Recent content by stepleton

Good catch, I stand corrected!

Would it be possible to share a video that films the screen from a little bit closer? Ideally, prop up the camera on something stable and position it so that it frames the whole screen. Begin filming with the computer running and then press the RESET switch so that we can watch the entire...

I'm afraid I don't have any bright ideas, unfortunately. I don't think I'll be more inspired based on your video; why not share it publicly on the forum? There are not many 5100 troubleshooters on here, but I suspect most are more clever than me :)

(mentioning just for fun) I had a Tek 4006 terminal start to fail at X deflection shortly before I was scheduled to exhibit it. I troubleshooted the problem down to a culprit op-amp but didn't really want the time or the trouble of extracting the its circuit board to get at the solder side (if...

I think one challenge for this concept might be timing-related. For example, per this TI datasheet for a tristate octal buffer, a healthy 74LS240 needs to be able to transition an output from low to high in 14ns, while a healthy 74S240 needs to do it in 7ns (assuming the actual circuit is...

I'm not sure the caveat is so important: do we really need to "fully test the chip"? If we're trying to troubleshoot a fault in-circuit, then we don't care about parts of the truth table that the circuit never uses. It is probably enough most of the time to discover a fault in a chip's ability...

@ibm5100 If it's making it through all of the power-up tests, then it's reading the ROS OK and validating its checksums/CRCs. Are you certain that this isn't a display problem with the bottom of the screen? What happens if you boot into APL and then press the EXECUTE key a bunch (to scroll the...

Apologies if this has been pointed out before, but Tektronix liked to use those miserable TI "side-wiper" IC sockets which many people find unreliable, and I can see some empty ones on your circuit board. You might want to include the possibility of a faulty socket in your troubleshooting.

This description matches my understanding based on the Lisa Hardware Manual. There are different versions of this document, but I think the MMU details are pretty much the same: https://bitsavers.org/pdf/apple/lisa/hardware/Lisa_Hardware_Manual_Sep82.pdf (PDF pages 27-39, 117-124)...

I put this forward in the hopes of learning from being corrected, but can't you map segments in multiple hardware contexts to the same physical memory segment? The Lisa OS does have shared libraries or "intrinsic libraries" as they call them, but I don't know how they work. I think I assumed...

5100 BASIC does not have PEEK and POKE unfortunately, but you can break into the built-in Diagnostic Control Program (DCP) and manipulate memory directly. This includes keying in programs in PALM machine code and executing them. Writing PALM programs like the one you describe should not be too...

I don't know from looking at compiled code, but the Lisa has a homemade MMU in discrete logic that can do address translation, so I'd guess relocatable code is not a priority and may indeed not be an approach that Lisa binaries take. (Yes, an MMU with a 68000; if software did any kind of memory...

Per the video, well enough to get them to run and survive eight hours of the built-in "monkey" testing (think fuzz testing). The biggest difference has been that the spellchecker for LisaWrite is not available: we never got the source code or data files for that as it presumably still belongs to...

Quite possibly! In the presentation, Alex mentions working on a fix to the infamous Lisa Y1.995k bug.

William Tooker and Alex Anderson-McLeod (aka @warmech and alexthecat123) have successfully recompiled the Apple Lisa operating system and the Office System desktop manager (think Finder) and tools (think applications) from the source code released a few years ago (thanks @Al Kossow ). Recording...