My oscilloscope just did something strange

Discussion in 'General Electronics Chat' started by adam555, Nov 20, 2013.

  1. ian field

    AAC Fanatic!

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    Some of them are more than a typical DMM can measure!

    In any case, the supply source resistance is so high, even a high input impedance DMM will load it and give innacurate reading.
     
  2. ian field

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    All ABS plastics are delicate!
     
  3. MrChips

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    I go by the rule "If it ain't broke don't fix it".
     
  4. adam555

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    So, you would recommend not to use it on any pot unless there's a good reason for it?

    I thought about that, but since most of the pots and switches were failing when it arrived -though they got better with use along these couple of months- I decided to take this opportunity and clean them all; just in case.
     
    Last edited: Dec 9, 2013
  5. adam555

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    Your last post made me doubt... aren't these switch cleaners also used to prevent damage and prolong life-span, or are they only used when something doesn't work well?
     
  6. MrChips

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    Spraying switch and control cleaner is not preventative maintenance.
    Use it once and you will have to use it again.
    I only use it when I have to, short of replacing the control.
     
  7. adam555

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    Glad I asked... I was about to put on every pot that passed through my hands.
     
  8. bountyhunter

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    I think some cleaner sprays are plastic safe, but obviously be careful.
     
  9. bountyhunter

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    Again it depends on the type. Some of the old cleaners had "conductive lube" in them that actually made the old pots turn smoother as well as cure the scratchies. Funny, I just had to use it on the pots on the amp I built for my TV speakers yesterday. Worked great, it was stuff I got at Fry's in a green can.
     
  10. ian field

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    Switch cleaner invariably contains lubricant - which catches *ANY* dust that would otherwise waft right past!

    On some occasions I've used GT85 - its like WD40, but fortified with PTFE, You'd think the PTFE would insulate contacts, but that hasn't been my experience.

    The lubricant is much more volatile and eventually evaporates leaving just the PTFE, but it contains a fairly aggressive solvent - so any ABS assemblies are little granules in no time flat!
     
  11. ian field

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    The ozone layer crisis and ensuing anti-CFC legislation has been a major game changer - I've heard reports of CFC free freezer spray causing massive static buildup on boards/components sprayed with it, as yet I've not heard any specific reports of unexpected behaviour with CFC free switch cleaner - attacking ABS plastics probably wasn't that much of a surprise!
     
  12. adam555

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    For what the label said I assumed I had to be specially careful with rubbers and soft plastics. But if it does damage ABS, then it would be a bit difficult to tell beforehand; as those are hard plastics.
     
  13. ian field

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    But looking on the bright side - it doesn't take much time.

    If the plastic is ABS, it turns into granules in literally a few seconds.
     
  14. adam555

    Thread Starter Active Member

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    That's definitely going to help a lot. :)

    Let's hope at least the switch cleaner manufacturers considered the plastics used in pots, or the pots manufacturers considered the switch cleaners when choosing the plastics. Because it doesn't make any sense selling a product that's going to dissolve the component that you are attempting to clean.
     
  15. ian field

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    Seems that everything is made of ABS these days!

    Last year I set about some preventative maintenance on my mountain bike gear twistgrip - consulting a supposedly respected book on bicycle maintenance, I was advised to use Finnish line PTFE grease - which is exactly what I did.

    A few months later the plastic housing just cracked in two as I tried to change gear!

    The shop mentioned that those twistgrips only last a year or two (the bike was scrounged on Freecycle and I'd had it a couple of years) - the shop does a special offer on GT85, 50% off with any cycle accessory (like WD40 but with PTFE) so I bought a can of that - the shop assistant commented; "oh yes - we clean every bit of a bike with that before we hand over to the customer".

    So now we know why the twistgrips only last a year or two!
     
  16. bountyhunter

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    Yeah, I remember when they forced us to change to "CFC free" flux stripper which absolutely did not work.

    Here is wisdom: non chlorinated brake cleaner spray is GREAT flux stripper and costs $2 for a can. It will also clean switches. But, most cleaners have acetone, xylene and some other "hot" solvents which attack some types of plastic.

    It surprises me there are any electronic components using that type of plastic as they often get "stripped" during the manufacturing flow.
     
  17. ian field

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    For flux cleaning, I just nip in the car accessory distributors and pick up a gallon of cellulose thinners.

    Being highly flammable, it needs to be handled with great care of course!
     
  18. alfacliff

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    Dec 13, 2013
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    older crt's sometimes have flakes coming off the heaters, this causes a grid to cathode short that can do that. sometimes a good tapping with the face of the crt down can get the flakes to move out of the electron gun.
     
  19. alfacliff

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    one possibly safe cleaner is "deoxit" popular amoung the antique radio restorers.
    cliff
     
  20. ian field

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    Good chance of breaking the neck off if you tap too hard! - and you don't want debris falling on the shadowmask and making extra shadows.

    A technique used in the trade called "brushing" - find an output on the LOPT that can draw a smooth arc at line frequency, ground all the CRT cathode pins and "brush" the remaining pins with the arc.

    This fuses the flakes into blobs that are more compact and don't get in the way, the CRT can be treated in its normal way up, so any loose debris eventually slides down the inside of the CRT bowl and hides under the edge of the shadowmask metal frame.
     
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