Old HC 5502 analog scope ( some display problems )

cowboybob · Feb 16, 2014

BGAmodz said:
Its exactly what i see a moving dot with slow frequency ....

That's just the "persistence" of the CRT.

https://en.wikipedia.org/wiki/Cathode_ray_tube#Phosphor_persistence

As the electron beam passes over the face of the CRT the resultant glow only lasts for a short time (milliseconds). Thus all you will see is the dot as it travels left to right at the slower sweep speeds.

BGAmodz said:
...i will try with higher frequency and see how this looks .

Once the sweep is triggered it will only traverse the scope face at the speed you have selected. A 0.5/sec sweep will, in your case, always just be a dot leisurely going across the CRT. Increased input signal frequecy will result in an actual trace for vertical transistions but the horizontal trace will remain a mere traveling dot.

And a CRT persistence duration degrades with use. Since you have a "legacy" device, the reduced persistence is more pronounced (and it tends to smear, or broaden). The "flicker" you are seing with AC is also an artifact of the persistence issue.

BGAmodz · Feb 16, 2014

So this is mainly due to an old Phosphor-coated inner side of the screen , is there a way to make it fresh again ?

KeepItSimpleStupid · Feb 16, 2014

Even fresh, it won't do what a DSO (Digital Storage Oscilloscope) would do. But, an ounce of prevention is worth a pound of cure. Use the minimum trace brightness to avoid burning the screen.

BGAmodz · Feb 16, 2014

KeepItSimpleStupid said:
Even fresh, it won't do what a DSO (Digital Storage Oscilloscope) would do. But, an ounce of prevention is worth a pound of cure. Use the minimum trace brightness to avoid burning the screen.

I see a nice looking graph on the picture on post 22 , its really worth it if i can get similar results , i just need to know how i can get the phosphor coating of the screen done .

KeepItSimpleStupid · Feb 16, 2014

If you use the calibrate tab on the front of your scope for the signal, it should look like you expect.

BGAmodz · Feb 16, 2014

KeepItSimpleStupid said:
If you use the calibrate tab on the front of your scope for the signal, it should look like you expect.

I see that the only way to get around this is eather change the CRT with a fresh one witch i don't think its going to be an easy find or figure out a way to improve the phosphor coating .

The reason i want to fix this is to display signals with tiny details like this one :

mab2 · Feb 16, 2014

BGAmodz said:
I see a nice looking graph on the picture on post 22 , its really worth it if i can get similar results , i just need to know how i can get the phosphor coating of the screen done .

I expect the waveform on post #22 is at a much higher frequency than 0.5Hz. even with a new crt I doubt your scope would show a trace like that at 0.5Hz.

If you really want to see waveforms at that frequency you need a storage scope - I did see once a free downloadable 'oscilloscope' program that would digitise the mic input of a PC and display it as a waveform - that would work OK at 0.5Hz; or there are lots of cheap DSO adaptors for computers on ebay which would do it even better.

The reason i want to fix this is to display signals with tiny details like this one :

you should be able to see details like those on your scope as it is - if the intensity isn't too high and the focus/astigmatism are set right.

cowboybob · Feb 16, 2014

BGAmodz said:
I see that the only way to get around this is eather change the CRT with a fresh one witch i don't think its going to be an easy find or figure out a way to improve the phosphor coating ....

New CRT only option. And, yes, not easy or cheap.

BGAmodz said:
...The reason i want to fix this is to display signals with tiny details like this one :...

As noted above, you can probably do that with what you have.

Play some more ( a lot more) with the scope, trying different sigs, scope settings (especially sweep speed, brightness and focus) and ambient lighting scenarios. I suspect you can get what you want eventually. You've got yourself a very nice, if dated, scope.

Little DSOs are cheap, have a lot of functions for the price and are portable, but I wish I still had my old Tektronix CRT type. Some nostalgia, sure, but I miss the much bigger screen and real knobs, ALL easily accessible and with a lot less cluttered screen .

KeepItSimpleStupid · Feb 17, 2014

CBB:

You really can't turn a CRO into a DSO.

You can only fix burnt phosphors, by replacing the tube.

cowboybob · Feb 17, 2014

KeepItSimpleStupid said:
CBB:
...You can only fix burnt phosphors, by replacing the tube.

cowboybob (post #48) said:
New CRT only option. And, yes, not easy or cheap.

KeepItSimpleStupid said:
...You really can't turn a CRO into a DSO. ...

KISS, my friend, you are, of course correct, but I don't know how you got that interpretation from my post.

KeepItSimpleStupid · Feb 17, 2014

The OP wants DSO like performance from a non-storage CRO.

cowboybob · Feb 17, 2014

I see what you're saying.

Thanks, KISS.

BGAmodz · Jun 4, 2014

Hello again , i guess its time to get this topic from the tombs again And i think now a really got some display problems

Any ways i was checking a power supply ( ON ) PWM IC with the prob on output pin and suddenly a small spark came out of that pin , am sure i shorted its pins somhow with the probe's head .

Now the scopes horizontal line has become leaning downward from the side , and stays like that even if you do a voltage test , and the same with channel 2 .

Can this be related to the circuitry near the probe's input ?? or is it something bad ?

JimB · Jun 4, 2014

Somewhere, probably on the back panel of the scope there will be a "Trace Rotate" control.
Try turning that to level the trace to the graticule.

JimB

BGAmodz · Jun 4, 2014

JimB said:
Somewhere, probably on the back panel of the scope there will be a "Trace Rotate" control.
Try turning that to level the trace to the graticule.

JimB

Hi JimB

Unfortunately that didn't solve it , the trace turns but i get no voltage reading , at least the CRT is showing the trace witch is good .

dr pepper · Jun 5, 2014

Sounds like you messed something up in the deflection circuit, probably after the attenuators, possibly a fet.
Do you have the schems?

KeepItSimpleStupid · Jun 5, 2014

If both CH1 and CH2 are affected, I'd be looking at the power supply and/or horizontal sweep. Trace rotation is more like a "tilt" control. CRT TV's did it with magnets on the neck.

dr pepper · Jun 5, 2014

My philips 'scope had a real fancy magnetic coil arrangement on the back of the tibe just for trace rotation.
I couldnt see this being affected, unless as kss just mentioned the power supply has been damaged, that is more likely if the 'scope ground has been connected to a voltage source with one side connected to ground

BGAmodz · Jun 5, 2014

Thanks to all of you above , i will do some checking and let you know

dr pepper said:
Sounds like you messed something up in the deflection circuit, probably after the attenuators, possibly a fet.
Do you have the schems?

https://i.imgur.com/YvOCIlY.jpg

dr pepper · Jun 5, 2014

That looks like the beam control circuit and the eht, the fault is more likely to be in the power supply schem, or the y amp/attenuator.
A fault on the schem you posted would either be a blank screen or a dim/unfocussed dot.

Old HC 5502 analog scope ( some display problems )

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