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What's wrong with this TV?

 
irob2345
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This is an Australian HMV from 1956 (625 line) displaying a PM5544 test pattern via a modulator, i.e. through the tuner. Obviously the VIF alignment is OK!

The yoke is a 70 degree UK-made part, probably sourced from EMI, and it has a variable trimmer to adjust for crosstalk.

Look at the "scallops" on the LHS. What do you think?

HMV A1 E1 first pic.

 

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Topic starter Posted : 28/07/2020 2:25 am
Nuvistor
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There appears to be some vertical shading in line with the scallops, ringing somewhere in the line scanning, I found it usually in the line linearity coil, damping resistor open circuit but could be in the scan coils.
That’s a good a guess has I have.

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Posted : 28/07/2020 7:39 am
irob2345
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Yes I thought it would have something to do with the linearity coil or the boost diode. But everything checked out OK. It got worse with increased width.

Anyway, to rule out the scan coils I checked the inductance of both H windings and found a 25% difference. Stripping it down I found that one of the ferrite "stator" discs was broken, on guess which side?!

So I have araldited it together and clamped it. Let's see how that works out.

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Topic starter Posted : 28/07/2020 8:04 am
Nuvistor
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@irob2345

Should be OK, see how it is when back together.

It’s the sort of fault most customers would not notice.

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Posted : 28/07/2020 9:05 am
Katie Bush
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I was thinking it may be ringing, then Frank mentioned open circuit damping resistor. I guess a broken yoke would give much the same effect, if you consider two resonant pieces where there used to be one, both 'jiving' at  different resonant frequencies.

I remember an early '60s EKCO my granddad brought in, showing very similar effects. In the end, it became my bedroom set for several years.

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Posted : 28/07/2020 8:25 pm
irob2345
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Well, gluing the ferrite back together improved things enough to allow it to be returned to its owner. Any width setting beyond what will fill the screen results in foldover about 1/3 of the way across as the core saturates, my guess. But the wrinkles are gone.

 

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Topic starter Posted : 02/08/2020 6:03 am
irob2345
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Here's a shot of the yoke before I dismantled it, the chassis (except for the mains transformer and the pair of 6N3s does it look familiar?) and the finished result ready for its owner. That rebuilt CRT is VERY bright!

Mr Ed on E1
Yoke prior
E1 A1 chassis

 

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Topic starter Posted : 02/08/2020 6:12 am
irob2345
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And the picture that should have been in the post above....

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Topic starter Posted : 02/08/2020 6:19 am
irob2345
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Let's try that again!!

Yoke fixed

 

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Topic starter Posted : 02/08/2020 6:20 am
Nuvistor liked
Nuvistor
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An excellent repair, can’t recognise the chassis but I didn’t see many HMV sets.

 

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Posted : 02/08/2020 1:21 pm