Thanks for yr interventions... i'll post asap, but itcan be quite a while.

 

Thanks for yr interventions... i'll post asap, but itcan be quite a while.

That's cool -- we'll 'resurrect' the thread when you return

Best regards
HP

 

I feel like lazarus..;

 

Can you input a sine wave and post a photo of what the oscilloscope screen looks like?

 

Can you input a sine wave and post a photo of what the oscilloscope screen looks like?

. Is the calibration signal 0,5 V; 0.5V/div;20mS/div; I have no sinus generator....

 

 

View attachment 90294

Looks like a resistor gone high in the amplifier for the X plates, either that or in the shift control.

 

Hey @patpin! --- Nice to see you back! You were one of the first poster's I 'met' following registration with ACC!

Another thought -- I've known a 'loose' deflection plate produce symptoms similar to those described -- are you able to illuminate any part of the far right portion of the screen via adjustment of the 'x-position' control?

Best regards
HP

 

Hallo, nice to "see" U again. I recovered but the scope didnt...
On EXT X mode (pulling knob at center of time/div) the signal occupies up to 4/5ths of the display. Without EXT X it is only 1/3th; the same for CHAN 2;

 

@ian field: Can you explain "shift control" ?

 

R66 and a few others etc aremarked with an asterix on the diagram which means they are not present on the PCB....!? I dont get that

 

R66 and a few others etc aremarked with an asterix on the diagram which means they are not present on the PCB....!? I dont get that

That usually means said components are located 'off board' (e.g. panel/chasis mounted controls and components mounted to same, etc...)

Best regards
HP

 

On EXT X mode (pulling knob at center of time/div) the signal occupies up to 4/5ths of the display. Without EXT X it is only 1/3th; the same for CHAN 2;

While that probably 'exonerates' the tube (i.e. rules out loose electrodes) it, nonetheless, should be possible to illuminate the extreme right side given sufficient x-axis input amplitude...

Assuming the tube is ok and in light of the (proper) linear operation of the horizontal (i.e. x-axis) amplifier there are only two possibilities:

1) Static (i.e. 'DC') 'imbalance' Re: horizontal deflection...
2) Magnetic interference (by inadvertently magnetized chassis, case, etc...) --- Very unlikely but not unheard of...

By way of 'stamping out assumption' Please try the following:
1) Set the instrument for External X-Axis input:
2) Set the gain of the channel processing the X-Axis input signal to maximum
3) Apply a Ca. 10v PP sine wave to the channel described in step 2 (above) --- Note: Please see postscript...

Rationale:
--Application of 10V PP to make certain the trace will more than reach the 'sides' at Max gain
--Use of a sinusoidal (as opposed to rectangular) waveform to produce a 'continuous' trace

Please advise us of your results

Best regards
HP

PS: For the sine wave 'generator' you may use any (line isolating) PS transformer featuring a low EMF output -- the output EMF is not critical...

 

@ian field: Can you explain "shift control" ?

I'm not sure how it works on a scope, but basically it imposes a small bias on one deflection plate and subtracts the same amount from the other plate.

The vertical plates are probably driven by a long tailed pair, so the shift control is probably as simple as an offset pot where the emitters meet the tail. The horizontal drive is a sawtooth, so the drive circuit is most likely different.

 

Hello thanks fr yr answ. What do you mean by max gain: I have from 5V/ div to 10mV/div; do you mean in this case 10mV/div; I only have a trafo generating 25V at hand (measured with voltmeter). I have tried with 25V AC and 10mV/div; horizontally nothing changes;
I also tried to augment the 'trace length' with another potmeter (R77)(on sweep generator). It helped a bit (20%) but not more at the end of the potmeter turns. In the last case the display is used for 50%. (not EXTENDED X)

 

Hello thanks fr yr answ. What do you mean by max gain: I have from 5V/ div to 10mV/div; do you mean in this case 10mV/div; I only have a trafo generating 25V at hand (measured with voltmeter). I have tried with 25V AC and 10mV/div; horizontally nothing changes;
I also tried to augment the 'trace length' with another potmeter (R77)(on sweep generator). It helped a bit (20%) but not more at the end of the potmeter turns. In the last case the display is used for 50%. (not EXTENDED X)

To clarify: In general, when such an instrument is set for 'External X-axis input' (AKA "X-Y" or "X,Y" mode) one channel will process the vertical (Y-axis) input signal whereas the other will process the Horizontal (X-axis) input signal...

I have from 5V/ div to 10mV/div; do you mean in this case 10mV/div

Correct -- Max gain=most sensitive range...

I only have a trafo generating 25V at hand (measured with voltmeter). I have tried with 25V AC and 10mV/div; horizontally nothing changes;

At a setting of 10mV Per division, 25V RMS (i.e. > 70v P-P) should produce more than 700 times the deflection required to 'reach' both 'sides'...

OK... This is going to sound a bit 'goofy' -- But I hope you'll give it a try all the same

1) Set the scope for display of the calibrate signal in such manner that it would, were the instrument properly functioning, give a full-width display...

2) Carefully - Physically invert the instrument while gently shaking same -- note any changes in the display...

Rationale: Inasmuch as we have investigated the 'usual electrical suspects' I am attempting to eliminate loose or 'open' electrodes (Spec. deflection plates and connections thereto) as possible 'culprits'...

Note -- There remains much more to be investigated on the electrical/electronics 'front'! -- I am merely attempting to 'rule out' "800 lbs gorillas" - as it were!

Best regards
HP

 

No change on shaking gently. I can also turn the tube on its long axis. No deformation of the signal either.

 

To clarify: In general, when such an instrument is set for 'External X-axis input' (AKA "X-Y" or "X,Y" mode) one channel will process the vertical (Y-axis) input signal whereas the other will process the Horizontal (X-axis) input signal...


Correct -- Max gain=most sensitive range...



At a setting of 10mV Per division, 25V RMS (i.e. > 70v P-P) should produce more than 700 times the deflection required to 'reach' both 'sides'...

OK... This is going to sound a bit 'goofy' -- But I hope you'll give it a try all the same

1) Set the scope for display of the calibrate signal in such manner that it would, were the instrument properly functioning, give a full-width display...

2) Carefully - Physically invert the instrument while gently shaking same -- note any changes in the display...

Rationale: Inasmuch as we have investigated the 'usual electrical suspects' I am attempting to eliminate loose or 'open' electrodes (Spec. deflection plates and connections thereto) as possible 'culprits'...

Note -- There remains much more to be investigated on the electrical/electronics 'front'! -- I am merely attempting to 'rule out' "800 lbs gorillas" - as it were!

Best regards
HP

The gorilla is a bit excessive - an angle grinder maybe?

 

The gorilla is a bit excessive - an angle grinder maybe?

That's what I get for mixing metaphors -- 'elephants in the room' might have been more apropos even if less 'dramatic'/'comic'

PS - angle grinder isn't parallel -- Did you, perchance, mean a organ grinder's monkey

Lousy auto-spellers!

 

No change on shaking gently. I can also turn the tube on its long axis. No deformation of the signal either.

Ok -- based upon that and other observations I feel we may safely assume the tube is in good condition

So.. Please allow me a little time (a day or so) to get caught up on 'life' -- then I'll carefully study the schematic with the aim of providing you with an 'interactive trouble shooting guide' (i.e. a list of measurements to make, components to check, etc...) --- In the meantime please watch the thread as further assistance may be forthcoming from others!

Very best regards
HP