Oscilloscope UNAOHM G4020 = BECKMAN 9020

[neuron]

Hi,
A friend offered
Oscilloscope UNAOHM G4020 = BECKMAN 9020

In first hours worked ok ... I saw the 0,2 V 1000Hz
and other signal in the cinescop.

But now I only see 1 or 2 dots (channel 1 or both or ch 2)

I can move the dots UP and DOWN, LEFT and RIGHT
so the screen - cinesc. is working.


I test the trigger, connect CAL 0,2 to ch 1 or 2
and the dot is in 1 , 2 or more lines up depend on VOLT/DIV
INV - and the dot go down invert.

A sinos. wave, I can rotate TRIG LEVEL and the dot follow
the wave.
But I can't see the wave in display

Some examples of scope:
https://www.youtube.com/watch?v=3nBYp1pN40U

https://www.youtube.com/watch?v=fPq1KgQ5ggQ

https://www.youtube.com/watch?v=5osskamWJHg

Attach - manual and schemat. I have the French version.

Can you please provide help?

Thank you,

Ruy

[eccerr0r]

Re: Oscilloscope UNAOHM G4020 = BECKMAN 9020

So you're saying your horizontal sweep/horizontal amplifier/time per division switch isn't working?

Did you set it to perhaps XY mode by mistake? This thing appears to have a sort of curve tracer built in, so I suspect it can also do XY but I don't have a good picture of the front panel for sure. If you have a high frequency sine wave you should get a line?

[stj]

Re: Oscilloscope UNAOHM G4020 = BECKMAN 9020

make sure it's not in X-Y mode and the timebase is o.k.

[neuron]

Re: Oscilloscope UNAOHM G4020 = BECKMAN 9020

So you're saying your horizontal sweep/horizontal amplifier/time per division switch isn't working?

Did you set it to perhaps XY mode by mistake? This thing appears to have a sort of curve tracer built in, so I suspect it can also do XY but I don't have a good picture of the front panel for sure. If you have a high frequency sine wave you should get a line?

Thank you for your help.

If I select XY mode the dots disappear.

and if I press Comp. Test ( curve tracer ) the dots vanish
This worked in first hours and I tested caps, trans. resist,


Beam Find work 1 or 2 dots in midle of screen.

In back, I can find a BNC with sawtooth ... and changing TIME / DIV, I tested with a DMM -
300 Hz -> KHz


I visualiz. the dots -> rotating the POS and the dots appear from left side.


Thank you,

Ruy

[eccerr0r]

Re: Oscilloscope UNAOHM G4020 = BECKMAN 9020

Do you have another oscilloscope? (All debug technicians should always own at least TWO oscilloscopes, better two 1-channel oscilloscopes than one 2-channel unit!)

If you can move the dots from left to right, then the horizontal output amps are working. As you get the proper ramp sweep output on the back, the problem is in the sweep/timebase oscillator output switch/mux reaching horizontal deflection. (Then again I have not looked at your scope's schematic yet.)

It still could mean trigger is not working.

Not a usual failure if it's not being caused by front panel selections...

[stj]

Re: Oscilloscope UNAOHM G4020 = BECKMAN 9020

Do you have another oscilloscope? (All debug technicians should always own at least TWO oscilloscopes, better two 1-channel oscilloscopes than one 2-channel unit!)

i have 4.
including a 4 channel DSO, a 50MHz handheld and a 100MHz 3channel one that can show 6 traces!!

[eccerr0r]

Re: Oscilloscope UNAOHM G4020 = BECKMAN 9020

i have 4.
including a 4 channel DSO, a 50MHz handheld and a 100MHz 3channel one that can show 6 traces!!

well I wouldn't expect any less from you! but the OP.... needs more than 1!

[neuron]

Re: Oscilloscope UNAOHM G4020 = BECKMAN 9020

Do you have another oscilloscope? (All debug technicians should always own at least TWO oscilloscopes, better two 1-channel oscilloscopes than one 2-channel unit!)

