Author Topic: PM3335 oscilloscope repair  (Read 7176 times)

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Offline JacquesBBB

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PM3335 oscilloscope repair
« on: February 15, 2015, 03:50:00 pm »
Hi,

I am trying to fix an PM3335 Philips/FLuke oscilloscope.

After fixing a defective plug, I got the signal on the screen, but with the addition of a 40 khz component.
See the attached picture of a 1 khz  square signal, with the same on the output of a TDS460.

I do not know much about oscillos, but I suspect that it should come from the power supply and I am trying to look at
the electolytics there.  But I have no obvious origin of  failure up to  now.

Can you confirm that it is the power supply that should be faulty ?

Thanks

 

Offline mij59

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Re: PM3335 oscilloscope repair
« Reply #1 on: February 15, 2015, 03:57:28 pm »
The power supply is a very good candidate for the fault.
The switching frequency of the power supply  according to the service manual is 45 kHz at 220V
 

Offline Smith

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Re: PM3335 oscilloscope repair
« Reply #2 on: February 15, 2015, 05:02:57 pm »
Sounds like the problem I had with my pm3055 ( basicly the same as yours without the digital onscreen part). Just check all psu caps on the psu board to be sure. 
Looks like your psu is the same as mine. You might want to replace the mains x2 cap too, they tend to crack and release the magic smoke. I just replaced mine 2 days ago.
« Last Edit: February 15, 2015, 05:08:52 pm by Smith »
Trying is the first step towards failure
 

Offline JacquesBBB

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Re: PM3335 oscilloscope repair
« Reply #3 on: February 15, 2015, 06:14:28 pm »
Thanks for the feedback.

I have taken out all electrolytics caps from the PSU, and find several bad ones.
The big ones from the main (68uF) seems to be OK (on the upper right corner of picture 1), as well as the 6800 uF ones
(the grey ones of picture 2).

I will change all  the other ones, but need to order them as I do not have very much axial electrolytics,
and do not see much how to replace them with axial ones. 
 

Offline Smith

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Re: PM3335 oscilloscope repair
« Reply #4 on: February 15, 2015, 06:51:58 pm »
I just replaced them with radial caps. Just make nice tight bends and use some insulating (kapton)tape if needed. If they are wobbly you could probably use some hot glue.

And dont forget the X2 cap http://i59.tinypic.com/103euzt.jpg
« Last Edit: February 15, 2015, 06:59:40 pm by Smith »
Trying is the first step towards failure
 

Offline JacquesBBB

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Re: PM3335 oscilloscope repair
« Reply #5 on: February 15, 2015, 08:02:25 pm »
@Smith

Thanks for the advice. I will see which caps I can replace with radials. It will save me some funds.

I tested the two 6800 uF caps and found, testing them out from the board.

A) 7402 uF  ESR = 0.12 R
B) 7520 uF  ESR = 0.12 R

And for the two 68uF  caps of the main, I have altogether (leaving them on the board ) : 140 uF and 0.48 R.

It seems that they can still go for a while.

The X2 cap of 220 nF seems also to be in good shape, physically, and tested (out of the board ) at 248 nF and 2.7 R.


I think I will take the chance to leave them all on the board. I am more concerned by other small electrolytic caps
that are on the other boards, but as a start, I will only concentrate on the PSU.

I am not very  familiar with very high voltages. I do not want to  touch the high voltage, but I would like to test the PSU
aside from the rest of the oscillo.
Do you think this is a problem ?





 

Offline mij59

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Re: PM3335 oscilloscope repair
« Reply #6 on: February 16, 2015, 05:34:41 am »
If you haven't, download the service manual of the scope.

Its safer to test the power supply in-circuit.
You  would probably need a dummy load to test the  power supply stand alone.
 

Online tautech

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Re: PM3335 oscilloscope repair
« Reply #7 on: February 16, 2015, 07:42:13 am »
Nothing special about basic test of a CRO PSU.
Good manuals specify exactly where the test points are.

ALL voltages MUST be to Service manual spec. (good DMM)
Ripple MUST also be in spec.
Many use a DMM set to AC for this and it will give a reliable reading of LF ripple.
SMPS ripple will likely require another scope to quantify the ripple.

PSU specs is always the first step in equipment repair.

Get the Tek troubleshooting link from the Repair board, it application principles are universal.
https://www.eevblog.com/forum/repair/repair-documents-and-links-sticky-me-please-mods/
Avid Rabid Hobbyist
 

Offline JacquesBBB

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Re: PM3335 oscilloscope repair
« Reply #8 on: February 16, 2015, 08:58:22 am »
If you haven't, download the service manual of the scope.

Thanks,

Yes,  I have dowloaded the service  manual. By the way, searching on google "PM3335" one finds easily the pdf manual in
http://frank.pocnet.net/instruments/Philips/HR/T&M/PM3335-37_sd_en.pdf
but the quality of the schematics is awful and not readable.

I found a better resolution on the original djvu file

http://bama.edebris.com/download/philips/pm3335/PHILIPS%20PM3335-37-SM.djvu

I could then convert it myself to pdf and get a much better pdf file (too big to post here).
Below  is the PSU schematics.

