Crazy soviet oscilloscope

[Trifaziux]

Hi,
I have an old soviet analog oscilloscope OML-2M and it seems to have a problem: Beam seems to be jumping crazy and doens't stay centered when changing the V/div settings. Also the beam would randomly start to jump all over the screen. Any advice what could be wrong with it?

[Macbeth]

Dirty pots. Get some switch cleaner on them.

[free_electron]

paint it red. that'll fix it

[Trifaziux]

paint it red. that'll fix it

now that's extremely helpful... 

[CatalinaWOW]

Dirty pots. Get some switch cleaner on them.

Not just the pots.  Probably has a number of multi-position wafer switches.  Same answer, cleaner plus vigorous switching.  Also check the input connections.

[Yansi]

No no....   Check vertical output transistors - one will be faulty.

[AutomationGuy]

can you please post of photo of it? I would like to see one.

[Trifaziux]

can you please post of photo of it? I would like to see one.

The scope:


old probe:


pardon my horrible desk 

[free_electron]

i change my advice. paint is not the solution. a large hammer is.    (sorry i'm in a strange mood today )

[Trifaziux]

i change my advice. paint is not the solution. a large hammer is.    (sorry i'm in a strange mood today )

this oscilloscope does not suit my needs but still, I use it from time to time. Paint might make it look pretier 

[T3sl4co1l]

In Soviet Russia, oscilloscope watches you! </accent>

Tim

[daddario]

Ah, yes - my very first own 'scope.
Describe the jumping around - does the trigger jitter or is the jumping around on the voltage axis?
While measuring equipment generally had slightly better "quality" components, this funky piece of gear wasn't considered one even by soviet standards. First thing you many want to check are caps and then clean the switches, it isn't suggested for nothing that those nasty P2K stand for Plohoi Kontakt. All in all, I'm afraid that the amount of time required to get this thing running could be used more wisely earning money to get a real scope.


Edit: Apparently can't use cyrillic in this forum.

[Trifaziux]

Ah, yes - my very first own 'scope.
Describe the jumping around - does the trigger jitter or is the jumping around on the voltage axis?
While measuring equipment generally had slightly better "quality" components, this funky piece of gear wasn't considered one even by soviet standards. First thing you many want to check are caps and then clean the switches, it isn't suggested for nothing that those nasty P2K stand for Plohoi Kontakt. All in all, I'm afraid that the amount of time required to get this thing running could be used more wisely earning money to get a real scope.


Edit: Apparently can't use cyrillic in this forum.e

apperently all of the used ones you can get here in Lithuania are from the cccp days. I think of buying a DS1052E, what do you think?
The jumping occurs on the voltage axis. Sometimes you can hear a tiny click sound and then it starts to jump arround, but stops after a minute or so. There are no relays in the scope as far as I know.

[AutomationGuy]

I have an old Hameg tupe scope. The high voltage contact of the tube is fuzzy and it clicks when a spark jumps from the cable to the tube.

[Trifaziux]

I've checked the connections one the crt and they're all fine.

[Yansi]

And have you replaced the damn vertical output NPNs?

[Trifaziux]

And have you replaced the damn vertical output NPNs?

no, not yet.

[TerraHertz]

The jumping occurs on the voltage axis. Sometimes you can hear a tiny click sound and then it starts to jump arround, but stops after a minute or so. There are no relays in the scope as far as I know.

Ah ha. The click is the trick. It's *definitely* a surface-tracking arc-over of the HV, probably the the EHT to the tube anode. Might be along the CRT surface around the metal button connector. Or somewhere in the PCB/ EHT supply components. Dust and moisture builds up till an arc occurs. That dries out the dust a little, then it takes a while to happen again. If this is happening on a PCB, maybe the charge is reaching other things and making the effects worse. But even if just on the CRT glass, the sudden drop in EHT makes the traces 'jump'. Lower EHT ==> less electron acceleration ==> more deflection effect from the plates.

Solution: take it apart, clean all dirty surfaces with a rag with solvent. Mineral Turps will do. Especially around the EHT plugs and cables.

[jrmymllr]

Ah, yes - my very first own 'scope.
Describe the jumping around - does the trigger jitter or is the jumping around on the voltage axis?
While measuring equipment generally had slightly better "quality" components, this funky piece of gear wasn't considered one even by soviet standards. First thing you many want to check are caps and then clean the switches, it isn't suggested for nothing that those nasty P2K stand for Plohoi Kontakt. All in all, I'm afraid that the amount of time required to get this thing running could be used more wisely earning money to get a real scope.


Edit: Apparently can't use cyrillic in this forum.e

apperently all of the used ones you can get here in Lithuania are from the cccp days. I think of buying a DS1052E, what do you think?
The jumping occurs on the voltage axis. Sometimes you can hear a tiny click sound and then it starts to jump arround, but stops after a minute or so. There are no relays in the scope as far as I know.

IMHO, don't buy a DS1052, buy a DS1054Z.  It's $70 more and better.

[Trifaziux]

the jumping
Jumping

[TerraHertz]

the jumping
Jumping

Hmm... Now I'm not so certain. EHT arc-over produces impulse increases in deflection factor, which then returns to normal pretty quickly, till the next arc-over. Yours acts more like a bad connection, switch contact, fractured component, or flaky semiconductor.
I'd still say open it up and clean it.

Besides, if you open it, you might be able to pinpoint where the click sound is coming from.
Here's a good way to locate small repeating sounds: Get some flexible plastic tube, 30 to 60cm  long, about 10mm dia.
Stick one end in your ear. Move the other end around in the equipment. It will become really obvious when you have the tube end close to the sound source.
It's like a stethoscope, only no metal parts. 

This works for locating smells too, but via the nose obviously.

[Macbeth]

Another great tip for isolating intermittent problems with semiconductors is a can of freeze spray and a hair dryer. Heat up with hair dryer to trigger the fault condition and then blast suspected components with freeze spray to recover from the fault. You will soon isolate the culprit 

[Trifaziux]

Another great tip for isolating intermittent problems with semiconductors is a can of freeze spray and a hair dryer. Heat up with hair dryer to trigger the fault condition and then blast suspected components with freeze spray to recover from the fault. You will soon isolate the culprit 

thanks   

[Deathwish]

You have to have at least a sneaking admiration for those Russians who used this kit when you see other posts such as the druga 3 radar one that they built using such equipment.

[wraper]

You have to have at least a sneaking admiration for those Russians who used this kit when you see other posts such as the druga 3 radar one that they built using such equipment.

Sure they didn't use such oscilloscopes. OML-2M is one of the lowest end oscilloscopes ever made in USSR. It's more a toy than serious scope.