So I'm going to attempt to update to a newer BIOS on a 286 I'm building up. The BIOS Chip Type is :
http://www.radiomuseum.org/tubes/tube_r4-th018.html
Never heard of that model before, sorry. 🙁
Perhaps it's just a one-time programmable EPROM chip of an eastern production ?
OTP's are essentially normal EPROMs, but without an UV window of quartz.
The "256" could hint of the size in Kilobits (256/8= 32 KB).
And since the pin count is 28, it could be likely something compatible to a 27C256.
27xxx or 27Cxxx were the de-facto standard for EPROM chips back in the day.
Reading wise, they should all behave pretty much the same.
I haven't tried yet, but some of the 28C and 29F series can be used as drop-in replacements.
Sometimes a tiny bit of re-wiring is required, but that's nothing a cheap plastic socket can't solve. 😉
Anyway, I really recommend to get a real EPROM programmer, not just a $5 BIOS flasher.
On the long run, they (real prommers) will save a lot of stress and dissappointment.
Personally, I had a good experiences with both a G550 and and TL866CS so far.
These units costs roughly about $50 (~40€) and work for most of the CMOS chips (27C???).
Edit: Oh, and let's don't forget the UV eraser. They can be bought really cheap from China.
Strangely, they seem to operate at 110/130V, though. Perhaps they are export devices for the market of the USB, dunno..
Anyway, since I'm in Europe, I have to use it with a step-down converter here.
If you go the same route, make sure you get a few 27C EPROMs also. And by different brands, if possible.
In case of doubt (or the lack of support in the programmer's database), programming these with the settings
for their "intel" or "amd" counterparts should do.
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