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EEVblog #1336 – DT71 LCR Tweezer Destructive Teardown + Lab Update

Destructive teardown o nthe Miniware DT71 LCR meter Tweezers Plus a lab move update. Forum: ...


  1. Is there any issue with some of the electrolytic caps going funny in a 25 year old device? I’d be tempted to replace them with new ones. Maybe solid polymer if possible.

    • Yes there are issues
      I have 2230/2232’s
      Their PSU often goes kaboom (first stage). you can replace the ic, the transistor, it burns again after some time(tested). I usually just hook up an external PSU directly to the internal intermediate 42V !!

      I read somewhere that it’s sometimes a shift in the inductance of the transformer, which explains why replacing other components does not cure it.

      • Dave, there seems to be a writing under the sticker “made in holland” could it be “made in taiwan” ?

        There may be asics in the input cans (that’s what provides the better noise factor of the old tek inputs)

        These asics were produced by TEK themselves before maxim bought their semiconductor fab, then manufactured bad chips, then discontinued these awesome chips altogether. this is why Dave can find awesome input stages only on old tek scopes.

        A lot of people who need low noise on low level signals buy the old Tek plugins and wire them as input stages to modern scopes : 7a22 : 10uV/ div (differential input)

        Some cool guys are even “rebaking” some critical chips for the 24xx scopes which fail often !!


        I suppose they reglue and rebond the die into the big heatsink to improve the thermal contact

    • Sure, but if it ain’t broke…

  2. Thanks Dave for this nice demonstration, but keep in mind to start calibrating instruments after a warming up phase at a minimum of 30 minutes or more depending on the devices mass. All parts should have their normal working temperature.

    • I agree with Jan. My Tek 2232 takes at least 10-15 minutes to settle after being powered up. During that time, the vertical position starts two ticks low and gradually drifts upwards. In the video it looks like maybe your 2225 was doing that too.

      Aside from that, I loved this teardown. No SMD, solid construction, serviceable — I wish things were still made this way.

  3. That angle looked a little off there Dave!

  4. Just try not to dribble on your electron gun.

  5. Tongue angle…
    so that’s what I was doing wrong…

  6. Great video. I have an old ’70s tek 485. I worry constantly about it giving up the ghost. It’s not that I can’t save up and get a rigol, or something, but I just love it so much! I downloaded the service manual and it has every hybrid package you can think of!

    Anyway, my question is this: Some of the pots (especially the horizontal adjust) don’t adjust smoothly anymore. I can make do, but is there something I can do to clean them?

  7. Great video. It encourages me to calibrate my 2215.

    Just one thing. You align the edge of the traces with the reticule lines during the adjustment. I think that the correct way is to align the center of the trace. But the difference will be small, even en bees’ perspective…

  8. Woohoo, no boring intro today, jump right to the action!…. AWW FUCK!!!

  9. “Half a bee’s ****!” First time I’ve heard that being used as a comparison….’but I like it!’ 🙂

  10. I find that if you get the tongue angle just off, that you might also get a dribble or two in your electronics. Hmm maybe a need a ‘dribble shield’?

  11. Awesome video of the Tektronix 2225 calibration, Dave ! Thanks! Where did you get your hands on the service manual, pray tell?

    Now you’ve given me some reassurance in buying an old secondhand o’scope. I luv it!

  12. I found a copy of the circuit diagram for the Tek if anyone needs it. 🙂


  13. Hi Dave, good video, fun and interesting to see the scope innards. You do a really good job of these. The scope is nicely designed. The little helical trim cap is fairly common in RF gear. The spring on the CRT grounds the conductive aquadag (colloidal graphite) spray painted onto the glass tube exterior. The tube interior is painted similarly, and has the 7KV final accelerator voltage connected. The glass of the tube forms a capacitor, which acts as the filter for the HV rectifier, and it can store the HV for days. The current capacity of the HV supply is low enough to prevent heart interruption, but it hurts like hell… or so I’ve heard. Loved the tongue angle. I do it too.

  14. awesome dave… i think this is one of your best videos ever… 🙂

  15. I just have to laugh that you post a video on a tektronix scope the day i was handed half a lab worth of tek gear,

    still i will say the 475 sounds more your style, more fiberglass rods and ingenuity in the selector cams than one can measure, just wish i could get the illumination bug figured out, but soon, SOON i may rival yours! 🙂

  16. Dave, that nice datasheet for 2225 you have, is it available from somewhere? I only have some scanned manuals, that one seems super nice :)… so if you are allowed to share it, I’d be grateful 🙂

  17. Hallo Dave,
    You ask if anyone else has a 2225 with the 1-watt resistor bodge. Well, I have such a scope with a 2… serial number (made in UK) and it does have that same resistor. It also has two additional small signal diodes (with teflon sleeving) on the underside. And the high-tension wire is routed quite differently. Also, the ribbon cables are color-coded (very brightly I might add) rather than the gray seen in your scope.
    You mention that yours was a rack-mounted scope. Did it not have the plastic back panel? I ask because mine does not have that cool metal can at the end of the CRT.
    Thank you for the blog and particularly this one. You gave me the courage to finally open the thing up and tweak the pots to bring a number of things back into line. I feel like I have a new ‘scope.
    – Michael

  18. Just bought a 2225 off ebay. It didn’t have pictures of the two traces, but I asked him and he said it was working. It also had a return policy, so if worse comes to worst, I’d just be out 10-15$ shipping. But everything seems to be working fine. Needs a little calibrating, but nothing bad.

    Thanks Dave for this video.

  19. I don’t have the specific model you asked for, but I have used it at the time of my engineering life.

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