Tektronix 576 Curve Tracer  - Page 1
Forum section: electronics / testgear

author: fmashockie
author_rank: Frequent Contributor
timestamp: October 31, 2023, 03:19:30 am
content: Hey everyone! So I'm look at purchasing a Tektronix 576 curve tracer that the seller says is not working. The seller doesn't have a thorough way to test it, but confirmed the CRT works.I was wondering if anyone can tell me more about these things. What are some potential issues that are common with these? Can they be easily restored or do they have a lot of propriety ICs/parts?How critical of a tool are they for someone who works in repairing electronics? Are there are other types of equipment that are more affordable that can do the same kind of testing?What would you consider a fair price to pay for one in non-working condition?Any input you can provide is greatly appreciated! Thanks!

author: bdunham7
author_rank: Super Contributor
timestamp: October 31, 2023, 03:27:00 am
content: I got one for $275 plus a road trip in OK-ish physical condition (one switch assembly broken, a few dark pixels on the readouts) but only intermittently working. It has a bad HV transformer and I've been trying to locate one since. Apparently someone had a batch custom-made, but I haven't reached anyone selling one yet. They're a pretty specialized use item, it's not an instrument most people will use every day.There are other ways of doing curve tracing, but the actual Tek units can put out some pretty serious power and most lesser devices can't.

author: Stray Electron
author_rank: Super Contributor
timestamp: October 31, 2023, 04:34:12 am
content: There are already a couple of pretty good threads on here about repairing the 576s. Did you read them?Congratulations on the purchase, they're great machines. As Bdunham pointed out, the HV x-former seem to the biggest weakness in them but the HV is necessary for the CRT to have any display so if the seller has confirmed that the CRT has a display then your HV xformer should be ok. The other problem with them is that knobs and sometimes switches get broken with rough handling so those and the adapters are hard to find and are expensive.I paid a grand for mine a couple of years ago but it was fully working, had no broken knobs and including 7 different adapters. That's less than the asking prices for the adapters alone on E-Greed.

author: mawyatt
author_rank: Super Contributor
timestamp: October 31, 2023, 01:28:21 pm
content: We picked up a Tek 577 locally that evidently was used at Sandia Labs, wasn't working but did have a display. The 577 and 576 are similar and you can locate service manuals online. We had to remove a modification to bring out the vertical and horizontal analog signals which suspect were for sampling with a ADC for display on a PC, then we were able to get the 577 working after replacing some PS caps, a couple op-amps, and some knobs which were broken.As mentioned by Stray E, the specialized fixtures are rare and expensive, so decided to Roll Our own as shown here.https://www.eevblog.com/forum/projects/smd-test-fixture-for-the-tektronix-576-curve-tracer/msg4553639/#msg4553639Good luck with your 576, these are nice instruments when working!!Best,

author: bdunham7
author_rank: Super Contributor
timestamp: October 31, 2023, 02:07:29 pm
content: Quote from: Stray Electron on October 31, 2023, 04:34:12 amMine works when it is cold, then fades out when it warms up. Opening it up and putting a fan on the HV transformer keeps it on indefinitely. The issue appears to be leakage in the HV winding that overloads the drive circuitry.

author: fmashockie
author_rank: Frequent Contributor
timestamp: October 31, 2023, 02:33:25 pm
content: Thanks everyone! I did do a bit more digging on the blog and found that there are numerous threads on these. You guys were very helpful and the threads I found also provided some of the most common issues with this.Mawyatt nice work with the SMD test fixtures! I'll need to take a closer look at those if I decide to move forward with this.I haven't purchased it... yet

author: Shock
author_rank: Super Contributor
timestamp: October 31, 2023, 03:35:37 pm
content: The 576 is discussed in Tekscope magazine. Youtube has a handful of videos and there are a few repair jobs posted on various websites. Otherwise all the documentation is out there. Unless it's been serviced it will likely need to be.As for practical use it's a versatile component tester. Ebay shows $300-400 used, unless it's a wreck $200 would be ok for a bunch of parts. As discussed the accessories have value.If your testing it be warned it has up to 1.5kV at the test socket and the safety cover switch can potentially be bypassed.

author: Martin72
author_rank: Super Contributor
timestamp: October 31, 2023, 10:10:17 pm
content: I've been fascinated by the 576 for a long time, if only because it has real "power", ideal for tracking down counterfeits (they are becoming more and more).But first, the device is quite expensive in good condition and it is relatively large.You can get all the documents including schematics for it, so I was thinking of transferring a device into the modern era, redesigning it with components from today.But I'm sure I'm not the only one who thought of something like that, so I think it's not so easy to do something like that.

