Old Fluke&Philips PM3350 - broken Y-Axis - Page 1
Forum section: electronics / repair

author: THPallround
author_rank: Newbie
timestamp: May 21, 2019, 03:37:49 pm
content: Hey folks,at the beginning of the year I bought a "propper functioning" oscilloscope on ebay.When I turned it on, I see, that the menu shown on the CTR is completly moved to the upper corner, so I only can see the "button row" Whyle testing the CRT with the intern testsignal, it came out that everything has moved in +Y by ~7Div.After downloading the Service Manual, i tried to adjust the Y-Axis like its given in manual. Unfortunately without success...As you can see in  the line is out of view, just some light is shining in from the top corner.I also replaced some explodet caps on the mainside of the PSU. But they are only there for EMV reasons. After throwing up the table, beeing sulk for some weeks while waching tons of YT-vids about faulty osc's I came up to write this forum entry.So I hope you can help me out of my brain dead end.I have uploaded some photoshttps://imgur.com/a/O2XCplOand the Service Manualhttps://elektrotanya.com/philips_pm3350_pm3352_sm.pdf/download.htmlso you can see what I have tryed to explain in my bad german mid scool englishIf you do need some more informations just ask, I hope that I can get this 80€ pice of copper work propper againGreetings Thomas

author: pbarton
author_rank: Frequent Contributor
timestamp: May 22, 2019, 04:52:11 pm
content: Possibly a problem in the Final Vertical Amplifier? Diagram attached.Check the power rails including those with a blue arrow +5, +12, +17, +48, -6.4 and -48V for DC level and AC ripple.If you could reply with the following measurements….Centre the front panel Vertical position control knob (Y) and measure the ‘red’ DC voltages (with a DMM) at X20, X21, X22, X23, also A, B, C and D.No input signal is required.

author: madao
author_rank: Frequent Contributor
timestamp: May 23, 2019, 03:44:30 pm
content: I has repair little brother (PM3335) of PM3350. But analog part is same.Same fail, but mirrored (trace is with readout compressed to lower)Cause is a failed 2N3866 in final stage of vertical amplifier.I would saying, check vertical amplifier backwarts.regardsmatt

author: THPallround
author_rank: Newbie
timestamp: May 26, 2019, 07:25:58 pm
content: Quote from: pbarton on May 22, 2019, 04:52:11 pmThis was also a thought of me, but I had no plan which measurements I have to do exactly.QuoteI'll make the measurements tomorrow and will post them.Thanks for quick reply!

author: THPallround
author_rank: Newbie
timestamp: May 27, 2019, 09:23:11 pm
content: Hello there,after I handled it to take the pcb's out of the oszi in one pice, I relized that this kind of flatcable ( on the same imgurhttps://imgur.com/a/O2XCplO) is peeled of from it's insulation. What's the best way to replace/repare it? Just use some wires or a shielded cable? I don't want to make more problems than improfmentsSo anyway I figured out all measurepoints you gave me. Tomorrow I hopefully can deliver some values.

author: pbarton
author_rank: Frequent Contributor
timestamp: May 27, 2019, 09:56:52 pm
content: Repair using Duct, Gaffer or Gorilla tape?

author: THPallround
author_rank: Newbie
timestamp: May 28, 2019, 02:42:34 pm
content: Quote from: pbarton on May 27, 2019, 09:56:52 pmThat was my first thought, but than I remeber, its bend kompletly while mounting it and I don't want it to make a short circuit.I think I will clean it up and pull a shrinking tube over each conductor.

author: madao
author_rank: Frequent Contributor
timestamp: May 28, 2019, 06:15:34 pm
content: oh, rotten-cable..2.54mm pitch flat cable is a option. Hot glue is important supplement to provided of realibilty.(or you can using 1,27mm cable,)regardsmatt

author: THPallround
author_rank: Newbie
timestamp: June 01, 2019, 10:36:25 pm
content: Ohh man... After I wondering about the fact, that the output on the CRT gets more vaulty I and making all measurements I realize, that I switched up some wires from changing the rotten cable...This shows clearly: don't work until midnightHopefully, I don't make it worse...You hear from me in the next days.

author: THPallround
author_rank: Newbie
timestamp: June 03, 2019, 08:34:08 pm
content: So I found time today. Measurements are posted as  onhttps://imgur.com/a/O2XCplOThere is some odd stuff going on at AC ripple as you can see. Hopefully, we can find the vault now.

author: madao
author_rank: Frequent Contributor
timestamp: June 12, 2019, 07:50:24 pm
content: I have repair other Philips scope with SMPS Power supply, there is also rotten-eletrolytics also cause for failure.You can replacing eletrolytics of PSU.How removing of PSU. Yes, it is difficult, if you don't know, how about it is.Left carry-handle must be pulled , while you're pulling PSU-PCB out of Philips. Otherwise, you couldn't pulled it out, because axle of carry-handle forces it down. Yes, it is mechanially nightmare.regardsmatt

author: THPallround
author_rank: Newbie
timestamp: June 13, 2019, 04:18:13 pm
content: Yes, it's a nightmare to get the PSU out... After I managed it the first time I modified the clampsSo you mean I should change all e-caps on the PSU-PCB?

author: madao
author_rank: Frequent Contributor
timestamp: June 30, 2019, 05:19:58 pm
content: Sorry for late reply.Only small eletrolytics on secondary side is needed to replacing.But i recommed, replace all on secondary side and little in primary ciruit.

author: THPallround
author_rank: Newbie
timestamp: July 01, 2019, 03:45:52 pm
content: No problem, we all have a real life tooOkay, I will order some new one for replacing. Any other parts that could be eventually faulty? I just want to try avoiding more shipping costs than needed