Author Topic: Philips PM3055 oscilloscope repair and teardown  (Read 32085 times)

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Offline vtl

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Philips PM3055 oscilloscope repair and teardown
« on: January 10, 2012, 10:43:16 am »
Seems like old scopes on ebay are in pretty high demand here in Australia and working ones usually sell for >$100, especially tek scopes.
But I was lucky enough to pick up a Philips PM3055 (needs repair) on eBay for $26 AUD! For that kind of money its definetly worth a punt and seeing if it can be fixed.

Scope looks very servicable and everything is throughole. The timebase PCB you can lift out and theres a slot in the plastic chassis where you can place it vertically temporaily while you work on the parts below. What you'll notice is the lack of screws for holding down the PCBs. They are all held in by either plastic rails or plastic clip-in fittings which can be a royal pain.

Whats interesting about the scope is that there is actually an LCD display to show the current settings and the CRT to show the trace. All the controls are digital with push buttons and the scope is even modern enough to have an autoscale button! High tech stuff here. Appears to have dual timebase too. The whole LCD and controls lift out as one module, quite nice and houses the main microprocessor

Overall the scope seems to be in fair condition. Theres some minor cracks to the plastic frame in some places, possibly from transit or drop damage. The scope appears to be fully complete with no missing parts and I can't see any signs of previous attempts of repair.

Repair

Seller says that it had been sitting for a while and now refused to power up. Seemed like the scope has been opened before, the IEC power connecter had been unscrewed and one of the plastic rails for the power board was broken. Upon powering up, a very loud whining sound comes from the power PCB, possibly from the EHT transformer (step up from 48 to 2100v). No trace, no LCD visible at the front. I did some searching on Google and there seemed to be other people with the same scope and symptom, possibly a common problem? If theres someone out there whos a guru with these kinds of scopes I'd appreciate some advice.

The power supply board was extremely difficult to remove. The plastic rails holding it in require you to press the tabs on the underside of the scope. But these tabs could not be pressed because the PCB prevented it. Bit of a catch 22 situation. I ended up putting zip ties (visible in the photos) to yank the board out just enough so the tabs could be pressed.

Quick inspection of the innards show no visible damage to anything on the power supply board, no burnt resistors, all caps look fine with no bulging and none test as short circuit. Tested all SMPS diodes, none test as short or open. I have an LCR meter on its way in the post so hopefully will be able to diagnose the caps when it arrives.

I should probably be testing voltages while this is running but kind of reluctant poking around the high voltage stuff while the scope is powered on.

« Last Edit: January 25, 2012, 04:55:57 pm by vtl »
 

Offline hacklordsniper

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Re: Philips PM3055 repair and teardown
« Reply #1 on: January 10, 2012, 11:23:50 am »
Nice scope!

I will suggest power supply problem since nothing works. Im interested what is that part on white leg with round red cylinder
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Online BravoV

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Re: Philips PM3055 repair and teardown
« Reply #2 on: January 10, 2012, 11:44:06 am »
Nice pictures, thanks !


Im interested what is that part on white leg with round red cylinder

I think thats a reed relay wrapped inside the red coil.

Offline vtl

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Re: Philips PM3055 repair and teardown
« Reply #3 on: January 10, 2012, 11:47:01 am »
Nice scope!

I will suggest power supply problem since nothing works. Im interested what is that part on white leg with round red cylinder

Reed relay. Glass reed switch thats housed inside a coil. Switch closes when coil is energized.

Yeah, definetly looks like a PSU problem. I've been looking at the service manual and it looks quite nice. The theory of operation is written out in laymans terms, even has advice on mundane tasks such as soldering.

Link if people want to have a look:
http://www.qsl.net/vk5bar/AHARS-Resources/Philips%20PM3055/PM3055%20Service%20Manual.pdf

Full 195 pages, theres another one floating around thats not the full thing.
 
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Offline tekfan

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Re: Philips PM3055 repair and teardown
« Reply #4 on: January 10, 2012, 02:32:27 pm »
Amazing that you got it so cheap. This scope should serve you nicely once it's fixed.

Yes, as the others say it's probably a power supply problem.
I have very bad experience with older (late 80's) Philips electrolytic capacitors. Some have lost almost 3/4 of their original capacitance. The two silver can ones on the left side of the transformer (5V power supply) also might have high ESR after all these years.

I can also see some film capacitors on the mains input for filtering. They look like Rifa brand capacitors. These were very good back in the day but in 20+ years cracks begin to appear on their sides and inevitably short circuit, blowing the mains fuse.

