Help with old hitachi analog scopes

Discussion in 'General Electronics Chat' started by bschoolc, Jan 8, 2013.

  1. bschoolc

    Thread Starter New Member

    Jan 6, 2012
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    Hey guys, first post here, but I've already learned a lot from this site, so thanks!

    I've recently picked up a couple old analog hitachi oscilloscopes on Craigslist. Models V-134 and V-152 F to be specific. They're both at least semi operational, as shown in the following pic: [​IMG]

    They both have some finicky spots in various knobs that affect and distort the displayed waveform, with the 134 being quite a bit worse. I've been able to coax a proper signal out of them in most settings, but some can be pretty unreliable. I've read that cleaning the switch contacts should help this situation, could anyone suggest a proper cleaner? Is there anything else I should be looking at?

    Considering I'll have to open the case, I'd also like to be sure I've discharged all the caps and deenergized anything else that may need it. Is there anything special I need to do to accomplish this? Just turn the intensity (power) switch on with the unit unplugged?

    Also, the 152 came with a copy of the operation manual, but that's all the documentation I have. Does anyone know if service manuals for them exist somewhere on the web? I've looked, but come up empty so far.

    Just out of curiosity, I searched for the date these scopes would have been made, but I've come up dry there as well. There doesn't seem to be much information about these things out there, at least not that I can find.

    Thanks in advance, and please let me know if I need to provide any further information. This isn't my first time working on electronics, but definitely my first time working on anything like this :)
     
  2. bance

    Member

    Aug 11, 2012
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    Hi bschoolc,

    I also have a couple of old scopes that I'm thinking of restoring...
    A Kikusui cos5020 and a tektronics 464. I'm quite a noob to electronics, I'm a builder by profession, I found a thread here that is very informative. Also I think there may be some info in the electronics resources thread that may help with the service manual. Good luck with it!

    HTH Steve.
     
  3. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Try moving the scopes to different parts of your bench. The magnetic fields used to focus the old CRTs may be interfering with each other - they both seem to be having the same vertical distortion.
     
  4. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Or they are both properly displaying the same distorted signal.
     
  5. bschoolc

    Thread Starter New Member

    Jan 6, 2012
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    Yeah, I didn't mention it, but that signal is just from touching the probe to my lathe. It's currently ungrounded, (I'm working on the controller) so it's just a big hunk of metal acting like an antenna and picking up noise from all the power lines running around. At least that's what I assume, the frequency checks out at ~60Hz. It was just what was convenient at the time I took the picture.

    That pic is actually one of the better ones I got, the traces were pretty stable. The problem I was talking about earlier was the signal dropping out or moving around when I wiggle the knobs. For example, wiggling the volts/div knob on the 134 or the vertical cal knob on the 152 results in a change in amplitude of the signal, or loss of the signal entirely. It really seems like that is due to dirty contacts on the rotary switches. I can get a video if it would be helpful.

    There are very likely other issues as well, but that's the big one at this point. I'm sure even if I get the knob issue sorted, there will still be significant doubt about the accuracy of the measurements I'll be able to make, but I'll at least have a reliable qualitative view of what's going on.

    I'm hesitant to do much until I know I've discharged any high voltage inside the things. Can anyone point me in the right direction there?

    Thanks!
     
  6. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    At that point, you are dealing with a really weak (high impedance) signal and any messing around will make it look distorted. Also, your ground pin is likely not connected to anything so even less robust signal and susceptible to noise problems like pots.

    There should be a calibration pin on the front of the scope (e.g. 1kHz square wave signal). Connect your probe to that (no need to ground the other end). All should be good. A good quality scope like a Hitachi will have surprisingly few problems - even if it is older than dirt.
     
  7. atferrari

    AAC Fanatic!

    Jan 6, 2004
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    If you mess inside them, keep in mind there is high voltage inside. And that means HIGH.
     
  8. bschoolc

    Thread Starter New Member

    Jan 6, 2012
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    I shot a couple videos of the scopes. Thanks for the tip on the high impedance potentially causing issues, hadn't thought of that.

    Here's the V-152F displaying the 0.5V 1kHz cal trace:

    V-152F Video (YouTube)

    Like I say in the video, it appears as if the pot for the cal knob is losing contact. I think the wiper must be losing contact at that position, and it's defaulting to the other end of its range by bypassing the wiper assuming its hooked up in the standard variable resistor configuration. I haven't located it in the schematic in the manual yet to verify.

    And the V-134 displaying its cal trace:

    V-134 Video (YouTube)

    This one looks like it has bad contacts in the switches for both the vertical and horizontal axes.

    Exactly. But what do I need to do to make sure I don't mess anything up? I mean besides not sticking stuff in it when it's powered up ;-). Are there any standard precautions I should be taking? This is pretty much the only thing keeping me from getting to work, just don't want to get zapped or fry anything.

