Philips PM3055 oscilloscope repair and teardown

[vtl]

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.

[hacklordsniper]

Nice scope!

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

[BravoV]

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.

[vtl]

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.

[tekfan]

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.

[vk6zgo]

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

[vtl]

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!

[vk6zgo]

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

[vtl]

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.

[vtl]

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

[vk6zgo]

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

[hacklordsniper]

Maybe you have a faulty connector or some bad solder joint.

Please post photos of scope in operation

[vtl]

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

[BravoV]

Congratulation, looks like its still in a very good shape and still performing really good.

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

[hacklordsniper]

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

[Chet T16]

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

[tekfan]

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?

[vtl]

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.

[vk6zgo]

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

[vtl]

[M. András]

wow its amazing

[Ryl]

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

[vtl]

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.

[Ryl]

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

[vtl]

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

[xbdt]

Hello, I do have a PM3055 for sale for parts. Only the power supply needs a repair. I saw that several on this topic are missing a potentiometer. If you want I can also sell these separate.
I used the power supply from this one to repair my PM3335.

[tautech]

Welcome to the forum.

You could also advertise it in the buy/sell thread.

Thanks for finding this thread. 
I've got a 3070 (100 MHz) that needs fixing too and it's always good the have additional resources for when I get it on the bench.

Edit.
I see you have advertised it.

[jitter]

Nice find!

We still have one of these at work. No one ever uses it nowadays, but I used it quite a lot until about ten years ago.
I tried to power it up the other day and got the same high pitched squeal. Perhaps the "Oops I'm faulty....oh no I'm not" applies to this one as well  . Maybe I'll try it again next week.

The operation is indeed a bit strange when compared to more conventional layouts, but you get used to it quickly.
XY is called "X-deflect" on these scopes.

Your's looks to be a 1990 vintage, datecodes on the ICs are late 1989.

Now that your's is working, it's worth checking out the ripple voltages on the several (low voltage) rails. At 25 years old the electrolytics will have seen better days and that might show as elevated ripple.

[jitter]

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

If vertical is horizontal instead swap probes between channels. And if the picture moves up instead of down, invert channel B.

[jitter]

We still have one of these at work. No one ever uses it nowadays, but I used it quite a lot until about ten years ago.
I tried to power it up the other day and got the same high pitched squeal. Perhaps the "Oops I'm faulty....oh no I'm not" applies to this one as well  . Maybe I'll try it again next week.

Tried it again, but the squeal is still there. Sounds like it's coming from somewhere near the back of the CRT. Possibly the same symptoms as yours. It's a PM3355, BTW.

How is the repair going?

[philoop]

Old thread but i want share my experience..
Got an PM3055 by accident, it made a squealing sound,
Opend it checked all connections...all good..
After reading this thread, i decided to stand the noise and waited a while ..switched it on and of some times.....and yep its working again...
The sound comes from a coil, and will fade after a while....
when some caps are saturated ...my best guess

[philoop]

from the manual:
 Take care that the switching-off and switching_on is at least 5 seconds.A shorter time interval might activate a protection circuit.
If this circuit protection is yet activated, (a squealing sound can be heard), it can be deactivated simply by switching off the instrument for 5 seconds.

[blargg]

Thanks for the tip about the scope squealing, and to try powering up again before giving up. It helped me confirm that my scope (PM3335) is basically working, and that replacing the power supply caps won't be a waste of time.

I had opened the scope when it squealed, desoldered each electrolytic from the power board and checked ESR and capacitance. Several were <50% original capacitance and a few ohms ESR, but not knowing whether replacing them all would still leave me with a dead scope was demotivating. I came across this tip so decided to resolder them and give it another shot, and it works.

I quickly measured rail voltages and took captures of ripple waveforms, confirming that some caps are pretty bad and that replacing them will be a worthwhile project to keep this nice analog/DSO scope around a while longer. There's some ~33kHz pulse on every rail, and a few have a much more pronounced sine wave ripple. The worst rails match the worst capacitors. Nice to have everything agree.

[bd139]

Make sure you replace the RIFA capacitors on the power supply board or it’ll try and burn your house down!

Every Philips item I bought has blown up so far due to them. Just replace them now.

My old Pm3217 had same noise on it.  Was the blue Philips axial caps on the secondary half of the switching supply.

The squeal is the switching power supply dropping into audio range. Probably a high esr cap somewhere.

[blargg]

I've read that modern low-ESR caps can cause older switching supplies to oscillate, due to increasing the Q higher than expected (I'd rounded up a bunch of ~40mOhm caps on Mouser but then read that they might be "too" good!). I'm having trouble finding the specs of the ESR of these old Philips blue electrolytics when they were new. There is a 030K0 marking I see on several (also 030 K0 FN), also F8 on some. What was the typical ESR of a good power supply cap in the mid-1990s? 500-1000 mOhm range? The options seem to be 1 ohm, 500m, 200s, and below 100.

[cheeseit]

I recently (finally) recapped my PM3055 and replaced all the electrolytics, except the two large 68µF/385V and the two 6800µF/10V that measured fine. Of the ones replaced only two were okay to marginal, the rest had ESR in the hundreds or kilo Ohm range and measured down to single digits in percent of their original capacity. It did still work though.

Below is what I used, some I had in stock and some I ordered. Might not be optimal but works perfectly and it took care of the squealing sound it made on startup that would slowly fade away over a couple of minutes, as well as some noise in the trace. You should definitely replace the RIFA caps too if your board is one of the versions that used them.

Axial
MAL202135151E3
MAL202135681E3
MAL202135689E3
MAL202190544E3
MAL203037339E3
516D226M063LL6AE3
107TTA010M
107TTA025M

Radial
ECA-1EM102

[johnmx]

I got a faulty PM3065 from a dumpster diving. The symptom was the common squealing from the power supply and nothing worked.
The handle bar is missing, the LCD has some damage and its backlight bulb was blown. According to the ICs manufacture date, this unit must be from 1988.

I replaced all electrolytic caps, including the three X2 caps on the power supply board. Also replaced the electrolytic caps from the CRT control unit and front unit.
Next removed the blown bulb from the LCD unit and inserted three small white LEDs (salvage from the LCD of an old PDA) in series with a 220 Ohm resistor.

Put everything back together and the oscilloscope is working again. No sound from the power supply.

Although the LCD has some damage it is possible to read all settings.

In the future I will replace all electrolytic caps from the other boards, if I have free time...

One thing to note, the plastic breaks too easily, especially the clamping lips that secure the PCBs. So extreme care is necessary.

Anyone knows how to use the remote function (via I2C)?
Is there any software to access the settings through I2C?

[Shock]

I think that squeal is the X2 cap dying violently with mains voltage across it.

The MAB8052 and I2C are discussed in the PM3065 service manual.
For the oscilloscope itself there is an external boxed IEEE-488 (GPIB) Interface option PM8953.
No idea what can be controlled from it.

There is another option PM8998 which is a front panel settings backup. A schematic for it is floating around on the net somewhere. To the best of my knowledge they both plug into the single DB9 at the rear of the oscilloscope, so it's one or the other.

Here is a shot of my first PM3065, none of that Fluke rubbish for me (just kidding).

(image removed)

[slbender]

I once had a scope like that, I think it was a PM 3052, it was similar.  Main problem all those little blue Caps that look like tootse rolls with axial wires, about 40 of them needed replacing.  Then the scope was bright and functional.  Cheap fix for a thirty year old (then) set. I think the replacements, I used radial parts rated at 50 volts, under ten dollars to get it working. 

Steven