Re: gEDA-user: Any TV repair gurus lurking?

[Darryl Gibson <n2diy@xxxxxxxxx>]

Peter Clifton wrote:
> On Fri, 2007-12-21 at 01:32 +0000, Peter Clifton wrote:
>> Hi,
>>
>> I'm fixing (or trying to) a TV for a friend, and wondered if anyone had
>> any wisdom relating to the following symptom.
>>
>> This is a Sony BE-3D chassis, and exhibits an intermittent fault. When
>> its doing it, the picture is still visible, but collapsed (jitteringly)
>> upwards towards the top of the screen. It doesn't stay collapsed for
>> particularly long. The sections of image which collapsed upwards also
>> narrowed horizontally, leading to a tapered looking screen
>> ---------------
>> |\           /|
>> | \         / |
>> |  \_______/  |
>> |             |
>> ---------------
> 
> Thinking out loud a little..
> 
> collapsing towards the centre could indicate raised EHT, but this
> doesn't really explain why its only happening towards the bottom of the
> image. The image didn't seem to get any dimmer / brighter, so beam
> current is presumably not going crazy.
> 
> The vertical problem is asymmetric, so might indicate a glitch in either
> the + or - 15V supply to the vertical drive amp. Those are derived
> straight off the flyback, so either not enough energy is getting into
> the circuit (dying B+?), or something is shorting it down
> intermittently?
> 
> What kind of symptoms would a bad yoke coil contact give (either H or
> V?)
> 
> Any guru style know-how / deduction would be much appreciated.
> 

This is a very weird set of problems.

RGB lines indicate a failure of the vertical amp, which the shrinking
picture also indicates.

Check the coupling capacitor between the vertical amp, and the yoke?

-- 
Darryl Gibson N2DIY
Ubuntu, free software for everybody. (TM)
RLU X 182668/379552

“Arms are the only true badges of liberty. The possession of arms is the
distinction of a free man from a slave.”   --  Andrew Fletcher, A
Discourse of Government with relation to Militias (1698)


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