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Old 28th Sep 2019, 7:01 pm   #1
high_vacuum_house
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Smile Motorboating Ekco TMB272

Good afternoon,
I am in the process of restoring an Ekco TMB272 television. I have been replacing the wax capacitors one at a time and now have a good raster and linearity. Since I started this restoration I have always had motorboating which I thought might disappear when replacing the wax capacitors as all I have removed so far have all been very leaky on my megger. The beat of the motorboating increases when switched from television to radio. With the regular beating of the motorboating causes the raster to flash for approximately 1-2" of the scan.

I have checked the main electrolytic with the Peak ESR tester which shows that the capacity has not fallen off and the ESR is reasonable so I don't think it has dried out. I am at a bit of a loss as to what is causing the motorboating. I was thinking maybe the metal rectifier though if one or both started to fail wouldn't it cause hum instead of motorboating? Any pointers as to what to look for next?

Many thanks,
Christopher Capener
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Old 28th Sep 2019, 7:48 pm   #2
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Default Re: Motorboating Ekco TMB272

I believe there is a second dual smoothing capacitor on the HT1 line, check this is not suffering.
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Old 28th Sep 2019, 8:05 pm   #3
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Default Re: Motorboating Ekco TMB272

This may be due to the IF decoupling capacitors especially those connected to the screen grids of the IF valves. Beware, some look like resistors with the same colour code markings. John.
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Old 28th Sep 2019, 8:07 pm   #4
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Default Re: Motorboating Ekco TMB272

Quote:
Originally Posted by Freya View Post
I believe there is a second dual smoothing capacitor on the HT1 line, check this is not suffering.
C68/71 dual 16ufd.
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Old 28th Sep 2019, 10:17 pm   #5
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Smile Re: Motorboating Ekco TMB272

Good evening,
I tacked a 10uF capacitor across C71 which made no difference. I think John maybe right, I haven't yet replaced the IF decoupling capacitors yet and most seem to be the usual Hunts mouldseal type so I shall start on changing these out one at a time and see what happens.
Wonder why Hunts went to the trouble and expense of slipping paper labels with the value on over their mouldseals when the value was printed on the case?

Many thanks for your suggestions.
Christopher Capener
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Old 28th Sep 2019, 11:23 pm   #6
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Default Re: Motorboating Ekco TMB272

With you changing the wax capacitors I had taken it that was all the paper ones. Johns suggestion is the way forward.
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Old 29th Sep 2019, 8:49 am   #7
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Default Re: Motorboating Ekco TMB272

Quote:
Originally Posted by high_vacuum_house View Post
Wonder why Hunts went to the trouble and expense of slipping paper labels with the value on over their mouldseals when the value was printed on the case?
Probably because they knew the cases would crumble and fall apart, put the paper round them to keep the bits in place!

Look out for the other little caps too, look like resistors but with rounded ends, normally dark brown and have the colour code of either brown black orange, or brown black red, Ekco had a habit of using both these and the Hunts mould seals together, they normally test completely O/C, with some going short, especially the ones decoupling valve heaters, they go off like firecrackers!

The TMB272 is a really good set when working properly.

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Lloyd
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Old 29th Sep 2019, 10:27 am   #8
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Default Re: Motorboating Ekco TMB272

I think those torpedo shaped capacitors that look like resistors ( and turn into resistors) were made by an Ekco owned subsidiary - EGEN.
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Old 29th Sep 2019, 11:13 am   #9
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Default Re: Motorboating Ekco TMB272

Circuit diagram of the sound section of the Ekco TMB272.
Check the 16uF electrolytic capacitor and all the decoupling capacitors in the IF amplifier. Instability in the sound stages has been known to cause picture patterning. Have you replaced the 250uF cathode bias capacitor?

DFWB.
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Old 30th Sep 2019, 10:56 pm   #10
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Default Re: Motorboating Ekco TMB272

Good evening,
Many thanks for your replies, I am getting somewhere slowly. I have been replacing all of the 0.003uF capacitors and the motorboating has now ceased. I still have a few more to change plus some 0.04uF hunts as well. All were showing low pF values on test. I have fed in a signal through the aurora and at the moment I get distorted sound and the line timebase is running too slow plus the vision looks weak and lacks contrast. I am sure that this is other capacitors and resistors out of tolerance.

Christopher Capener
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Old 1st Oct 2019, 4:45 pm   #11
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Default Re: Motorboating Ekco TMB272

Don't forget the .1uf waxie in the tuner. Easily replaced but you will have to remove a few sets of channel coils to gain access. Don't mix 'em up!J.
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Old 1st Oct 2019, 5:55 pm   #12
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Default Re: Motorboating Ekco TMB272

Don't forget the video detector diode which feeds the video amplifier valve grid via a lowish value resistor if you've got weak video.I used a germanium diode to replace it.
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Old 1st Oct 2019, 6:05 pm   #13
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Default Re: Motorboating Ekco TMB272

You will need to change all those .003uF caps,always bad news anyway .
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Old 6th Oct 2019, 9:54 pm   #14
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Smile Re: Motorboating Ekco TMB272

Good evening,
I have been making progress with my TMB272 Most of the 0.003uF capacitors have now been replaced as well as most of the Hunts mouldseals. I did the 2 in the tuner and gave all of the contacts a good clean whilst I was there. I also replaced the vision detector diode which seemed to cure the constantly varying contrast issue. I spent more time than I should looking for the cause of the distorted sound which turned out to be crud in the speaker voicecoil. giving it a good poke made it go away at least for the moment. The picture shuffle plate was shuffled to get the picture better centred.

I just need to finish replacing the 0.003uF capacitors though I have run out now and have got some more on order from the BVWS capacitor service.

I have also got the vibrator unstuck and it is now vibrating on 12V DC. Will have to see how it performs on 12V DC after finishing the recapping and tweaking.

Christopher Capener
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Old 7th Oct 2019, 8:23 am   #15
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Default Re: Motorboating Ekco TMB272

Looking good and the crt,s are normally ok on these sets,probably due to the fact they were never a main set.
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Old 8th Oct 2019, 8:46 am   #16
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Default Re: Motorboating Ekco TMB272

Good tube, they usually are. You will need to replace the metal type caps in the frame circuit to get it linear. One is usually wrapped in polythene in the vicinity of the FOPT. The linearity should be 100%. They will read OK on cap testers but will have a noticeable effect on the frame lin if not replaced. Good luck with it. John.
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