author: alm
author_rank: Super Contributor
timestamp: October 31, 2023, 10:19:20 pm
content: Quote from: Martin72 on October 31, 2023, 10:10:17 pmThere are certainly curve tracers made with more modern parts, though mostly for hobby use since professional semiconductor testing has moved on to testers that consist of a bunch of source measure units that sweep through the required ranges. Keithley will happily sell you such a box in exchange for a second mortgage on your house.I think making a modern curve tracer with the voltage and current ranges of the 576 might be expensive compared to a used 576.

author: David Aurora
author_rank: Frequent Contributor
timestamp: October 31, 2023, 10:48:35 pm
content: Quote from: fmashockie on October 31, 2023, 03:19:30 amHow have they confirmed that the CRT works? There's only so much you can know about the CRT without actually displaying anything or running it for more than 30 seconds. Try to at least sweep some stuff across the screen (you can display quite a bit without any fixtures or devices to test by switching display modes/using the offset controls and sweeping the voltage)The transformer (and CRT) are the most famous showstopper issues as far as I know. I can't remember the exact details, but there is info around (I think probably athttps://groups.io/g/TekScopes/messages) about serial number ranges of the problem transformers. When I bought mine last year that was something I checked with the seller and referenced against the bad ranges before buying.Mine actually arrived with a smashed CRT so I've spent a bit of time in there cleaning out broken glass and replacing that (not a game you want to play...), and then doing a bit of calibration, and I found it quite easy to get around inside and work on. Some stuff is a bit tricky to get to, but at the end of the day it's old Tektronix gear so very repairable and has a great service manual.I definitely wouldn't say they're critical for most people working in electronics, they're niche as fuck. If you don't know if you need one or what you'd do with it, you probably don't need one. But on the other hand, you can do a LOT with them. I use mine mostly for vacuum tube testing/matching, but it has saved me tonnes of time testing all sorts of components (and even as a super overkill octopus tester). I don't think you'll find anything of similar functionality cheaper unfortunately, to get the same voltages/power/functions as a 576 you're either going for similarly priced tracers in other models or you're jumping up a level into SMU setups.Fair price really depends on what's wrong with it. If there's any doubt at all about the HV transformer or CRT, it'd be worth fuck all to me (maybe a few hundred USD?). No display is not the complete end of the world (I actually run mine with both the CRT and into software), but there's a fair bit of work to do that and digital only wouldn't be too convenient for quick tests so I wouldn't pay a lot to be painted into that corner.

author: fmashockie
author_rank: Frequent Contributor
timestamp: November 01, 2023, 02:41:08 am
content: Quote from: Martin72 on October 31, 2023, 10:10:17 pmI've been fascinated with them as well ever since I learned of them! It wouldn't be something I'd need often either. I work as a lab equipment engineer at biotech company. We have a wide range of equipment both old and new. And a lot of the equipment we have, the manufacturers don't provide service manuals with schematics. Therefore, it can be difficult to source replacement semi-conducters when they fail. I figured this could be helpful in testing/comparing suitable alternative parts. I also wouldn't mind trying to restore one that needs some repair. But I don't really have the capabilities to fix a broken CRT.Not sure how the seller verified the CRT is good. I'll have to get some more info on that. I don't have access to it in person. If I can't get more info on its condition, I might pass it up. I might try something like the Peak Altas DCA75. But as others have mentioned, it doesn't provide much power.

author: fmashockie
author_rank: Frequent Contributor
timestamp: November 01, 2023, 04:29:30 pm
content: Well I pulled the trigger on it! I either just purchased an expensive large paperweight or the coolest piece of equipment I've ever owned. I'll find out soon enough!

author: Grandchuck
author_rank: Super Contributor
timestamp: November 01, 2023, 04:32:53 pm
content: I hope the seller packs it well!

author: mawyatt
author_rank: Super Contributor
timestamp: November 01, 2023, 04:39:01 pm
content: Quote from: fmashockie on November 01, 2023, 04:29:30 pmHopefully this will be in good condition and restorable!!Lots of knowledgable folks on here with these and that could help if you run into a roadblock when debugging.Good luck!!Best,

author: Shock
author_rank: Super Contributor
timestamp: November 01, 2023, 10:57:57 pm
content: Start a repair thread and take lots of photos.

author: bdunham7
author_rank: Super Contributor
timestamp: November 02, 2023, 12:12:47 am
content: Quote from: Grandchuck on November 01, 2023, 04:32:53 pmI drove nearly 1000 miles (round trip) to avoid that very issue.

