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Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders. |
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14th May 2018, 5:22 pm | #1 |
Octode
Join Date: Apr 2007
Location: Hampshire, UK.
Posts: 1,574
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Philips PM 3365A - wobbly display
The PM 3365A is one of my favourite 'scopes, it has everything you need and nothing you don't. I've designed more stuff using these than any other model, they are so easy to operate.
However, a common problem seems to be a "ragged" display when switched on from cold, the last 2 or 3 I've seen have all done it. It shows up worse in digital than in analogue mode, where the text at the bottom is unstable (especially at the edges) and the traces noisier than they should be. After half an hour or so the situation improves greatly and everything functions normally. In analogue mode the symptoms are less severe, but still noticeable for critical work. At a guess it looks like hash from the power supply or the EHT generator getting into the rest of the circuit, however a quick check around reveals nothing obvious amiss. The layout and construction of the interior does not lend itself to easy fault finding, does anyone have any experience of fixing these? |
14th May 2018, 5:37 pm | #2 |
Octode
Join Date: Jan 2007
Location: Dorridge, West Midlands, UK.
Posts: 1,474
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Re: Philips PM 3365A - wobbly display
In one I had all the small blue caps on the PSU were shot replacing them brought it back to proper working order, I believe it is a common problem on these scopes.
Fish out your ESR meter. see also here https://www.youtube.com/watch?v=evGf4LMaixI Chris |
16th May 2018, 9:29 am | #3 |
Octode
Join Date: Apr 2007
Location: Hampshire, UK.
Posts: 1,574
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Re: Philips PM 3365A - wobbly display
Thanks for the tip - they all look OK and nothing gets hot in that area but appearances can be deceiving. Its a shame that the double sided print makes it so difficult to remove and test things but hopefully it will be working properly again soon.
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16th May 2018, 11:37 am | #4 |
Dekatron
Join Date: Jun 2016
Location: London, UK.
Posts: 3,687
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Re: Philips PM 3365A - wobbly display
Agree with chriswood1900. I had a PM3315 from Pamphonica a year or so ago now. That had a shorted Philips blue axial capacitor in it. Eventually they go high ESR which drags the rails down and then the power supply starts dropping out.
Also make sure you replace any of the RIFA gold ones in the inlet section. They are at prime exploding age at the moment and make a right mess! |