I would definitely try a different power supply first of all.

It may be possible there's a dry solder joint on a power rail is getting warm and expanding to the point where it breaks contact. You could try doing an inspection of the board and seeing if you can spot any such joints.

I doubt it's your case, but I had an Athlon XP system behaving similarly when the CR2032 battery died and lost its settings. The root cause was the automatic CPU/RAM speed configuration which didn't work right. After setting the speeds manually again it worked again. It was on an early jumperless motherboard.

But as others suggested, try another PSU and maybe try with only 1 stick of RAM to minimise variables. You could also lower your CPU clock speed to see if it becomes more stable all of a sudden.

Disconnect all the front panel switches, leds & speaker and try it once by shorting the power switch pins, just to rule this possibility out.

Thank you all for your help and replies. So today I finally had the time to check it out and here's what happened:

I picked my spare PSU from the leftovers, and ironically it's the exact same model as the PSU in the case - Primer LC-B300-ATX. I opened them both, the PSU in the case has some bulged caps about to start leaking in the future, and the extra PSU had all caps looking fine. So I tried the extra one, remaining suspicious, but it's all I had.

Installed it, powered up the PC with the case open, heard a mild pop and saw some faint and non-smelly magic smoke. Turned everything off and checked it out. The smoke really seemed to come from the right, the front panel side (drives). Removed from the case and opened up each drive, a Panasonic floppy drive, an Asus CD reader and a HP writer. Didn't see any signs of something blown up and none of them smelled. Opened up the extra PSU that I just tested and didn't see or smell anything either, not even the smallest resistors/diodes had any signs. At last checked out the motherboard, which was immaculate.

Proceeded my kamikaze testing style one more time without any drives, only the Mobo, CPU (which has a Gelid fan controller connected) and RAM. Post beep, all normal. Connected the floppy drive just for kicks. No power and obviously no floppy seek. Funny enough, removed it and tried the bare configuration again and the CPU fan didn't spin on startup. Removed the fan controller, same thing. After a try or two, it started normally, post beep again, etc. Reconnected the fan controller, all normal again. So I decided to stop and cut my losses. My beginner's money is on the PSU.

Really wish the pop came from the floppy drive as it's the easiest replacement for me. Do you guys have any idea what could have been?

Just to recap, clarify and help guide future readers of the thread with similar problems: this PC has had the same hardware for years, with no issues. It was up until yesterday that I started having the problems described in the OP, so until further proof I'm inclined to think it's just both PSUs causing me various issues.

The motherboard always powers up and post beeps apart from that weird transition after reconnecting the floppy drive, so I'll be optimistic for now and assume it's fine. I didn't connect the HDD at any moment as I really don't want to risk it, it's a heavily configured build and it really would be a massive pain to reinstall everything...

Being pointless to proceed without a new trustworthy PSU, I'll just leave the PC with the bare minimum, install it when I get one, and go from there, drive by drive, with a new floppy one. My doubt is, what modern PSUs do you recommend for old PCs? I imagine they have molex connectors but how do you connect the floppy drives to those modern PSUs?

As always thank you for all your help and replies

Old psus are death.

kolderman wrote on 2023-06-04, 20:52:

Old psus are death.

What modern PSUs would you recommend for an ATX Pentium III build? How do you connect these modern PSUs to floppy drives, if you do at all?

Replied in another thread but I'll leave it here for completion purposes:

i have some local options to choose from, a Corsair VS 350, a VS 550, a CX 430 and a CV 450. The prices are very similar, so what would be the better option?

Also, as a beginner I have to ask: how would I connect a floppy drive to these PSUs? Will a simple molex to floppy power adapter do the trick?

andre_6 wrote on 2023-06-04, 21:22:

kolderman wrote on 2023-06-04, 20:52:

Old psus are death.

What modern PSUs would you recommend for an ATX Pentium III build? How do you connect these modern PSUs to floppy drives, if you do at all?

Pretty much anything you want - the only exception is running SocketA systems that lack a 4-pin AUX connector (which almost all do) - modern PSUs don't power the 5V rail enough.

As for floppies etc, there are ample adapters from Molex connectors to pretty much any other connector you can dream of, just search fleaBay.

kolderman wrote on 2023-06-04, 22:07:

andre_6 wrote on 2023-06-04, 21:22:

kolderman wrote on 2023-06-04, 20:52:

Old psus are death.

