Ekco T344

[Radio Tech]

Thanks for putting your drawing in Stephen, much appreciated. After changing the psu caps I powered the set up, could not hear any timebase whistle but after switching the set off there was a spot disappearing in the centre of the screen. But will progress on slowly.

Regards

Ken

[Freya]

Posted a clip of the relevant section from the genuine Ekco sheet, there's not much that's going to stop it oscillating capacitor wise. C91,C93,C94 also C85 boost if not already done, plus C72 & C73 later

[Radio Tech]

Hi Stephen

Have got as far as getting a picture on the screen, I found the dual 2uf and 500uf electrolytic u/s and also changed C101 and HT rectifier as the HT was sitting at 170V now around 190V, after a short while the width starts to shrink and then picture starts to fade off, I am at the moment suspecting the 30P4 and U26, I would change these for known good but haven't got these as spares, the only one I have got is the U191. But got a lot more to do as yet, and checking resistors as I go.

Keep you all posted

Ken

[Nuvistor]

The width coming and picture fading could be damp in the LOPTX. If there is nothing obvious it may be worth drying the TX out.
Was the 2+500mfd cap on the frame PCB, the 500 being the frame output cathode decoupling? Cant remember what the 2mfd is for.
Frank

[Lloyd 1985]

Just a thought,I had this very problem with my T368, and it wasn't a damp lopty causing it, it was a capacitor, using the Trader sheet 1498/T203 for the T368 and T371 the cap is labelled C94 (0.01uF), looks like it goes via 1k resistor to the grid of the line output valve. It is located on the PCB with the 2 line output valves on it. If anyone has the data for the T344 (which I don't) maybe they could see if it is the same component layout as the T368 and work out what the T344's equivalent of C94 is? It might even be the same.

Regards,
Lloyd

[Radio Tech]

Hi Lloyd

The 2uf decouples g2 on the 30FL1 and the 500uF is the cathode bypass on the 30PL13 both I have changed as both were leaky and way out of value. I also found the 4.7K 2k High which is on g2 of the 30P4 LOP valve and the .003uf which decouples to deck reading 17uf. I now have a more stable picture but the width I think now is down to checking those string of resistors r81, r83, r87 in the width adjustment and getting hold of a known good 30P4, pity a PL36 wont do but it will not, and getting a good U26.

Here's a picture of the test card on it.

More to follow,

Ken

[Radio Tech]

Have now changed the 3 resistors in the width adjustment chain, there were two that were supposed to be 82 Ohms but these read 96, and the 56 ohm read 78 Ohm, and I changed one of the 0.25uf caps that are on each end of the chain.

Pressing on

Ken

[Restoration73]

Use the replacement 30P19 as many new old stock are cheap and common.
Many GEC sets with direct sync had fold over on the left, normally cured with the
picture shift magnets. Line over scan is normal as I think it is a 5:4 ratio tube.

[Radio Tech]

Hi folks

Here's a pictures of the set the first with the horizontal hold slipping, the next is where I have adjusted the hold, and the third is after its got warmed up, I am sure this is being caused by either the line o/p valve failing or the U26 starting to give up.

Regards

Ken

[Freya]

If the width is getting less the longer the set is on then it might be damp in the lopt still, your third picture looks to show the focus is off which may mean the EHT is dropping.
I agree the output valve is most likely low emission causing low width, which could also be the case on the 30FL1 and your line speed being low initially.

[Radio Tech]

Hi Stephen

I thought of trying the line o/p valve first and then the eht rectifier, if this doesn't do justice then I will try the 30FL1 and go from there, of course it very well could be the lopt showing signs of a small amount of dampness somewhere, only time will tell as I progress.

But thank you for your input, it helps a lot.

