ST just died

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sut
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ST just died

Postby sut » Fri Dec 16, 2016 9:59 am

Just went to power up my ST and after an initial 'flash' no power at all. I've tried with a different power lead still no pulse.

What's this likely to be ? Is it an easy fix or am I better searching for another ST ?

This is my third ST since I got into retro gaming. My Spectrum and Sega consoles never seem to go wrong But I constantly seem to have reliability issues with ST's.

The ST was the machine I had as a teenager so it has the most nostalgia of all my systems.
My current ST is a 520 STfm which I was going to upgrade next year to 1 meg.

EDIT: Mods feel free to move my post as I've noticed I posted it under the 'professionals' board. Apologies.

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Re: ST just died

Postby joska » Fri Dec 16, 2016 10:32 am

I'd start by checking the PSU. I've had a couple of ST PSU's where the rectifier was blown leaving the PSU dead.
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Re: ST just died

Postby soviet9922 » Fri Dec 16, 2016 4:37 pm

Maybe you have check your ICs if they are socket ed maybe they got loose or have corrosion in the pins.

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Re: ST just died

Postby siriushardware » Fri Dec 16, 2016 6:17 pm

sut wrote:Just went to power up my ST and after an initial 'flash' no power at all. I've tried with a different power lead still no pulse.
What's this likely to be ?


Dead / No Life? A power supply problem. The power supplies in these are removable modules so there's absolutely no reason to discard the whole machine, and you have various options besides trying to fix the PSUs you have, but let's take a look anyway.

Trying another mains lead was a good start. Next thing is to take the machine apart and look at the PSU - with the power lead disconnected entirely from the machine - and look at the PCB of the PSU. There is usually a glass fuse in a clip-in holder on the PSU PCB. Is that fuse OK?

If it's blown, your options are to

-(Less technical). Replace it with the exact same type, turn on the machine and see if it stays on. Only do this once. If it blows again, don't replace the fuse again as there is a fault somewhere on the PSU. You'll have to fix it or replace it.

-(More technical). Have a look around anything likely to have caused the fuse to blow first. Besides the fuse, does anything else show obvious visual signs of distress (black soot marks, vapourised copper deposits?) Be aware that under certain fault conditions the high voltage capacitors may store a charge for quite some time after the mains input has been removed. It won't kill you but you won't forget it in a hurry. If there's no obvious problem, replace the fuse, but again only once, as above.

If the above is out of your comfort zone, user exxos here on this forum offers various options from refurb / repair kits for existing ST power supplies, ST power supplies which have already been refurbed, and (just in) an entirely new 21st century design high-spec replacement power supply for the ST range.

You used the word 'flash but you weren't very specific about that. A Flash on the display screen? A flash from inside the unit near the power switch?
Last edited by siriushardware on Fri Dec 16, 2016 6:22 pm, edited 1 time in total.

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Re: ST just died

Postby spiny » Fri Dec 16, 2016 6:20 pm

the built in power supplies have a fuse:

psu.jpg


check that first. However, it has probably blown for a reason, so if you replace it and it immediately blows again, the PSU could be faulty.
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sut
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Re: ST just died

Postby sut » Fri Dec 16, 2016 10:08 pm

siriushardware wrote:You used the word 'flash but you weren't very specific about that. A Flash on the display screen? A flash from inside the unit near the power switch?


Sorry I meant the power light flashed and also a flash from inside the unit near the power switch. Nothing on the display screen.

Thank you all for your suggestions I will open her up tomorrow and report back.

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Re: ST just died

Postby charles » Sat Dec 17, 2016 12:21 am

fuses really do flash ,,,
what is the st a 2amp 250v quick fuse

if I had a deeper technical edge id love a list of every part
on the board of st power supply

buy all new parts and rebuild the psu .......

same situation as you,,,,my psu blew a year ...or two ..or three? ago
,,,never did get 100% rectified

good luck
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Re: ST just died

Postby dlfrsilver » Sat Dec 17, 2016 9:11 am

yes, i enjoin you like everyone else to check the fuse, and also do the capacitors removal for new ones. Contact Exxos on this board for new ones :)

That's not a too serious problem, your PSU only need a "renewal" :)
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sut
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Re: ST just died

Postby sut » Sat Dec 17, 2016 10:53 am

I replaced the fuse this morning and got the same quick flash of the power light then nothing again.
So sounds like the PSU has gone thanks for all your help everyone.
I'm going to get in touch with exxos and see how to around replacing the PSU.

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Re: ST just died

Postby dlfrsilver » Sat Dec 17, 2016 11:01 am

sut wrote:I replaced the fuse this morning and got the same quick flash of the power light then nothing again.
So sounds like the PSU has gone thanks for all your help everyone.
I'm going to get in touch with exxos and see how to around replacing the PSU.


Good idea :)
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Re: ST just died

Postby troed » Sat Dec 17, 2016 12:17 pm

Hmm.

I'd remove the PSU and then check for shorts between GND and 5V / 12V. A new PSU is of no use if you have a short on the motherboard (which would be a reason for the fuse to blow).

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Re: ST just died

Postby dlfrsilver » Sat Dec 17, 2016 1:09 pm

troed wrote:Hmm.

I'd remove the PSU and then check for shorts between GND and 5V / 12V. A new PSU is of no use if you have a short on the motherboard (which would be a reason for the fuse to blow).


Good point, checking for any dust sheep (those are prone to make short circuits..)
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Re: ST just died

Postby soviet9922 » Sun Dec 18, 2016 9:33 pm

You can very easy wire the power plug from your Atari PSU to a PC ATX one, they are switched, and just power off when you have short no need to remove fuses.
Use it for testing so you can determine if you need to purchase a new PSU or you have a problem on your motherboard.

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Re: ST just died

Postby exxos » Sun Dec 18, 2016 9:41 pm

If its blowing fuses then likely the main switching transistor has blown, but as already point out, the rectifier can also can bad.
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