Tektronix 7603 with 7B53A and 7A26 plug ins

[Refugee]

It looks like an awkward part to get hold of.
Still at the end of the day I still have a good scope and it will be able to take pride of place in my workshop.
I will keep searching.

[AlanBeckett]

My 7623A appears to have the same Display Board. I haven't looked inside but it looks pretty accessible from the Diagrams.
Is it easy to remove?

Alan

[Refugee]

There should be no reason to remove the board unless the fault is a passive component..
The main thing I need is to know what is on pin 11 of U2126 with the brightness at maximum, minimum and off.
Pin 11 appears to be loading the pot on mine.

[AlanBeckett]

OK, my 7623A still works OK. The Side Panel proved a bit resistant but succumbed in the end.
The Board looks the same. Where's a good place to pick up 0V? Is the Chassis good enough?
Do you want the Measurements for Brightness or Readout?

Alan

[AlanBeckett]

OK, I've had a quick look.
Measurements are against the Chassis.
I have to think you mean the Readout Intensity because the Intensity Control doesn't make any difference.
So:-
Max: -400mV with approx. -400mV Negative-going Pulses.

Mid Range is a bit tenuous so I turned it down until the Readout just disappeared:  -300 mV with 400mV Negative-going Pulses.

Off: +2V with approx 500mV Negative-going Pulses.

It all looks very clean.
I can take pictures.

Alan

[Refugee]

What I am getting is pretty close to what you are getting if you have been testing pin 11 on U2126.
Pin 12 is another matter altogether having about 600mv of negative pulses and no DC component and disconnecting the Z axis cable makes no change. There is no other connections to the Z axis track. The manual says it should be 6 volts
The test scope is set to 200mv per div.
What is your pin 12 doing?

[AlanBeckett]

Yes, they were Pin 11 Referenced to the Chassis.
I'm afraid my Pin 12 looks a lot nicer than yours:-

       

The Trace is Referenced to the Bottom Graticule Line where the Second Trace is. It's still Referenced to the Chassis. The Probe is x1.

Alan

[AlanBeckett]

Slowed the Timebase down one Click.

   

The Readout Intensity only varies the Pulse Amplitude not the DC.

Alan

[Refugee]

It certainly is looking like we are getting close to being able to say for certain that U2126 is the cause of my problem.
I will for now check that everything else is on cal and use it as it is until I find another U2126. It is now the best scope I have got and I well be able to use it as it is in the mean time.
It is also missing the bottom blue cover and the finger guard from the power transistors on the back and the screws that hold them on.
Perhaps I need a scrap frame for those and a couple of knobs that are not original.
Not bad since at least one other has been in there before me.

[AlanBeckett]

I think you've done infinitely better than most getting this far.

I can't see anything round U2126 that should damage it. Do you want to try mine? Of course there's always a risk attached to that sort of thing but that's life.
If you want to give it a go PM me your Address and I'll fish it out and put it in the Post. I assume there's just no Readout without it in, not that I use mine a lot, 'scope that is.

Alan