Ken

[Radio Tech]

While I wait for some valves to arrive I checked R72 a 270 Ohm is the cathode bypass on the frame op valve, this read 393 ohms somewhat different to the value stated, the original is or was supposed to be within + - 5%. The other odd thing is that the chain of resistors for the width are marked on the ERT sheet as all 56 Ohm but the circuit in the radio and television service book indicate two at 82 Ohm and one at 56 Ohms, it makes wonder which is correct although the originals were marked as 82 x 2 and 56. But why I wonder did they put an 0.1uf at each end of this chain when both circuits only show one.
I am sure someone has the answer to this.

More to follow

Ken

[Freya]

The circuit posted in #22 is from the genuine Ekco T344 service sheet, I would always go from that.
R72 is 270 ohm in 17", 300 ohm in 21 ", the Ekco sheet shows C86 0.1uf at one end and C91 0.25uf at other.
How do your voltages compare with those given for both ends of the resistor chain ?

frame circuit added

[Radio Tech]

Hi Stephen

I haven't checked voltages either end of that chain but will do this, I replaced the 30P4 and width improved but the picture had some sound bars on it and as the set warmed the picture width just starts to go down, I did wonder if the electrolytic caps I have used for the smoothing are good enough for the job although the HT doesn't drop much below 190 I think it was, the old dual capacitor had 750m/a ripple on it and I do not know what the ripple rating of the ones I put in, all I know is they are the correct values and rated 450V.
Best wishes

Ken

[Freya]

Did you get the 0.1uF in the tuner, these cause odd problems, there is also a dual smoother one section on the tuner HT2 line after the 100 ohm resistor, the other on the screen of the sound output valve. These dual cans cause problems on Ekco sets with one or both sections.
The Main smoothers will most likely be fine with whatever you have used.

[Radio Tech]

Hi Stephen

I measured the voltage at either end of the chain that controls width and the end that has an 0.25uf measured 190V the other end measured 196V. I haven't changed the 0.1uf that is on one end of the width resistor chain as this is a little difficult to get to and I did not want to disturb the tube, I have changed the other dual smoother cap I had to use two separate ones for this but I hadn't realised there was an 0.1uf in the tuner but will have a look to find this.

Will update as I progress

Ken

[Freya]

Sent you a copy of the Ekco sheet as requested, its zoomable. Any problems let me know.
Is your Boost voltage around 600 volts ? there are a few caps around this area that could be pulling it down.

[Radio Tech]

Hi Stephen

Will check boost volts, I think I have changed most of the caps around this area but none the less will re check.

Thanks for sheet

Ken

[Radio Tech]

Have checked the boost voltage with an AVO and got 600V, I am beginning to wonder about the 120pf capacitor strapped on the LOPT and those ceramic ones on the base of the 30P4 and U191, for some strange reason the set gives a full screen picture and a nice one at that for around ten minutes then after this period the width slowly but surely starts to shrink, picture quality seems to remain, I have even checked the mains tapping to make sure it is in line with our mains supply here which is 230V, the resistance values of the mains dropper are a little out but I do not think this is the main problem, it is when the set warms up, I have even tried a new 30P4 and still have this odd problem with the width.

Any further advice grateful.

Ken

[Lloyd 1985]

Have you any way of blowing cold air into small area's of the chassis? This sounds so much like the problem I had with my Ekco similar to yours. I don't recommend buying a can of freezer spray and blasting it all over the place near hot valves, what I used was a large blower fan with a rubber hose attached to it's output (see the link to the restoration of my set I posted a while back), and carefully blew cool air at bits on the chassis to see if it made any difference. Eventually I got the little ****** that was causing the width to come in, and blowing cold air on it made the width come back, and leaving it to heat up again made the width shrink all over again.

Does the HT drop at the same time as the width comes in?

Oh, there was another capacitor that caused some problems for me, over on the RF side of the chassis, a dual 16+16uf, it was leaking rather badly, and I found it just as it was about to go bang! It was rather hot, and the bung was bulging a bit. Might be worth looking for if you haven't already had to change it

Regards,
Lloyd.