problem with ekco T 231

[petertheorgan]

Hi Everybody

I wonder if I can pick your brains ,
I have an ekco T 231 that is working nicely but it still has a few faults

With no sound fed into aurora , the picture is stable but any sound fed intends to "unlock" the horizontal hold whatever the position of the volume control

also there is "flaring" on the left side of the picture which you can clearly see on the attached testcard photo

also the black square tends to spread to the right , this gets better as you turn the brightness up but the set still seems lacking in contrast

also the volume will not turn right down but I know that this is due to a faulty pot

all the capacitors in the set have been changed ,,,,,, any ideas where I ought to be looking next ,,,,,,,its 90% there and I would like to have it perfect if that was possible

I await your replies with interest , feel free to ask any further questions

Thanks in anticipation

Peter

[Steve_P]

Try it on more than one channel, and check the tuning. Make sure the coil biscuits are connected properly. Might be worth swapping the tuner valves out? Check the voltages against the manual/trader sheet.

Realign as per the sheet.

This looks to me like either severe misalignment or a tuner fault.

Cheers,

Steve P.

[Mike Phelan]

Originally Posted by petertheorgan

also there is "flaring" on the left side of the picture which you can clearly see on the attached testcard photo

also the black square tends to spread to the right , this gets better as you turn the brightness up but the set still seems lacking in contrast

Peter
That looks like a line sync/line blanking problem - the video information is appearing at the left-hand side of the line flyback (line foldover).

To see if it is that, if you rotate the line hold slightly, so it does not unlock, but just moves the picture slightly, does the foldover "unwrap" itself when the raster picture rightwards?

Any of Ekco's favourite Hunts Moldseals still there in the line sync stages? Flywheel sync diodes OK?

[TNC]

I had a similar problem (sound affecting h/lock) with an Ekco TMB272 - it turned out to be excessive sound signal - having a David Grant modulator I just lowered the audio output. In my experience Ekcos seem to be very sensitive.
If you don't have a separate audio o/p control, try attenuating the whole signal.

Trevor.

[Mikey405]

Hi Peter.

I think I would be looking at the IF curve here. It looks like a pretty wishy-washy response across the range to me. Also if the audio is getting into the video then this would also lead me first to the early IF stages (If it isn't simply that the audio level is too high as Trevor suggests). It may not necessarily be an "alignment" issue (I.e. someone twiddling), but it could be a component fault in the signal section causing the poor response. It's probably a silly comment, but if all the caps have been replaced in the IF section, it would be worth double checking that they have been replaced with the correct values. Getting the decimal point in the wrong place is just the sort of daft thing that I would do and this could have a very big impact on the response curve.

Sorry I can't offer anything a bit more specific Peter...

Kind regards.

From Mike.

[Heatercathodeshort]

Hello Peter,
Have you checked the action of the video response trimmer in the cathode of V6 the video output valve? It may be tarnished and intermittent. It may be worth checking the condition of D1 the vision detector diode. J.

[Danny]

Hi try an attenuator i recon this will sort it , great sets these and i havent ever had to realign one yet. your arora gives more output than was available origanaly available . a passive splitter may also help in losing some signal. Danny

[petertheorgan]

Thank you everybody for your help
I have made the following tests and this is what I have found
1) changing channel does not affect the problem
2) slightly tweeking the horizontal hold has no affect on the streaking on the left hand side of the screen untill the picture breaks up completely
3) attunating the signal also appears to have little affect
4) the effect is worse at low brightness setting and improves as you advance the brightness
5) I have plenty of brightness but contrast control does not appear to make a vast difference

I am more than happy to bring the set to anybody who is not too far away
feel free to pvt me

Peter

[Mike Phelan]

(2) proves it's not a sync problem - it is looking like an IF or video stage fault as others have suggested.

[Danny]

Hi ive just remembered a fault i had on a 17" ekco with similar problems and i had overlooked a couple of those bumble bee type caps in the if. yep replacing these cured the fault. it does sound like audio is breaking through . if you were in my location you could bring it round . Danny

[ENGLISH VICTOR]

Try checking all anode components in the video amp, especialy the cap between the video amp and the cathode of the crt if one is fitted. It will not fix the sound problem, from memory the sound trap is tuned by a Philips beehive trimmer under the chassis.
I have no circuit of the set and am going from memory. I do recall that these sets were very stable and rarely if ever needed a full alignment unless someone had "tightened all the screws"
Victor.

[Heatercathodeshort]

Peter, Did you check the response trimmer I mentioned earlier? As Victor stated, these sets are incredibly stable and I'm going to stick my neck out here and say that alignment will not cure your fault. This is a video amp fault causing poor response.
Danny mentions the I.F. screen grid decoupling capacitors. I totally agree but they usually cause a peak white screen or patterns. Well worth a try.
The trimmer is a flat postage stamp sized ceramic/mica assembly with a centre adjusting screw. You can safely give this a twiddle to see if it is intermittent but nothing else!
The tube looks a real cracker [Mazda CRM171/172] Regards, John.

[ENGLISH VICTOR]

Also check video detector,
Victor.