Having philips PM3214 scope repaired, should I bother?

[240z4u]

Having philliips PM3214 scope repaired, should I bother?

Hey guys, I aquired a philips PM 3214 through work. The scope belongs to the company, but something is wrong with it. I have another scope so I am going to ask if I can keep this one (if its worthwhile).

The problem is, I absolutely cannot get the darn probes calibrated to show me a nice flat square wave from the test pattern on the scope. The probes are fine, they work well on the BK 2120 that I have here. I also tried using the calibration signal off the BK 2120 to see if the signal was odd in the phillips.

There is something wrong (I think, I am pretty noob-ish) and am wondering if I should even bother with it. I want to use it to troubleshoot audio circuits.

Thanks! - Evan

 

[SY]

What does the square wave look like?

 

[240z4u]

Let me try to describe it, sorry no camera here at work.

The trailing edge of the square wave is curved, both on the top and the bottom of the wave. It looks like over-compensation adjustment on the test probe. I am unable to get it dialed in though.

Evan

EDIT; The controls are dirty and this very well may be the culprit! I also notice that lines on the X axis are not perfectly straight...

EDIT EDIT; The real problem is only on channel A. I may try to deoxit the controls.

Evan

 

[SY]

Yeah, clean the controls and it may be worth jiggling the trimmers a bit. If that doesn't do it, don't bother any further. It's a 25MHz scope, which is pretty marginal anyway.

 

[240z4u]

Thanks SY, Ill do that and see what happens.

Evan

 

[240z4u]

Seems to be better, but still not great. Off to the corner of crap that doesn't work with this one.

Evan

 

[megajocke]

Are you sure your probes are compatible with the oscilloscope? The probe or its manual should say what scope input capacitance range it has. The input capacitance should be printed either beside the input or in the scope manual.

edit: I had one of those PM3214 actually. It's quite nice except that the switches get dirty and intermittent. Contact cleaner worked on mine though.

 

[240z4u]

Well, if thats the case maybe ill stick with it.

The problem is if I touch the knobs, the scope screen jumps around (dirty contacts I am assuming). I wasn't able to get in there very far. Maybe I just need to suck it up and take the entire thing apart to get to them.

All the switches seem good after cleaning.

Evan

 

[megajocke]

Mine only had dirty push-buttons and some pots. I remember the push-buttons and pots were pretty easy to get contact cleaner into but the attenuator switches and timebase switches may have been inside screened boxes. These were good though on mine so I didn't need to clean them.

 

[240z4u]

Those are the exact pots that really need the cleaning. You have given me the motivation to really dig into it. Thanks alot.

Evan

 

[Steerpike]

I have a 3214, it's a very lovely scope to use, even if oldish.
Taking it apart is not difficult, but does take some time - lot's of bits to unplug, and unscrew.
Definately worth some effort.

 

[240z4u]

Man, and to think I was going to give up on this thing.

Its very complex compared to what I have seen on the BK one that is at work. I wish I understood it a bit better, but Ill muddle through it.

Evan