One can never have enough oscilloscopes.
 

Online vk6zgo

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Re: Philips PM3055 repair and teardown
« Reply #5 on: January 10, 2012, 03:08:05 pm »

Dear old Philips are quite idiosyncratic in their design.
I have commented in another thread about their "navel-gazing" propensities-----There is only one way to do it,the Philips way!
That said,if you can make it go,it's a fantastic bargain!
Good luck!

VK6ZGO
 

Offline vtl

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Re: Philips PM3055 repair and teardown
« Reply #6 on: January 11, 2012, 02:55:21 am »
Thanks for the advice tekfan, I'm thinking that a lot of the caps are probably bad from siting in 40 degree Australian summers. Possibly dried out and lost a lot of capacitance.

Few things I forgot to mention before:

eBay listing included probes, the user manual and the pouch that clips onto the housing of the scope.

Trigger holdoff knob has sheared off, not a big deal since it's not something I use regularly. I have a Rigol DS1052e scope anyway for capturing packet bursts. I will probably cut a lot in the remaining plastic so I can adjust with a screwdriver if needed.

I can't find a build date anywhere? Says Made in Holland on the back with the model and option code. The manual says printed in 1986 but I'd be interested in the history of these scopes.

Looking at the power supply theres a whole line of modern looking electrolytics with vent holes. In fact they don't even exist in the service manual I have, the diagrams show axial ones. I probably have some newer revision.

Included some more pictures, taken apart the LCD/controls board. Has an old school Intel 8052 as the main processor. Inside the module theres the controls PCB and the LCD pcb. Seems like the LCB pcb is the only board I've seen so far with SMD parts, I assume theyre just the drivers for the LCD segments. Also theres a nice little incandescent bulb with a diffuser to illuminate the LCD screen.

Included a better photo of the power supply board too. Very nice PCB, proper FR4 and double sided, none of this crap paper based PCBs you see these days. Whats annoying is that they have no silk screen so you can't tell from a glance the component designators. The service manual has everything but its a pain having to cross reference everything.

Theres some peculiar components I havent encountered before. The mains smoothing caps and the silver 6800uFs have 3 pins, presumably for more mechanical support since two are common? Also these wierd looking rectification diodes. Theyre some sort of hermetically sealed glass package. Some are pretty high spec, fast reverse recovery and high current.

I still have yet to take the preamplifier PCB out thats shielded by the metal casing. I'd rather concentrate on getting the thing fixed first though. Still waiting on that LCR meter, damn Australia post!
 

Online vk6zgo

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Re: Philips PM3055 repair and teardown
« Reply #7 on: January 11, 2012, 03:44:44 am »
Pretty boards----very "Philipsy"!

Yes,the 3 pin caps are for better physical stability---if I remember correctly,Sony used them, too.

The round glass encapsulation on the diodes was fairly common,back in the day,--nothing special about it.
The diodes in the  rectifier in the switchmode output circuit do need to be fast-recovery types,but the ones which rectify the mains to give around 300 volts DC don't.

As the thing is "squawking",it seems like it is getting mains power,etc.
There may be excessive load on the supply,so it may be an idea to remove some of the loads to see what happens.
As this is a Philips circuit,it may need some load to operate (some switchmodes don't,some do),but it should be OK it you remove them one by one---be very carefull--this board has 240v AC,probably 300v DC,& DC 2100v on it !

The  only circuitry which handle significant power are the deflection circuits,so if you disconnect them first,the supply may come back up.
Anyhow,have fun,but,again ,Be Carefull!

I have seen quite a few of this generation of Philips 'scopes on EBay,mostly at bargain prices,but I can't remember seeing any in service anywhere I worked.
There were usually a few of much older vintage,& lots of Philips LCR bridges,Signal Generators & the like.
I wonder who bought all those  PM3055s originally!

VK6ZGO

 

Offline vtl

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Re: Philips PM3055 repair and teardown
« Reply #8 on: January 11, 2012, 06:53:58 am »
Thanks for the tips, I really didn't want to power the scope up to test, afraid that leaving it on would ruin something in the scope if its in fault condition.

But I had a go anyway:

Ran the scope with only the CRT connected, still got the whining sound. Then the sound went away, somethings probably failed open circuit or something now. Power consumption with everything hooked up is 45w, which appears in spec according to the service manual. But with only the crt anode connected to the power board the thing still consumes 20w.

