68kMLA Classic Interface

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SE/30 Intermittent Twitching Screen
Posted by: 68krazy on 2017-07-13 15:21:14 Hey everyone, I've got a fully-restored SE/30 that is giving me screen issues. It's the one from this thread: https://68kmla.org/forums/index.php?/topic/30045-full-recap-of-my-new-se30-with-many-pictures/ I've attached a video of the screen issue I'm having (can upload to YouTube if the attachment is an issue for you guys). The screen twitches intermittently. A nice sharp slap to the side of the machine makes it go away for a while. Here's what has been done to the analog board so far: -Full recap of all electrolytics -C15 replaced with film capacitor -Yoke connector resoldered (all old solder completely removed) -Flyback resoldered (all old solder completely removed) Not sure where to go from here. What other cold solder joints could cause this issue? IMG_1303.MOV
Posted by: apm on 2017-07-13 15:59:09 It looks like a vertical sweep problem, and if whacking it temporarily cures it then it's very likely mechanical, probably a bad solder joint. Check and resolder the components in the main signal path of the vertical yoke: especially C9 and R13, and height potentiometer R4. Secondarily check U2 and the smaller passive components around there: R8, R11 etc.
Posted by: Alex on 2017-07-14 01:45:14 I wish I knew exactly what to recommend in terms of a resolution to the issue reported but I don't. Nonetheless, I do want to present you with "The Dead Mac Scrolls". I hope this book covers the symptoms you report and a potential solution. The_Dead_Mac_Scrolls.pdf The book is OCR'd so open it in your favorite PDF reader and use some search terms to find a resolution. I hope it helps. Kind regards —Alex Santos
Posted by: Alex on 2017-07-14 01:57:18 I found these two pages of interest, it in fact does sound like a solder joint might be cracked. I am no expert here but if possible a continuity test is probably in order but I think you know more than me. Kind regards —Alex Santos
Posted by: Alex on 2017-07-14 02:13:22 I also would like to refer you to "Macintosh Repair & Upgrade Secrets", another excellent book by Larry Pina. Search for "intermittent" and you will find what I hope will help you on your journey to repair. Also, check the cable to inspect the CRT pins for tarnish. As per the manual: " The CRT pins are made of copper. Ideally, they should be clean and shinylike thebottomofanewcopperpan.Ifthey'restreaked withdarkblue, you'vedefinitelygota problem. Forthesame reason thatadiscolored copper pan doesn't heat evenly, discolored copper pins don't conduct properly. Clean them with cotton swabs dipped in metal cleaner, dry them carefully, reattach the cable, and everything will be OK. " Again, this book is OCR'd so you can search for symptoms that match yours and any potential resolution. Macintosh_Repair_&_Upgrade_Secrets_1990.pdf If you resolve the issue, for the sake of the community, would you be so kind to document the answer here please.
Posted by: Alex on 2017-07-14 02:36:04 I may have found another source for you. See section 4.1 of the "Classic Mac Repair Notes". Classic Mac Repair Notes .pdf
Posted by: Scott Squires on 2017-07-14 12:23:09 All these PDFs are useful in general, but they don't address 68krazy's specific problem. They really belong in their own thread. apm has already identified the most likely solution here.
Posted by: techknight on 2017-07-15 07:14:29 You forgot all the other solder joints. I have done a few analog boards, and they are RIDDLED with bad solder joints, flyback, yoke plug, all the regular molex plugs, to/from power supply and yoke PCB, as well as logic board. You need to resolder the entire board. That is the only true fix here. Also these PDFs are only good for issues that happened 20+ years ago, sure they CAN be somewhat relevant today, but you have to think. These PDFs were written in the beginning of the bathtub curve. Not the end of it as now.
Posted by: 68krazy on 2017-07-16 11:37:42 Thank you everyone for your input. I will sit down one of these days and resolder the entire thing, with special attention paid to the components/signal path that APM pointed out.
Posted by: Alex on 2017-07-18 12:19:05 All these PDFs are useful in general, but they don't address 68krazy's specific problem. They really belong in their own thread. apm has already identified the most likely solution here. I suppose you are right. Needless to say I was trying to be helpful, in fact posting all those took some time but I know what you mean. I respect your view completely. I could only find, from what I posted that it could be a bad solder joint.
Posted by: Scott Squires on 2017-07-18 12:47:32 They are helpful documents and I appreciate your effort. We should consolidate them somewhere central so that they're easily found and referenced. I hope you continue to contribute these resources and don't let my comment discourage that. I just wish we had a better organization system.
Posted by: CharlieFrown on 2017-07-25 00:43:50 I also find these old books obsolete, out of 10 compact Mac problems, they didnt hit the nail in any case.. so do the math. The only relevant book would be the one written by techknight.
Posted by: techknight on 2017-07-26 15:47:04 haha. To be honest, I am not a very good writer. :-S
Posted by: 68krazy on 2017-07-28 00:22:57 I reflowed all the solder joints today with flux. I'll update you guys in a week or two about whether or not this cured the problem. (I will eventually buy a good solder sucker and actually resolder the entire board; reflowing is a temporary fix)
Posted by: 68krazy on 2017-07-28 00:33:01 Well, got my answer to that pretty quick. It's still doing it after reflowing the entire analog board :-/
Posted by: techknight on 2017-07-28 16:34:01 ok then you need to check the vertical deflection circuitry. Easiest thing is to work the height control back and forth, it could be dirty. Next thing is solder joints, and the 3rd thing would be the wire connections from the yoke plug back to the yoke, or the yoke itself. Last thing could be the vertical IC itself. Too many links in the chain here, and you need to exercise some basic electronics troubleshooting to figure this one out.
Posted by: 68krazy on 2017-07-28 23:10:03 Work the vertical height pot back and forth... this is so glaringly obvious, how was it not the first thing I tried? Thank you techknight! I've worked the pot back and forth. If that doesn't do it, I will check the solder joints on the yoke itself and resolder the entire neck board.
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