Philips PM3055 oscilloscope repair and teardown

[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