Hitachi horizontal diff amp fault

[gkmaia]

I got on a road blocker and not sure where could my problem be.

My SWEP OUT & HPOS signal are ok and responding to controls.

My current SW3 is ok and sending the character/dot signals through Diff amp 2 when readout is enabled. But it does it by simply stop feeding the signal through TR882.
The signal that comes from IC1111-2 does not change so seems SW3 is always on.

The X1 signal is ok and responding to controls. 0v OFF and 5.8v ON but it is not switching neither Current SW 1 and 2 on. Therefor I get no signal output on collectors of Tr831 & 832.

I've attached a schematic with some measurements. I also toke TR863, 865 and 867 and they are all fine.

I did test IC 864 and it seems to have tested ok. But I am not 100% sure about it. I am sure its base is not shorted to ground otherwise my X1 signal would never go 5v.

That is what is odd... the base of TR863 goes to 10.7 when X1 is 0v which in theory should get TR863 to conduct as base is 10.7 and emitter is 12. That is more than 0.7v to get it to conduct. And I should be seeing some voltage out of the collector. But nothing... only 0v.

So if IC864 was faulty OPEN (not shorted) I should only loose the 10X magnification function. But 1X should work regardless.

I am stuck here... i cannot find a reason for collectors of TR863 and 865 to be stuck on 0v... I see no shorts there. there must something that is impeding them to conduct but it is beyond my knowledge.

Also tried to play with the blanking input but no luck.