Philips PM3232 oscilloscope, display trouble

[wari72]

hello!
I have an old Philips PM3232 oscilloscope with the following display trouble: very weak luminosity at the centre area of the crt, no possible setup of focus and intensity. the situation remain unchanged if the blanking signal (crt pin 4 through R831) is deconnected and or if the transistor TS801 removed!
any idea?
thanks

 

[mvs sarma]

WELCOME TO ETO

It is nice that you posted the manual while asking for help.

can you check the power supply voltages, especially -1500 and 160V, later try to check as per contents of page 72, 73?

At times , if you press 'beam find' you might locate the trace or spot.

Of course a dynamic discussion helps faster, and that might need a live chat

 

[wari72]

Thank you for your suggestions.
The power supply voltage seems to be correct and the checking steps on pages 72-73 do not have a significant impact in this case. In fact I susspect a CRT failure, since the blanking region is independent of the X-position setting, but there is no visual sign that confirms this.

 

[debe]

After looking at the manual i would be checking the Focus part of the circuit as its a split beam & could cause bad focus in the center of the screen.Be suprised if its a faulty screen.

 

[mvs sarma]

Except that the emission of electrons reduces a little after few decades, many CRTs wont fail just like TV picture tubes, as Oscilloscopes are used for limited time.

that can still be managed by little increase of filament current, judiciously so as not to overkill the cathode coating. mostly high value resistors in the CRT related circuitry show open or higher values causing such issues.

 

[wari72]

Thank you for your relevant explanations that I will consider in reviewing the crt circuit.

 

[bamikanariesoep]

Hi Wari,

Succes with your PM3232. Recently I got one also, so I am very pleased with your posting of the service manual.
I am still missing the user-manual.
Do you have it by any chance, and if so could i get it (digitally) ?

Thanks Herman

 

[Reloadron]

Hi Herman and welcome to the ETO forums.

If you click on the manual in the first post you should get the options to open it or save it. You can open it and read through it. If it is what you want with the manual open click file and choose save. That or initially choose save. It is a common .pdf file.

Ron

 

[wari72]

Hi,
I'm sorry I have no user manual for PM3232!

 

[mvs sarma]

Any general oscilloscope user books work equally well. the PM3232 service manual describes each knob and switch.
Thus, i suppose that there is no need for a specific service manual.

 

[Reloadron]

Hi,
I'm sorry I have no user manual for PM3232!

What am I missing here? The very first post in this thread includes the manual. It is easily downloaded. Here it is attached to this post.

Ron

 

[edsaldana]

Hi, my PM3232 cannot control the channel A Ya position. When I have the input at mode at 0, the minimum I can bring the trace down is just above the reference line at the center of the screen.
If I select AC or DC mode and connect the probe to the 600mV cal signal, I can see the square signal but again the position is on top of the center ref line on the screen. And when I tried to adjust the position with Ya, instead of changing the position what it changes is the amplitude.
I followed the instruction in page 79 by adjusting the DC offset but did not work.
Any clues?
Thanks