UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - CRT is brighter to one side [Hitachi CTP213]

1100 man · 29th Dec 2018, 12:32 am

R727 & CR703 provide the 800V supply to the screen potentiometer. If this 800V supply is missing, you would not get much on the screen.

R727 does look to be burnt although what you can see is a piece of sleeving over the top of the resistor. The value of the resistor needs to be measured with a multimeter to confirm whether it is OK or not. It is marked on the circuit as a 1.8K safety resistor which means it should be replaced with the correct type.

If it has failed, there will be a cause. The most likely is that the diode CR703 has gone short circuit. It could also be C731 or C850 although these are both small value non electrolytic types so are not that likely to fail. You would need to test CR703 with a multimeter to confirm if it has failed.

All the best
Nick

29th Dec 2018, 12:32 am	#127
1100 man Octode Join Date: Apr 2016 Location: Ventnor, Isle of Wight, & Great Dunmow, Essex, UK. Posts: 1,377	Re: CRT is brighter to one side [Hitachi CTP213] R727 & CR703 provide the 800V supply to the screen potentiometer. If this 800V supply is missing, you would not get much on the screen. R727 does look to be burnt although what you can see is a piece of sleeving over the top of the resistor. The value of the resistor needs to be measured with a multimeter to confirm whether it is OK or not. It is marked on the circuit as a 1.8K safety resistor which means it should be replaced with the correct type. If it has failed, there will be a cause. The most likely is that the diode CR703 has gone short circuit. It could also be C731 or C850 although these are both small value non electrolytic types so are not that likely to fail. You would need to test CR703 with a multimeter to confirm if it has failed. All the best Nick