20-05-2015, 06:54 PM
OK, been very careful getting the timebase speed switch assembly out, all 16 wires lengthened and re- attached to the pcb.
Power up and we are back where we started, 2 dots in the middle won't move.
I have checked R152,R137,R136,R138. They are certainly not high but it is impossible to isolate them without cutting them out.
TR82 has 13.6v on the base, but there is only 0.1v across R136 so it is not conducting. That transistor is an FRB749, new to me, ( which has a beta of 77 ) spec says BC109C but the other transistors which should be BC109C too, are BC239C. Swapped a BC239C into TR82 from TR72 and vise versa. No change.
I have checked all diodes on this pcb, all OK.
Beginning to loose patience with this 'scope, its just so difficult to work on. I have a DM63 with a focus problem that may be a better bet!
Power up and we are back where we started, 2 dots in the middle won't move.
I have checked R152,R137,R136,R138. They are certainly not high but it is impossible to isolate them without cutting them out.
TR82 has 13.6v on the base, but there is only 0.1v across R136 so it is not conducting. That transistor is an FRB749, new to me, ( which has a beta of 77 ) spec says BC109C but the other transistors which should be BC109C too, are BC239C. Swapped a BC239C into TR82 from TR72 and vise versa. No change.
I have checked all diodes on this pcb, all OK.
Beginning to loose patience with this 'scope, its just so difficult to work on. I have a DM63 with a focus problem that may be a better bet!
Boater Sam.
