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I have an old Apple //e clone, bought in Brazil (but assembled who-knows-where-on-Earth) that has not been touched for over 15 years.

At least, from what I could see, it is a //e -- but not enhanced, since it has lowercase characters, but came with 48k RAM (is that correct?). When booting, instead of "APPLE ][", "APPLE //e" or any clone brand name, it prints "COMPUTER" on the screen (now that is an informative message!)

When it was working, I remember the character generator had some problem (some characters displayed kind of weird on screen, with some pixels missing sometimes, but not always). So I was wondering if I can dump its content, maybe debug and fix it, and put a new EPROM in its place. But I don't know what kind of EPROM it is -- there is no useful information on it, and all I can see is that it's a 24-pin chip, with the round hole in the middle for recording.

What IC could I use to replace that one? And what kind of gear do I need to dump the old one's contents and write the new one? Would a MiniPRO TL866CS, for example, do the job? (it's easier for me to get a MiniPRO than any other EPROM recorder)

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The standard US Apple //e Video ROM was pin compatible with 2732 (4k) EPROMs, but some foreign models (UK, German, French, Italian) used a 2764 (8k) compatible ROM with two character sets.

Your clone might be the same or it might be different - the best way is to try to decode the pinout using either a logic probe (while on) or even a multimeter (while off) to trace the voltages and signals.

In any case the larger question of how to read and write EPROMs is better covered in discussion forums or blog posts such as this fairly comprehensive one.

Unless it's been improved recently the MiniPRO TL866CS might need a work-around to use 25V instead of 21V to program a 2732 (see the circuit below), or at least a tolerant 2732 that accepts 21V. Here's another site that discusses various aspects of programming old EPROMs with the TL866.

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Technical Trivia

Since you ask about the "Apple //e character generator", perhaps I should point out that unlike earlier Apple II video ROMs, the //e Video ROM actually contains all the possible bit patterns that are output by the video hardware, including LORES and HIRES patterns. Your clone might not be the same.

The TEXT patterns are stored in the first half of a 4k ROM ($000-7FF) and in the first and third quarters of an 8k ROM. The patterns are in reverse bit order and inverted. For more technical details see page 8-40 in James Sather's Understanding the Apple IIe.

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    It was also a common hack to connect the extra address pin on the larger EPROM to a switch somewhere (often added to the keyboard), so you could switch between the US charset and the national charset. (In Germany, that would lead to "APPLE ÄÜ" when booting ...) As OP is replacing the EPROM anyway, maybe get a larger one, and burn a local charset, too. – dirkt Jan 18 '17 at 8:20
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    @dirkt: Yes, I just needed to get home and verify on my PAL //e. – Nick Westgate Jan 18 '17 at 22:16
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    @Jay: I've added a link to someone who was trying to burn a //e ROM with the TL866CS and had trouble with some 2732s. They eventually succeeded. YMMV – Nick Westgate Jan 18 '17 at 22:16
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    I added some final notes about the contents of the //e video ROM compared to the Apple II. That's about all I can think of that's relevant, but let me know if I missed something. – Nick Westgate Jan 20 '17 at 4:53
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    @Jay: Yeah, and The Wayback Machine doesn't have it. Well, I doubt you need to build that circuit anyway. Check out the extra link I added (lots of interesting info there including EPROM types and fake TL866's!) and the forums it links to. As I said, burning is a big topic probably better served by blogs and forums like the first link I gave to www.classic-computers.org.nz. – Nick Westgate Jan 24 '17 at 3:16

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