Philips PM3230 problems

[b0b4u]

Hello, I am 14 and I bought a scope(this is my first scope). It is the Philips  PM3230. I got it for a really good price. However, it has a few problems.

First, I think it need trigger adjust. I think so because the signal moves left and right. I can get it to stay still with the time per division fine adjustment, bit it starts moving again after some time. If I want the signal to stay in place for longer time, I have to use the option for showing the falling edge of the signal. Also, I think this is because I am new to scopes, but when I select a timebase, I have to adjust the fine adjustment so the signal would stay in place. But as soon as I increase/decrease the time base, the signal becomes out of sync and it sarts "vibrating".

Second, I noticed that the signal(wave) is more clear on the sides of the CRT screen. It is blurred on the middle of the screen.

Third, the two channels start moving up and down sometimes. This usually happens when the scope starts up.

Can someone help me to fix these problems?

[Zenith]

I don't think I'm going to be much help here but I'll try.

I believe this is a valve (electron tube) scope and not ideal for a beginner as a first scope. Much better would be something like a Hameg 203, and ideally you would see all functions working before you buy it.

The first thing you need is the manual, definitely the operating manual but also the service manual. I had a quick look on the web and the only version I could find is in Dutch.

It sounds to me as if the trigger just isn't working, not that it needs adjustment. It could be because of a valve being defective, maybe it's some other component. Usually you need another oscilloscope to sort out a problem like that. It could be that you don't know how to use it, and so the operating manual would be good to have.

It's usual for a trace to be sharper in the centre than at the sides of the screen or the other way round. Whether it's a problem depends on how much. It's called astigmatism. There's usually an astigmatism control which may be accessible through a hole on the front and is adjusted by a screwdriver. The control may be internal and so the cover has to come off to adjust it.  There's usually a procedure where you adjust the astigmatism control and focus and intensity to get the best trace across the screen. Most scopes have this problem to some extent, even after adjustment. Some scopes, particularly older ones, are never very good in this respect.

The two channels moving up and down sounds as if it's caused by old resistors which are not stable and change value as they warm up.

I'd say you are too young to be taking the covers off this scope and fiddling with it. I wouldn't like the idea of me at the age of 14 doing that. The EHT for the CRT and the HT for the valves can kill you.

[grumpydoc]

It's a hybrid valve/transistor design.

Make sure the Normal/TV frame switch is set to Normal and that the Y_A/Ext/Y_B switch is set to whichever channel your input signal is connected to (presumably A) and not "Ext" or the other channel, finally make sure the "Level" knob is in the "Auto" position.

I'd agree  with Zenith it is not the best beginner 'scope and by "a good price" I hope you mean less than about 25 lev, bandwidth is 10MHz so it will be usable for audio work and maybe AM radio work but not much more.

The traces moving up and down as the 'scope warms up probably just reflects the fact that it is a valve design and they take at least a few seconds to warm up and settle down.

Interestingly very early oscilloscopes did not have a trigger and to get a steady trace you had to adjust the timebase slightly, as you are doing now.

The service manual, in German, is here https://bama.edebris.com/download/philips/pm3230/PM3230%20manual.pdf

[vk6zgo]

The triggering problem may be due to the type used.

In almost every one of the more modern analog Oscilloscopes, triggering is achieved by selecting the source of triggering, then in turn, the type of triggering-------"auto" or "normal".

The "trigger level" control is then adjusted to set the voltage level of the observed signal at which stable triggering occurs.
Older 'scopes had an additional "stability" control, which also needed "tweaking".

Examples are the Telequipment "Serviscope S31", & even the Tektronix 545a, (although the stability control was not used in the "auto" position of the latter).

Both of the examples had "stability" as a proper knob on the front of the instrument, but it appears that the PM3230 presents it as a trimmer pot instead.

It is heavy work searching through a service manual in another language, but it seems that "stab" may have been considered a " set & forget" control by Philips, but it could have been "tweaked" by some hopeful user, & just needs resetting.

The description of trigger setup in the "Servicescope", although a different instrument, may be helpful to understand how such systems are set up
.https://w140.com/tekwiki/images/0/01/Telequipment_S31.pdf

As to the PM3230 manual, it may be a good idea whilst searching through it, to open up a split screen with a translation website, to check your "guesses" as you go.

The "out of focus in the middle of the sweep" thing is as Zenith due to 'astigmatism".
I can't see any sign of an adjustment for this in the pictures of the front of the 'scope, but it is possibly at the rear.
The manual does refer to "astigmatisme" adjustment in passing, & from memory it is shown in fig 32, but I can't remember where the reference & the fig are.

[b0b4u]

Okay, thanks for the help. I fixed the problem with the astigmatism and  it was pretty simple, there were two potentiometers inside. So I adjusted the pots and everything is good. However, the problem with the trigger is still present. I am really interested in electronics and I really want to have a working scope, that's why I am working on this one. I know that the voltages inside are crazy high but I am really careful because(the anode voltage is around 3.2kV)

Thanks for the help

[b0b4u]

I got the scope for 100Lev

The traces continue to shake after the scope has warmed up, so the problem should be somewhere else. Do you think I should replace all of the tubes?

[b0b4u]

Okay, Thanks for the help. I will try to translate the manual and hopefully fix my problem

[Zenith]

Do you think I should replace all of the tubes?

Probably no, but It depends what the tubes cost. I'm not at all familiar with this oscilloscope, but I'd guess they are mainly ECC88/6DJ8, in which case they were discovered long ago by the valve hi-fi crowd and are now quite expensive. If you suspect it's a valve in the trigger circuit you could swap it for a similar one elsewhere in the scope and see if the problem moves with the valve, assuming you are not swapping bad for bad.

As I said earlier, I don't think this is a good choice for a first scope. I wish I could be more helpful.