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Old 11th Sep 2019, 10:24 pm   #1
matspar
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Default Ekco TSC93 9" console (1949)

Good evening all. I am restoring this nice little Ekco set and have reached the point where I am stuck and could do with some advice.

After all the usual checks and some replacement caps and resistors in the power supply she was successfully powered up and displayed a very good raster. The front end was totally deaf and I spent some time correcting this and was making good progress.
I powered the set up the next day and was greeted by the unusual fault condition of line collapse. Eht heavily damped and reading only 2kv. Having read some of John W's previous write ups I initially pounced on C28 & C29 (100pf) mica caps in the line oscillator, but with no improvements.

I have been through the line timebase countless times and haven't yet traced the fault. All the relevant waxies have been sustituted and all resistors within tolerance. The correct line drive waveform appears to be present on the R36 side of C30 and reading - 40v. The line scan coils are intact and showing an acceptable resistance reading.
I have replaced V7 (SP61) line oscillator) and V10 (PY31) boost diode with no change. I don't have another line output valve V8 (6P28) to try.
Cold checks on the oil filled lopt have revealed nothing amiss, and I've read that this type is very reliable.

What am I missing?! is the 6P28 a likely culprit here?
+30v is present on the top cap (grid) of V7. The Trader sheet suggests there should be a negative voltage present here. With a signal applied the scan opens to around one inch wide. HT and all other voltages appear correct (so far)

Any thoughts would be most welcome!!
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Last edited by matspar; 11th Sep 2019 at 10:32 pm.
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Old 12th Sep 2019, 2:27 pm   #2
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Default Re: Ekco TSC93 9" console (1949)

Quote:
Originally Posted by matspar View Post
+30v is present on the top cap (grid) of V7. The Trader sheet suggests there should be a negative voltage present here.
Hi Matt,
I'm not seeing where it suggests this in trader sheet 980.

There should be a negative bias on the grid of V8 of course and this comes from the boost voltage. Check R38, C31, R40, C33 (note the positive wire goes to chassis) and C34. Also C35 if fitted to will leaky, try running the set with it disconnected.

I hope that gives you something to look at that you haven't already covered.

Cheers
Andy
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Old 12th Sep 2019, 5:57 pm   #3
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Default Re: Ekco TSC93 9" console (1949)

Can you scope the output from the SP61 line oscillator? The output stage looks as if it is working but if you need a 6P28 I can send you one. I'm certain I have a few spare. Did you actually replace the two 100pf capacitors? They tend to go O/C in fact my own TS88 appears to be suffering from a similar problem! I might have a look soon.
The capacitors Andy has suggested are well worth a second check.

The line output stage on these Ekco models is incredibly reliable as is the whole receiver. John.
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Old 12th Sep 2019, 10:39 pm   #4
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Default Re: Ekco TSC93 9" console (1949)

Problem cured! Thanks for your suggestions Andy and John. The raster briefly reappeared after poking around near C34 and vanished again. A very close look revealed a solder splash between one side of C34 and deck which was shorting out the scan coils and the game was up. How did I miss this!! I'm now back where I was and even have the beginnings of a test card! Happy days!
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Old 13th Sep 2019, 9:06 pm   #5
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Default Re: Ekco TSC93 9" console (1949)

Great! The sync coupling cap is hidden behind the rear strut. That will get rid of the cogging. Nice CRM121B tube. John.
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Old 17th Sep 2019, 9:21 pm   #6
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Default Re: Ekco TSC93 9" console (1949)

I found that coupling cap John, a nasty cracked old Hunts so this was shown the door, along with most of the waxies and a 0.1 oil filled Spraque which was quite nasty! I now have sound and vision but on different channels. Vision on 61.74mhz (chan4) but no sound. Sound is great on chan5 (63.25) but no vision. What is the answer here?! Can this be corrected with realignment or will it need more than this. Have to say I'm a bit stuck again!
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Old 17th Sep 2019, 10:40 pm   #7
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Default Re: Ekco TSC93 9" console (1949)

Now sorted! The slug in L23 was half hanging out. Slowly winding it back in restored sound to Ch4. Happy days!
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Old 18th Sep 2019, 5:31 pm   #8
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Default Re: Ekco TSC93 9" console (1949)

Ha! ha! Yes I think I mentioned that in the TS88 series I posted many years ago. In my case all the cores were hanging out of the bottoms of the RF coils.

Well Done! Regards, John.
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