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Yes, i have it!I've traced the schematic. My first guess is C756 is faulty.
Do you have a voltmeter if I ask you to take measurements?
Brian.
So sorry for the challenges! The maximum voltage value before it shuts down is 27.7VSorry for the delay, I've spent the last day in hospital so I couldn't write back!
I suspect the problem is the +200V supply to the video amplifier stages is missing or has dropped very low. Please do the following and tell me what your meter reads:
CAUTION - There are very high voltages near to where I need the measurements, be very careful not to directly touch anything!
Measure on the small circuit board at the back of the neck of the CRT. It might be marked "CPT PWB".
1. use a DC voltage range suitable for measuring up to 1000V.
2. locate the connector (E805?) that has 7 wires going to the main board.
3. Find pin 1 of the connector, if they are not numbered, it is the one that links to R811, R812 and R813.
4. Connect the red meter probe to that pin.
5. Connect the black meter probe to pin 3, they are numbered sequentially. If it isn't marked, pin 3 connects to R804, R805 and R806 as well as several other components.
6. Switch on.
The voltage should quickly rise to about 200V before it shuts down. Please let me know what it actually reads.
Brian.
I tried to resolder all the joints and even to change the components, D751 and C756 but the problem still there!!That is a good sign, for the scan to be full width but that voltage so low indicates a problem in generating the 200V line. The lower that voltage is, the brighter the screen will be and the less the likely it would be for the real video to show through.
I've attached the service manual, it isn't very clear I'm afraid but the best I could find without buying it from Hitachi.
The 200V comes from (page numbered 13 at the bottom) pin 6 of T701. I think it is 6, it's the top left pin on the schematic, then through D751 to C756. T701 must be working to produce any picture at all so it is almost certainly something between it and the CRT base panel. Before changing any parts it would be worthwhile looking under the main circuit board at the solder joints on T701, D751 and C756. T701 is a fairly large component and it is quite common for the solder joints to break because of how much it expands and contracts with temperature changes. It would be a good idea to resolder its pins just to be sure.
Brian.