[sdiy] Why do LCDs die?

[rsdio at audiobanshee.com]

On Dec 30, 2018, at 8:17 PM, MTG <grant at musictechnologiesgroup.com> wrote:
> A lot of the Z80 machines really push the timing to memory map those LCDs. I don't know what it is exactly since I've never really studied the Z80. There is one guy doing a bunch of Z80 upgrade work these days, but I can't recall who. Anyway the MRC .. U118 is a 74HCTLS on the ones I fixed. I had to replace it with a 74LS00. Then it was fine. Don't ask me how I came to that conclusion but maybe with a schematic in front of me I could say better.

None of the problems with LCDs are specific to the Z80 or the 74LS00. Yes, they were pushing the timing, but the thing about digital is that once you work out the timing successfully, it’s not going to change. Sure, parts can go bad, and you can replace them with faster parts, but you can’t change the timing of a system that was designed as an integrated whole. You probably just got lucky, finding a marginal part and replacing it with one that actually met or exceeded the original timing requirements.


> The Yamaha TX7 is another odd beast to fix and it's not even a Z80 (it's a 6303 which is a 6801 more or less).

This era of machines were all designed around 8-bit chips that ran around 1 MHz or 2 MHz, or maybe 4 MHz with 4 clocks per instruction - same difference.


> Not sure I would pop an OLED or VFD in these two machines as they are finicky enough with LCDs.

Agreed.

I have no experience with OLED, but my understanding is that an LCD lasts 25 times as long as an OLED, so you’re not doing yourself any favors by replacing an aging LCD with a new OLED.

"The light that burns twice as bright burns half as long."

Brian Willoughby