Rebuilding powersupply of Phillips 3244 scope - Page 1
Forum section: electronics / testgear

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: December 18, 2014, 03:50:52 pm
content: Hi,Got a second hand phillips PM3244 scope this weekend (for free!). However, internally, the .22uF capacitor for mains filtering was broken (so I removed it). After that, the scope worked fine.When I asked someone if I should or shouldn't replace the filter cap, he told me I should consider replacing other capacitors (the larger electrolytics as a minimum) as well, since they age and could distructivly fail damaging the rest of the device. He event told me I could consider rebuilding parts of the supply.So, should I just replace the capacitor that was actually damaged, replace the electrolytics as well or just try to see if I can manage to build an entirely new powersupply board (I haven't yet looked into the actually possibility of doing so, I know the scope uses some custom phillips IC's you can't get, but I don't know if the powersupply actually has any of those, I believe it's pretty much jellybean-only)?

author: oldway
author_rank: Super Contributor
timestamp: December 18, 2014, 06:22:34 pm
content: If it works properly, do not change anything.Optionally, you can check the power supply. (voltages and ripples)But don't replace nothing if you are not 100% sure that it is faulty!And this 0.22µf is not necessary, the scope works very well without it.

author: amc184
author_rank: Regular Contributor
timestamp: December 18, 2014, 06:24:51 pm
content: I would replace the mains noise suppression capacitor, just make sure you use a Class X2 rated MKP film one.Replacing the electrolytic capacitors in the rest of the 'scope is probably worthwhile. This piece of gear is getting pretty old now, and many of the elcaps won't be anything near original spec now. My first 'scope was a Philips PM3267, and it wouldn't ever trigger at low frequencies until I did this. I wouldn't look at replacing the supply though, there's very little point in that.

author: tautech
author_rank: Super Contributor
timestamp: December 18, 2014, 07:28:15 pm
content: I will secondoldway's reply with additional advice.Carefully inspect E caps for signs of leakage and/or dome'ed ends.As much old gear was conservativly designed, untill full failure of caps they appear to function correctly.If possible catch them before they go pop or leak all over the PCB.Good score, hope it serves you well.

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: December 18, 2014, 08:31:01 pm
content: Quote from: tautech on December 18, 2014, 07:28:15 pmI will check the PCBs this weekend. From what I can remember, none of the PSU ones seemed to bulge or leak. I don't know about those on the other PCB's.So, no replacing the mains filter cap?

author: tautech
author_rank: Super Contributor
timestamp: December 18, 2014, 08:53:50 pm
content: Quote from: TheUnnamedNewbie on December 18, 2014, 08:31:01 pmMains filter cap: for piece of mind, replace it if/when you can. But no panic to do so.PSU caps LV & HV are likely under the most stress, but if all seems well, just use the scope but the moment things aren't quite right.....investigate.Use it as much as you can and you will notice when things are not right.Get the TEK troubleshooting pdf from the first post in the Repair board and keep for reference.

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: December 19, 2014, 06:38:05 am
content: Quote from: tautech on December 18, 2014, 08:53:50 pmI will. I also found soms nice PDF's of some service manuals which also includes a step by step guide for troubleshooting that I've stored on my computer.http://bee.mif.pg.gda.pl/ciasteczkowypotwor/Philips/pm3244.pdflink to the manualThanks for the help!TheUnnamedNewbie

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: December 19, 2014, 04:52:36 pm
content: Had a PM3263 of mine blow that cap. A very common issue for those scopes. Had to quickly remove it to the outdoors as the room filled with toxic smoke.Did some tests on the filter caps they seemed great, actually higher than the rated 330uF. Now the problem is a broken pot. The knobs do not like being pushed back on to the wimpy pots. Poor way to attach knobs. Too cheap to use setscrews.No idea where to get those.Not too impressed with the overall quality of PM scopes.

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: December 19, 2014, 06:32:33 pm
content: Quote from: SoundTech-LG on December 19, 2014, 04:52:36 pmSad to hear! Although Im not exactly a heavy user of all it's features, from what I can tell the scope feels very-well built. And hey, what can I say, I got it for free, so I'm not going to be complaining any time soon!