derkom's attempt

[derkom]

Just a quick update. Replaced all three multiplexers and the DAC, soldered by hand this time (and I'm quite comfortable with the quality of the solders) and there's no change.

It seemed like if anything, after I resoldered all the data lines last week, things got worse, because I was seeing significantly less of the flickering screen and more white. It eventually seemed to get to the point where it was basically just white (with black border if on my LCD).

I have swapped out all the buffer chips and the shifter, no changes there either.

The computer is running. It's just somehow not getting the video to the right place.

Next I will probably reinspect all the solders with the microscope. It's been a while since I've taken a good close look at that. I may not get time to do this before my Christmas holiday, though, so nobody worry if I don't make progress. I'll get back to it when I can.

[exxos]

I dont think you have a video output related issue, the data going to the shifter is corrupted. So the inputs to the shifter , something is wrong. So you need to meter out each line from the shifter to where it goes and see which line isn't working. Also check lines on a scope and see if anything isn't looking right. Also make sure you can pass RAM test fully with YAART and make sure RAM is totally stable.

[derkom]

I dont think you have a video output related issue, the data going to the shifter is corrupted. So the inputs to the shifter , something is wrong. So you need to meter out each line from the shifter to where it goes and see which line isn't working. Also check lines on a scope and see if anything isn't looking right. Also make sure you can pass RAM test fully with YAART and make sure RAM is totally stable.

Yep, (re-re-)checking all the lines all the way to the shifter is on my list of stuff to do. I agree that I don't have a video output issue. I wasn't happy with the amount of heat those chips took when installing the first set, but there was nothing but that hunch to point in their direction. Since I have the same problem now with new chips, about which there is no heat concern, and whose solders I'm very comfortable with, and it's definitely not the shifter, it has to be something downstream. Will test it all to exhaustion.

Can't really test the RAM with YAART, since I can't see any output, but at least back when I was getting *some* video, it appeared to be passing the diag cart RAM test. Need to run some more of those tests using serial connection, although I wasn't getting any serial output either last time I had it hooked up that way. But it's been a while since I did that, so my reflowing work earlier may have fixed that issue. (Will of course fix the known serial port issue before expecting input to work.)

The actual RAM I've been using (both a 4 MB Falcon board and a 16 MB SIMM) is known to be good, and I have reflowed everything associated with RAM on the board, so I do not have reason to suspect any problems there. I would also expect to be running into crashing if that were the case, and the system seems solid. Would make a great headless server.

[exxos]

Check lines like DE as its the enable data on line to the shifter.

[derkom]

Okay, I am back home from Christmas holiday, having observed the progress of the video DAC debugging, so the first thing I did was pull up the three legs on the DAC, and...

H4-013.jpg (219.97 KiB) Viewed 3674 times

H4-014.jpg (418.57 KiB) Viewed 3674 times

...and with the BLiTTER installed...

H4-015.jpg (459.78 KiB) Viewed 3674 times

I imagine that at some point in my debugging odyssey, I solved the original problem, probably at the point where I was no longer seeing any flickering screen, and then due to the brightness issue, it looked like my problem actually might have gotten worse, when in fact it was just an additional problem.

I do notice that the video is a little bit dirty (doesn't really show in these photos). There's a bit of interference moving about in the white. Maybe the caps around the DAC aren't installed well? I didn't redo those when redoing all the SMT stuff.

[PaulJ]

I do notice that the video is a little bit dirty (doesn't really show in these photos). There's a bit of interference moving about in the white. Maybe the caps around the DAC aren't installed well? I didn't redo those when redoing all the SMT stuff.

My white was also dingy when I was using the resister network to bias the 3 analog input lines. When I took the resister divider off and let the 3 inputs float it cleared the dingy white up.

[derkom]

My white was also dingy when I was using the resister network to bias the 3 analog input lines. When I took the resister divider off and let the 3 inputs float it cleared the dingy white up.

No resistors on mine. I simply pulled up the legs.

[exxos]

It can be generated from the actual cable as well. The 47pF caps on the RGB lines help clamp that to a point. I was looking into building some RGB scart cables which were individually screened, but that cable doesn't exist anymore

[derkom]

It can be generated from the actual cable as well. The 47pF caps on the RGB lines help clamp that to a point. I was looking into building some RGB scart cables which were individually screened, but that cable doesn't exist anymore

Could be. The cable I'm using isn't exactly high quality. Once I get things to a somewhat more assembled point (which will be after fixing the serial port at least), I'll plug it into the SC1435 upstairs, which uses a different cable, and see how it looks there.

[btl]

It's alive !