Author Topic: philips pm3055 oscilloscope repair (Read 13095 times)

PhilippeD · « **on:** August 09, 2013, 10:09:40 pm »

Hello everyone,

I'm new here.
I've been watching daves blogs for some time now and I've seen a lot of youtube movies about osciloscopes.
So as adviced in the videoblogs I went looking for an old analog osciloscope and I found this philips pm3055 on the internet.
The seller told me it was fully working and when I received it, I plugged it in and it seemed to be working fine.
However a few days later I wanted to play some more with it and it was still working at first. But after some time it started to release smoke and made the sound of a short circuit somewhere inside.

I decided to open the housing and I pulled out the board with the power supply. The most obvious thing I could see was a blown capacitor and I also found some 3kV ceramic capacitor leading to the crt that seem to blackened. I attached some pictures.
I would like to know if this demage can have come from something I did or I just bought something that was on the edge of breaking down anyway..

I would like to know if you think I would be able to repair this or not.

echen1024 · « **Reply #1 on:** August 10, 2013, 03:24:12 am »

I think you should just try and use a multimeters and probe around the components just to see that they are working. Please don't do this connected to power though. After that, make an inventory of the broken bits, and replace them, and see if it works after that.

jahonen · « **Reply #2 on:** August 10, 2013, 05:47:14 am »

It looks like that X2-class filter cap has gone bad, replace it with a new one and it should be fine. It should be replaced with a capacitor of same X2-classed one since they are intended to be connected between mains live and neutral.

Regards,
Janne

jancumps · « **Reply #3 on:** August 10, 2013, 06:36:44 am »

Mine ( a PM 3305) died too in the same circumstances. Worked when I tested it at the sellers house. Died after a few minutes when I used it at home. Although it made the magic smoke noise when dying, there were no components that smelled or looked burned.
I used Echen1024's approach and checked the power supply components. After replacing the defect ones (fuse, the largest electrolyte capacitor and the rectifier bridge) it started working again.

dzseki · « **Reply #4 on:** August 10, 2013, 09:48:07 am »

Those blue philips electrolyte capacitors are notoriously going bad in these days, 80% of those that I've tested in the past few years were all bad, I suggest to replace all of those if they're not bad already, they will soon!

Shock · « **Reply #5 on:** August 10, 2013, 03:26:55 pm »

Service Manual
Operating Manual

PhilippeD · « **Reply #6 on:** August 10, 2013, 04:35:54 pm »

Thank you all,

I've been probing it with the multimeter as suggested.
I can not measure capacitance (Don't have a capacitance meter yet) so I guess I can not do much with my multimeter to test the caps.
Anyway it seems that all caps can still hold a charge. I could charge them a little with the ohm meter and see them discharge with the voltage meter.
Except for the x2 filter cap that died. That seems to be the only one not charging up anymore. (I didn't expect anything else

)
So I'll start replacing that one.

kape · « **Reply #7 on:** August 10, 2013, 05:22:00 pm »

I couldn't open the files that Shock has linked here, but if you need the schematics of the PSU, just send me PM and I'll send my service manual to you.
My PM3365 is a bit faster version of PM3305, but the PSU is the same, I think.

I also had broken power supply and after repairing it, the scope lasted for many years. Last year the final vertical amplifier broke, but I got it repaired.

EDIT: Got the manuals opened, but it took a while to download....not the fastest servers there..

Cigarsnob · « **Reply #8 on:** August 11, 2013, 12:34:19 am »

I recently got a PM3295 and my 250V X2 filter cap as well...I'm hoping that's the only issue. Hope replacing the X2 filter cap works for you. I'm curious to hear back while I wait for my X2 filter cap to come in.

Shock · « **Reply #9 on:** August 11, 2013, 06:12:00 pm »

Try opening the files again should work this time.

PhilippeD · « **Reply #10 on:** August 11, 2013, 06:52:57 pm »

I already had the service manual but thanks

Still need to get a new cap.

PhilippeD · « **Reply #11 on:** August 18, 2013, 05:20:59 pm »

I replaced the blown x2 filter cap and the scope is powering up again without smoke or strange sounds

But now the trace looks very dim in the middle, almost invisible. The sides are bright

I suppose the filter cap was not the only component that broke down.
Anyone an idea what it can be?

Shock · « **Reply #12 on:** August 22, 2013, 02:13:24 pm »

I guess start at the basics.
Hook up the probes to the calibration/test frequency and ground.
Hit the auto button.
Adjust the Intensity, Focus and Illumination till you get a decent trace.

Report back what steps you took and what results you get.

MrTheKod · « **Reply #13 on:** October 11, 2013, 01:05:16 am »

Exactly the Same thing happened to me. Once I had replaced the x2 Cap. All was well for about 3 days then the 1.6a Fuse Blew...
I had a look about inside could see nothing obviously wrong. So replaced the fuse thinking it was a random blow. Nope.

I need to have a closer look at the PSU and am planning to swap out as Many of the Caps as seems sensible.

Happened about a month ago and my little room still smells feintly of Magic.

stennly · « **Reply #14 on:** June 11, 2014, 09:49:26 am »

Hi everybody,
it seems I am another member of the club

I got my first scope and after 10 minutes of being powered up, the back started to release smoke, but not the type that you get from transistors.
As you can see in the photos, the mains cap is gone and the two smaller ones have cracks on them as well.
Should I replace only these ones, or should I go all out and replace all of them, including the electrolytics, which seem fine, but I do not have a capacitance meter to confirm.
I’m going to look at the circuit closer, but from what I've seen so far no active parts were hurt.

Any input is appreciated

tautech · « **Reply #15 on:** June 11, 2014, 10:06:15 am »

If the scope was still going when you shut it down, you can likely only replace those. Then power up in series with a light bulb for a while. But for piece of mind......

stennly · « **Reply #16 on:** June 11, 2014, 10:16:16 am »

Thanks for the ultra fast reply,
the test signal was still showing nicely while the smoke was coming out, so that's what I'll do.
Now just to hope my local store has the parts in stock...

If it works after that, someday, I might go ahead and change most of the other ones as well.
"If it isn't broken, keep fixing it till it breaks"

stennly · « **Reply #17 on:** June 11, 2014, 05:41:42 pm »

I've managed to replace the capacitors in front of the rectifier and all seems to work fine.
I had the scope on for about 30 minutes to test it out and the only thing that I don't like is the transformer getting a bit warm/hot, I can feel the heat through the side panel.
Using a cheap IR thermometer, with the top lid off, I got a temp reading of about 40-50 degrees C.
Am I just being picky and this is completely normal or should I look for a problem in the circuits?

There is a slot for a 60mm fan in the back of the scope, but none of the PM3055s have it installed and from the vent locations it would seem that the air wouldn't cool the power supply section anyways..

tautech · « **Reply #18 on:** June 11, 2014, 09:57:47 pm »

To be sure that the PSU is not stressed, you need to check all output rails are to spec, voltage and ripple. You will need to access another scope for ripple check.
This may identify failing output smoothing caps that are loading the PSU.
I have seen 1000uF caps measure less than 10uF, but your IR thermometer should see them as hot.

Start another thread to see if other scope owners have similar temps in their transformers.
Check to see if the transformer has previously run hot, localized discoloring etc

stennly · « **Reply #19 on:** June 12, 2014, 06:37:20 am »

Seems like something I should be able to do.
Once again, thanks for the quick advice.


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Author Topic: philips pm3055 oscilloscope repair (Read 13095 times)

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