Refurbishing the KeyTek MiniZap

-August 21, 2015

One of the more popular older ESD simulators was the KeyTek MiniZap. This simulator had exchangeable air and contact discharge tips and could be adjusted as high as 15 kV. It will also provide up to 20 pulse per second discharges, which will approximately simulate electrically fast transient (EFT) pulses. Refer to our EMI troubleshooting book, in the References below, for more information on applying it in this way.

There were two different styles; the earlier one with the bar graph and the newer one with a digital display. Both may be purchased on the used market for a fraction of the original cost of about $20k. If you purchase one of these used, be sure both tips are included, as well as the battery charger and grounding cable.


Figure 1 - The popular KeyTek MiniZap ESD simulator.

While rugged and easy to use, there are two common failures for this model - the NiCad batteries eventually won’t hold a charge and the two variable knobs at the top tend to crack. The knobs are easy to replace with standard set-screw knobs. This article describes how to replace the existing NiCad AA cells with new ones.

I ordered new 1000 mAH cells (with solder tabs) from Zbattery.com at about $2 each. Once they arrive, then we’re ready to operate on the patient.


Figure 2 - The simulator with the bottom cover removed. The battery pack is located to the left.

First, remove the six screws in the bottom of the case. Carefully removing the bottom cover reveals the battery pack containing four AA cells soldered to a plug-in daughter board. Carefully unplug this board, noting the orientation. I find it best to document the repair with photos.


Figure 3 - The battery pack plugs in to the main PC board, making it easy to replace the old cells.

With a large-tipped soldering iron, carefully unsolder the cells one-by-one, replacing each with a new cell as you go. Avoid removing them all at once, as I did, because it’s too easy to lose track of the proper polarity and you’ll have to carefully trace out the circuitry to avoid installing one backwards.

The new cells usually have some amount of charge, so be sure to verify the correct installation with a voltmeter. Plug in the daughter board, observing the proper polarity, and reinstall the bottom cover. Give it a charge for a few hours, and you should have a revived MiniZap!


References

Thermo Scientific MiniZap 15 Product Info

MiniZap user manual. There are many on-line archived sources for the manual - primarily from test equipment rental companies. Here’s one from Test World.

André and Wyatt, EMI Troubleshooting Cookbook for Product Designers, SciTech Publishing, 2014.

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