PSU issue / only have a 5V on both, need advise :)

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TheDark91
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PSU issue / only have a 5V on both, need advise :)

Post by TheDark91 »

Hi to all,

I purchase an Atari 1040STE, when i power on the device, there is no sign of life... no led, nothing.
After unboxing the cover, i check the different voltage output, all voltages seem good except 5V.

I only have a 5V on both, can you confirm that I should have both +5V at the output of the power connection?
Is there anyone who can tell me which component(s) need to be repaired?

I have seen different new power supplies, which one would be the best if I had to replace it?

Is it possible to have a power supply with the right power supply connection?

Thank you for your help.

Best Regards.
Steve
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Re: PSU issue / only have a 5V on both, need advise :)

Post by Steve »

The blue cable should be 5v and the red should be 12v. Usually it will be a blown MOSFET. But if you're unfamiliar with PSUs I would advise you just buy a new PSU as it can be dangerous. Exxos sells new PSUs in his store.
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PhilC
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Re: PSU issue / only have a 5V on both, need advise :)

Post by PhilC »

@Steve sorry to disagree but on a standard STFM power supply, 5v is red and 12v is blue. So two 5v wires, 2 grounds and one 12v.

Its a good idea to recap all psus these days due to old age and the potential damage they can cause to other components.
If it ain't broke, test it to Destruction.
Steve
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Re: PSU issue / only have a 5V on both, need advise :)

Post by Steve »

Oops 🤐

Yes ignore me lol. Except cautionary part.
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exxos
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Re: PSU issue / only have a 5V on both, need advise :)

Post by exxos »

Are you testing it under load ...
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viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
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TheDark91
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Re: PSU issue / only have a 5V on both, need advise :)

Post by TheDark91 »

I powered up the power supply circuit using the power-on button, then I measured the different voltages directly on the connector (which connects the motherboard)
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exxos
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Re: PSU issue / only have a 5V on both, need advise :)

Post by exxos »

TheDark91 wrote: Sun Dec 06, 2020 1:12 pm I powered up the power supply circuit using the power-on button, then I measured the different voltages directly on the connector (which connects the motherboard)
But is it plugged into the motherboard when you test ?
https://www.exxosforum.co.uk/atari/ All my hardware guides - mods - games - STOS
https://www.exxosforum.co.uk/atari/store2/ - All my hardware mods for sale - Please help support by making a purchase.
viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
Just because a lot of people agree on something, doesn't make it a fact. ~exxos ~
People should find solutions to problems, not find problems with solutions.
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rubber_jonnie
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Re: PSU issue / only have a 5V on both, need advise :)

Post by rubber_jonnie »

Got to agree with @exxos, the PSU needs to be under load in order to correctly measure the voltages, either plugged into the mainboard or a suitable load.

As @PhilC said, Red is 5v, Blue is 12v, however only 5v is required to power on the ST itself, and if you're getting 5v off load, that will drop on load and probably won't be good enough.

It sounds like the 12v side has gone bad, but because you don't know what is wrong with the PSU, whilst you could recap and replace the mosfets, if there is some other problem, you might find that even after all that, the PSU is never quite right and might fail again.

Personally I would try to repair, but in your situation, if you're not able to do that, then a replacement from exxos is good, plus there are alternatives like the Meanwell RD-50A which are cheap and easily available, but just need a bit of wiring up.
Collector of many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...
TheDark91
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Re: PSU issue / only have a 5V on both, need advise :)

Post by TheDark91 »

exxos wrote: Sun Dec 06, 2020 1:53 pm
TheDark91 wrote: Sun Dec 06, 2020 1:12 pm I powered up the power supply circuit using the power-on button, then I measured the different voltages directly on the connector (which connects the motherboard)
But is it plugged into the motherboard when you test ?
No, does it was important?
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rubber_jonnie
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Re: PSU issue / only have a 5V on both, need advise :)

Post by rubber_jonnie »

TheDark91 wrote: Sun Dec 06, 2020 4:22 pm
exxos wrote: Sun Dec 06, 2020 1:53 pm

But is it plugged into the motherboard when you test ?
No, does it was important?
Yes it must be plugged in to the mainboard or on an artificial load, please read my previous post about that.
Collector of many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...
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