LCD screen now works can press the buttons and responds to everything, CRT still dead

Checked all power rails :
+5V=+5.02 (All good and crowbar circuit not active)
+12V=+12.35
-12V= -12.55
+17V = +16.93
-17V = -16.77
-48=-48.5
+48V=+44.9 - Seems a bit low since the other voltages are much tighter to spec. Checked on multimeter on AC for noise and was mucher higher than the other rails. Significant because this is the rail that is stepped to -2100V and 14kV and now the CRT isnt going. Maybe the 22uF smoothing cap on the 48 output is bad and now theres not enough voltage for the CRT?

When I turn the unit off the CRT flashes, probably a spike from the left over charge?

I certainly hope theres its not a problem with the HV multiplier, doesn't look like its a part thats easy to get.
 

Offline vtl

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Re: Philips PM3055 repair and teardown
« Reply #9 on: January 11, 2012, 06:58:48 am »
Hmm WTF!! Started playing with the trace controls and its working? CRT shows a trace!!! The scope seems to have fixed itself? Was the 1980s the era of electronics with self healing capability?

In any case i'm not complaining, will reassemble and do some runtime tests + photos
 

Online vk6zgo

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Re: Philips PM3055 repair and teardown
« Reply #10 on: January 11, 2012, 08:09:39 am »
Philips equipment had a habit of developing "Oops,I'm faulty-----No,wait,I'm OK now" problems.
Hopefully,you will hear no more of it,& the beast will give you many happy hours of use!

VK6ZGO
 

Offline hacklordsniper

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Re: Philips PM3055 repair and teardown
« Reply #11 on: January 11, 2012, 10:33:25 am »
Maybe you have a faulty connector or some bad solder joint.

Please post photos of scope in operation
Oh, the joy of sending various electronics to silicon heaven
 

Offline vtl

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Re: Philips PM3055 repair and teardown
« Reply #12 on: January 11, 2012, 11:26:11 am »
Been playing with the scope for the last few hours, all seems functional. I might consider swapping the mains capacitors, seems like they're heating up a little.

Very wierd layout with the pushbutton interface. I'm only 22 so I picked it up pretty quickly but I can imagine people using scopes for 30+ would be very annoyed with it.

Scope runs well, no screen burn in and has a nice sharp trace. The CRT has a backlight feature so you can see the graticules if you use this in low light. Looks pretty nice although seems fairly pointless unless the room is pitch black.

From the few tests I've run it seems that the vertical is pretty much perfect but the horizontal is a bit out and needs some adjustment. In the pics I've fed a 1KHz sine and the 1KHz square from the Rigol cal point. I don't have a function generator so I just used the output of my computer soundcard. RCA->BNC adapter is really handy for this. Now I have to dig through the sea of service procedures to find out how to adjust the horizontal.

Was getting a bit annoyed with my Rigol scope when measuring low noise stuff, eg the noise of power supplies. This is much better for it and obviously doesn't suffer from the slow screen updating. Should be a nice addition to the nerd cave. Great buy for $26, didn't even need to pay shipping, just picked it up locally here in Melbourne. The seller is probably kicking himself now :P
 

Online BravoV

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Re: Philips PM3055 repair and teardown
« Reply #13 on: January 11, 2012, 12:11:12 pm »
Congratulation, looks like its still in a very good shape and still performing really good.

Damn ... only  $26 !!! Have to admit I'm jealous !  ;D  lol

Offline hacklordsniper

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Re: Philips PM3055 repair and teardown
« Reply #14 on: January 11, 2012, 01:30:10 pm »
I will give you 30 $ for this crap, get rid of it!

Im just joking, quite interesting principle with the LCD, i never seen it, nice scope and great find
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Offline Chet T16

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Re: Philips PM3055 repair and teardown
« Reply #15 on: January 11, 2012, 01:48:38 pm »
Nice scope, even forgetting about the price! I had my eye on one similar while waiting on a 2225.

I love the design of them
Chet
Paid Electron Wrestler
 

Offline tekfan

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Re: Philips PM3055 repair and teardown
« Reply #16 on: January 11, 2012, 02:20:53 pm »
Very nice. Great to see it working. This one is probably from 1990.
I am amazed that the LCD screen backlight is still this bright. Does it use LEDs or some sort of incandescent lamp arrangement?
One can never have enough oscilloscopes.
 

Offline vtl

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Re: Philips PM3055 repair and teardown
« Reply #17 on: January 12, 2012, 02:53:19 am »
Thanks for the comments, yes I was particularly lucky to get it at this price, used scopes are quite expensive here. For example I was watching these tek 2225s and they went for $160-$170 on auction + $35 shipping. You basically have to have the email alerts and wait ages for a bargain to come.

