Dead Exxos PSU out of the blue

Repairs & upgrades.
mikro
Posts: 106
Joined: Mon Aug 28, 2017 11:22 pm

Dead Exxos PSU out of the blue

Post by mikro » Wed Jun 13, 2018 8:57 pm

Hi guys,

I hope this is the right place to post. I purchased one 230V PSU from Chris on 30/08/2016 but instead of celebrating our two-year anniversary ;) the unit has just died. :-( There was no smoke, sound, physical manipulation, it was in my STE from the day zero and just suddenly ... stopped. Had the STE running, switched off, then switched on and after a couple of seconds the STE just turned off. After that both the PSU and STE didn't show any life signs (not even the power LED on the STE).

Knowing next to nothing about PSUs, what basic checks can I do before shipping to Chris? I checked only the real basics like whether the switch works, whether the fuse hasn't been killed for some reason or whether I'm getting input voltage on the PSU. For instance, shouldn't I get a few volts on the output connector, like the red+black or blue+black wires?
IMG_20180613_213729.jpg
IMG_20180613_213729.jpg (2.86 MiB) Viewed 549 times

User avatar
exxos
Site Admin
Posts: 3410
Joined: Wed Aug 16, 2017 11:19 pm
Location: UK
Contact:

Re: Dead Exxos PSU out of the blue

Post by exxos » Wed Jun 13, 2018 9:25 pm

Measure the voltage both sides of the fuse, then at least you know what side of the circuit the problem is at. You should get about 30VDC or there abouts. If you don't then the transformer isn't getting power. If you don't get voltage both sides of the fuse, then likely fuse has simply blown.
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.

mikro
Posts: 106
Joined: Mon Aug 28, 2017 11:22 pm

Re: Dead Exxos PSU out of the blue

Post by mikro » Thu Jun 14, 2018 8:29 am

Thanks Chris. I tried to measure it as you suggested (I hope when we talk about the fuse we mean that thing covered by translucent plastic, right? :) [top right corner on my photo]).

When I measure DC voltage, I'm getting about 500 mV ~ 1.5V on one side and about 500 mV on the other side. However when switched to AC, I get 5.8V on both ends. Does it say anything to you?

User avatar
exxos
Site Admin
Posts: 3410
Joined: Wed Aug 16, 2017 11:19 pm
Location: UK
Contact:

Re: Dead Exxos PSU out of the blue

Post by exxos » Thu Jun 14, 2018 10:30 am

mikro wrote:
Thu Jun 14, 2018 8:29 am
Thanks Chris. I tried to measure it as you suggested (I hope when we talk about the fuse we mean that thing covered by translucent plastic, right? :) [top right corner on my photo]).
Yes.. The cover does clip off.. but you can measure on the pins top or bottom of the PCB..
mikro wrote:
Thu Jun 14, 2018 8:29 am
When I measure DC voltage, I'm getting about 500 mV ~ 1.5V on one side and about 500 mV on the other side. However when switched to AC, I get 5.8V on both ends. Does it say anything to you?
Are you measuring from the fuse to 0V on the PCB ? IE, Where the screw holes are are gnd...

If you are measuring that way, then seems like the board has no power, which is delivered from the transformer via the rectifier.. As either are unlikely to fail, It suggests the transformer does not have mains voltage going to it.
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.

mikro
Posts: 106
Joined: Mon Aug 28, 2017 11:22 pm

Re: Dead Exxos PSU out of the blue

Post by mikro » Thu Jun 14, 2018 3:27 pm

exxos wrote:
Thu Jun 14, 2018 10:30 am
Are you measuring from the fuse to 0V on the PCB ? IE, Where the screw holes are are gnd...

If you are measuring that way, then seems like the board has no power, which is delivered from the transformer via the rectifier.. As either are unlikely to fail, It suggests the transformer does not have mains voltage going to it.
This was the crucial information. For some reason I thought it's a great idea to use GND outside the PCB. So yes, I can measure about 23.5VDC on the top of the fuse (see my photo above) and nice 0V on the bottom. What I shouldn't I guess?

User avatar
exxos
Site Admin
Posts: 3410
Joined: Wed Aug 16, 2017 11:19 pm
Location: UK
Contact:

Re: Dead Exxos PSU out of the blue

Post by exxos » Thu Jun 14, 2018 3:28 pm

mikro wrote:
Thu Jun 14, 2018 3:27 pm
This was the crucial information. For some reason I thought it's a great idea to use GND outside the PCB. So yes, I can measure about 23.5VDC on the top of the fuse (see my photo above) and nice 0V on the bottom. What I shouldn't I guess?
Fuse blown then..

