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7B53A not working as delayed tb


Fabio Sturman
 

I have an oscilloscope 6733 with two 7A18 and one 7B53A. The vertical channels are ok, the time base works ok as main time base but has the following problem. When I pull the TIME/DIV or DLY TIME the delayed time base do not work. The display is not intensified. When I rotate CCW an depress TIME/DIV or DLY TIME the display remains blank but shows the time-per-division of the delayed time base. It seems that the delayed time base is not triggered. How can I solve this problem. I changed the two CA3046 but the problem remains.
Fabio


Jean-Paul
 

Mainframe is 6733 or 7633?

Obvious to check first

delayed à so fail with ext source?
buttons delayed trigger slope coupling source checked?
Delayed trigger control level / runs after time delay exercise and cleaned?

Jon


Wojtek Krzywicki
 

Check the switch, which toggles the time base, often breaks off the PCB.


Roger Evans
 

Fabio,

The switch that Wojtek refers to is a microswitch whose lever engages with a plastic cylinder with end plates attached to the outer time/div shaft. It can also fail to operate if the plastic cylinder has moved slightly on its clamp screws. You should be able to check the operation of the microswitch with the 7B53A on the bench and the side plate off.

I don't have access to a 7B53A immediately but I would expect to see the B time/div displayed on the readout as well as the A time/div as soon as you pull the main time/div knob. If you don't see the second horizontal readout I would strongly suspect the microswitch.

Regards,

Roger


Richard Steedman
 

The symptoms you describe are entirely consistent with the microswitch (S252) not switching properly. There is a small metal rod that pushes against the white plastic cylinder when the grey time/div knob is pushed in. (Rotate the time/div to 0.1ms to see it when the right side screen of the plugin is removed.) This rod can jam in the 'pushing' position when the grey knob is pulled out such that the white plastic cylinder does not move and the microswitch does not switch. If it is jammed, it should just need a disassembly and clean to fix, perhaps adding a tiny blob of silicone grease.


Fabio Sturman
 

Richard, Roger,
the switch "RUNS AFTER DELY TIME" is ok, "PULL FOR INTENS" (S252) is ok and also the switch connected to the red knob "CAL". Normaly only readout for Time Base A is displayed. When I pull "PULL FOR INTENS" for one moment appears the readout for Time Base B. If I rotate "TIME/DIV or DLY TIME" CW nothing changes. If I press "PULL FOR INTENS" the main trace disappears and shows only the readout for Time Base B. I try to use only Time Base B with external trigger but nothing happens.
Fabio


Fabio Sturman
 

Problem solved!
I tested every transistor with a simple Multi-funcion Tester - TC1 (14EUR) ad found Q426 defective.
Fabio


Roger Evans
 

Hi Fabio,

I can't find Q426 on the schematics or the parts list - is it a typo or can you which schematic I need to look at?

Many thanks,

Roger


Fabio Sturman
 

Roger,my mistake, Q462 not Q426!Fabio.


Roger Evans
 

Thanks Fabio, I just wanted to work through the circuitry to see why the delayed time/div did not appear on the readout.

Roger