The digital interface is quite interesting. They've exclusively used reed relays, so its very quiet and you only hear the faint chirp of the relays. The BNCs also have an automatic 10x sense and the included Philips probe has an extra metal ring to close the circuit. Not even my Rigol has that! I don't know if its possible to manually set 10x if you're not using Phillips probes though, may need to put a metal washer at the BNC to activate it.

Tekfan, the LCD backlight is just an incandescent lamp powered by -12V. Its pretty dim even with just fluroscent lighting but the segments are always clear and easy to read. Wouldn't be hard to solder in an LED+dropper resistor since the bulb is just soldered in with some flying wires.
 

Online vk6zgo

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Re: Philips PM3055 repair and teardown
« Reply #18 on: January 12, 2012, 04:53:13 am »
Out of curiosity,I Googled for "Philips PM3055",& found that on most  EBay sites around the world,these 'scopes are quite expensive,around the $200 mark!
That said,I have seen them fairly cheap on EBay.com.au in the past---not as cheap as $26 ,though!
I was thinking about one before I bought my Tek 7613 at a Hamfest for $135

A lot of people in Aust see the Philips CROs,say "Eek !It's not a Tektronix/HP!",& don't make a bid,but in other countries the Philips name is more prestigious.
I might just bid for one if it comes up cheaply------NO! I don't need four Oscilloscopes!

VK6ZGO
 

Offline vtl

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Re: Philips PM3055 repair and teardown
« Reply #19 on: January 25, 2012, 04:53:09 pm »

 

Offline M. András

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Re: Philips PM3055 oscilloscope repair and teardown
« Reply #20 on: January 25, 2012, 09:11:45 pm »
wow its amazing
 

Offline Ryl

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Re: Philips PM3055 oscilloscope repair and teardown
« Reply #21 on: February 20, 2012, 04:26:15 pm »
Hi from Belgium,

I found this post thanks to Google.
I purchased the same oscilloscope not long ago for about 150€ not far from home. It is a great one !
It was in correct condition (but not as good as yours). It also has a broken button (the "LEVEL MTB" one), which is kind of annoying (see pictures in this post).
It isn't "broken into the oscilloscope" as in your pics and I can still move it with a pair of pliers, but it isn't very handy and damages the remainders of the button.
Knowing that I dont want to take apart the oscilloscope to replace the button (I saw these ones were sometimes temperamental), do you have a quick and efficient solution for it ?
Something to stick (will it work, will it be reliable ?) or anything else to advise so I can fully get back the control of the button ?

Thanks a lot for your help (and please sorry my English),
Ryl
 

Offline vtl

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Re: Philips PM3055 oscilloscope repair and teardown
« Reply #22 on: February 21, 2012, 01:13:16 am »
There doesnt seem enough plastic left to do anything. You can cut a slot in the face so you can turn it with a screw driver if you want. But I think you should just open up the scope and fix it properly. It is not difficult and you won't damage anything.

You only need to open up the top metal cover of the chassis with 2 screws and you don't need to touch anything else to get to the control panel.

The control panel is held in by 1 screw in the back and lifts out as 1 unit:



You then pull out all the knobs and you can pull the PCB out of the plastic shell:



The knobs and switches are throughole components and can be easily desoldered. The PCB is high quality and it is unlikely youll damage anything. I suggest swapping the knob out with one of the other knobs. I would chose the "Level DTB" knob because it doesn't seem to do anything, even in DTB mode.
« Last Edit: February 21, 2012, 04:27:53 am by vtl »
 

Offline Ryl

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Re: Philips PM3055 oscilloscope repair and teardown
« Reply #23 on: February 21, 2012, 07:17:55 pm »
Thanks a lot for the tips, I'll let you know about that.

Today, I tried to run Youscope on my PM3055. But it seems that the display is flipped in both x and y directions. For example, text is coming from the upside and goes down. The same holds for the x-axis.
I used the output of a Macbook. From my smartphone (playing MP3 with horrible output), it seems that everything is correct.
Do you have an idea of how to invert signs on both x and y-axis ? I searched a bit, without success.

Thanks for your help,
Ryl
 

Offline vtl

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Re: Philips PM3055 oscilloscope repair and teardown
« Reply #24 on: February 22, 2012, 01:24:52 am »
Regarding the knobs, if you're feeling a bit more adventurous you can take the entire front panel off and swap the illumination knob instead. I've just realized the Level DTB knob is potentially useful once you get it in the correct mode.

Youscope instructions are on my site (connections, triggering):
http://dvactronics.com/?p=53

 


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