18-05-2015, 09:29 PM
Thanks for the reply one and all, I know I face a challenge with this box of bits.
The scope will show 2 stable spots in the vertical centre of the screen at adjustable intensity and focus. one for each channel. Astigmatism works ok
The Vertical positions can be adjusted at will and input to either channel will produce a vertical trace, a line only.
There is no horizontal sweep at all and no X positional adjustment will move either dot. X mag does nothing, Beam locate will switch dots on and off. Trigger is to internal and makes no change when put to external.
I have no other working scope so I cannot check gate or sweep output directly.
I have done a close inspection, nothing disconnected or distressed. An all device wiggle gives nothing. The 2 X drive and 2 X output transistors have been removed and tested ok, what a job getting them back in.
+300 , -14 and +14 volts rails are to the X amp though +14 is at 11.88v and 300 is at 287v.
Disconnecting the +14 from the X amp circuit does not significantly increase the voltage.
Both dots are immovable horizontally no matter what the controls are set to.
Reading through the service guide suggests that the X amp is at fault but its a complicated circuit and taking pot luck and guessing is not a way to proceed. The circuit diagram is sadly lacking in voltage readings apart from supply rails.
I considered checking every transistor on that pcb but access is terrible, it takes a lot of very careful fiddling to get them back in.
It would appear that the only access to the back of the pcb is after tube removal which rules out dynamic testing.
The scope will show 2 stable spots in the vertical centre of the screen at adjustable intensity and focus. one for each channel. Astigmatism works ok
The Vertical positions can be adjusted at will and input to either channel will produce a vertical trace, a line only.
There is no horizontal sweep at all and no X positional adjustment will move either dot. X mag does nothing, Beam locate will switch dots on and off. Trigger is to internal and makes no change when put to external.
I have no other working scope so I cannot check gate or sweep output directly.
I have done a close inspection, nothing disconnected or distressed. An all device wiggle gives nothing. The 2 X drive and 2 X output transistors have been removed and tested ok, what a job getting them back in.
+300 , -14 and +14 volts rails are to the X amp though +14 is at 11.88v and 300 is at 287v.
Disconnecting the +14 from the X amp circuit does not significantly increase the voltage.
Both dots are immovable horizontally no matter what the controls are set to.
Reading through the service guide suggests that the X amp is at fault but its a complicated circuit and taking pot luck and guessing is not a way to proceed. The circuit diagram is sadly lacking in voltage readings apart from supply rails.
I considered checking every transistor on that pcb but access is terrible, it takes a lot of very careful fiddling to get them back in.
It would appear that the only access to the back of the pcb is after tube removal which rules out dynamic testing.
Boater Sam.
