Nekonomicon - Magic smoke came out of my Sun 3/50

pmjett
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Who joined March 28, 2007, 1:29 p.m.
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Wrote the following at April 13, 2010, 8:28 p.m...

I finally found an old Sun 3/50 to tinker with, and upon putting power to it, and getting the power supply to spin up, a power resistor on the motherboard burst into flames. Really. Flames. In disgust, I filed it away in exile in the attic. Recently, I ran across a power supply pinout for the silly thing in obsolyte, and my interest was rekindled

Anyone have any opinions on whether I should even bother trying to graft an AT/ATX power supply into the thing and try again? Would a power supply and/or motherboard failure mode like that toast most other important things on the board? It would seem so, but the allure of a 68020 is calling to me. I'm supposed to be writing my thesis, and I have to be particular about how to fritter away my time. :mrgreen:

thanks,
mike

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bigD
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Wrote the following at April 13, 2010, 8:38 p.m...

Yes, you need to get this thing up and running. Sun 68K is sexy, sexy, sexy.

Then run the C-Ray benchmark on it.

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porter
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Who joined Nov. 1, 2006, 11:37 p.m.
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Wrote the following at April 13, 2010, 10:12 p.m...

I run mine diskless using SunOS 4.1 served by a i386 Solaris box. It's quite quick for what it is.

recondas
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Who joined June 6, 2004, 5:55 p.m.
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Wrote the following at April 14, 2010, 4:02 a.m...

pmjett wrote:

Recently, I ran across a power supply pinout for the silly thing in obsolyte, and my interest was rekindled

It would seem so, but the allure of a 68020 is calling to me. I'm supposed to be writing my thesis, and I have to be particular about how to fritter away my time.

Sounds like an interesting recovery project, but if I had only a small amount of time to fritter away I'd pull some 10/4 cable and wire up some 220V outlets....... you could probably find *something* to plug into 'em.

<not to mention finally have the opportunity to test the splice on your GVO>.

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RetroHacker
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Who joined May 22, 2008, 6:23 a.m.
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Wrote the following at April 14, 2010, 10:01 a.m...

I'd say go for it! I cobbled an AT power supply onto a 3/50 a few years back - it was really, really easy to do.

-Ian

pmjett
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Who joined March 28, 2007, 1:29 p.m.
and authored 78 notes

Wrote the following at April 14, 2010, 6:20 p.m...

recondas wrote:

I'd pull some 10/4 cable and wire up some 220V outlets....... you could probably find *something* to plug into 'em.

Ha! Indeed. I better do it before it gets hot again, since I have no cooling capabilities where the outlets can go. For some reason, my wife won't let me plug the rack into the dryer plug in the kitchen. What's up with that?

No, it really would be an interesting recovery project, and I have plenty of small form factor ATX (like a flex-atx) supplies with enough chutzpah to cover the requisite 150W. I'm all for it, but my question is really more of a "should I bother trying?" because if the whole board is toast then it'd be wasted effort to graft the supply in. So in order of likelihood would such a failure be because of:

a failed power supply

an out-of-spec power resistor

a short/failure on the MB to draw enough current to flame the resistor
Any guesses?
mike

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kjaer
Big Fan
Who joined May 7, 2008, 7:47 p.m.
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Wrote the following at April 14, 2010, 6:26 p.m...

pmjett wrote:

a short/failure on the MB to draw enough current to flame the resistor
Any guesses?
mike

This is almost without a doubt the culprit. Your PSU is probably fine. Make sure it's actually a resistor that flamed, and not an inductor.

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RetroHacker
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Who joined May 22, 2008, 6:23 a.m.
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Wrote the following at April 14, 2010, 6:56 p.m...

I would lean to believe that your board is fine, and it was the power supply that failed. Are you sure it was a resistor and not a tantalum capacitor? I see those fail in smoke and flames in old equipment fairly regularly.

It's real easy to rig up another supply to power your machine - shouldn't take long to just wire it up and see if it works.

You can also check the board for shorts by checking the resistance between the 12 and 5v rails with a meter.

-Ian

pmjett
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Wrote the following at April 16, 2010, 6:35 p.m...

RetroHacker wrote:

Are you sure it was a resistor and not a tantalum capacitor? I see those fail in smoke and flames in old equipment fairly regularly.

Good call. I opened the box up again in a fit of task avoidance, and noticed that indeed the flamed part is a tantalum cap next to a power resistor. I guess in my muddled head I remembered incorrectly. A little googling seems to suggest that it's possible for a tantalum (or any other cap I suppose) to randomly fail after >20 years. But, it looks like the primary failure mode for a tantalum cap is excessive current via a short, so detective work will be in order to try and eliminate that or just bad karma. I'll bench test the power supply (with suitable ballast resistors to stabilize the regulation).

Right after I pull the 10-4 romex to power ye olde Onyx2 rack. Cross my heart...
mike

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RetroHacker
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Wrote the following at April 17, 2010, 9:48 a.m...

pmjett wrote:

RetroHacker wrote:

Are you sure it was a resistor and not a tantalum capacitor? I see those fail in smoke and flames in old equipment fairly regularly.

Good call. I opened the box up again in a fit of task avoidance, and noticed that indeed the flamed part is a tantalum cap next to a power resistor.

