Dynatron (Pye 697 chassis) - frame collapse

[Tazman1966]

Hello to one and all.

I'm on the cadge for some information (again !)

I recently collected a Dynatron CTV170 (I think) fitted with the Pye 697 chassis (Thanks Mikey)

When I got round to looking at it there was intermittent frame collapse - actually more collapsed than working! Also no colour but the picture when okay was fantastic (in black and white - brilliant CRT). I found that a couple of times when poking around with the Digital Multimeter the scan would open up and would not collapse again. When the scan was okay I did find the cause of the no colour - crystal on the decoder board was incredibly dry jointed - one side not soldered at all. How it could have ever worked I'll never know.

Anyway after doing some voltage checks on Plug 10 on the FTB panel with it in situ they were (a) +19.9V, (b) + 22.5V, (c) -23V and (d) +11V - not too bad.
The voltages on the output transistors, VT26 and VT27 were close to spec as well.
Then I removed the plug to recheck the voltages and everything seemed in order but with the rails rising to +30V and -30V without a load which I expected.
I then rather stupidly just plonked the plug back in with the set switched on and had another think. Hmm... one final check on the power supply/LTB panel for cracked print - there's certainly enough bridged tracks - I finally found that the print from the edge connector to the frame scan coils had a minute crack in it. Ah-ha thinks me! Problem solved.
I soldered an insulated wire bridge between the offending section and re-checked the continuity. Hurrah, job done, I thought.

Fired the old girl up again expecting full scan but no. I re-checked the voltages on the Plug 10 and they were much lower than before so I had a check on the output transistors and the voltages were all over the place. Now what, I thought? I took out the transistors and tried some resistance checks with my DMM and they were certainly not the same as each other.

Did I kill one or both when I plonked the plug back on with the set still switched on? What do you all think? And where do you find BD124 transistors now?

Your help will be very much appreciated. I'll post some pics as soon as I get my home computer back on line as I'm posting this on my work computer (after hours I hasten to add )

All the best and look forward to hearing from you.

Tas

[MALC SCOTT]

Use BD131 transistors for the BD124 types. I might have a complete frame panel if you get stuck. Cheers, Malc.

[radiohm]

Hi Taz.

Grandata have BD124P transistors at 50p +vat. (Don't know what the suffix "P" denotes though, its not in my "Towers").

www.grandata.co.uk

Regards.

Mike.

[Hunts smoothing bomb]

Hi Tas,

I have a complete 697 chassis, it came from my working set I was fixing up. I can send you the FTB panel if you like for cost of postage.

Oh... don't do what I did and leave the room with the set turned on, that's how I got these spares. The damn thing caught fire and was beyond repair :-(
You can see the set working here from last year under the post "Dynatron CTV10 help required" page 2.

Cheers
Lee

[MALC SCOTT]

Grandata have BD124P transistors at 50p +vat. (Don't know what the suffix "P" denotes though, its not in my "Towers").

Suffix P = plastic type body.

[Steve_P]

You might find a page on Mikey's site useful.

http://www.oldtechnology.net/

Click on OLD TV, TV SERVICING ARTICLES and pick the 3rd one down! And please change BOTH transistors.

Cheers,

Steve P.

[Tazman1966]

Morning Guys.

Thank you all for your suggestions.

Malc - I already tried Grandata but they were out of stock.

Lee or Malc - I will take up one of your offers of the complete FTB panel inc transistors. Please reply via the thread and I'll PM you back.

...And I'll keep you all updated as to my progress.

Bye for now,

Tas

[Welsh Anorak]

To follow Steve's advice ...and the AC128 as well!
Tas - I've PM'd you and there's a circuit description copy in the post.

A spare panel seems a good idea, though - for a small panel they could be a swine to repair!

Glyn

[Mike Phelan]

Tas
If you still have no colour when you have sorted the FTB, suspect the two 4n7 Suflexes in the reference oscillator near the xtal - they go O/C.

[Tazman1966]

Hi Chaps!

First, thanks to everyone for your ideas and a big thanks to Lee for the replacement panel which was waiting for me when I got home from work this evening.

After transplanting that into my set (a CTV16 not 170 as I first typed ) we have a picture, hurrah! I re-checked the voltages - a little more tricky on the replacement panel as the output transistors are mounted on top of the board and not clipped to the side of it - and they are much more sensible: phew!

Next it was time to tackle the geometry and convergence which was pretty easy. I only just managed to get the blue horizontals to line up at the top and the bottom with the blue amplitude control right at one end but very acceptable.
It's amazing how the memories and therefore the ability come flooding back after so many years of not even seeing let alone working on a Pye Hybrid chassis. The grey scale is perfect but the colours were not quite right.
The B-Y seemed low - fleshtones were quite pinky and blues were pale - quite difficult to describe in print - so I swapped the blue PCL84 valve over with the green one but it made not a jot of colour difference (if you'll excuse the pun ) so remembering the advice I gave to Lee before about odd colours I turned the blue colour difference pot (RV27) up to max and the colour was much better.
The only thing left to do now was Hanover bars on certain colours. I've had a bit of a play with the PAL balance and it has improved it to a good extent but it is still not quite right so I'll have to investigate that tomorrow.

