Dead SC1224

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MaLICiouS
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Dead SC1224

Postby MaLICiouS » Thu Mar 25, 2010 10:18 pm

Hello again! It's been quite a while (having an affair with my speccy) ;)

Some time ago (I think about 5 months) I acquired a SC1224 monitor at a flea market. As you would expect, I was in heaven
(the SC1224 is quite rare in Sweden, as far as I've noticed).

An hour or so after bringing it home, picture and sound went out. I saw smoke. Uh-oh.
So, do you have any ideas as to what went wrong? Obtaining a new monitor is near impossible as I've previously stated, and I'm quite experienced with soldering, so that isn't a problem.
I'll take pictures if you request them. I don't exactly know which parts are relevant, and I don't feel like dismantling more than I have to.

Cheers!
Last edited by MaLICiouS on Fri Mar 26, 2010 9:28 am, edited 1 time in total.
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Re: Dead SC1224

Postby wthorbjo » Fri Mar 26, 2010 5:15 am

If both picture and sound went at the same time, my first guess would be that the power supply is bad. A likely culprit could be one or more capacitors that have dried out and failed due to age. I would suggest examining the PSU board for signs of bulging capacitors or sticky residue. Replacing the capacitors isn't very difficult if you know which end of the soldering iron gets hot, and most types and values of capacitors should be readily available from your local electronics supply house. Might be a good idea to replace all of them, since any that haven't failed yet may be close to failure.

Of course, you may find that repairing the PSU leaves you with a fully working power supply and a monitor that is still broken in other ways. That is the joy of vintage electronic equipment :D
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MaLICiouS
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Re: Dead SC1224

Postby MaLICiouS » Fri Mar 26, 2010 9:26 am

Thanks for the quick reply!
wthorbjo wrote:my first guess would be that the power supply is bad.

That was my first guess too, but it's good to have confirmation. I've previously replaced the electrolytic capacitors on a PC motherboard, so it'll be a breeze.
wthorbjo wrote:Of course, you may find that repairing the PSU leaves you with a fully working power supply and a monitor that is still broken in other ways. That is the joy of vintage electronic equipment :D

Yes, you're always in for a surprise :) It's amazing it's been working for the past 25 years. Try that with a modern flatscreen; you'd be lucky to get past 10.

I'll put updates in this thread.
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Re: Dead SC1224

Postby MaLICiouS » Fri Mar 26, 2010 11:07 am

Update: I found the culprits. Three caps in the PSU are leaking, one of them (the big one, reservoir cap?) bulging and VERY MUCH leaking. Transformer and voltage regulator look OK visually. Can't be sure, though. Caps on the monitor's main board look OK.
I'll take a trip to the electronics store in the near future, an I'll let you all know how it turns out.
Again, thanks for the help!

Update 2: The power LED is lighting up, so obviously the secondary side isn't completely dead as it is.

Clarification:
  • Leaking: C950, C966, C961
  • Heat bubbles: C956

The heat bubbles (at least I think it is) on C956 worries me. I don't think it's within my power to repair this PSU.
Any ideas?
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Recased Falcon030 with CT2, 64MB TT-RAM, 4MB ST-RAM, FreeMiNT/XaAES, EtherNEC and 40GB HDD

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Re: Dead SC1224

Postby wthorbjo » Sat Mar 27, 2010 3:12 am

MaLICiouS wrote:Update: I found the culprits. Three caps in the PSU are leaking, one of them (the big one, reservoir cap?) bulging and VERY MUCH leaking. Transformer and voltage regulator look OK visually. Can't be sure, though. Caps on the monitor's main board look OK.
I'll take a trip to the electronics store in the near future, an I'll let you all know how it turns out.
Again, thanks for the help!

Update 2: The power LED is lighting up, so obviously the secondary side isn't completely dead as it is.

Clarification:
  • Leaking: C950, C966, C961
  • Heat bubbles: C956

The heat bubbles (at least I think it is) on C956 worries me. I don't think it's within my power to repair this PSU.
Any ideas?


Most likely, there's been a "cascading failure", where one or more caps has failed initially, causing others to fail later. My guess would be that the transformer is ok, since an iron-core transformer is pretty hard to break, and you probably wouldn't be getting any power at all (ie no LED) if it was dead. I'm not sure if the voltage regulator in this PSU is a single chip or made from discrete components. Either way, it could be damaged by overvoltage or overheating caused by the cap failure, or it may be fine. Same goes for the rectifier etc. If you don't see any scorch marks or burning on the components or the PCB, chances are that they are ok. I would try replacing the caps and any other components that appear damaged, and see where that gets you.

Alternatively, you could try to source a replacement PSU board from somewhere, but that may be tricky.

You can find a ZIP file with schematics and troubleshooting information for the SC1224 here: http://atari4ever.free.fr/hardware/doc/sc1224.zip. Lots of other useful information at http://atari4ever.free.fr, by the way.

Good luck!
wthorbjo
Edmonton, AB, Canada
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MaLICiouS
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Re: Dead SC1224

Postby MaLICiouS » Mon Mar 29, 2010 4:19 pm

Thanks a lot! I'll let you know how it goes!
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Re: Dead SC1224

Postby 3AtariSTE » Wed Mar 31, 2010 10:09 am

MaLICiouS wrote:Thanks a lot! I'll let you know how it goes!


Hello
If the power supply is ok, could be the flyback transformer broken.
I repaired an CM8833 replacing the fbt (i saw it smoking).
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Re: Dead SC1224

Postby Desty » Thu Apr 08, 2010 3:29 am

MaLICiouS wrote:Yes, you're always in for a surprise :) It's amazing it's been working for the past 25 years. Try that with a modern flatscreen; you'd be lucky to get past 10.

You said it! I picked up a Polaroid 22" (or so) LCD about a year ago, intending to set it up with my STE once I'd found a SCART cable or better (eh, still haven't gotten around to that). Tested it when it arrived, looked fine... boxed it up until a couple of weeks ago, whereupon I found that once turned on, it shows the Polaroid logo, then the display powers off, even though the power LED indicates that it's on and not in standby. Before doing a factory reset (which didn't help), I could hear perfect audio from the tuned in aerial channels.

Googled it, and apparently it (and lots of other Polaroid LCDs) has some duff capacitors which die after... about a year. :evil: :evil: :evil: :evil: Time to get good at soldering... but part of me would prefer to drive to the nearest offices of Polaroid and throw it through the window (with a polaroid photo of me doing a goatse pose for added bonus).

So for now it's stuck with an orange (ack) SM124 which apparently has no volume knob. :?
tá'n poc ar buile!


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