Hi there!
I know this has already been covered in a topic, but I just wanted to ask what I should keep in mind when overclocking the TI 84+. When it comes to tools, I think that I am well-equipped: I own a very good Ersa soldering station with very fine tips, optivisors, SMD resistors and a scope. I read that you need to replace either the capacitor or the resistor. Should I change the cap or the resistor? And to what value? Should I add a trimmer and matching hole in the case for fine adjusting under different conditions? And lastly, how do I "overclock" the LCD? This was also mentioned in the original post, but the resource linked is gone. Also the calc was bought in 2014, in case something has changed during the last years. And if it is risky, I am willing to risk it, as I still have a 84+ CE-T.
Thanks in advance for the help!
I explained on WikiTI how to overclock older TI-84 Pluses, and even added pictures. There's even a solder-free method you can do using a pencil. It doesn't let you overclock as much, but it's far less risky. Unfortunately, the newest TI-84 Plus I have is still over ten years old, so the pictures might not match your hardware. If your hardware is different, it would be interesting to see some pictures.

The LCD itself cannot be overclocked; it generates its own clocks internally, on-die. However, TI has manufactured a lot of calculators with slow LCDs; to an overclocked CPU, a normal LCD will also appear slow. There's a program called ALCDFIX that can correct for slow LCDs, but it needs to be rerun frequently. zStart is a popular alternative that doesn't have that limitation.

Also, a lot of games actually run on the CPU's slow mode, for compatibility with the TI-83 Plus's slower CPU. The OS itself and any games compatible with the fast CPU mode will automatically switch to fast mode when appropriate. Try not to be like Alex from Linus Tech Tips and destroy your resistor pads; the way LTT did it, both CPU modes are now the same speed.
First of all: thanks for the fast answer!

Well, I will certainly give zStart a try. And I won't be using the lead pencil method, as I can solder SMD fairly well (given that I have good leaded solder), and I want a permanent performance boost for calculating.

I mean, a ~50% performance increase (if we assume that performance raises linearly with clock speed) is a big deal when you trial-and-error during a class test so you can get a sense for how to solve the problem at hand. What about the trimmer though? A big poti with cables will induce additional capacitance, and may harm the stability of the system.

So what do you think about adding a small modboard like the modchips in video consoles? My plan is to have it rigidly fixed to the board, and it should have either a poti or a small trimmer cap in it, but I am not sure what is a better idea.
Yes, long leads on a trim pot will add capacitance, negating some of the trim pot's effect. The leads can also pick up EMI. Unfortunately, I can't really give you any guidance on how much of an issue that could be. In the past, people have mounted the trim pot to the case, requiring somewhat lengthy leads to the trim pot. If you have a small trim pot you can affix to the PCB (either with solder or just glue), you could eliminate that.

I really recommend against trying for anything above 20 MHz. The flash chip is only spec'd for 20 MHz. You might be able to get 25 MHz to get work, but it would not be stable. The occasional misread could not only cause crashes, but it could also cause incorrect calculations, especially if faults are rare. You don't want to be wondering whether your calculator is giving correct results. Although highly unlikely, it could even cause unrecoverable corruption in the flash chip.

And just to be clear, any time you do a calculation, graph an equation, or run a BASIC (not assembly) program, the OS will switch to fast mode.
Well, but "fast mode" is still "only" 15 MHz, correct? And if I get the system up to 22 MHz, which my calculations regarding the performance increase were based upon, then I still should get the desired performance increase, shouldn't I?
And if not, whar is the point in overclocking anyway?

Also, yes, I wanted to design a small custom PCB to solder on. Maybe I will use some other THT components (if present and uncritical for operation) as additional fixpoints. I won't be making the PCB myself though, as companies such as JLCPCB can make them dirt-cheap, and I can make tinned vias, which would be necessary for mounting, and it's faster and more convenient anyway.
Well I guess you can go for it then.
  
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