What modern PSUs would you recommend for an ATX Pentium III build? How do you connect these modern PSUs to floppy drives, if you do at all?

Pretty much anything you want - the only exception is running SocketA systems that lack a 4-pin AUX connector (which almost all do) - modern PSUs don't power the 5V rail enough.

As for floppies etc, there are ample adapters from Molex connectors to pretty much any other connector you can dream of, just search fleaBay.

Thank you fore your help, I didn't know most of those PSUs still have a floppy connector. I just hope they have enough Molex ones to connect the HDD and both CD drives

andre_6 wrote on 2023-06-04, 22:22:

kolderman wrote on 2023-06-04, 22:07:

andre_6 wrote on 2023-06-04, 21:22:

What modern PSUs would you recommend for an ATX Pentium III build? How do you connect these modern PSUs to floppy drives, if you do at all?

Pretty much anything you want - the only exception is running SocketA systems that lack a 4-pin AUX connector (which almost all do) - modern PSUs don't power the 5V rail enough.

As for floppies etc, there are ample adapters from Molex connectors to pretty much any other connector you can dream of, just search fleaBay.

Thank you fore your help, I didn't know most of those PSUs still have a floppy connector. I just hope they have enough Molex ones to connect the HDD and both CD drives

They don't, hence the need for adapters. But you can also get splitters, just split a MOLEX into 4 other MOLEX connectors and then use them to power whatever you want. For example, I do something similar to power a GOTEK floppy emulator, a SD/IDE adapter, and some small fans, all of a single MOLEX. It's way easier than you seem to be thinking. And if MOLEX disappears from PSU guess what...you can get SATA-MOLEX power adapters too. All the voltages are still there (except for -5V).

kolderman wrote on 2023-06-04, 22:25:

andre_6 wrote on 2023-06-04, 22:22:

kolderman wrote on 2023-06-04, 22:07:

Pretty much anything you want - the only exception is running SocketA systems that lack a 4-pin AUX connector (which almost all do) - modern PSUs don't power the 5V rail enough.

As for floppies etc, there are ample adapters from Molex connectors to pretty much any other connector you can dream of, just search fleaBay.

Thank you fore your help, I didn't know most of those PSUs still have a floppy connector. I just hope they have enough Molex ones to connect the HDD and both CD drives

They don't, hence the need for adapters. But you can also get splitters, just split a MOLEX into 4 other MOLEX connectors and then use them to power whatever you want. For example, I do something similar to power a GOTEK floppy emulator, a SD/IDE adapter, and some small fans, all of a single MOLEX. It's way easier than you seem to be thinking. And if MOLEX disappears from PSU guess what...you can get SATA-MOLEX power adapters too. All the voltages are still there (except for -5V).

Exactly the info I needed, thank you. Would have done it long ago if I knew it was that simple!

andre_6 wrote on 2023-06-04, 20:41:

Primer LC-B300-ATX.

I'm pretty sure you meant Premier LC-300-ATX and I'm also pretty sure I once had one of these. This PSU is one of the poorest quality PSUs available back then and it is a gutless wonder.
The vast majority of 300W PSUs from that era will be of better quality and will have better protection that may help prevent damage to your hardware if it fails.

Having said that, all of these supplies are now old and will usually be in need of some maintenance, which has its own issues (I wouldn't recommend attempting to repair or service an old PSU unless you know what you are doing).

Usually a brand new PSU is the easiest way out and on top of that it will definitely provide better protection than that Premier PSU. That PSU was never a good one.

Tetrium wrote on 2023-06-05, 07:39:

I'm pretty sure you meant Premier LC-300-ATX and I'm also pretty sure I once had one of these. This PSU is one of the poorest qu […]
Show full quote

andre_6 wrote on 2023-06-04, 20:41:

Primer LC-B300-ATX.

I'm pretty sure you meant Premier LC-300-ATX and I'm also pretty sure I once had one of these. This PSU is one of the poorest quality PSUs available back then and it is a gutless wonder.
The vast majority of 300W PSUs from that era will be of better quality and will have better protection that may help prevent damage to your hardware if it fails.

Having said that, all of these supplies are now old and will usually be in need of some maintenance, which has its own issues (I wouldn't recommend attempting to repair or service an old PSU unless you know what you are doing).

Usually a brand new PSU is the easiest way out and on top of that it will definitely provide better protection than that Premier PSU. That PSU was never a good one.

