AbeOwitz Posted March 21, 2021 Share Posted March 21, 2021 (edited) I picked up an STF in bad shape a while ago. Was able to fix some things, but I'm stumped with this one. Same pattern in both low & med res. Have not tried Hi-Res yet. (My hi-res monitor is also on the fritz. Prob. needs new caps.) I've reseated all socketed chips, swapped the power supply with a known working one. Also swapped the video chip, no changes. Bad EPROM/RAM? Bad capacitor? (No floppy hooked up here. Mouse and OS seem to work fine, just a video output issue...) I'm going to dig deeper, but figured I could ask here first to save me some time, in case this has been seen before. Any suggestions? Thanks Edited March 21, 2021 by AbeOwitz Quote Link to comment Share on other sites More sharing options...
ChildOfCv Posted March 21, 2021 Share Posted March 21, 2021 Looks like an analog sync problem to me. Did you try other monitors? If that's an Atari ST monitor, it may have a "H Hold" adjustment on the back to play with. Quote Link to comment Share on other sites More sharing options...
AbeOwitz Posted March 21, 2021 Author Share Posted March 21, 2021 Thanks for the reply. :-) Right now, I'm running it though a Framemeister RGB to a Dell 2007 LCD. My other ST's work fine with the Framemeister. So, I'm pretty sure the problem is in this machine. Quote Link to comment Share on other sites More sharing options...
Cubeast Posted March 21, 2021 Share Posted March 21, 2021 (edited) How is the condition of the Atari's monitor socket? Edited March 21, 2021 by Cubeast Quote Link to comment Share on other sites More sharing options...
ParanoidLittleMan Posted March 21, 2021 Share Posted March 21, 2021 Well, this looks as bad filtering of power , especially if that bad area is moving slowly up/down. Even if PSU is changed with one what works well in other ST it is possible. There is filtering with electrolyte capacitor on motherboard too. So, if both (in PSU) and on MBO are weak, +5V, +12V might be bad. Looking with oscilloscope is best what can do, before going in some component replacements. Quote Link to comment Share on other sites More sharing options...
AbeOwitz Posted March 21, 2021 Author Share Posted March 21, 2021 7 hours ago, Cubeast said: How is the condition of the Atari's monitor socket? It's good. Note that the distortion occurs at the same vertical line all the time. There's no rolling or randomness to it. Quote Link to comment Share on other sites More sharing options...
AbeOwitz Posted March 21, 2021 Author Share Posted March 21, 2021 (edited) 7 hours ago, ParanoidLittleMan said: Well, this looks as bad filtering of power , especially if that bad area is moving slowly up/down. Even if PSU is changed with one what works well in other ST it is possible. There is filtering with electrolyte capacitor on motherboard too. So, if both (in PSU) and on MBO are weak, +5V, +12V might be bad. Looking with oscilloscope is best what can do, before going in some component replacements. What's weird is the distortion occurs at exactly the same lines every frame. There's no rolling or randomness to it. So, whatever's wrong is occuring in sync with the video. I just watched a video where the STFs didn't have circuitry for composite sync? That on this model one can't just combine HSYNC and VSYNC? Edit: Found this, lessee if I have those components around... resistors yes, diodes probably, maybe transistor... https://www.atari-forum.com/viewtopic.php?p=310158&sid=5cabebd9f99a8943281e32ce45dc361b#p310158 Edited March 21, 2021 by AbeOwitz Quote Link to comment Share on other sites More sharing options...
AbeOwitz Posted March 21, 2021 Author Share Posted March 21, 2021 Found this schematic. I'm not using composite, just RGB & H & V sync, so that's not it either... Quote Link to comment Share on other sites More sharing options...
AbeOwitz Posted March 21, 2021 Author Share Posted March 21, 2021 OK, so monochrome works fine. That eliminates a lot. Quote Link to comment Share on other sites More sharing options...
AbeOwitz Posted March 21, 2021 Author Share Posted March 21, 2021 First image is 5v & 12v power. Looks clean. 2nd image, Red is Horiz Sync. Yellow is Vertical Sync. Note the downward spike there... Noisy Vertical? Quote Link to comment Share on other sites More sharing options...
AbeOwitz Posted March 21, 2021 Author Share Posted March 21, 2021 (edited) . Edited March 22, 2021 by AbeOwitz Quote Link to comment Share on other sites More sharing options...
AbeOwitz Posted March 22, 2021 Author Share Posted March 22, 2021 (edited) My GBS8200 also fails on this STF, can't sync at all. Works on my STE though. (As best as can be expected for a stock GBS8200) Edited March 22, 2021 by AbeOwitz Quote Link to comment Share on other sites More sharing options...
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