68kMLA Classic Interface

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A $40 mac plus

Posted by: luckybob on 2017-08-07 22:22:27 Snagged this off craigslist:   This thing is GRUNGY.  Like it was stored in a barn.  Long story short, the seller said it chimed, but no video.  I got it and it didn't even do that.  Tore it apart and there were cold solder joints on the analog board going to the logic board.  5 minutes with a soldering iron fixed that.  Still no video. Hopefully it isn't something serious, I can hear it working, it tries to boot from disk.  A bit of research on the analog board is my next step.

Posted by: BadGoldEagle on 2017-08-07 22:59:29 Does whacking the side of the unit do anything? Have you tried the brightness knob? Sometimes, turning it ever so slightly restores the picture. The flyback could be bad, that would suck... but "new" old ones are still available. And, last but certainly not least... When you refreshed the joints, did you replace the old solder or did you just reflow it? The latter doesn't always work. BTW, nice find! I got a Plus ED a couple of months ago, also with an Analog board related issue for 50€. Yours was cheaper and has the external disk drive. Real neat! Mine displays a bright vertical or horizontal (can't remember now) so it's a whole different issue... I've ordered some new caps hoping it'll fix it.

Posted by: luckybob on 2017-08-07 23:27:27 I re-flowed it with some new solder.  I think I saw 3 ish bad joints on that large cable and fixed them, but they weren't even that bad.  I never realized you had to do a complete wick and replace.  I did check all the connections, and all the trannies/diodes. I can hear the flyback kick on for a split second when I power the system.  There is no static buildup when I power it on.   I did notice the flyback might have been replaced.  The last person did not bother to clean the flux off.  Also when I did open the case and discharge the flyback, it did give a very healthy spark.  Is there supposed to be a bleed resistor in the circuit?   I even powered it up in the complete dark, it makes no effort to light up.

Posted by: luckybob on 2017-08-08 00:04:08 Reading about others analog board problems, it seems everyone is hating on J1 and C1.  Well I took another look, and I had forgotten to plug J1 back in. Didn't matter, still black screen.  So I'm going to re-cap this thing. any thoughts on this guy to replace C1?  http://www.mouser.com/ProductDetail/Nichicon/UEP1H4R7MDD/?qs=sGAEpiMZZMvwFf0viD3Y3VtTL3hlGy6IpB96XumWLyc%3d

Posted by: BadGoldEagle on 2017-08-08 08:04:47 Oh so the 3.9uF 25V cap is C1... That's the only one I didn't buy, thinking it was non important, but apparently it is! It's also nearly unobtainable. Apparently, the higher the voltage, the better the cap is. Don't know about the capacitance though.

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