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ST Tech Woes/Help (my own darn fault)


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#1 Blur2040 OFFLINE  

Blur2040

    Chopper Commander

  • 246 posts
  • Location:Columbusish, Ohio, USA

Posted Tue Dec 19, 2017 9:36 AM

I have a 520 ST (original, external floppy version).  It used to mostly function...

 

It would boot to TOS, but floppies wouldn't work.  It worked intermittently when I first got it...then less and less then not at all.  I took it out recently, determined to figure it out...and I did.  I noted that it seemed to be trying to work...and then it did...for a single boot.  Hurrah.  Then it didn't when I put it all back together.  I determined that it was likely a bad solder joint.  Got out a hair dryer and warmed up the board.  It would work.  Let it cool down, flaky as biscuits.  I suspected that it was either the floppy port or the socketed DMA chip.  So, in the hopes of narrowing it down...and not wanting to resolder ever damned joint on the board...I got out some foil to shield the rest of the board...so I could heat things individually...

 

See where this is going?  I got sloppy, turned it on with the foil in place, while I had the DMA chip uncovered...but surrounded with foil.  It then booted to either a uniform blank screen, or, sometimes a black box in the middle with wavy lines...and some rectangles.  Sometimes gray with some vertical lines.   You should have heard the sad little noise I made.  At any rate, I was very upset, was hopeful that it was just a loose something...started pulling/reseating chips.  In my panic/sadness, I reseated the DMA chip backwards...that got quite toasty.  Fixed it, turned back on...still does the same thing...So...that DMA chip is probably dead.  Believe it or not, I'm usually quite competent in electronics repair/diagnoses.

 

At any rate, I've ordered a new DMA chip, which will take a few weeks to get here.  Anybody have any ideas for me to fiddle with it in the meantime?  Should it boot to TOS without the DMA chip?  Or did I bork something bigger like the 68000?

 

Also, there's a local ST on craigslist...a 1040 which I can get for about $100 bucks.  Should I just throw in the towel and get a new one?  

 

Advice?  



#2 Bama OFFLINE  

Bama

    Space Invader

  • 24 posts

Posted Thu Dec 21, 2017 8:12 AM

Get the 1040ST for use (play) now.

Keep working on the 520ST, too.

You will have your cake and eat it too!




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