Phillips (fluke) pm3394A calibration incomplete - Page 1
Forum section: electronics / repair

author: demented74
author_rank: Newbie
timestamp: August 08, 2022, 09:14:27 pm
content: Hi, I have just joined the forum so if I'm posting in the wrong place please let me know.I have a Phillips PM3394A which although from the 90's has had very little use. I last used it about a year ago, and having had a period of illness, It sat in the workshop unused. The batteries are energiser lithium and are in excellent condition.Today I turned it on and noticed that the Text was almost out of view at the edges of the display. both X and Y are overscanned. (the effect you would get if the E.H.T was low, but it is fine, brightness and focus are perfect.I left it to warm up for 1 hour and pressed the auto cal button. Auto cal ran, but said " calibration incomplete, please repeat auto cal"I have now run it several time with the same result. Everything else works fine, but unless I can get it to calibrate properly, it really isn't much use in its present condition. and would only be able to show waveforms and no measurements possible.If anyone has come across this problem and has a solution, I will be forever in your debt and very grateful for any advise. Thanks in advance.P.S. It has the math plus option if that makes any difference.

author: wn1fju
author_rank: Frequent Contributor
timestamp: August 08, 2022, 10:21:30 pm
content: I have the "B" version, but I assume it is probably very close to your "A" version.One normally has to do a manual calibration first. The autocal button sort of assumes that the manual calibration has been done successfully.I quote from the service manual for the "B" version, chapter 7, where it says, "Operation of the front panel CAL key activates the automatic calibration. AUTOCAL can only function usefully if the manual adjustments (especially the 'screen calibrations') are correct."Get yourself the service manual and follow their procedure. Normally I would suspect you had memory loss due to malfunctioning backup batteries, but you say your batteries are OK. Make sure there is no corrosion on the tabs of the battery holder. That got me once!

author: srb1954
author_rank: Super Contributor
timestamp: August 09, 2022, 05:30:03 am
content: The autocal is only supposed to make small adjustments to the parameters to counter minor drift. The manual states "The CAL key is used to make a fine adjustment of the oscilloscope's input .... a fine adjustment once a week or even every month is sufficient"It may be that, if the scope has not had an autocal for a long period, some of the parameters have drifted so far that autocal is unable to correct them. In which case, you may have to perform the manual calibration steps to bring the incorrect parameters back to within range of the autocal compensation program.Since several parameters seem to be out of spec it might pay to first check that none of the power supply rails have drifted out of spec before looking more deeply into other circuitry.

author: demented74
author_rank: Newbie
timestamp: August 09, 2022, 02:45:23 pm
content: Thanks for the info, Is there anywhere that I can get the calibration information from? I looked online but with no success.

author: HighVoltage
author_rank: Super Contributor
timestamp: August 09, 2022, 02:56:51 pm
content: This problem usually happens when 2 of the 4 channels are not at zero in the digital mode.1. Set the scope to analog with all 4 channels on and nothing connected to the input.2. all 4 traces should be at zero for each of the channels3. Switch to digital mode- When all is good, all 4 traces will still be at the respective zero- Most likely you will see 2 trace lines out of reach, maybe even off screen.Usually it is Channel 1-3 or Channel 2-4 effectedIf this is the case, you need to replace a hybrid chip that is no longer available unless you take it off another instrument.

author: demented74
author_rank: Newbie
timestamp: August 09, 2022, 04:33:37 pm
content: Hi, thanks for the suggestion, I tried that and all four traces remain excactly on the centre line in both modes.Does anyone know of a link to the manual calibration procedure?

author: HighVoltage
author_rank: Super Contributor
timestamp: August 09, 2022, 05:42:56 pm
content: That is really good news for you.Before you touch the manual calibration, run all the self tests!The manuals can easily be found onlineJust search for "Fluke PM3394B service manual"Post a picture of what you think is wrong with your scope!

author: demented74
author_rank: Newbie
timestamp: August 09, 2022, 10:51:51 pm
content: Thanks againJust found this which covers the PM3394ahttps://www.opweb.de/english/company/Fluke/PM3394AExactly what I need and more.I would be lost without my favorite 'scope!