I have a question of the output electrolytic  capacitors that I am replacing. 
I am changing all caps :
C6101,C6102, C6103,C6104,C6106,C6107, C6108,C6109,C6111,C6112,C6113,C6114,C6116,C6117,C6119,C61121.

Do I need to put exactly the same caps value ?  or can I increase the specifications ?

For example, can I replace the 22 uF  (C6117,C6119,C61121) by 47 uF (with at least same voltage
specifications ) ?

And as well replace the 150 uF (C6107, C6109) by 220 uF ?


Its safer to test the power supply in-circuit.
You  would probably need a dummy load to test the  power supply stand alone.

Yes, I am a little bit concern with the floating wire with 15kV output. On the other hand, owing the position of the board, it is not  very easy to test the outputs in-circuit. I will see how I can devise a diverted output for testing.

@tautech. Thanks for the link. I had already seen it, and it is actually useful. I have several other oscilloscopes that I can use for testing the ripple of the PSU.

 

Offline mij59

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Re: PM3335 oscilloscope repair
« Reply #9 on: February 16, 2015, 09:18:10 am »
There's no need to replace with a higher value capacitor, although it shouldn't be  a problem. 
Its more important with what kind of capacitor you use, low esr, 105 C, genuine brands like Panasonic etc.
 

Online tautech

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Re: PM3335 oscilloscope repair
« Reply #10 on: February 16, 2015, 09:29:41 am »
You should be able to acess all the critical LV voltages at a PCB interconnect.
The Manual SHOULD specify the test points.
Time for some study.  ;)

No need to get anywhere near the PDA lead.

Get a scope on the LV rails and FIND which one has the ripple.

I certainly wouldn't go replacing smoothing caps until you find the rail that is the problem.
Then you might consider testing a few others to check they hadn't dried out as well.
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Online Shock

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Re: PM3335 oscilloscope repair
« Reply #11 on: February 16, 2015, 10:02:32 am »
C6007 and C6008 the large filter caps have consistently caused problems on these series scopes as well as the X2 spontaneously combusting all due to the age of the components.
Soldering/Rework: Pace ADS200, Pace MBT350
Multimeters: Fluke 87V, 117, 27/FM               >>> WANTED STUFF <<<
Oszilloskopen: Rigol DS1054Z, Phillips PM3065
 

Offline JacquesBBB

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Re: PM3335 oscilloscope repair
« Reply #12 on: February 16, 2015, 02:41:56 pm »
I certainly wouldn't go replacing smoothing caps until you find the rail that is the problem.
Then you might consider testing a few others to check they hadn't dried out as well.

Too late, I already removed all electrolytic caps from the board.
In fact, I needed to do that to order the missing parts, and actually, there were quite a lot that were out of specs :


C uF        V           mes C uF    ESR Ohms
                                   
68          16          48           5.8
68          16          45         19.0
220         25         179         1.9
33          40          29          140.0
150         16          82          4.7
68          63          66          5.0
100         10          75          4.3
150         16          79          13.0
220         10          188         2.6
100         25          68          8.7
100         25          54          140.0
100         25          75          15.0


I imagine that all the ones that are listed here need to be changed.  As I do not wish to have too many references,  I will put 47 uF (which I have ) for all 22 and 33 , 220 for the 150.
I have  ordered today at Mouser the 220 and 68 that  were missing, and expect to  get them for next week end. I will  tell you then if
the fix is successful.
« Last Edit: February 16, 2015, 02:56:31 pm by JacquesBBB »
 

Offline Smith

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Re: PM3335 oscilloscope repair
« Reply #13 on: February 16, 2015, 06:12:20 pm »
The pm3055 service manual shows how to test the power supply (page 163) including needed resistors and power rating. Should be the same as yours.
Trying is the first step towards failure
 

Offline JacquesBBB

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Re: PM3335 oscilloscope repair
« Reply #14 on: February 20, 2015, 11:28:45 pm »
I have changed most of the electrolytic caps of the power supply board using radial caps instead of axial, as they
are much less expensive. The board is not as elegant as before, but it will be OK.

I put back the board, and tested it directly, and it worked !
I no longer have  the wiggle  at 40 khz.

I will just have to tune it a little bit now, to see if I can improve it a little bit,  but mostly to
practice  on an oscilloscope  that I got for free on a dumpster.

Thanks you all for   the  advices  that were very helpful.
 

Offline meeder

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Re: PM3335 oscilloscope repair
« Reply #15 on: March 26, 2015, 11:17:06 am »
I just replaced them with radial caps. Just make nice tight bends and use some insulating (kapton)tape if needed. If they are wobbly you could probably use some hot glue.

And dont forget the X2 cap http://i59.tinypic.com/103euzt.jpg

The X2 cap in my PM3055 (50 MHz version) also went out two weaks ago. I still have to replace it though.
Made a nice crackle and a *lot* of magic smoke :)
The rest of the PSU PCB looks like it is in extremely good shape though.

 


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