Smoke from MegaSTe PSU (PSM-5341) !

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Pacman
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Re: Smoke from MegaSTe PSU (PSM-5341) !

Post by Pacman »

Exactly! Makes perfect sense and just what I did, but it still won't work.
I even disassembled the "low noise" wire and tried the adapter cable, connecting it directly to the HDD power connector. Still nothing.

So I removed the heatshrink and braiding of the fan wire itself and look what I found:

Noctua_melted_fanwire.jpg
Noctua_melted_fanwire.jpg (184.62 KiB) Viewed 3198 times

It appears the 3 wires have been melted into each other during the heatshrinking process! I suppose I've just been lucky getting it to work when connected directly to the MSTE power supply fan connector because of being flexed at a specific angle.
So I'm going to cut the wires past the heatshrunk area and try to re-attach the metal connectors (I don't have any new ones unfortunately, so I'll see about soldering them instead of crimping), then see what happens....

PS: I just heard back from Noctua and they told me that the minimum voltage this fan (A6x25 FLX) can operate on is 4.4V. Good to know.
STe | MonSTer with dual IDE-CF memory card adapter | NEC Multisync 1990SXi | ST_ESSC | RSVE | Link '97 | Sony HD floppy drive/AJAX controller | Exxos HD floppy module | Battery-backed Ricoh realtime clock module | Discovery cartridge | C-Lab Unitor-2 | C-Lab Export | C-Lab Combiner | C-Lab Steady Eye | C-Lab Human Touch | Unicorn USB

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Steve
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Re: Smoke from MegaSTe PSU (PSM-5341) !

Post by Steve »

I highly recommend you do not run the PSU fan on low speed. Some of the mosfets in the PSU run extremely hot and will blow. Take this advice from the guy who made this mistake, PSU blew and sent 8v into the 5v on motherboard....
czietz
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Re: Smoke from MegaSTe PSU (PSM-5341) !

Post by czietz »

I'm very well aware that this thread is about a MegaSTE. But since the same PSU is used in the TT, too, and someone might come across this thread later, I want to add that in the TT good airflow (i.e., not throttling the fan) is beneficial to keep the -5 V regulator cool: https://www.exxosforum.co.uk/forum/viewt ... =10#p38511
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Pacman
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Re: Smoke from MegaSTe PSU (PSM-5341) !

Post by Pacman »

Thanks to both of you for the warnings.
So unlike the ST/F/M/E power supply, the TT/Mega STe power supply itself needs cooling?
I always thought it was mostly about a hot internal HDD (which a normal ST doesn't have) and the increased processor speed (also something a normal ST doesn't have) which would make the whole computer hotter.

Good news: after cutting the (melted) fan wire it now works great, also with the low noise adapter cable (147 Ohm resistance through the +12V wire)! I measured around 6.1V to the fan with that adapter cable and the computer is now whisper quiet. I can feel a slight airflow coming out of the fan.
The big question is if this is enough cooling or not?

Steve: you mentioned very hot MOSTFETs in the PSU overheating and blowing. Is this normal? A design shortcoming? Something that can be remedied by replacing the MOSFETs with ones that have better ratings? I certainly don't want to blow up the PSU and definitely not the motherboard with 8V instead of 5V, but I also value a silent running computer.
STe | MonSTer with dual IDE-CF memory card adapter | NEC Multisync 1990SXi | ST_ESSC | RSVE | Link '97 | Sony HD floppy drive/AJAX controller | Exxos HD floppy module | Battery-backed Ricoh realtime clock module | Discovery cartridge | C-Lab Unitor-2 | C-Lab Export | C-Lab Combiner | C-Lab Steady Eye | C-Lab Human Touch | Unicorn USB

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Re: Smoke from MegaSTe PSU (PSM-5341) !

Post by Steve »

@Pacman

No it is normal for them to run hot, these ones are around 81 degrees c. You absolutely need good airflow in this PSU.
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Pacman
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Re: Smoke from MegaSTe PSU (PSM-5341) !

