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A blast from the past
Older folks may recall the famous Tektronix 576 and 577 curve tracers from half a century ago. A few of these have survived the decades and ended up in some lucky engineer’s home/work lab.
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We were able to acquire a Tek 577 curve tracer with a Tek 177 standard test fixture from a local surplus house that had been used at Sandia Labs, but it was not functional. Even being non-functional, these old relics still command a high price, which set us back $500!! With the help of an on-line service manual and some detailed troubleshooting, the old 577 was revived by replacing all the power supply’s electrolytic capacitors and a few op-amps, plus removing the modifications Sandia had installed.
Once operational we went looking for the various Tek device under test (DUT) adapters for the Tek 177 standard test fixture, these adapters are indeed rare and likewise expensive which sent us on the DIY journey!
The DIY journey
Observing a similar path to Jay_Diddy_B1 [1], we set out to develop a DIY adapter to replace the rare and expensive Tek versions. Like the popular T7 multi-function component tester, which employs a small ZIF socket for leaded-component attachment that works very well; we decided to do the same for the custom Tek adapter using the right and left sides of the ZIF socket to facilitate DUT comparisons with the Tek 177 standard test fixture. This can be seen in Figure 1.
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Figure 1 Custom ZIF-based Tek 577 adapter where the right and left sides of the ZIF socket facilitate DUT comparisons with the Tek 177 standard test fixture.
As shown in Figure 2, a low-cost PCB was developed with SMD ferrites added to the nominal “Collector” and “Base” 577 terminals to help suppress any parasitic DUT oscillations. Connectors were also added to allow for external cables if desired (something we have never used). The general idea was to use the 6 banana jacks as support for holding the PCB in place with the ZIF on top of the PCB where one can directly attach various DUTs.
This approach has worked well and allows easy attachment of various leaded-components including the T0-126 and T0-220 power devices.
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Figure 2 The custom adapter installed on the Tek 177 standard test fixture.
Applying the curve tracer to an SMD DUT
However, this still leaves the SMD types in need of a simple means to apply with the Tek 577 curve tracer with the 177 fixture; we set out to investigate this.
After studying the methods Tektronix utilized, we discovered some low-cost toggle clamps (found on AliExpress and elsewhere) which are used for clamping planar objects to a surface for machining. Figure 3 shows the custom toggle clamps used on a custom SMD DUT along with the custom adapter installed on the Tek 177 standard text fixture.
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Figure 3 Custom toggle-type SMD adapter for the Tek 577 where using the pair of toggle arms allows both the right and left sides of the Tek 177 fixture to be utilized for direct SMD component comparisons.
These clamps could be repurposed to act as a clamp to hold a SMD DUT in place, which resulted in a custom PCB being developed to mount directly on top of the ZIF-based PCB previously discussed (Figure 4).
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Figure 4 The custom SMD PCB that can be used with toggle clamps. This can be installed on the Tek 177 fixture for the Tek 577.
The toggle arms allow slight pressure to be applied to the SMD DUT where the leads make contact with the PCB’s exposed surfaces. Using a pair of toggle arms allows both the right and left sides of the Tek 177 fixture to be utilized for direct SMD component comparisons.
A connector on the rear of the PCB is mounted on the bottom side and mates with another connector on the ZIF type PCB, which allows connection to the 6 banana jacks that plug into the Tek 177 Fixture. Four nylon standoffs provide mechanical support and hold the two PCBs together. This setup allows easy SMD component installation and removal with little effort. Figure 5 shows both adapters for the Tek 577 with 177 standard test fixture.
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Figure 5 Both adapters for the Tek 577 with 177 standard test fixture.
Both the ZIF and the SMD Adapters have served well and allow most components to be easily evaluated with the old Tektronix 576 and 577 curve tracers. Figure 6 shows the custom toggle-type SMD adapter in action with pair of DUTs.
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Figure 6 Custom toggle-type SMD adapter in operation with pair of DUTs.
A word of caution
Just a word of caution when using these and any adapters, fixtures, or leads with the Tek 576 and 577 curve tracers: these instruments can produce lethal voltages across the exposed terminals. The Tek 177 standard test fixtures were originally supplied with plastic protective covers and sensor switches which removed the DUT stimulus when the plastic cover was open. In the old Tek service manuals, there was a modification method to defeat the Tek 177 sensor switch which many engineers employed, and many also removed the plastic protective covers.
Anyway, I hope some folks lucky enough to have an old Tek 576 or 577 curve tracer with Tek 177 standard test fixture find these custom DIY adapters useful if they don’t already have the old Tek OEM elusive adapters!
Michael A Wyatt is a life member with IEEE and has continued to enjoy electronics ever since his childhood. Mike has a long career spanning Honeywell, Northrop Grumman, Insyte/ITT/Ex-elis/Harris, ViaSat and retiring (semi) with Wyatt Labs. During his career he accumulated 32 US Patents and in the past published a few EDN Articles including Best Idea of the Year in 1989. All posts by Mike Wyatt below:
References
- “EEVblog Electronics Community Forum.” SMD Test Fixture for the Tektronix 576 Curve Tracer – Page 1, www.eevblog.com/forum/projects/smd-test-fixture-for-the-tektronix-576-curve-tracer/.
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