver!"...... And so he did! 

Jerry was held in such high regard that even after retirement he was still to be found in many a workshop around the county, especially on the approach to Christmas, helping out with the worst of the worst basket cases.

Some developments and as Till would say "Glasnost", a lesson I've learned today is not to doubt yourself, and then jump to conclusions to reinforce a false belief.

This debacle all started when after installing the new Single Standard IF PCB and still having the unlocked problem. I followed Johns advice below about removing LOPT connections from 20/21 and the new resistor.

Posted by: @jayceebee

The high triode cathode on the PCF802 reactance stage is I suspect due an imbalance of WF22/23 from the LOPT. Try running with the reference pulses disconnected from pins 20/21 of the LOPT and see if it's anywhere near the quoted 5.8v, it will not be exact but with the small amount of direct sync provided by R4077/C4011 you may just about achieve a weak lock by adjusting L4501/2.

If you do get the cathode volts a lot lower then it is probably because the the flywheel feedback pulses are widely imbalanced and you will need to keep experimenting with R4070/2. You will probably struggle to get WF23 to it's correct value but whatever you can get it to try and make WF23 the same amplitude by changing the value of R4070 and adjusting the flywheel balance pot.

You need to disconnect the lead that feeds the -ve 47v pulse from the LOPT and I’ve just remembered the one from your newly added tag strip as we found a better tap off point for the +ve going pulse

Pretty clear really, but somehow I managed to convince myself when putting things back, the orange wire from the new resistor had come from pin 7, despite clearly stating myself it came from 1.

Posted by: @crustytv

Ok that now makes sense, when you said this morning to remove the pulses from 20/21, I thought what....there's nothing on '20' to remove other than the link from '14'.

So I'll remove the -47V pulse from 21 (green) and the orange from pin 1 that is providing the +ve pulse to the new tag board. 👍

This accounts for the recent problems with the overheating R4072. So reverting the wire back to the correct position (7) in the LOPT has resolved that problem.

This leaves the inverted waveform 23, this is NOT as far as I can tell of my making, but was present from the moment the new SS board was installed.

Now for some interesting observations of where we are

With the scope connected to the cathode of X4141, monitoring for waveform 23, I can lock the raster. I can remove the tool, and it remains locked for a quite a while. Removing the probe results in the lock being lost, going into free run, add the probe again and the lock is re-established.

Still no idea what any of this means or proves, except I was the idiot that caused the excess current problem in R4072 by attaching the additional resistor to the wrong lopt pin. However, one other interesting observation, making that mistake, removed the inversion from Waveform 23. With the wire back where it should be, the inversion is back.

At least I got to the bottom of it, and I can install the ITT which will hopefully address the low +/- flywheel pulses and perhaps remove this inversion problem.

Oh and if I have the colour control at half way or above the lock is even more stable, turn the colour control to off and the lock is lost. This next photo is with the colour killer valve removed, and the colour control set at three-quarters, followed by what the cathodes of X41040 & X4141 show.

I said it would come in and curl up by the fireplace! - Now it just needs feeding and taming!

It’s probably purring now or is that just intercarrier buzz? 😆 😆 

Posted by: @crustytv

Not sure where to start with this update as there's been so much going on. To try and cut a very long story short, we needed to source a pulse from elsewhere on the PYE LOPT, for the X4141 discriminator diode. We settled on getting this from Pin 7 via a suitable resistor. 

As you can see you weren't wrong and if you remember I recommended starting with a ridiculously high value resistor because I thought there would be an awful lot of energy there. Why this was working but is now giving the results you have now is a mystery from here.

John and I have been discussing this offline and have decided that we're ceasing any further work trying to integrate this PYE LOPT.  The ITT LOPT has been posted, I'm hoping it may arrive before the weekend, but we will have to see. In preparation, I started to revert some of the mods we did to the G6, for the PYE LOPT such as borrowing the 190V from R4088 and reinstalling R7280 back on the decoder.

Fingers crossed the ITT LOPT which is a pull from a spare chassis, is OK and not having any shorted turns. I'll test on arrival, if OK, transpose the wires from the PYE LOPT wires onto the ITT.