Post by Pacman »

Do you mean full airflow without any lowering of the fan voltage at all, or would some lowering be OK (for instance to 9V instead of 12V as suggested earlier by Frank.Lukas)?
STe | MonSTer with dual IDE-CF memory card adapter | NEC Multisync 1990SXi | ST_ESSC | RSVE | Link '97 | Sony HD floppy drive/AJAX controller | Exxos HD floppy module | Battery-backed Ricoh realtime clock module | Discovery cartridge | C-Lab Unitor-2 | C-Lab Export | C-Lab Combiner | C-Lab Steady Eye | C-Lab Human Touch | Unicorn USB

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Re: Smoke from MegaSTe PSU (PSM-5341) !

Post by Steve »

I would grab a Noctua but run it at its full speed personally, that way you have a quieter fan but its airflow is still good.
edit: if you want a silent Mega STE you should look at going down the Pico route
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DoG
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Re: Smoke from MegaSTe PSU (PSM-5341) !

Post by DoG »

Noctua is famous for silent fans but it has not great airflow if you start comparing it with other fans of same size.
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Pacman
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Re: Smoke from MegaSTe PSU (PSM-5341) !

Post by Pacman »

I realized I had another "low noise adapter cable" (NA-RC10) that came with my Noctua A6x25 FLX fan, so I gave it a go.
The fan spun noticeably faster, but the noise level was still very acceptable. I measured the fan voltage and it was around 8.9V (so, similar to Frank.Lukas' suggestion earlier of lowering the fan voltage to 9V).
In summary I now have 3 choices:

1) direct fan connection to PSU fan connector (12.6V fan voltage measured, 3000 RPM/19.3 dB(A))
2) Noctua NA-RC10 low noise cable between fan and PSU fan connector (51 Ohms, 8.9V fan voltage measured, 2400 RPM/14.5 dB(A))
3) Noctua NA-RC12 ultra low noise cable between fan and PSU fan connector (147 Ohms, 6.1V fan voltage measured, 1600 RPM/8.2 dB(A))

Steve: I don't know how you blew the PSU by overheating it; if you lowered the fan speed (and by how much) or if you left the fan unconnected, and I'm certainly no engineer, but I would think Atari over-designed the PSU if even by a little bit to accomodate for extra heat from the HDD and CPU, so if you remove that (and the fact that a disconnected HDD also means less drawing of power), wouldn't that leave some room for lowering the fan speed? By the way, does anyone know which fan was originally factory-installed in the MSTE and its specs? Would be interesting to compare it with the abovementioned Noctua replacement.
STe | MonSTer with dual IDE-CF memory card adapter | NEC Multisync 1990SXi | ST_ESSC | RSVE | Link '97 | Sony HD floppy drive/AJAX controller | Exxos HD floppy module | Battery-backed Ricoh realtime clock module | Discovery cartridge | C-Lab Unitor-2 | C-Lab Export | C-Lab Combiner | C-Lab Steady Eye | C-Lab Human Touch | Unicorn USB

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Re: Smoke from MegaSTe PSU (PSM-5341) !

Post by Steve »

Pacman wrote: Sat May 08, 2021 10:46 am Steve: I don't know how you blew the PSU by overheating it; if you lowered the fan speed (and by how much) or if you left the fan unconnected, and I'm certainly no engineer, but I would think Atari over-designed the PSU if even by a little bit to accomodate for extra heat from the HDD and CPU, so if you remove that (and the fact that a disconnected HDD also means less drawing of power), wouldn't that leave some room for lowering the fan speed? By the way, does anyone know which fan was originally factory-installed in the MSTE and its specs? Would be interesting to compare it with the abovementioned Noctua replacement.
It doesn't matter whether you have load or no load, those voltage regulators will get up to max temp even without load. I think the 2400rpm you mentioned should be ok. Atari didn't over or under engineer the PSU, they didn't make it. Mine blew when I was using the 'silent' noctua cable. I'm just trying to give you good advice, up to you if you want it :)
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