On 14 Dec 2009, at 01:45, John Robertson wrote:
> Colin O'Brien wrote:
>> FInally got some spare time to check this out today. The voltage at G1 is climbing, others (G2 etc) are stable.
>>
>> Thoroughly inspected the board but all components check out ok, even replaced a few just to be sure. The thing is this voltage increase seems to be coming into the board from G1.
>>
>> If I set both pots to 0, I start out with 0V at Pin 2 of P500 (G1). Then it starts climbing, I remain at 0 or close to 0 on the pot side of R518 but on the P500 side it keeps growing to about 50V when I cut it off to avoid damage. At that point everything is very bright and retrace lines are visible. A quick check to other pins shows no change.
>>
>> Not sure where to go from here.
>>
>> Thanks,
>> Colin
>>
>>
> This sounds like a problem with the HV section. Can you pull it out and set it on the bench and feed it 35VDC to see if the HV and other voltages are stable? I put the HV lead into a ceramic cup to avoid shocks, and leave a HV probe touching it to monitor the HVDC...if it changes, turn off the HV and then feel the HV diode - as it is not connected to a picture tube there will be no stored charge - it should only be around room temperature or warm to the touch, hot means it is bad.
Just ran this test.
WIth a steady 35VDC on input I get no wild variations but a steady increase in output.
Over a 5 minute period I got the following changes:
HV: 12.21kV to 12.37kV
P900-5: 93.9V to 94.9V
P900-3: 421.4V to 425.9V
The diode remains at room temperature.
Colin
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Received on Wed Dec 16 17:08:16 2009
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