The ITT LOPT was posted out yesterday and arrived today. Cleaned and tested, the scope ring was inconclusive, but I've had that before on some LOPTS. Using the JABCO LOPT tester confirms it as OK. Guess the real proof is in the TV.

Now the difficult bit, figuring out how on earth I'm going to mount this into the limited space I have for the LOPT. It's not as easy as the PYE as the ITT is on a fairly large PCB with lots of bitey bits that can cause issues, It's going to need some thought. Then there's the hook-up to the G6.

Practice fit, I think this is the best I'm going to be able to achieve with the limited mount points on the LOPT, available space and optimum orientation.

Wasn't happy with the little bracket I added to the bottom of the ITT. I then had a brainwave, why not use one of the ends from the dead Philips G6 LOPT's. As luck would have it, the holes lined up to attach to the ITT. I can now securely mount the ITT LOPT, to the existing G6 LOPT points. Result!

Just a quick question, do the numbers printed on the circuit diagram correspond with the pins of the new PCB or the transformer?

I suspect also you will need to remove the VDR R414 and the capacitor C303 on the new tx PCB as they are duplicated on the original G6 circuitry.

There are 15 points shown on the cct and 15 points on the LOPT, two from the overwind do not terminate on the PCB

This looks somehow more civilised than the PYE jobbie - Either that, or I'm going 'boz-eyed'. The take off for the tripler looks closer to what it should be - Let's say, a bit more refined than simply nicking a bit off the top of the 509.

At least for the moment, it should be more like plain sailing in the wake of those who have done this mod before.

I'm mindful of a verse from "Good King Wenceslas"

Mark my footsteps good, my page,

Treads't thou in them boldly,

Thou shalt find the Winter's rage,

Freeze thy blood less coldly.

The tune used to the Christmas carol is based on "Tempus adest floridum" ("The time is near for flowering"). Also rather apt?!

If the CVC5 line output transformer connection No.3 becomes the 0V connection then No.1 will become -350V and No.5 +350V. Both 30 volts higher than the pulses produced by the G6 transformer but should be OK to serve as the reference pulses for the line flywheel discriminator.   The lower voltage pulses can be produced by a separate winding. 

Till Euelnspiegel.

Components on the PCB

• C308 180pF 8kV
• C303 220pF 8kV
• C306 330pF 6kV
• R422 1.8K 4W
• R414 VDR E298 950V

Posted by: @katie-bush

This looks somehow more civilised than the PYE jobbie - Either that, or I'm going 'boz-eyed'. The take off for the tripler looks closer to what it should be - Let's say, a bit more refined than simply nicking a bit off the top of the 509.

Hi Marion, the PYE LOPT Chris used did indeed have an overwind which with a tripler would have eventually achieved 25kV. The LOPT Chris chose wasn't a manufacturers original but a clone by Weyrad, in this case the primary and overwind were on the same bobin. Weyrad often did this if I recall correctly and hey were also much more reliable in my opinion.

Preparation for the rewiring

When the PYE LOPT was installed, the G6 plugs PL7 & PL8 were mapped onto the PYE LOPT pins. Rather than making life complicated and trying to translate PYE pin back to G6 Pin to ITT pin, I decided to make life easier. So PL7 & PL8 were removed from the PYE LOPT entirely, I then labelled all the wires with their corresponding G6 LOPT connections. Now it should be a simple matter of following the G6 to ITT map as originally designed by Keith (CTC15).

Notes for my benefit and this log:

Revert G6 LOPT panel back to G6 for the following:

1. R5040 back to 220K
2. R5036 back to 3.3M
3. R5037 back to 3.3M
4. C5017 back to 150pF 8kV

Revert on Timebase:

R4072 back to 33K

Remove from ITT LOPT:

1. C303
2. R414

Change on ITT LOPT:

1. C306 to 330pF 12kV (C2 on diagram)
2. R422 to 100K 5W (R1 on diagram)
3. C308 to 150pF 12kV (C1 on diagram)

Of course, all this needs to be thoroughly checked and rechecked.

Question, does C306 really need to be 12kV?

There's no way there's 12kV pulse from the TC of the PL. On the ITT, C306 is already a 330pF at 6kV, so even ITT didn't see the need for 12kV. Likewise for C308, although I do have some 12kV of those. I don't have any 330pF 12kV in stock, only 6kV so would need to order some.