I use 4A quick blow...
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.

mikro
Posts: 106
Joined: Mon Aug 28, 2017 11:22 pm

Re: Dead Exxos PSU out of the blue

Post by mikro » Thu Jun 14, 2018 3:32 pm

exxos wrote:
Thu Jun 14, 2018 3:28 pm
Fuse blown then..
Is this related to this: http://exxoshost.co.uk/atari/last/psu/i ... m#exxosmod by any chance?
I use 4A quick blow...
I'm sorry, you lost me here. :) What does it mean?

User avatar
exxos
Site Admin
Posts: 3410
Joined: Wed Aug 16, 2017 11:19 pm
Location: UK
Contact:

Re: Dead Exxos PSU out of the blue

Post by exxos » Thu Jun 14, 2018 3:42 pm

mikro wrote:
Thu Jun 14, 2018 3:32 pm
Is this related to this: http://exxoshost.co.uk/atari/last/psu/i ... m#exxosmod by any chance?
Possible.. Though that normally happens more-or-less right away, not 2 years down the line..

The fuse blows on over voltages either on the 12V or 5V rails. Though I had huge trouble with specs of parts at the time, hence writing about it. I wanted the quickest "Trip" circuit possible to protect peoples machines , though its probably a little bit to sensitive in some cases.. but that's not really a bad thing.

If I wrote a value on the back of the PCB, like 0.350 or something like that, its the default bias trip voltage of the crowbar circuit. Measure across the top right resistors (behind the TO220 package) and see what voltage you get there. That voltage should match the one on the back of the PCB.. That will tell you if something has drifted out of spec causing the problem on my site or not.

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.
mikro wrote:
Thu Jun 14, 2018 3:32 pm
I'm sorry, you lost me here. :) What does it mean?
4Amp quick blow fuse.. 20mm.. its a standard part..


EDIT:

Looks like you have one of the later boards anyway, that's already had the NXP diodes fitted...
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.

mikro
Posts: 106
Joined: Mon Aug 28, 2017 11:22 pm

Re: Dead Exxos PSU out of the blue

Post by mikro » Thu Jun 14, 2018 4:01 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..
Maybe the fact it was connected to Australian power network and then switched to European one plays a role here?
The fuse blows on over voltages either on the 12V or 5V rails. Though I had huge trouble with specs of parts at the time, hence writing about it. I wanted the quickest "Trip" circuit possible to protect peoples machines , though its probably a little bit to sensitive in some cases.. but that's not really a bad thing.
I agree, better safe than sorry. One question about blowing the fuse: shouldn't be the circuit broken then? I mean when I try to check connection between both fuse pins (on the PCB), I get the usual beep, i.e. existing connection.
If I wrote a value on the back of the PCB, like 0.350 or something like that, its the default bias trip voltage of the crowbar circuit.
Looks like 0.2 to me:
IMG_20180614_164651.jpg
IMG_20180614_164651.jpg (2.39 MiB) Viewed 475 times
Measure across the top right resistors (behind the TO220 package) and see what voltage you get there. That voltage should match the one on the back of the PCB.. That will tell you if something has drifted out of spec causing the problem on my site or not.
Hmm, I have only one resistor there and it gives me exactly nothing on both ends. Do I need to replace the fuse first to see that voltage?
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.
Will do and report back.

User avatar
exxos
Site Admin
Posts: 3410
Joined: Wed Aug 16, 2017 11:19 pm
Location: UK
Contact:

Re: Dead Exxos PSU out of the blue

Post by exxos » Thu Jun 14, 2018 4:07 pm

mikro wrote:
Thu Jun 14, 2018 4:01 pm
Maybe the fact it was connected to Australian power network and then switched to European one plays a role here?
Looks like a 230V PSU going by text on the bottom.. As long as you are still running it on those voltages they should be no problem.
mikro wrote:
Thu Jun 14, 2018 4:01 pm
I agree, better safe than sorry. One question about blowing the fuse: shouldn't be the circuit broken then? I mean when I try to check connection between both fuse pins (on the PCB), I get the usual beep, i.e. existing connection.
You should remove the fuse to test it... Obviously as you have 23VDC one end of the fuse and nothing at the other, the fuse is broken.
mikro wrote:
Thu Jun 14, 2018 4:01 pm
Hmm, I have only one resistor there and it gives me exactly nothing on both ends. Do I need to replace the fuse first to see that voltage?
Circuit needs to be powered up and operating properly to see a voltage there...
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.

Post Reply