TV22 frame collapse

[mark pirate]

I will check through the set again today, I am sure that all the replacement caps I have fitted are the correct values and fitted in the correct places, even the one hiding behind the tagstrip!

I have swapped both ECL80's for known working ones, the PZ30 and PL38 have been tried in my Pye LV51F and are fine, the only original cap is the main smoother.

I would re check your work around the frame stage. As you would have been unable to test your work when re capping due to the blocking TX being OC, then It could be due to something being disturbed here.

It is quite possible that something has been disturbed when recapping the set, I will go through it thoroughly today.

John, the replacement blocking tx was removed from my untouched TV24 and the resistance readings are fine, it is definitely wired in correctly (see photos).

I will check for o/c controls, but all were working ok when I had the connection from the heater chain to the ECL80 in place.

Failing that Mark, haul it up the A24 to my place and we can sort it out together!

Thanks for the kind offer John, I may well be bundling it in to the van and heading your way if I can't solve it today!

Mark

[mark pirate]

Here are the photos I forgot in the last post.
The first one shows the original blocking tx during the recapping, the second photo shows the replacement still in situ on the TV24.

Mark

[Heatercathodeshort]

There is a nasty .01uf waxie in your first picture. This looks like C6 [Newnes] connected to the grid side of the blocking oscillator. The test to the control grid of the output section of the ECL80 only checks the output stage is working. Coupling from the frame oscillator is via the vertical form pot and the height control. Try feeding the heater pulse into the top end of the height control and see if you get a scan. J.

[mark pirate]

Hi John, the photo was taken during the re capping, C6 has been replaced.
I am still getting nowhere fast with this set, I have rechecked everything but still no joy, I have tried your suggestion of feeding the heater pulse into the top end of the height control, and I am getting a scan.

The first picture is the scan going in to the ECL80, the second is going in to the height pot.

Mark

[Boom]

What value is that horizontal resistor stitched on at the bottom of the board Mark? It should be 390k but I can't see the colour bands.

[mark pirate]

Dave, you are correct, it is a 390K, the original was cracked so it got replaced during the recapping.

I have been out in the workshop again to double check the replacement caps, but all are correct, this fault is beginning to challenge my sanity!

Mark

[Boom]

Have you taken voltage readings of the triode section of the ECL80 Mark? There can't be that much wrong with it.

Have you damaged the replacement transformer maybe? A spare one I have here measures 494 Ohm on the left pair of wires (looking the board as you have it) and 549 Ohms on the right pair.

[Freya]

I have had a couple of those make yellow capacitors that are open circuit, 0.01uf only so far.

Stephen

[HamishBoxer]

Going by the yellow spot on line blocking tx,s all looks well But the spacing is different of wires between the top on the tx??

[Heatercathodeshort]

One thing is for sure. It will be something silly, these sort of faults always are. If you have a triode and connect it's grid to one winding, it's anode to another on the same core, it has to shriek!
Something is being overlooked and believe me I had many faults like this during my 40 years in the service trade.
It must be something to do with that transformer, wiring or connections. I know you have rechecked this but I'm wondering if an incorrect connection has been made on the reverse of a tag strip. Failing this it might be necessary to cobble together the frame oscillator stage 'breadboard' fashion and attempt to get it to oscillate. I have a blocking transformer from a Pye FV1 that should work in the TV22.
I'll flag you down on the A24... John.

[HamishBoxer]

Can beat you John, 45 years plus in the trade .Not bragging it's a complaint!

[mark pirate]

I have a blocking transformer from a Pye FV1 that should work in the TV22.
I'll flag you down on the A24... John.

I will try to grab a bit more workshop time today, I agree it has to be something simple, if I can't sort it today I will be heading down the A24

Mark

[Heatercathodeshort]

Originally Posted by HamishBoxer

Can beat you John,45 years plus in the trade.Not bragging its a complaint!

Well Hamish,I started working in a television shop after school from 4pm till 7pm and all day Saturdays and retired from the shop in 2002 after starting on the 10th November 1966 at the age of 18.
I appear to be still doing it and have more junk now than I had in the shop days.. That makes 53 years if you count the school years. So gotcha by a few years! Happy Days! John.
PS. Thinking about it, did they have telly in Scotland 40 years ago?

[HamishBoxer]

Without going too far OT,i started in 1961 at 15 take that off my 66 years equal 51 years in the tv trade plus a few years before with crystal sets about age 10 or 11.Still got a scar on my leg through using a fire iron for soldering when in short trousers.

Re tv in Scotland i did not live here till 2006 was in Doncaster and district.

[Steve_P]

Try going on one side, then the other, of C61.

(Between the Height control and the secondary of T4.)

Cheers,

Steve P.

[Heatercathodeshort]

O.K. Hamish, you win! John.

[Heatercathodeshort]

Mark's lack of frame scan certainly was a puzzle but we got there in the end. As expected it was a simple wiring error when recapping the main chassis. After checking all the voltages, presets, resistors and connections to the tag board housing the frame blocking oscillator transformer, I decided to check for any pulse at the anode of the ECL80 frame oscillator with the scope.
It was the most peculiar shape and amplitude and it was noticed that operation of the horizontal hold affected the shape!
After much head scratching the fault was finally traced to an incorrect connection.
C22 a .02 capacitor in the boost H.T. circuit had been inadvertently connected to the wrong tag on the central board. It was very neatly soldered to the junction of C10 and C9 part of the frame sync clipper circuit and was thus plonking a massive line pulse directly into the anode circuit of the oscillator thus damping the frame blocking oscillator.
Correcting the mistake gave us normal operation with the hold control central position and plenty of height to spare.
This is a very easy mistake to make particularly with Bush receivers with tag board construction. We have all done these simple mistakes and will continue to do so. Maybe if smoke had filled the workshop upon first switching on, the fault may have been less puzzling but as it turned out in this case it presented only a frame collapse.
The part of the relevant line circuit is encircled. It was only necessary to remove the top end of C22 from the incorrect tag and resolder it to the positive end of the 2uf boost capacitor. I will leave Mark to post the finished pictures. We both had a good afternoon playing with my junk. Nice to meet you Mark and hope to see you again soon. Regards, John.

[Boom]

Nice one.

[mark pirate]

I have had a very enjoyable day at John's place, and was glad to get to the bottom of the frame collapse fault, even if it was of my own making

The set is now working well, the tube certainly looks to have plenty of emission, it just remains for me to recap the receiver chassis and replace the EHT lead and a couple of wires to the dropper, as the insulation is cracking up.

I will leave Mark to post the finished pictures

I think you will have to do the honours John, as the CD did not copy the photos!

It was a pleasure to meet you John, and thanks again for helping me with the Bush.
The invitation stands to Come and play with my junk collection sometime.

Mark

[Heatercathodeshort]

Strange that one Mark. I did open the pictures up after burning them.
Maybe the TV22 had the last laugh after all!
Pictures taken of underside and test card.