If you can move the dots from left to right, then the horizontal output amps are working. As you get the proper ramp sweep output on the back, the problem is in the sweep/timebase oscillator output switch/mux reaching horizontal deflection. (Then again I have not looked at your scope's schematic yet.)

It still could mean trigger is not working.

Not a usual failure if it's not being caused by front panel selections...

Thank you very much for your info.

1 - At moment no ... but in a few days ... I have one.
Sorry don't understand ... its better 4 Scopes 1 CH ... instead a Scope with 4 CH?

2 -" ... I can move the dots UP and DOWN ... "

Vertical output amps work?

" ... As you get the proper ramp sweep output on the back ... "
I don't know if the waveform is ok ...
I rotate TIME / DIV, and the DMM -
300 Hz -> KHz

3 - "... It still could mean trigger is not working ..."

I explained in previous post:

I test the trigger, connected CAL 0,2 V to ch 1 or 2
and the dot go UP ( DOWN ) 1 , 2 or more lines up ( down) depend on VOLT/DIV

INV - and the dot go down invert many lines depend on VOLT / DIV.

A sinos. wave - I move TRIG LEVEL and the dot trigger the sin wave, moving slowly up or down the dot as I rotate the TIG LEVEL.


4 - "...front panel selections ... "
I would like to clean the Knobs, Handles, Pulls and Switches what you suggest? Alc. Isop.?


If TIME / DIV is 5, 10 us I saw the dot and a trace ( tail ) with 1 cm.

Regards,
Ruy

[eccerr0r]

Re: Oscilloscope UNAOHM G4020 = BECKMAN 9020

Might be best if you post pictures of the exact screen (and controls) of your device, it's hard to tell what you see by text. A good cleaning of the time/div switch is good just to make sure.

Since you can move the dots up and down, vertical deflection is working.

So you do see some horizontal deflection of the beam even if it's not fully across the screen?

Yes having another scope is good because then you can use one to debug the other. I don't think 4 1ch scopes are necessarily good, but having two 2-channel scopes is better than having one 4-channel, the dual trace scopes are helpful unless your only 2-channel scope is dead...

[stj]

Re: Oscilloscope UNAOHM G4020 = BECKMAN 9020

if it is not triggering you should not see a static dot.

as it's been around a bit, first idea is to open it and check for loose connectors.

[neuron]

Re: Oscilloscope UNAOHM G4020 = BECKMAN 9020

Might be best if you post pictures of the exact screen (and controls) of your device, it's hard to tell what you see by text. A good cleaning of the time/div switch is good just to make sure.

Since you can move the dots up and down, vertical deflection is working.

So you do see some horizontal deflection of the beam even if it's not fully across the screen?

Yes having another scope is good because then you can use one to debug the other. I don't think 4 1ch scopes are necessarily good, but having two 2-channel scopes is better than having one 4-channel, the dual trace scopes are helpful unless your only 2-channel scope is dead...

Yes

Some pics ... feeling of device


"if it is not triggering you should not see a static dot.
as it's been around a bit, first idea is to open it and check for loose connectors. "

Ok I will test.

Regards,
Ruy

[stj]

Re: Oscilloscope UNAOHM G4020 = BECKMAN 9020

does the x-pos control in the upper right efect the dot position?
and make sure "single" isnt pushed.

[redwire]

Re: Oscilloscope UNAOHM G4020 = BECKMAN 9020

It might be in component test mode. Check the C.T. button is not in.

[neuron]

Re: Oscilloscope UNAOHM G4020 = BECKMAN 9020

does the x-pos control in the upper right efect the dot position?
and make sure "single" isnt pushed.

Let me rephrase ... explain ...

If the Scope is working properly and you select XY or
Test Comp = Curve Trace you get a dot in middle of screen or
in CT a single line ... because no component in the leads.
only volts.

In this case I don't get nothing in the screen. :-(
Because the dots are hid. in left side - border.

Everything in middle position (X-POS, Y-POS) or
off (HOLD-OFF ->MIN, VAR-CAL off, etc)
DELAY -> N
Push Buttons -> not press ... none

Lets begin.