Tantalums fail shorted all the time - just because. It's gotten to the point where I recognize the smell and just ignore it. They're used as bypass caps, and when they fail, they pretty universally don't affect the operation of the device they're in. They fail shorted from age, then overheat and burn. Once they've burned themselves out, they go open circuit, and life returns to normal.

I have a Compaq Portable 286. When I plugged it in from being sitting for years, it came on and worked for about a minute before a tantalum in the power supply let go. Smoke poured profusely out of the vents, and the computer continued to work just fine, booted happily from a DOS disk, not skipping a beat. Being that it's such a royal pain in the neck to remove the power supply from one of those machines, I just left it alone. Thing still works flawlessly.

Clip that tantalum out, and I'll bet that the computer works just fine with the existing power supply.

-Ian

nekonoko
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Wrote the following at April 17, 2010, 12:14 p.m...

RetroHacker wrote:

Thing still works flawlessly.

I've had the same experience. Both my Apple III and Apple Lisa had tatalums explode in their power supplies with huge quantities of acrid smoke pouring out the vents, and both machines continue to operate just fine without them.

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SAQ
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Wrote the following at April 17, 2010, 5:36 p.m...

nekonoko wrote:

RetroHacker wrote:

Thing still works flawlessly.

I've had the same experience. Both my Apple III and Apple Lisa had tatalums explode in their power supplies with huge quantities of acrid smoke pouring out the vents, and both machines continue to operate just fine without them.

Check the board to be sure everything's fine. "Blasting caps" can sometimes damage traces and other stuff - they burn hot.

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pmjett
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Wrote the following at May 6, 2010, 10:32 p.m...

pmjett wrote:

Right after I pull the 10-4 romex to power ye olde Onyx2 rack. Cross my heart...mike

Ah. ahem. Well I guess I broke that promise. And what's more, since senility seems to be setting in, the box is actually a Sun 3/80 , and not a 3/50 as I incorrectly recalled. But the good news is that after replacing the first torched tantalum, then torching another, and replacing that, I have this:

Code:

  Sun-3/80 Boot PROM Selftest (Rev. 2.9.2)
  
  (Press <Esc> to abort tests or <Cntrl-L> for the Loop Menu)
  
  System Enable Register Read Test {pass 0x00000001}  00:16:59
  
  PROM Checksum Test {pass 0x00000001}  00:16:59
  
  Clock/Calender Device  {pass 0x00000001}  00:17:00
  
  I/O Mapper RAM Write/Write/Read Test {pass 0x00000001}  00:17:01
  
  I/O Mapper RAM Address Test {pass 0x00000001}  00:17:01
  
  I/O Mapper RAM 3-Pattern Test {pass 0x00000001}  00:17:01
  
  <Memory Size = 0x00000008 MB>
  
  Memory Address Test {pass 0x00000001}  00:17:01 01
  
  Memory Read Byte Alignment Test {pass 0x00000001}  00:17:06
  
  Memory Write Byte Alignment Test {pass 0x00000001}  00:17:06
  
  Bus Error Register Test {pass 0x00000001}  00:17:07
  
  Level 1 Interrupt Test {pass 0x00000001}  00:17:07
  
  Level 2 Interrupt Test {pass 0x00000001}  00:17:07
  
  Level 3 Interrupt Test {pass 0x00000001}  00:17:07
  
  Configuration Memory Check  {pass 0x00000001}  00:17:07
  
  LANCE Controller Check  {pass 0x00000001}  00:17:07
  
  ESP SCSI Controller Check  {pass 0x00000001}  00:17:07
  
  Floppy Controller Check  {pass 0x00000001}  00:17:07
  
  Printer Controller Check  {pass 0x00000001}  00:17:07
  
  <P4 Video RAM Board NOT Detected>
  
  END OF SELFTEST # 0x00000001 (SELFTEST PASSED).
  
  #PASSED = 0x00000001, #FAILED = 0x00000000
  
  <Initializing Main Memory 0x00000008 Megabytes Initialized>

Now I need to save up for a framebuffer.

And install the wiring for the Onyx2

mike

EDIT: I forgot my manners. Thanks to everyone who was kind enough to give me feedback! You guys were right, hinky tantalums.

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kjaer
Big Fan
Who joined May 7, 2008, 7:47 p.m.
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Wrote the following at May 8, 2010, 1:19 a.m...

That's good news!

I have several 3/80 motherboards all exhibiting the same fault - there is a wire-wound inductor next to two large SMT caps (I believe these are electrolytic, but have not looked very closely yet), which are very close to the PSU header. It is overheating (and charring) due to an effective dead short on the -12V rail. I haven't yet identified the failing cap(s). Out of curiosity, which two caps did you replace?

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pmjett
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Who joined March 28, 2007, 1:29 p.m.
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Wrote the following at May 8, 2010, 5:51 a.m...

kjaer wrote:

Out of curiosity, which two caps did you replace?

The very ones you are talking about: C17118 and C17119, 33 uF, 16V SMT tantalums. Just to check it, I grabbed some Radio Shack 47uF 35V electrolytics. I'll order up some better stuff from Mouser, and do it right. I couldn't find any shorts, I guess the 21 year old Kemet caps finally cut loose because of their age and the particular service they are in on the board.

Good luck with your 3/80 motherboards. It was very satisfying seeing it go to the PROM.
mike

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nekonoko
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Wrote the following at May 8, 2010, 9:04 a.m...

Very cool! I have a 3/80 in the closet myself. I should probably drag it out sometime and see what its current status is.