Dead Exxos PSU out of the blue

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mikro
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Re: Dead Exxos PSU out of the blue

Post by mikro » Fri Jun 15, 2018 6:19 pm

exxos wrote:
Thu Jun 14, 2018 3:42 pm
Possible.. Though that normally happens more-or-less right away, not 2 years down the line..
Though as you say it was working one moment and not the next, it could have just been some fluke.. I would change the fuse and see how it goes before looking into it deeper.
Unfortunately, it doesn't seem to be a fluke. I changed the fuse, exactly the same type (fast 4A, 250V) and the moment I turned the PSU on, pfzzzzz.... the fuse looked like a light bulb for a fraction of second and that was it. Another dead fuse in my hand. I still have two more but I doubt their fate will be different unless we figure out something.

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Re: Dead Exxos PSU out of the blue

Post by exxos » Fri Jun 15, 2018 6:29 pm

If you can remove the SCR it won't blow the fuse.. Then you can check the bias voltage across the resistor I mentioned earlier. Of course this is assuming that is the problem.. if you shorted any outputs that will also blow the fuse.
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Re: Dead Exxos PSU out of the blue

Post by mikro » Fri Jun 15, 2018 9:24 pm

exxos wrote:
Fri Jun 15, 2018 6:29 pm
If you can remove the SCR it won't blow the fuse.. Then you can check the bias voltage across the resistor I mentioned earlier.
OK, this did not help. I desoldered the rectifier (in green, just to be sure) and the thing in red... gave me one hell of a smoke:
IMG_20180613_213729-new.jpg
IMG_20180613_213729-new.jpg (1.42 MiB) Viewed 434 times
Of course this is assuming that is the problem.. if you shorted any outputs that will also blow the fuse.
If I got the idea where the SCR is right, then it looks like the over sensitive tripping wasn't the problem, yes. :-/

I guess the only thing left to do now is to send you the PSU and hope you can find some time to look at it.

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Re: Dead Exxos PSU out of the blue

Post by exxos » Fri Jun 15, 2018 9:59 pm

mikro wrote:
Fri Jun 15, 2018 9:24 pm
OK, this did not help. I desoldered the rectifier (in green, just to be sure) and the thing in red... gave me one hell of a smoke:

Why are you desoldering random things I not even mention ?! What smoked ?! The regulators are pretty much indestructible!
4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

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Re: Dead Exxos PSU out of the blue

Post by mikro » Fri Jun 15, 2018 10:12 pm

exxos wrote:
Fri Jun 15, 2018 9:59 pm
mikro wrote:
Fri Jun 15, 2018 9:24 pm
OK, this did not help. I desoldered the rectifier (in green, just to be sure) and the thing in red... gave me one hell of a smoke:

Why are you desoldering random things I not even mention ?! What smoked ?! The regulators are pretty much indestructible!
I'm sorry Chris but you're not making very clear statements, esp. for me who is not a professional electrician. You said "If you can remove the SCR" ... to my knowledge, SCR stands for "Silicon controlled rectifier" and looks exactly like the thing I circled in green. We have been talking about voltage measurements in top right corner so my understanding was that this is the component you are talking about to remove to get the voltage values on the resistor. If you meant something else then I'm sorry but then again, you didn't express yourself very clearly.

What smoked is circled in red on the photo. It was really a lot of smoke.

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Re: Dead Exxos PSU out of the blue

Post by exxos » Fri Jun 15, 2018 10:19 pm

mikro wrote:
Fri Jun 15, 2018 10:12 pm
What smoked is circled in red on the photo. It was really a lot of smoke.
I don't know how 50V ceramic caps can smoke.. That is practically impossible during normal operation..

You will have to send it back to me to investigate as I really do not understand whats going on.

The Only way to smoke those capacitors is if you had a 110V primary and ran it at 240V to double the input voltage to the circuit. even so, the electrolytics caps would smoke first.. but that would also likely kill the regulators anyway, which would blow the fuse.
4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

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Re: Dead Exxos PSU out of the blue

Post by mikro » Fri Jun 15, 2018 10:28 pm

exxos wrote:
Fri Jun 15, 2018 10:19 pm
I don't know how 50V ceramic caps can smoke.. That is practically impossible during normal operation..
I was equally surprised, trust me. What I did was to desolder the SCR (assuming that's the one in green circle), installed another fuse, switched on the PSU and pfff....
The Only way to smoke those capacitors is if you had a 110V primary and ran it at 240V to double the input voltage to the circuit. even so, the electrolytics caps would smoke first.. but that would also likely kill the regulators anyway, which would blow the fuse.
I have no explanation at all. As mentioned, the PSU worked fine in Australian power network and the EU has more or less same voltage levels. I had the STE running for a few weeks before this incident happened.

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Re: Dead Exxos PSU out of the blue

Post by exxos » Fri Jun 15, 2018 10:33 pm

You will have to send it back to me so I can do tests. I don't know how something can fail like that.
4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

https://www.exxoshost.co.uk/atari/ All my hardware guides - mods - games - STOS
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Re: Dead Exxos PSU out of the blue

Post by mikro » Fri Jun 15, 2018 10:36 pm

I've sent you an email to atari@exxoshost... for postage details.

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Re: Dead Exxos PSU out of the blue

Post by czietz » Sat Jun 16, 2018 9:01 am

exxos wrote:
Fri Jun 15, 2018 10:19 pm
I don't know how 50V ceramic caps can smoke.. That is practically impossible during normal operation..
SMD ceramic capacitors are sensitive to mechanical stress, e.g. when the PCB is (even slightly) bent. They can fail "short" in that case. So if these capacitors are on e.g. a supply rail, after the failure they will get a lot of current. => Smoke.

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