Nothing in the screen ...

Rot. the X-POS (white mark in middle ) the dot emerge
from the left side.
And I can move anywhere in the screen.

It might be in component test mode. Check the C.T. button is not in.

Read my last posts.




I would like to clean the Knobs, Handles, Pulls and Switches what you suggest? Alc. Isop.?



The Youtuber - Bruce Parman - bap8guy - usual. in the Forum ?

He repair this units.

https://www.youtube.com/channel/UCYi...vwudcjPwj80N-Q

https://plus.google.com/108120951169835381639

Regards,
Ruy

[stj]

Re: Oscilloscope UNAOHM G4020 = BECKMAN 9020

have you looked inside yet?

[eccerr0r]

Re: Oscilloscope UNAOHM G4020 = BECKMAN 9020

This is where the second scope would be good. Because we are getting sweep output from the back (but how good of a ramp output is it? Aha..need another scope.) the sweep generator is working as far as I can tell. This output is directly used for the X deflection through R6001 and R961.

But you say you can move the X dot from left to right with the X pos potentiometer, so the X amplifier is working depending on T908. But one can't work without the other.

Some observation is conflicting here. Well, unless if one of R6006 or R961 is broken, HG1 connector is broken, or the wire broke...

[neuron]

Re: Oscilloscope UNAOHM G4020 = BECKMAN 9020

This is where the second scope would be good. Because we are getting sweep output from the back (but how good of a ramp output is it? Aha..need another scope.) the sweep generator is working as far as I can tell. This output is directly used for the X deflection through R6001 and R961.

But you say you can move the X dot from left to right with the X pos potentiometer, so the X amplifier is working depending on T908. But one can't work without the other.

Some observation is conflicting here. Well, unless if one of R6006 or R961 is broken, HG1 connector is broken, or the wire broke...

Thank you very much for your detail research.

BEAM FINDER ok

And the Y ... I can't see any vertical lines, only one dot.
Vertical Final Amplifier is ok

Any control before this blocks?


" ... have you looked inside yet? ..."
search for any ...


Regards,

Ruy

[eccerr0r]

Re: Oscilloscope UNAOHM G4020 = BECKMAN 9020

Show a photo of the insides to us, I picked out one wire from the schematic, perhaps we can find that wire in a picture for you to inspect, at least visually, if you don't have another scope to check it.

But wait, you say vertical amplifier is OK, so if you feed in an AC to the vertical inputs, you should be able to see a vertical line, perhaps requiring the use of the beamfinder button. If you're not getting any vertical line with an AC input, then we have some strange dual failure that my be just a switch problem.

[neuron]

Re: Oscilloscope UNAOHM G4020 = BECKMAN 9020

Show a photo of the insides to us, I picked out one wire from the schematic, perhaps we can find that wire in a picture for you to inspect, at least visually, if you don't have another scope to check it.

But wait, you say vertical amplifier is OK, so if you feed in an AC to the vertical inputs, you should be able to see a vertical line, perhaps requiring the use of the beamfinder button. If you're not getting any vertical line with an AC input, then we have some strange dual failure that my be just a switch problem.

This is great ... Thanks.




" ... say you can move the X dot from left to right with the X pos potentiometer, so the X amplifier is working ..."

I can move CH 1 and Ch 2 dot up and down with the Y POS I, II potentiometer, I deduce
"Vertical Final Amplifier is ok" ?


" ... the use of the beamfinder button." Please explain.

Regards,
Ruy

[eccerr0r]

Re: Oscilloscope UNAOHM G4020 = BECKMAN 9020

If you can move the Y pos pots and its respective dot can be moved up an down, it demonstrates quite a bit is working - multiplexer is working, and yes, the Y finals are working. Doesn't show much about the preamp condition.

But what can you do with the X position, from the front panel, anything at all?

If the trace that would have shown a vertical line off screen is brought to the center with beamfinder, then you would be able to see it with beamfinder depressed. It's just proof that the vertical input amplifiers are working too.