Dead Exxos PSU out of the blue

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exxos
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Re: Dead Exxos PSU out of the blue

Post by exxos » Sat Jun 16, 2018 9:54 am

czietz wrote:
Sat Jun 16, 2018 9:01 am
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.
True, though they are on a tiny PCB so that shouldn't really happen. They only smoked when Mikro removed the SCR (crowbar) though thats on the 5V and 12V rail, so to blow the fuse would take higher voltages than normal.. Even so, regulators generally short out totally to gnd which would blow the fuse as well. Though I can't see any way a cap would blow right after removing the crowbar.

I can only assume at this point a regulator has blown and caused the smoke.. not the capacitors themselves.. Though the regulators are current limited & thermal protected. So one failing is unlikely. Only possible reason would be stress on the regulator which would physically crack it after it was screwed down.. but again unlikely it would fail 2 years down the line like that.

Only possible thing I can think to kill the thing, is connect 5V to 12V without a load.. 12V into the 5V regulator could possibly kill it, it would blow the fuse (over voltage crowbar) , so when the SCR was removed, the regulator is now faulty and smoked.. even so, that would seem unlikely as it would pull likely more amps than the fuse rating and the fuse would blow again. But its the only thing I can think of killing the thing based on what has been done so far.
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Re: Dead Exxos PSU out of the blue

Post by czietz » Sat Jun 16, 2018 10:10 am

In the meantime I've seen your more detailed picture of the caps (http://www.exxoshost.co.uk/atari/last/psu/exxosmod.jpg) and I agree that they should not be subjected to mechanical stress. Cracked ceramic capacitors usually occur either on big PCBs that bend/flex unevenly or next to areas where force is applied, e.g. connectors, screw holes etc.

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Re: Dead Exxos PSU out of the blue

Post by exxos » Thu Jun 21, 2018 1:16 pm

PSU arrived today.

I first put it on my bench power supply and powered it up, there seem to be something shorting out the power supply so I just kept turning up the amps until something blew :twisted: I saw a flash where those capacitors are, then the current drop down to virtually nothing.

It seems on that little capacitor PCB had been arcing between PCB traces where the capacitor was. The capacitor itself does not seem to be faulty (I only checked it was O/C not the value) . As to why this would happen when there is about 2mm clearance between the two traces I don't know. Unless there was a hairline wisp of solder or PCB trace which had not been cut back enough.

Those particular boards were done with a CNC machine by guy in the UK, as such they were actually bare copper which may have aggravated the problem with the traces not been varnished like normal PCBs are. Even so, the solder connections are obviously bare anyway, so I don't think that would really be a possibility.

The input voltage only gets to around 25volts so somewhat baffled really. If it was more around 100+volts then it would make more sense. The only other thing I can think is if it was particularly humid that day and the board simply got damp. :shrug: it was probably just really bad luck somewhere on that mini PCB. In any case, those mini boards were done away with in later versions anyway.

I do have 1 spare board from the last production I did, I ran out of transformers so it never got finished. So what I will do is transplant the transformer from the power supply and fit it to the new board, then just send the newer board to Mikro..
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Re: Dead Exxos PSU out of the blue

Post by mikro » Thu Jun 21, 2018 1:32 pm

Wow, that was quite fast shipping (sent as a normal parcel, no extra service paid).

I think some PSU curse has been put on me recently:

- Exxos PSU broke after two years of 5* service (despite my awful soldering back then)

- Since this was my STE's PSU, I decided to finish my experiments on an STFM. Powered up - nothing. When moving with the mains cable I could get it working, then again not etc... in the end I had to resolder the compoments (...only to find out the very same advice on Chris's PSU web :))

- OK, so while the STFM PSU was in the works, I decided to do some stuff on one of the Falcons I had been using for past few days. Powered up - tsk-tsk-tsk-tsk sound with power LED blinking like crazy. I guess ageing capacitors? Will have to recap, fortunately I have one kit from Chris lying around

This all happened during ONE WEEK. With all PSUs working fine a few days before that. Unbelievable.

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Re: Dead Exxos PSU out of the blue

Post by Petari » Thu Jun 21, 2018 1:46 pm

mikro wrote:
Thu Jun 21, 2018 1:32 pm
... Unbelievable.
Maybe should checking electric power in your house. Overvoltage, bad ground can harm PSUs .
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Re: Dead Exxos PSU out of the blue

Post by exxos » Thu Jun 21, 2018 1:49 pm

That does sound like a run of bad luck :(

I don't know if you have one already.. but I run all my stuff though a battery backed UPSU these days. The mains voltage here is terrible, constant drop outs, over voltages. I think it was the reason my PC PSU kept on failing.. Though I invested in a UPSU (and a really huge UK made PC PSU) and no problems for past several years now. Its pretty cool in power cut times, as at night the whole road can be in darkness, and I am unaware the power has even gone off now :lol:
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Re: Dead Exxos PSU out of the blue

Post by Atarian Computing » Thu Jun 21, 2018 3:28 pm

A UPS is a must. I have a APC SmartUPS 1400VA in my rack. Brings comfort to my soul when I hear it clicking away during power fluctuations.

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Re: Dead Exxos PSU out of the blue

Post by exxos » Thu Jun 21, 2018 3:37 pm

Atarian Computing wrote:
Thu Jun 21, 2018 3:28 pm
A UPS is a must. I have a APC SmartUPS 1400VA in my rack. Brings comfort to my soul when I hear it clicking away during power fluctuations.
Sounds like the one I have here :)
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
https://www.exxoshost.co.uk/atari/last/storenew/ - All my hardware mods for sale - Please help support by making a purchase.

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Re: Dead Exxos PSU out of the blue

Post by rubber_jonnie » Thu Jun 21, 2018 4:44 pm

Atarian Computing wrote:
Thu Jun 21, 2018 3:28 pm
A UPS is a must. I have a APC SmartUPS 1400VA in my rack. Brings comfort to my soul when I hear it clicking away during power fluctuations.
Just refreshed the batteries in mine, also an APC. Since I'm running VM's, and power is crappy round my way atm, I wouldn't have it any other way!
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Re: Dead Exxos PSU out of the blue

Post by Atarian Computing » Thu Jun 21, 2018 4:53 pm

rubber_jonnie wrote:
Thu Jun 21, 2018 4:44 pm
Atarian Computing wrote:
Thu Jun 21, 2018 3:28 pm
A UPS is a must. I have a APC SmartUPS 1400VA in my rack. Brings comfort to my soul when I hear it clicking away during power fluctuations.
Just refreshed the batteries in mine, also an APC. Since I'm running VM's, and power is crappy round my way atm, I wouldn't have it any other way!
Sweet. I got new batteries as well. I've got an HP DL360P running a few VMs and a Dell R210ii as my Pfsense firewall. A Cisco C2960S is my switch for now. A Synology NAS as well. Fun stuff.

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