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Old 3rd Dec 2023, 7:35 pm   #1
Richard_
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Default Philips PM3233 Oscilloscope issue.

Hello.
I have acquired a nice old oscilloscope which seems to work except that the trace seems to be limited to only around 1/3 of the available screen in the X direction. This is despite adjusting the X knob up to the max.
Anyone any ideas or is the unit basically kaput?
Richard.
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Old 3rd Dec 2023, 7:50 pm   #2
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Default Re: Oscilloscope issue

Does the X Position control move the display across the screen? It appears to be a dual function control, but I can't read the blue writing.
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Old 3rd Dec 2023, 7:53 pm   #3
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Default Re: Oscilloscope issue

It's quite likely to have basic things wrong like electrolytic caps if it's unrestored. Old professional lab gear isn't easy to sort out - it's a specialist area.
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Old 3rd Dec 2023, 8:18 pm   #4
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Default Re: Oscilloscope issue

Philips PM 3233.

Lawrence.
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Old 3rd Dec 2023, 8:22 pm   #5
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Default Re: Philips PM3233 Oscilloscope issue.

Thread title updated.
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Old 3rd Dec 2023, 8:23 pm   #6
Malcolm G6ANZ
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Default Re: Philips PM3233 Oscilloscope issue.

The dual function on the x position is 'pull for x5 mag
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Old 3rd Dec 2023, 9:25 pm   #7
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Default Re: Philips PM3233 Oscilloscope issue.

Thanks.
The X knob is a pull-out X5 type but the trace still stops dead at the 3rd grid square unfortunately .
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Old 3rd Dec 2023, 9:30 pm   #8
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Default Re: Philips PM3233 Oscilloscope issue.

Front panel in more detail.
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Old 3rd Dec 2023, 9:38 pm   #9
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Default Re: Philips PM3233 Oscilloscope issue.

Doubt it's capacitors, but you should start by checking the power supply voltages against the manual.
The three vernier controls should be set their "cal" positions, for the scaled voltage & time per large division on the CRT to be correct.
If the X position is not moving the trace from one side to the other and the power supplies are correct, then it's going to be something related to deflection, possibly a transistor.
The good thing about Philips scopes of this age, is they don't normally have any unobtainable parts.

David
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Old 3rd Dec 2023, 9:49 pm   #10
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Default Re: Philips PM3233 Oscilloscope issue.

If it has Lokfit transistors, they are suspect. My old Philips scope ended up having most of the Lokfits replaced over time. Check the ones in the X amplifier. I seem to remember having a similar problem....basically only half the X amplifier is working. You need to try and obtain a circuit....makes life much easier!
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Old 3rd Dec 2023, 10:04 pm   #11
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Default Re: Philips PM3233 Oscilloscope issue.

Manual available here https://www.opweb.de/english/company/Philips/PM_3233

Doesn't appear to have Lokfits so usual testing starting with power supplies.....
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Old 3rd Dec 2023, 10:49 pm   #12
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Default Re: Philips PM3233 Oscilloscope issue.

The arrangement of the deflection plates in the CRT will make the X direction a lot less sensitive than the Y direction, so the X amplifier output stage is more critical on being able to swing enough so if there is a power suply rail gone low, it is more likely to be noticed in not being able to X shift across the whole CRT width than it is to be found by the Y deflection being limited.

Consequently, with any scope fault, check ALL the power rail voltages first. In many cases power supplies are the fault.

The X amplifier can be checked by stopping the timebase, X-Y mode is good for this, and moving the spot left-right while watching the voltages of both X plates.

If there is a 'beam finder' or 'trace finder' button, it reduces supplies or bias current to the later parts of both X and Y amplifiers to limit the amount the spot can be deflected. The idea being that a far-deflected spot is not off of the screen somewhere, but limited showing the direction of deflection "He went thataway!" in other words.

Scopes can do a lot to help you fix them once you get comfortable with how they work and once you pick up a few tricks.

David
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Old 4th Dec 2023, 12:14 am   #13
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Default Re: Philips PM3233 Oscilloscope issue.

. . .If you have another oscilloscope available then you can make a quick test at connector BU6 (TB Out) on the back panel – there should be a 16 V pk–pk sawtooth on here with a small horizontal initial flat section at –2 V approximately before the ramp starts rising towards +14 V – this flat start is the T.B. "hold–off" period, implemented in all modern oscilloscopes to give time for the C.R.T. spot to return to the left before the next sweep is triggered!

If this looks OK then your fault can only be associated with the X deflection amplifier TS603, TS604, TS605, TS606, TS607, TS608, TS609 and TS611 – these are all common TV transistors and you should have no problem getting replacements!

Finally check the +12 V, –12 V and +160 V supplies from the power supply unit, and make sure there's no disconnected leads from the T.B. unit to pins 6 & 7 on the C.R.T. base – this is a very easy Oscilloscope to fault–find and repair, and a safe one as the power supply operates only off –24 V from a mains isolating transformer!

. . .If the waveform at BU6 is not as I describe it, then your fault is further back in the Miller run–down and hold–off circuitry, and the waveforms given in the circuit diagram on the right–hand side of the page should help locate the area where the fault is – I can discuss this in more detail later if need be!

Chris Williams
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Old 14th Dec 2023, 10:13 pm   #14
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Default Re: Philips PM3233 Oscilloscope issue.

Hmm.
Thanks - but repairing this is probably outside my skills envelope. I'm thinking of other ways to give this some life.
I've seen these kits for turning an oscilloscope into a clock. That might be feasible for me but would I run up against the same issue of lack of x deflection?
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Old 15th Dec 2023, 4:15 pm   #15
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Default Re: Philips PM3233 Oscilloscope issue.

If you're not happy about your ability to fault–find and/or repair an oscilloscope, and I applaud you for admitting so, rather than attempt a repair and risk causing irreparable damage, or what's worse, risking a potentially fatal electric shock, then my advice would be to post in the Forum Section "Repair and Restoration Services Wanted", and request help from another Member!

For the same reasons, I strongly suggest you do NOT attempt your own conversion of an Oscilloscope to a clock, as this requires detailed knowledge of the oscilloscope X and Y amplifier circuits, and as there is a suspect fault in your X final amplifier of your PM3233, you would be still stuck where you began, and more importantly, oscilloscope clock conversions require connection to the CRT blanking circuits which operate at high negative E.H.T. potential, again with the risk of potential fatal electric shock to the unwary!

Chris Williams
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Old 17th Dec 2023, 2:34 am   #16
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Default Re: Philips PM3233 Oscilloscope issue.

Sound advice. Thanks Chris.
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Old 17th Dec 2023, 3:45 am   #17
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Default Re: Philips PM3233 Oscilloscope issue.

Just rotate the 'Time/cm' knob fully anti-clockwise. This should stop the timebase and use the Y input channel A as a linear, analogue X input. If you leave that socket disconnected it's zero volts inputted.

Try the X-shift and the Ya shift knobs and see if you can move the spot

This is a quick check to determine if there is an X amplifier or a timebase problem.

If you're not going to fix it yourself, it'll help whoever does know the scale of the task.

David
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