68kMLA Classic Interface

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SE/30 Board Mystery Issue
Posted by: smrieck511 on 2024-04-22 15:21:23 Yup. Fascinating; where did you tap the probe? It sounds like the issue really is related to the traces. (If the pattern is indeed a vertical jailbar). When I connected UE8 pin13 to the neighboring pins 12 or 14, the screen lit up, but it was a mess...I could roughly make out what would be a flashing disk icon and cursor though..and I could move the cursor. I'll upload a picture when I get home.
Posted by: smrieck511 on 2024-04-22 18:04:57 Here's a short video of the weirdness I get when I connect pin 13 to 12 on UE8... otherwise the screen is black.
Posted by: smrieck511 on 2024-04-22 19:30:01 And a still picture.
Posted by: rickrob on 2024-04-22 22:12:13 Connecting pin UE8 pin 12 to pin 13 is shorting the Vid(6) input to the Qh output-- forcing a signal to the PAL UG6. I'd double check every connection on UE8.
Posted by: smrieck511 on 2024-04-22 22:19:58 Connecting pin UE8 pin 12 to pin 13 is shorting the Vid(6) input to the Qh output-- forcing a signal to the PAL UG6. I'd double check every connection on UE8. Thanks. I've checked all of the pins to ground, +5 and PAL chips. All of those are good. The pins that are Vid(*) are not clear to me. I'm new to schematics so I'm not sure where those ones are going. It looks like they are all connected on the schematic but with small circles?
Posted by: smrieck511 on 2024-04-22 22:27:52 also, would this imply that the PAL chips and video ROM are not part of the problem and it is isolated to the U*8 chips and related traces?
Posted by: Kouzui on 2024-04-22 22:47:14 The pins that are Vid(*) are not clear to me. I'm new to schematics so I'm not sure where those ones are going. It looks like they are all connected on the schematic but with small circles? That's just for diagram simplification. The pins you want to check are the numbers in red. (For example, the VID(6) line goes from pin 12 of UE8 to pin 22 of UC6).
Posted by: smrieck511 on 2024-04-22 22:58:50 Thanks! I've double checked every pin on UE8 to destinations and there are no continuity issues.
Posted by: smrieck511 on 2024-04-23 07:13:23 I double checked every pin on UD8, UE8, UF8 and UG8... they all check out with no broken traces to destinations. My next step is to replace UE8 and possibly other U*8 chips. Replacements should be here tomorrow.
Posted by: smrieck511 on 2024-04-23 16:45:12 Definitely found some serious crud under UE8.
Posted by: rickrob on 2024-04-23 16:58:09 Definitely found some serious crud under UE8. I'll say. Can you post a pic when it's cleaned up?
Posted by: smrieck511 on 2024-04-23 16:58:56 I'll say. Can you post a pic when it's cleaned up? yep. Will do.
Posted by: smrieck511 on 2024-04-23 19:12:59 Well it's clean(er) and I have a bodge wire to UC6 pin3 (Vid5) in my future.
Posted by: rickrob on 2024-04-23 20:34:07 Well it's clean(er) and I have a bodge wire to UC6 pin3 (Vid5) in my future. Take a look at pin 2, close to the pad. There's a line across the trace. Not sure what that is. Could be solder mask...
Posted by: smrieck511 on 2024-04-23 20:46:33 Take a look at pin 2, close to the pad. There's a line across the trace. Not sure what that is. Could be solder mask... I see what you mean. I cleaned it off, but yeah, that was still black corrosion. It never ends...The pad does have continuity to UC7 pin2 (VID0).
Posted by: jmacz on 2024-04-23 21:47:28 Not sure if it’s just the pictures… but there seems to be a lot of broken traces around C9 and UJ11. I had lots of problems on my SE/30 due to broken traces around the vias near C9. Did you check continuity before and after the vias in that area?
Posted by: smrieck511 on 2024-04-23 21:55:31 Take a look at pin 2, close to the pad. There's a line across the trace. Not sure what that is. Could be solder mask... I see what you mean. I cleaned it off, but yeah, that was still black corrosion. It never endsThe pad does have continuity to UC7 pin2 (VID0). Not sure if it’s just the pictures… but there seems to be a lot of broken traces around C9 and UJ11. I had lots of problems on my SE/30 due to broken traces around the vias near C9. Did you check continuity before and after the vias in that area? I will double check. It does seem to boot fine and has sound. Just video problems.
Posted by: smrieck511 on 2024-04-24 09:26:29 Drumroll please..... Repaced UE8 fixed it!! Thank you all so much for your help! This was next level repair stuff for somebody who's just done a few recaps in the past.
Posted by: rickrob on 2024-04-24 11:29:00 Drumroll please..... Repaced UE8 fixed it!! Thank you all so much for your help! This was next level repair stuff for somebody who's just done a few recaps in the past. Awesome! I think the clue was when you forced the output of UE8 to the UG6 PAL. I was thinking UE8 might be bad when that happened. Another one saved.
Posted by: rickrob on 2024-04-24 12:18:27 Where did you get the extension cable for the logic board? I could use one of those.
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