author: mawyatt
author_rank: Super Contributor
timestamp: November 02, 2023, 12:52:21 pm
content: Quote from: bdunham7 on November 02, 2023, 12:12:47 amYikes, now that's dedication!!Where did you have to go to get your 576?We were lucky our 577 showed up at a local surplus site within 5 miles, but had been previously transported and damaged from NM.Best,

author: bdunham7
author_rank: Super Contributor
timestamp: November 02, 2023, 02:09:59 pm
content: Quote from: mawyatt on November 02, 2023, 12:52:21 pmA Goodwill warehouse in Tuscon, Arizona. I was pretty sure it wouldn't survive the trip via UPS poorly packed. I've spent too much time and effort doing physical restoration and mechanical repairs of instruments and I've got two more that need the body shop waiting for me in my garage. It's just amazing to me that the ultimate fate of so many of these things is to be smashed by negligent handling.

author: fmashockie
author_rank: Frequent Contributor
timestamp: November 02, 2023, 02:48:25 pm
content: Thats awesome you guys were able to pick yours up in person or find them locally. I got this one on eBay for $500.I will definitely document the repair process! I've been filming my repair adventures and putting them up on YouTube so I will do this with this one as well! Can definitely share that here in the repair thread.

author: fmashockie
author_rank: Frequent Contributor
timestamp: November 05, 2023, 04:51:05 pm
content: Preface: I'm not sure if I should create a new thread for this or add it to an existing one. I can see there are a lot of different threads on the 576. I'll just keep this update here since I don't have a repair question about it... yet.Well it arrived yesterday! I almost had a heart attack when I saw the package - the side of the box was torn open. But fortunately, they did pack it with plenty of bubble wrap. It arrived in the condition as advertised; better than I anticipated actually! Visually it looks in great shape. A few issues I noticed immediately:-The max peak power/watts knob: plastic ring with power settings has separated from the knob. Will have to glue it back to it once I find the correct orientation.-The HV protected cover is missing and the interlock switch was stuck in the pressed down position-Springs on the Step Family and Rate gang switches are either stuck or do not stay depressedBut other than that, everything looks pretty good! CRT works! I started putting it through the 'First Time Operation' steps via the service manual. It seemed to be responding to the settings normally. I've never used one of these before so I'm kind of learning as I go. I began finding issues as I started learning more about the unit's function.1) The HV safety interlock was engaged so I needed to find how to disable it without the protected cover. So I removed the standard test fixture to get a closer look. That's when I noticed a resistor on the terminal selector switch was literally snapped in half (I believe its R376, a 22ohm). So I replaced that.2) I continued looking into how to bypass the HV interlock. The service manual I found provides a procedure for disabling it by soldering some jumpers to the J300 connector. But that is buried deep in the unit. So I decided to see if there was another way. I started looking at the actual HV interlock switch which for my unit is on a small PCB that is screwed to the underside of the test fixture (interestingly all the other PCBs on the unit state copyright 1968, but this little PCB says 1985. Maybe this test fixture is from a newer unit?). Anyway, the switch that is triggered by the protection cover is a Motorola MOC70W2 which I actually found a datasheet for. It is a U slotted photoelectric sensor. It has two infrared emitting diodes on one side and two phototransistors on the other. This MOC70W2 clearly was faulty - I tested it out-of-circuit and verified that. Plus, as I said, the switch was stuck in the depressed position and it still would not disable the HV interlock. The MOC70W2 is glued to an actuator that passes through the U slot - I had to remove it to get a better idea of how it worked. For my mod, I removed the MOC70W2 from the little PCB. I soldered in two red LEDs on the cathode/anode/cathode anode side (not sure if the LEDs are necessary). And then two NPN transistors on the emitter/collector/emitter/collector side with their bases connected between the series connection of the LEDs (I suppose you could use diodes instead of transistors). Reassembled everything and it worked perfectly! Granted, I would like to find something to cover the test fixture during high voltage testing for safety purposes, but if anyone is looking for a simple bypass mod, this worked great! Also, the red LEDs look kinda cool shining thru the test fixture inputsNext I tested a resistor and a diode - I observed the correct IV curves for both of them! So this thing is definitely showing signs of life! This is as far as I got, but I will keep troubleshooting/testing/repairing as I continue to investigate this gem! Photos attached below!

author: fmashockie
author_rank: Frequent Contributor
timestamp: November 05, 2023, 04:54:40 pm
content: Just some additional photos I couldn't fit in my other postSome closes up of the bypass mod included.

author: fmashockie
author_rank: Frequent Contributor
timestamp: November 07, 2023, 07:09:53 am
content: Video I put up on my YT channel documenting the repair/restoration so far.I have another thread going on the repair of this guy in the Repair Forum. So this will be my last update here. But feel free to follow along there! Could really use the help from those of you who own one of thesehttps://www.eevblog.com/forum/repair/tektronix-576-curve-tracer-restorationrepair-questions/