Connect with us

My next project? What do you think?

Discussion in 'Troubleshooting and Repair' started by (*steve*), Jan 18, 2019.

  1. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,160
    2,676
    Jan 21, 2010
    I picked up a very sorry HP410C.

    I'm not sure if it's been wet, or in a corrosive atmosphere, or what.

    1547807020206159.jpg

    The handle seems to have quite a bit of surface rust.

    1547807164917992.jpg

    I wonder what it looks like inside?
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,160
    2,676
    Jan 21, 2010
    Here's a view in the top.

    1547807749942913.jpg

    The ceramic cap has a lovely pattern on it, probably from stuff falling in through the ventilation holes.

    I can only see a single tube, and the shield on it looks pretty rusted. Oddly enough, that's all that appears significantly rusted. I think the chassis is aluminium, so while it looks a bit crusty, it seems mostly just in need of a clean.

    One board there looks to be in remarkably good condition. I expect the gold playing of the PCB tracks has something to do with that.

    1547807750080916.jpg

    And looking from the other direction, the various adjustment trimpots look nice and clean!

    1547808393294276.jpg

    At first I was concerned about the almost unreadable meter, but that seems to be just an accumulation of dust. I rubbed some of it away with my finger.

    154780861640035.jpg

    I think there may even have been an AC probe for this. I don't have it at the moment, but looking at where it plus in, and remembering something that was also where this was found...

    Anyway, I'm sure this will require serious work to get it in a condition where I would even think about applying power. Should I take it on?
     
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,160
    2,676
    Jan 21, 2010
    Wow, there's some very interesting design aspects of this meter.

    It uses neon bulbs and light sensitive resistors to control modulation and synchronous demodulation to (I think) allow the use of an AC coupled amplifier to amplify the input signal.

    Here is a manual.
     
  4. Tha fios agaibh

    Tha fios agaibh

    1,875
    592
    Aug 11, 2014
    I suspect your like me and enjoy fixing things just for the heck of it.
    I say it'd be worth it just for the fun of it provided you have the free time to invest.

    As far as functionality, I suspect it wouldn't be the most reliable piece of equipment and certainly not the prettiest.

    If you don't really need an extra meter I might pass on it because it probably doesn't have much resale value.
     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,160
    2,676
    Jan 21, 2010
    Fun may be the best reason. Any reward is going to be something other than financial.

    I've been skimming through the manual (on my phone -- urgh!) and it seems all the transistors are germanium. There's also lots of "high tolerance" resistors (1% carbon composition) with unusual values like 70k, 6M, etc.

    Some other parts are pure unobtainium, but I've not seen any physical damage yet. I'm hoping it was put away because it was obsolete or because it had some easily fixed fault.
     
  6. Tha fios agaibh

    Tha fios agaibh

    1,875
    592
    Aug 11, 2014
    I would do some tests to make sure the meter itself is working properly. I imagine even a high quality jeweled movement can be compromised by corrosion even when sealed.

    It would suck to rebuild that thing only to find out that the needle movement sticks.
     
  7. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,160
    2,676
    Jan 21, 2010
    Very good point. I'll also do some basic checks on the transformer.
     
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,160
    2,676
    Jan 21, 2010
    Well... The meter movement works. Up to a point :-(

    At about 80% of the deflection, something starts rubbing. If forced a little further, the movement sticks, although a tap on the front of the meter frees it up again.

    I used my meter in the ohms and diode check ranges as a quick and dirty current source. The resistance if the meter is 188.5Ω, by the way.

    This may be the first thing to look at.
     
  9. Tha fios agaibh

    Tha fios agaibh

    1,875
    592
    Aug 11, 2014
    That's a horrible sign. I'd guess there's dirt or corrosion on the bearings, magnet or spring. I'd be hesitant to cleaning it because it may throw off calibration.

    You could try feeding a extremely low frequency signal (a few hz at obviously limited current) to see if a back and forth needle sweep may free it up.
     
  10. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,160
    2,676
    Jan 21, 2010
    Well, it only takes the removal of 14 screws and desoldering 2 joints, but the meter is out!

    It's complete with a QA sticker and an "individually calibrated" sticker.

    1547970290826473.jpg

    1547970290706258.jpg

    I wonder what I will find inside?

    And I guess this is going to void the warranty, right?
     
  11. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,160
    2,676
    Jan 21, 2010
    Warranty voided!

    The problem looks simple enough. There is some corrosion that the moving coil brushes against as it gets near full scale deflection.

    1547972053671758.jpg

    Do you think it's possible to scrape away at that rust without either damaging the movement or getting the rust stuck against the magnet?

    I can't use a steel tool, and that corrosion is pretty hard.

    On the other hand, it is just a 1mA meter with a custom scale.
     
    Ian likes this.
  12. bushtech

    bushtech

    867
    138
    Sep 13, 2016
    Chemical rust remover?
     
  13. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,160
    2,676
    Jan 21, 2010
    Will that remove rust without damaging the very fine parts in the vicinity? That entire image shows a section about 1cm across.

    Do you have any suggestions of what rust remover I might use? I guess application with a very small paintbrush would allow me to get it just where it's wanted.
     
  14. bushtech

    bushtech

    867
    138
    Sep 13, 2016
    I would start with something like CorrosionX

    IMG_20190120_125102[1].jpg
    Just a suggestion. I'm no expert, so use at your own risk
     
  15. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,160
    2,676
    Jan 21, 2010
    That seems to be fairly difficult to get here. I do like that it's compatible with electronics though.

    There seems to be both a corrosion removal (not safe for electronics) and a protection version. Does the protective version also act to remove rust?

    I see there are various options containing phosphoric or hydrochloric acid. For fairly obvious reasons I'd prefer to steer clear of those. Alternatives described as "chelating" seem safer, but possibly a little messy.
     
  16. bushtech

    bushtech

    867
    138
    Sep 13, 2016
  17. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,160
    2,676
    Jan 21, 2010
    The only place within 400km or so of me no longer stocks it :-(

    I may have to shop around :)
     
  18. bushtech

    bushtech

    867
    138
    Sep 13, 2016
    Feel for you, also in the boondocks, nothing is just around the corner
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-