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WP34s flash technical erase procedure
01-30-2015, 03:43 AM (This post was last modified: 01-30-2015 03:59 AM by John Galt.)
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RE: WP34s flash technical erase procedure
Hi Marcus,

I fully appreciate your description of the "frustrating state" in which your soon to be WP 34S is for all appearances, dead. As Walter states in his manual, despite that appearance in all likelihood the calculator is perfectly OK.

There are a few suggestions:

When you wrote you were using the 3V output present on the USB to serial converter I was very skeptical. In that regard I do not believe you will have any more (or less) success using the Prolific device vs. the FTDI. Its 3V output just doesn't have enough current.

For what it's worth a very similar project to yours using the Prolific device is detailed here, with great credit toward Jebem's design. From that, I took what I considered the most important design elements. It's 100% reliable.

From what I did, which involved many bonehead mistakes (not the least of which was confusing the pinouts of an LM1117 with the 7805 regulators I'm familiar with) I conclude it must be rather difficult to permanently kill the calculator. It's pretty resilient.

If you are concerned it's dead, measure the power supply current when it should be "on". If in doubt, press "on". That always turns it on. Conversely, Reset always turns it off. Power supply current in the "on" (but apparently dead) state will be approximately 8 mA. Press Reset and it will fall to zero.

I think your problems will be over if you use a real power supply instead of the 3V from the FTDI device. Even a single CR2032 battery is perfectly OK. If it gets weak though, you'll have flashing miseries. Weak cells may still measure 3V under no load, but if they're weak, they'll crash under load.

The LM1117 was a significant reason for building the box. The last thing I want to worry about is flaky power. Will the calculator erase properly with inadequate power? Who knows. I suspect that lies at the crux of your miseries.
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RE: WP34s flash technical erase procedure - John Galt - 01-30-2015 03:43 AM

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