    Thanks again!
     
  9. atferrari

    AAC Fanatic!

    Jan 6, 2004
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    My experience is just from when I opened my analog scope and after looking for some points to test I realized that the connector for all voltages above 1KV was just few cm from my hand. I remembered the ID of that connector just by sheer luck. Scaring.
     
  10. BReeves

    Member

    Nov 24, 2012
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    Awe, it's low current and will only hurt for a second or two :D

    To the OP, sounds like you have already nailed the problem with dirty contacts. You can try some of the varrious spray contact cleaners on the market. Make sure anything you spray into the pots is specifically for variable resistors. Some of the real agressive cleaners will destroy the pot.
     
  11. MrChips

    Moderator

    Oct 2, 2009
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    Before you open the scopes and go poking around, maybe there is nothing wrong with the scopes.

    Touching the tip of the probes to your hand or a metal object is not a good signal source for evaluating a scope. You need a proper signal. Most scopes have a calibration signal on the front panel.

    Use the PROBE CAL output at the top of the front panel.
     
  12. bschoolc

    Thread Starter New Member

    Jan 6, 2012
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    Thanks for the tip on specific cleaners. I've got some CRC Contact Cleaner already, and from what I've found, that may be the wrong thing to use.

    I found this video describing cleaning pots/contacts in audio equipment, and he recommends this cleaner from RadioShack, basically looks like rebranded Deoxit. I'll be getting this unless someone says otherwise.

    Check out post #8. The pic with the weak signal was just the best I had on hand when I first posted. I'd checked on the probe cal as well.


    I'm still wondering if there's something I'm missing with regards to discharging. At this point I'm planning to just unplug, leave the power on for a while to hopefully discharge anything, then be careful as I'm poking around. Any further advice would be appreciated!
     
  13. ScottWang

    Moderator

    Aug 23, 2012
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    Replace all electrolytic capacitors If you can, at least replace all Electrolytic capacitors under 1000uf.
     
  14. MrChips

    Moderator

    Oct 2, 2009
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    Going around replacing electrolytic capacitors is something I do not do.
    I have >50-year old electronics that continue to work fine without servicing.
     
  15. bschoolc

    Thread Starter New Member

    Jan 6, 2012
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    That's the approach I plan to take. Is there a way to know if they're bad? Other than visible bulging of course. I assume it would also depend on their location in the circuit, so that may be a tough question to answer. Any tips on what to look for would help though.
     
  16. BReeves

    Member

    Nov 24, 2012
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    Just a persional opinion but I agree with this.. The bad cap issue showed up in computers in early 2000 because some companies were buying cheap caps from china. I wouldn't be too worried about the caps in your scopes, odds are they were manfactured in Japan and are quality componets.
     
  17. BillB3857

    Senior Member

    Feb 28, 2009
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    Be careful of using Deoxit. I sprayed some on some rotary switches a few years ago and it crystalized the plastic wafers. They started to fall apart as soon as I started to turn them after the spray. Had to find fifty ten position rotary switches. Lost our shirt on that repair!
     
  18. ScottWang

    Moderator

    Aug 23, 2012
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    About the old instrument.
    1. If lucky enough that it's maybe never have any problem like as yours.
    My scope already over 20 years, I had replaced the switch and some electrolytic capacitors, but it's working fine now, and this is not too bad.

    2. Repair businessman and second hand seller, and many people will doing the thing that replace all the electrolytic capacitors, of course not all of them, but it's really useful somewhat that it can be avoid many problem to occurred.

    3. When any intruments or a scope having the problem, I will try to trace the circuit and fix it if I can.

    So, although I offer the idea, but I didn't do that except the power supply for PC in some bad situations, I called the item 2 is a "lazy way", if someone can't trace the circuit and still try to troubleshooting, then it's a good way.
     
  19. BReeves

    Member

    Nov 24, 2012
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    Other than my S.A. comment, looks like nobody really answered you concern about high voltage. Connect one end of an alligator clip lead to the chassis and the other end to the metal part of a screwdriver. Not sure about the small scope CRT's but look for a heavy wire that goes into what looks like a suction cup on the side of the CRT. Slip the end of the screwdriver under the suction cup and it will discharge the high voltage cap. You should hear it when you have touched the clip the wire is connected to under the rubber cup.

    Again, not sure about the small crt's in scopes but I have seen the old TV crt's hold a charge for months after they have been unplugged.
     
  20. bance

    Member

    Aug 11, 2012
    315
    34
    Don't know how safe it is but you could try this or this.....
    Maybe someone else can comment on the validity of the method?

    The link I posted earlier suggested "So I cleaned it by soaking a paper strip in IPA and moving it back and forth between the contacts."

    HTH Steve
     
    Last edited: Jan 9, 2013
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