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• 1 yr Update

  Michael O'Brien • 02/23/2016 at 06:59 • 1 comment

  So it's been just over a year. I had misplaced my V200 for about 2 months while not being to work on it. Charged up the batteries and it still works flawlessly. I've been very busy at my place of work and have been moving foward with some lighting projects which I'll put up here later. I've not have any crashes outside of the ones in the test I've mentioned and everything is still stable @ ~27.5-27.6 MHz. I'll be working on the back lighting in the near future and also I've identified the LDO for the LCD drivers. I have not though, been able to identify which LDO models they are.

• Need some help reverse engneering

  Michael O'Brien • 02/13/2015 at 06:57 • 0 comments

  Somewhere someone knows something I do not. It was more than a decade ago that overclocking these calculators was common knowledge. Half of the sources have disappeared over time and the other half tell you nothing more than the instructions and the maximum speed the calculator will run at and why. The 6 overclocks I've done support this information, i.e. 22 pF w/ 1.43 kOhm resistor being the fastest OC and sometime unstable with stock SRAM, but I'm still at a loss to quantify the circuity of the clock generator which is why I wanted to do this mod in particular.

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• Success!

  Michael O'Brien • 02/11/2015 at 09:27 • 0 comments

  So, the results are different than expected, but that is just fine. I'm running my V200 at 2x the speed it came from TI. For those who are TL:DR with my logs, you need a 1.21 kOhm resistor and an 18 pF capacitor. I never ran the MD5 checksums as I didn't see anything that presented as instability and I had a continuity problem in a wire from the battery pack that I couldn't be bothered to fix and taking that extra step was too tedious. That at sending a new OS file took about 3.5 min and I had to repeat this test at least once on each over clock after waiting for everything to cool down because even the contrast of the screen was affected by the hot air rework. Results posted after the break.

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• Let the Tests Begin

  Michael O'Brien • 02/10/2015 at 23:07 • 0 comments

  Preliminary pre-testing notes:

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• Testing Methodology

  Michael O'Brien • 02/08/2015 at 22:15 • 0 comments

  The new RAM is in place and the V200 is operating just fine; no reason why it shouldn't. I'm not worried so much about the viability of the RAM, though this removed one more variable to go wrong with the overclock. That said, there aren't a whole lot of tools to testing the hardware of TI's 68K calculators. From the limited programming in TIGCC that I've done, there are a few types of tests that will 'stress' the different components of the hardware: RAM, CPU, FLASH. As such, I've come up with a rudimentary list of tests.

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• Parts & Amazon

  Michael O'Brien • 02/06/2015 at 04:17 • 0 comments

  After fighting with Amazon for not knowing how to count to 10 whilst stopping at 1, seriously, I now have some ground springs for my low capacitance probe that I'm using for measurements. It is only 100x, not 10x, but for what I do, I don't mostly need a 10x probe. Anyhow, now that these are in, I have the tools for executing the upgrades.

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• Diving in with Calamity and Confusion

  Michael O'Brien • 01/30/2015 at 07:03 • 0 comments

  On my TI-89, one of the battery contacts on the PCB was heavily corroded and it took a good deal of time and heat to reflow solder to make a new pad. I did this to the V200 as a preventative measure too, but I guess I heated up the nearby fuse to where it blew. So I used the one from my '89. That then blew today as well...

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• Frequencies

  Michael O'Brien • 01/23/2015 at 09:25 • 0 comments

  For some reason the 47 pF value for the caps is sitting in my mind. Either after 'calibration' the LC meter is so far off that it read both my TI-89's and my V200's caps 51 pf, both ~8% high, or both of them are within their 10% tolerance and reading 8% high, or the LC meter is right. I have a bunch of uF caps, but no spare pF caps so I'll defer to Occam's razor and say that both caps are 51 pf.

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• Nor Flash

  Michael O'Brien • 01/23/2015 at 08:06 • 0 comments

  Well, this one is a bit of a gamble. Unlike SRAM, it seems like there hasn't been a need in the NOR Flash market for any sizable increases. The 4 MB LH28F320BFHE-PBTLZ2, organized as 2 MBit x 16, has a read cycle time of 80 ns and a top operational speed of 5 MHz. The fastest replacement I can find is made by Spansion.

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• The Actual Beginnings...

  Michael O'Brien • 01/22/2015 at 21:51 • 0 comments

  Yeah, I wrote these two in reverse order because one idea is easy to follow through one, even though it was not the original cause behind all of this. Despite it's slow AMS, the V200 is very dependable and I use it from unit conversions and calculations all of the way to the occasional derivative or integral. That said, I spend a lot of my free time awake in the not so bright time of day. Though night is more peaceful, it is considerably darker. As such, I've wanted to see how difficult it would be to make a custom backlight for my V200 so I took it apart.

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