exxos's Atari, Amiga & retro forum

fenarinarsa wrote: 21 Jan 2022 01:13 Well, I've just tested the C301712 on my STE with my tool and I can also hear audio cracks. I guess putting it into my STE doesn't fix anything then.

C301712 is to be expected to cause problems, so why are you saying it doesn't fix anything ?

I did a quick video.

The shifter on test is the top one in the image below. The other shifters I could not access the floppy drive it just came up 2 bombs each time. So I was unable to run the program on those. Thankfully the top one in the list did actually load the program from floppy.






Interestingly in the first video clip, the TV has the usual " background noise" but with the second shifter it was virtually silent. Not really sure what was going on there as I did not mute the audio or anything.

Also the background raster effect seems to be a lot more consistent and stable with the 588 shifter.

exxos wrote: 21 Jan 2022 11:32 C301712 is to be expected to cause problems, so why are you saying it doesn't fix anything ?

I wondered if a C301712 in an STE instead of a MSTE would make things turn better :)

You've got quite a lot of shifters... all from dead STEs? If so that would mean the faulty shifter is more frequent than the correct one

fenarinarsa wrote: 21 Jan 2022 13:22 You've got quite a lot of shifters... all from dead STEs? If so that would mean the faulty shifter is more frequent than the correct one

I don't really remember how I ended up with the shifters. All I remember is testing them some years ago (maybe 10+ years ago ?) and finding they didn't work in STEs. I assumed they were out of some other machines with a similar shifter. I just put them in my parts box to look into another day.

It is probably worth noting that the background raster pattern seems a lot more consistent and " diagonal" with the stable 588 shifter.

exxos wrote: 21 Jan 2022 18:22 It is probably worth noting that the background raster pattern seems a lot more consistent and " diagonal" with the stable 588 shifter.

That's interesting because it's really the simplest blitter loop you can do. And 68000/blitter timings are expected be the same on every STE!

Maybe I can enhance this test program to make a more easy to visually detect vertical visual shape.

fenarinarsa wrote: 21 Jan 2022 19:52 That's interesting because it's really the simplest blitter loop you can do. And 68000/blitter timings are expected be the same on every STE!

Maybe I can enhance this test program to make a more easy to visually detect vertical visual shape.

I might try GB6 on it as well, but may not be sensitive enough to detect those sorts of timing differences.

Other than one test being marginally slower (which I'm not overly concerned about anyway)

The first test causes graphics artefacts along with drawing the main GB6 window and blitting tests. none of the other tests seem to cause artefacts.






Incidentally turning the blitter off does not cause artefacts on the first test and the blitting tests, but drawing the main GB6 window still causes artefacts ( but only when it is actually drawing) it is otherwise still as long as nothing is changing on the screen.

I'm not saying there is a problem with the blitter, it just seems to be more of a problem with this "buggy shifter".

I have ordered the buffer boards for the 16Mhz clock as a side note.

Only just got home. Thought I would try a "random" thought and just put a 47R in series with the 16MHz clock.

Quickly tried 2 of the "1991" 1712 "buggy" chips where the machine wouldn't even boot half the time, and now the video glitches are gone and the blitter operations run fine!





I didn't expect it to be that simple. So I suspect a single simple buffer on the 16Mhz line will be more than enough. But I can't do more tests until my buffer boards come. At least that is a huge step forward and a likely solution to that problem is now in grasp!

The audio pops are still there, so there seems to be 2 main faults going on. Though the noise seems to be appearing on pin 4 & 7 etc of U501. Placing some pF there greatly reduces the audio clicks. So just noise basically which needs snubbing out. I can't help but feel if they were LS types then it might not be such a problem. :shrug: I may try it if I can find some LS types.Not sure if they delays will upset things or not..

EDIT:

Basically 1 volt spikes at a quick scope out. The total rise to fall pulse is 40ns. But it also oscillates downwards after about 20ns. ( forgot to take a zoomed in image :roll: )

OK I couldn't leave alone. So rolled the dice on some 33pF caps..




Totally silent and no graphics glitches with both mods done.

Maybe I should re-release my DAC fix kits now :lol: :roll: