Early Mega PSU getting real hot

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JonB
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Early Mega PSU getting real hot

Postby JonB » Thu Apr 26, 2012 3:57 pm

I've just got a replacement Mega power supply. It looks like an early one as shown on the Atarifreakz web site (didn't come from there though). Running it up one of the heatsinks (the one furthest from the fan) is getting VERY hot, as is the big fat resistor next to the wires that connect to the motherboard. The heat ramps up quickly, within a minute or two, and I am concerned there may be an explosion and some magic smoke in the near future.

Other than that it is working and the Mega is displaying a nice desktop. I am soak testing it right now.

So, is this heat normal for the earlier power supply designs?
Too many retro computers here: 1040STfm, Mega4, Ultrasatanx2 , Amiga A500, A500+ and A1200, Acorn Atom x2, BBC Micro, Electron, Spectrum 48k x2, +48, +128k, QL, Oric Atmos, ZX81, Memotech MTX512, Amstrad 6128 x2..

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Re: Early Mega PSU getting real hot

Postby MRAtari » Thu Apr 26, 2012 6:30 pm

all heatsinks on Atari PSU's get hot (especially nearest the big fat capacitor as this is the mains / primary side) and seeing as the Mega ST PSU gives more output i'd guess it would get hotter... hence they had a fan

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Re: Early Mega PSU getting real hot

Postby carlywhoo » Thu Apr 26, 2012 10:35 pm

JonB wrote: I am soak testing it right now.


Didn't think water and electricity could mix? :lol:

What is soak testing?

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1024MAK
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Re: Early Mega PSU getting real hot

Postby 1024MAK » Fri Apr 27, 2012 9:49 am

carlywhoo wrote:
JonB wrote: I am soak testing it right now.


Didn't think water and electricity could mix? :lol:

What is soak testing?

He means he has left his system on (possibly running a test program or an game / application he can "play" or monitor) for an extended time to see if it continues to work correctly over this extended time.
:megaphone: http://en.wikipedia.org/wiki/Soak_testing :mrgreen:

Mark
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1024MAK
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Re: Early Mega PSU getting real hot

Postby 1024MAK » Fri Apr 27, 2012 10:11 am

JonB wrote:I've just got a replacement Mega power supply. It looks like an early one as shown on the Atarifreakz web site (didn't come from there though). Running it up one of the heatsinks (the one furthest from the fan) is getting VERY hot, as is the big fat resistor next to the wires that connect to the motherboard. The heat ramps up quickly, within a minute or two, and I am concerned there may be an explosion and some magic smoke in the near future.

Other than that it is working and the Mega is displaying a nice desktop. I am soak testing it right now.

So, is this heat normal for the earlier power supply designs?

The big fat resistor is big and fat because it is designed to dissipate a lot of heat (correctly called a power resistor).
Same applies to heatsinks. They are designed to transfer the heat from the device (normally a transistor, diode or integrated circuit [chip]) to the air so that the heat is dissipated.

It is hard to tell if such items are operating at higher than normal temperatures unless you have another known good unit to compare with, or you already know what to expect.

Power resistors and heatsinks are often too hot to touch (and be careful as some heatsinks are at a high voltage).

If there are no other problems or symptoms (like discolouration of the PCB near the hot items), I would suggest that the PSU is operating normally. For all systems that use fans to aid cooling, ensure that you keep the air path clear and operate it with the case on as designed. This allows the fan to blow air over the heatsink :mrgreen:

Mark
Falcon, Atari 520STFM, Atari 1040STE, more PC's than I care to count and an assortment of 8 bit micros (nearly forgot the Psion's)

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Re: Early Mega PSU getting real hot

Postby DarkLord » Fri Apr 27, 2012 1:07 pm

I think he meant "soak" as what is commonly called "burn in" time here. :)

BTW, where did you buy it from? A lot of places do soak/burn in on parts. I
know Best Electronics does this on a lot of their items.

Also, if you really concerned about it getting hot, you can improve the airflow in
a Mega ST by removing the plastic slots that cover the fan in the rear of the case.

Best Electronics recommends doing this for extended use. I did it for the Mega ST4
that I use to run my BBS, because it's on 24/7. They are pretty restrictive, with
narrow spacing when you look at them. It's not hard to do either.

HTHs. :)
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Re: Early Mega PSU getting real hot

Postby Kriegor » Fri Apr 27, 2012 6:09 pm

1024MAK wrote:If there are no other problems or symptoms (like discolouration of the PCB near the hot items), I would suggest that the PSU is operating normally.

Mark


However some dark yellow/brown-ish residue on heatsink solders seems to be nothing to worry about, it's just flux residue from soldering as flux is used to make those high-temperature solder joints. At least this is what i've been told, please correct me if i'm wrong!


JonB: It would be interesting to get some photos on that PSU if it's possible! I am having some issues with a Mega PSU myself and it would be great to have a photo of a working one to compare with :) And also after soak testing it, i would suggest to disconnect it, wait for two days and then plug it in again and start it up. My PSU works fine when it has been plugged in for a while, and it can run for hours without any issues when it has. However after disconnecting the power cable and waiting for a couple of days, it initially doesn't start at all when connected and switched on it just seems completely dead, after a minute or so left switched on it does start right out of the blue but makes the ST act very strange, and after a couple of minutes of that it works fine and runs stable for hours. So make sure to test your new PSU for those kinds of errors too! :)

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Re: Early Mega PSU getting real hot

Postby JonB » Fri Apr 27, 2012 8:40 pm

Hi guys

Thanks for the good advice. :) Yes, soak test means leave it on under load for a while and see if it pops. It didn't, but the fan noise was getting on my nerves.. it needs a better quality fan that is properly balanced. This one vibrates too much.

Darklord: I bought it from a forum member - Chandler. I originally thought it was a Best Electonics one, because it looks so chunky, but I now reckon it came from Atarifreakz, as it is identical to the one on their site.

Kriegor: I'll take a load of pictures this weekend and upload if I get time. In the meantime, follow the link to the Atarifreakz online shop and look at the Mega PSU photo, it is one of those.

1024MAK: Power resistor. Yes that's it - except it is on the other side of the board right next to the output connector. Most odd. I recognise flux and know heat sinks get hot (and that they are often carrying high voltages, which is why I never handle it when it is plugged into the mains!), but my experience is with one other Mega PSU and a couple of ST PSUs, none of which get this hot; having said that, it is an entirely different design - and it looks new as Chandler described it, so I am not complaining here, just checking out a concern.

Actually it started smelling odd for a while, like burned electronics, but if it really is a new unit that is right because the components will be new and need burning in.
Too many retro computers here: 1040STfm, Mega4, Ultrasatanx2 , Amiga A500, A500+ and A1200, Acorn Atom x2, BBC Micro, Electron, Spectrum 48k x2, +48, +128k, QL, Oric Atmos, ZX81, Memotech MTX512, Amstrad 6128 x2..


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