I haven't cleaned the old girl up properly yet and neither have I got the legs for it yet but after showing it off to the wife - the Dynatron that is - I took some photographs. I'm hoping to move the set out of the garage (workshop) and into the house if my powers of persuasion work!

All the best for now,

Tas

[Tazman1966]

...and here's some more photographs showing the front controls, door and even a picture of the great way that all of the Pye hybrids switched off with a red, a green and a blue spot in the middle of the screen which slowly fade away - altogether now ahhhh!

Bye for now,

Tas

[Focus Diode]

Excellent Tas, another old set up and running! I would imagine the sound quality on these Dynatron versions must be superior to the Pye and Invicta models which were awful!

Indeed a PYE CT205/2 developed no sound at all suddenly. Surprisingly the speaker itself turned out to be the culprit. They're non standard so I ended up having to use an 8ohm type with additional resistors in series to get that right.

The improvement in sound quality was startling, but there was nothing I could do about the slight but noticeable purity error at the speaker side of the tube!

Cheers,
Brian

[Tazman1966]

Hi Brian.

There certainly is a much richer sound quality to this set with its larger than usual loudspeaker mounted underneath the screen.

Back out to the garage...ahem!...workshop soon to tart up the cabinet and then have another tweak on the decoder to try to completely eliminate the Hanover bars which are now I must admit pretty faint.

All the best,

Tas

[Tazman1966]

...and here's the set out of the garage and into the house. There's a shot of the LTB/Power panel. Not all of the mended tracks is my work! There's been a lot of mending done on this panel in the past. Anyway, we watched the whole of the London Marathon on it today and it performed faultlessly.

Cheers,

Tas

[Mike Phelan]

Looks good, Tas. I think the main reason for the Pye version having poor sound was the speaker; the little Mullard AC187/188 module has quite good performance.
Have you changed the 2m2 grid leak resistors to 680k on the PCL84s to avoid future trouble?
Has it a wired remote?

[Tazman1966]

Hello Chaps.

Simon - It is bright and sharp! I'm at work at the moment but it is AFAIK a Mullard "Colour Screen" A56 120X

Mike - I haven't checked the resistors yet. Will the PCL84's run cooler after the mod? They're certainly very hot!

Tas

[Hunts smoothing bomb]

Hi Tas,

It is quite possible the PCL84s will run cooler with the 680k mod, the 2m2 grid resistors tend to go high and then the PCLs pass too much anode current, that was one of the last things I did to my Pye before it incinerated itself!

It's great to see your set displaying good bright pictures like that and I am glad I was able to help out a fellow enthusiast, although it was down to the loss of my set really.

Has yours got a plastic four push button remote control also fitted with three pots? volume, brightness and colour?

I still have mine if you're interested.

Happy viewing

Lee

[Focus Diode]

The repairs to the LTB panel are typical! Surprisingly the red fuse cover has survived! Don't forget the LTB/PSU panel is LIVE when the set's switched off and plugged into the mains.

Mike's suggestions are sound and will save a great deal of trouble in the long run. The PCL84s do run quite hot but the mod will prevent overheating and the valves going into grid current with consequential damage to the already fragile CDA panel. I had a case of fading red with an overheating PCL84 which was cured on changing those resistors without having to replace the valve.

The pictures are superb, well done! I used a 22" Pye CT205/2 domestically for a couple of years around 1999/2000. Having sorted out the usual problems initially it worked well although the CRT was past its best. The set only broke down once after nine months, the very common 100K resistor burn up and blown 2.5A mains fuse due to the A1 capacitor going s/c. It was back in action within minutes having spares to hand!

Just looked at your FTB panel and noticed those horrible black and silver CALLINS electrolytic capacitors on the CDA panel. Would be well worth replacing these!

Cheers,
Brian

[Mike Phelan]

Funny that I missed mentioning the field service engineer's life preserver aka fuse cover - it is so unusual to see one still extant - most ended up in pockets, glove boxes or toolboxes!

Brian has covered the PCL84 mod, so I won't repeat it all.
Even if the 2m2s are still in tolerance, you don't need much grid emission to pull the anodes down.

If you have the CDA panel out, rub some switch cleaner on the underside edges of the print and the chassis frame where they sit.

[Tazman1966]

Hello guys.

Lee - It is the one with four push buttons on the front for tuning with the fifth one for remote control operation. I haven't got the remote for it at the moment; I have the jumper lead connected inside to allow for non-remote operation. I will hopefully be getting the remote for it soon though (Cheers Mikey405)

Brian - I may well have a go at the electrolytics on the FTB. I did this on the original panel in an effort to restore frame scan and think that you may be right with this idea - the height control is at one end of its travel with just enough height.

Mike - I'll do the switch cleaner job on the contacts when I do the resistors.

Thanks again chaps.

Tas