LisaList2

Good find, I'm interested to see it in action - it looks like my first thought was correct, this is a Tektronics 4010/4050 graphics terminal emulator program that appears to have gotten ported over to the Mac later in life: https://books.google.com/books?id=zC4EAAAAMBAJ&pg=PA46&dq=%22tekalike%22+mesa+graphics&hl=en&sa=X&ved=2ahUKEwib8fPSnt-MAxXkRTABHZemF_wQ6AF6BAgIEAM#v=onepage&q=%22tekalike%22%20mesa%20graphics&f=false


I also found some snippets on Google Books implying that Tekalike did actually ship for Lisa... the dealer pamphlet also says Mesa Graphics was writing software for Lisa in 1983, think this is what they were writing? http://www.bitsavers.org/pdf/apple/lisa/marketing/Lisa_Dealer_Presentation_1983.pdf

Just added DC42 (BLU 0.9) Twiggy disk images for all three disks to the files section: https://lisalist2.com/index.php/topic,629.0.html

This is a problem from a Lisa 2/5 that dates back from 2023, that I had never solved, and that I put on the backburner for a while. See here

https://lisalist2.com/index.php/topic,423.0.html

The video board is actually from a different system (a 2/10), and I use the "bad" system as my work horse. Now that the video board works, I'll get back to working on my 2/5.

What I/O board ROM version is 9F (H/9F in your pic)? Don't think I've come across that one before...

Edit: I wonder if that has something to do with your I/O board error during POST.

Edit 2: I/O board error 57 seems to be related to the disk controller and / or your Lisa Lite adapter board in a 2/5, per https://lisafaq.sunder.net/lisafaq-hw-rom_error_codes.html

Never mind, I traced a short that I made on the board while reflowing the contacts. Looks like I've got everything under control now. So in the end, it was resistor R28 that got fried in the process of recapping C18. It's only my second resistor problem in my 10+ years of Mac and Lisa tinkering !

Progress ! I usually don't check resistors that do not look burnt, but becoming desperate, I did. One of the resistors feeding TDA1170 (R28) showed 470 kOhms when it should be only 56k. After a quick swap, I get a much better image (below). R28 is actually next to C18 on the board, and it's possible that it got a bit too hot when I soldered C18, leading to failure.

The image is still squashed a bit, clearly exhibiting a vertical linearity issue. I'm surprised to see a second problem, but I'm not complaining 

Thanks @AlexTheCat123. I desoldered the Vlin pot but it measures perfectly. I did not check the other ones but they all seem to respond normally to tuning. Plus the video is actually no longer jumpy.

I saw somewhere that you have experienced issues with the vertical deflection controller TDA1170N, and replaced a few. Did you ever see any of these symptoms ? And is it a difficult/tricky job to do ?

I know you said you've already tried messing with the pots, but have you replaced any of them? In my experience, a bouncy screen like this is often caused by a flaky pot, and replacing it fixes everything right up. I'd focus on the HEIGHT one first, but it's probably a good idea to just replace them all because replacements are cheap and the originals are just so unreliable all these years later.

Just posted this on 68kmla. If anyone can help, that would be fantastic. Thanks !

https://68kmla.org/bb/index.php?threads/lisa-video-board.49827/

When the VIA is shifting out bits, the maximum shift rate available is phi2/2

On the 2/10 I/O Board, the VIA phi2 is CPUCLK/4, so about 1.25 MHz.

On the Lisa 1/2 I/O Board, the VIA phi2 is the 68K's E clock, which is CPUCLK/10 (with a 60/40 duty cycle IIRC, but that doesn't matter here).
With a stock CPU Board, E is about 500 KHz, and with an original 16 MHz XLerator, E is 1.6 MHz.

So the slowest hardware configuration's maximum shift rate is 250 KHz per bit, making the byte rate about 31 KHz. So that suggests the output in the audible spectrum will essentially average to the count of high bits - one of nine amplitudes corresponding to 0 bits high to 8 bits high.

The shift register can be set to shift bits slower than that using the T2 counter, but then you'll hear individual bits.

I expect one can manage to write a new byte at the same rate as it is shifted out, so you end up with performance of a 3 bit 31 KHz DAC.

If you simultaneously change the volume, I suppose one might get close to a 6 bit DAC.

Good luck!

Another potential advantage of modulating the volume:

In PDM, the representation of "no sound" (that is, a flat line at 0) is 101010101010101010101010: 50% on/off at the highest frequency possible. If we just play that at a fixed volume, there are a few possible consequences, not quite all exclusive of each other:

(bad:)
- This frequency is audible, or within the Lisa's audio system, it generates audible resonant tones. Annoying!
- Same, but maybe too high for humans, still audible to any pets.

(fine:)
- The audio system doesn't have adequate bandwidth for that frequency and so it essentially gets smoothed out and behaves like a DC bias on the speaker.

My money is on the (bad) outcomes being more likely, in which case being able to turn the speaker right down is going to be a big quality of life improvement. But even if things are (fine), I'm still pretty sure that relieving PDM of the need to recreate the audio's dynamic range will be an important quality win.