PM3055 oscilloscope PSU repair (didn't work) ... (edit: got it!!!)

[Atheus]

Another question if you don't mind. I can't seem to find this addressed in the user manual or find anything on Google. When I calibrate the scope - so X/Y position, timebase, V/div - everything I need to do to get that calibration signal nice and clear - as soon as I turn it off it seems to 'forget' all the settings (all those set digitally - obviously knobs and probe trimmers work) and start from scratch again.

Am I missing something? Is there a way to get this thing to save it's settings? Or am I expecting too much from an old device? I know only what I've learned in the last few days about scopes so go easy... is it common to have memory of some kind, like an EEPROM, where this stuff is saved? Or will I need to re-calibrate it each time? Is it a normal thing to just leave these devices turned on to keep the settings you've spent ages trying to get right?

[george.b]

I think this is quite niche, and the product itself I can't find many reviews for... but does anyone have any experience with this sort of thing?

https://www.amazon.co.uk/dp/B06XCD3P9L/ref=wl_it_dp_o_pC_nS_ttl?_encoding=UTF8&colid=39AC15SYOFVA&coliid=I1G3E532K1U4XK

Wouldn't this be great for hardware/firmware and 'IoT' development? Dual LAN to simulate a router, two WIFI antenna ports (so you can use that as a third network or test new antenna designs), serial/COM ports of course, five of those, and all the usual as well.

I imagine this running command line Linux, sitting on my electronics workbench (rather than my desk), with the colours set to all green on black

What I did was something kinda like that, yeah: I found an used HP thin client for cheap (T5570, specs: http://www.parkytowers.me.uk/thin/hp/t5570/index.shtml), installed a SATA hard drive and put Linux on it. Been using it to control a little CNC machine via the parallel port and to program PICs with a serial programmer. Works fine for my purposes

Another question if you don't mind. I can't seem to find this addressed in the user manual or find anything on Google. When I calibrate the scope - so X/Y position, timebase, V/div - everything I need to do to get that calibration signal nice and clear - as soon as I turn it off it seems to 'forget' all the settings (all those set digitally - obviously knobs and probe trimmers work) and start from scratch again.

Am I missing something? Is there a way to get this thing to save it's settings? Or am I expecting too much from an old device? I know only what I've learned in the last few days about scopes so go easy... is it common to have memory of some kind, like an EEPROM, where this stuff is saved? Or will I need to re-calibrate it each time? Is it a normal thing to just leave these devices turned on to keep the settings you've spent ages trying to get right?

As the owner of a PM3055 myself: not that I know of. The horizontal/vertical position controls are analog, so those settings are kept; the other settings are lost. I've never paid much thought to it, though. I'm okay with having to set it up again, if I turned it off, next time I turn it on again, I'm probably measuring something else anyways - doesn't mean I keep it on all the time, though

[capt bullshot]

It's even got a data to PC output, and an LCD, which is priceless. The buttons digitally change the time base etc and it all shows on the LCD. Min/max voltage, Hertz, trigger mode... it's almost like a digital scope with an analog screen.

Sorry to disappoint you here: the LCD does nothing but to show the actuall settings, no values to measure.

Eh? "does nothing but to show the actual settings" - isn't that what it's for? Rather than looking at a knob and trying to read off an exact timebase...

Yes, the LCD shows the setting the same way a knob would do. It shows the setting, not the "actual" thing (sorry for that confusion). Likewise the knob shows the setting, not the real thing. These knobs aren't analog in the way that you turn them continuously and then have to guess the setting, they are "digital" (having steps clearly corresponding to their scale). This LCD works the same way, just switching the steps internally controlled by the buttons. So the LCD is just comparable to the position indicator of the knob. Same for the Volts per div. settings

Edit: as george.b pointed out, the LCD based settings forget everything that you've set up using the buttons when you turn it off and on again. The scope always starts with the same default setting. Thats an clear advantage for the good old mechanical knobs (they don't turn on their own).

Regarding the timebase and other settings, not even digital scopes display the "actual" thing but the setting. They're able to calculate measured values of many kinds from the data, yes that's an real advantage over an analog scope.

I think this is quite niche, and the product itself I can't find many reviews for... but does anyone have any experience with this sort of thing?

https://www.amazon.co.uk/dp/B06XCD3P9L/ref=wl_it_dp_o_pC_nS_ttl?_encoding=UTF8&colid=39AC15SYOFVA&coliid=I1G3E532K1U4XK

Wouldn't this be great for hardware/firmware and 'IoT' development? Dual LAN to simulate a router, two WIFI antenna ports (so you can use that as a third network or test new antenna designs), serial/COM ports of course, five of those, and all the usual as well.

I imagine this running command line Linux, sitting on my electronics workbench (rather than my desk), with the colours set to all green on black

Yes, why not. I'm running such small boxes (not this particular one) as linux servers (no need for COM ports or WIFI). I'm more into low power consumption.

[SergiiB]

I write all this in detail because it has taken me 3 days (only a few hours each night but still...) to do this and I could find no decent description of this procedure online. Even the video teardowns seem to miss the bit where they actually remove the PSU, and questions about how to remove it on forums usually end in "I've given up" or "I got it!" without explanation. Hopefully this post contains the right SEO keywords to turn up the next time someone has this problem.

Actually removing PSU is extremely easy. Please see picture:
1. Push that to side to allow the board to get pass it.
2. Push board up from that opening underneath you marked red in your post with a screw driver or similar.

[SergiiB]

I was reading this thread and found out that caps on my board are bad.
But in addition to three RIFAs I also have a funny one. I don't even know what technology it is and should it be replaced too?

[capt bullshot]

Looks like a film capacitor, you might try to look it up in the service manual. I wouldn't replace it just because.

[Polymaff]

Don't know if anyone is still following this thread.

The capacitor is a 1nF, 1%,  630v  -  a film type will do.  It is not a particularly stressed component, so leave it.

The PSU board is very easy to remove. The official method is to bend each of the flexible retainer clips (a typo in the manual - "lips" is clips without the letter c - geddit?) and then slide the pcb up and out.  The method SergiiB describe works - but only because the clips are really too far apart

A very nice 'scope.

[SergiiB]

Thanx Polymaff.

I left it already as "capt bullshot" suggested, so far scope is still working (though it is not frequently used).
Initially I thought it was some kind of a paper cap and I saw a video on YouTube that all paper caps MUST be replace because they 100% bad. Happened to be not a paper cap.

Regards, Sergii

[Polymaff]

By the way, there were several versions of the PSU Board, so don't be surprised if photos on the web don't look quite like your own. Particularly around the power line input circuitry.

I'm not aware of ANY paper capacitors in the PM3055, so I reject the Youtube advice!  Given that this is such an old model, it is the electrolytics which might be the most suspect capacitors - particularly if the scope is out of use for some time.

Working in the Philips Group when these scopes first came out, I saw quite a few of them.  I still have a PM3055 that the service department gave me when I retired.  The only thing it has needed in the 16 years since then are LED replacements for the two weird (typical Philips!) incandescent lamps.

[SergiiB]

Yes, my did not look like original author's one. Slightly different.

But I did check all electrolytic caps, all are surprisingly good after God knows how many years.  Only changed 4 RIFAs (they say they blow up) and 1 switch IC for calibration generator.