Hi Tetrium, thanks for the input, I guess I learned it the hard way. I'm fairly confident that it was the floppy drive that gave the pop and magic smoke, but to be fair I didn't find any signs of that in any of the floppy or CD drives, mobo or even the killer PSU. It was a very faint and non smelly type of smoke that seemed to come from the drives and front panel side of the case. I guess I'll start by getting the new PSU first and go from there, trying it out with the basic config then adding the drives one by one. I won't even try the HDD until I'm totally sure it's all fine by then. But the board always powered up and beep posted even after the pop and magic smoke, so I'll be optimistic.

And I guess I'll just replace the remaining ATX PSUs in my builds one by one as time goes by and be done with it. At least I think that was the last of the Premier PSUs 🤣!

Finally installed the new PSU and checked everything. For completeness' sake and for future users searching for solutions to a similar problem:

1. The original PSU suddenly shut down by itself mid-use, blinking one light in the front panel constantly, as if it was in standby mode. From that point on it only managed to stay on between 30 secs - 1 min after each boot.

2. Replaced it with the same exact model (and only extra one) that I had stored away - the now infamous Premier LC-300-ATX - they were the same model but looking inside they were clearly different revisions. Inside the original there were some caps about to start leaking. The replacement one looked fine, so I plugged it in for a test.

3. Started the PC with the case open and magic smoke ensued, however it still beep posted. The smoke clearly came from the side of the drives/front panel however it was very faint and non-smelly, I couldn't find any trace of anything blown up inside any of the drives . Fortunately I hadn't plugged in the HDD just in case.

4. With a new PSU I checked drive by drive and the floppy drive was dead, but both CD drives worked. Testing them I noticed that now they didn't work when plugged in together in the same IDE cable as before, no matter the cable order/positions. The jumpers remained like before so the problem's elsewhere. Checked with multiple IDE cables, same behavior. With both plugged in, the BIOS recognized the HP drive although misspelling its name, and the Asus one was never recognized at all. I even got a "bad slave drive check/fail" on boot or something like that, referring to the HP. If I plugged them one at a time they recognized correctly and worked absolutely fine. I only ever use the Asus one so I left the molex connector on the HP just to hear it start while turning on the PC as I'm used to the sound, and disconnected its IDE. Clearly something's not right here but I'm all out of solutions, plus it really could be worse. I'm sure the PSU caused this quirk in some way to one of the drives or maybe both, but I have no clue.

5. Plugged everything else and now it's fine, with a new floppy drive of course. The case is significantly heavier now which is a testament to the new PSU's components when compared to the Premier's killer PSU.

In conclusion, the Premier LC-300-ATX killed one floppy drive and caused a slight quirk with the IDE secondary connections. As a beginner my lack of knowledge made in my head installing a new modern ATX PSU much more complicated than it is. I didn't even know modern PSUs came with floppy connectors, let alone 2 or more molex connectors, plus the adapters that you can add with no problem!

So to anyone who still has old ATX PSUs from the Premier brand, or even just old ATX PSUs in general, I highly recommend you remove them and get some modern ones asap. I was very lucky in the sense that it only caused me slight issues, but I'm definitely not willing to risk it again.

Thank you as always to everyone for all the help and replies, always learning thanks to all of you!

andre_6 wrote on 2023-06-15, 20:58:

Finally installed the new PSU and checked everything. For completeness' sake and for future users searching for solutions to a s […]
Show full quote

Finally installed the new PSU and checked everything. For completeness' sake and for future users searching for solutions to a similar problem:

1. The original PSU suddenly shut down by itself mid-use, blinking one light in the front panel constantly, as if it was in standby mode. From that point on it only managed to stay on between 30 secs - 1 min after each boot.

2. Replaced it with the same exact model (and only extra one) that I had stored away - the now infamous Premier LC-300-ATX - they were the same model but looking inside they were clearly different revisions. Inside the original there were some caps about to start leaking. The replacement one looked fine, so I plugged it in for a test.

3. Started the PC with the case open and magic smoke ensued, however it still beep posted. The smoke clearly came from the side of the drives/front panel however it was very faint and non-smelly, I couldn't find any trace of anything blown up inside any of the drives . Fortunately I hadn't plugged in the HDD just in case.

4. With a new PSU I checked drive by drive and the floppy drive was dead, but both CD drives worked. Testing them I noticed that now they didn't work when plugged in together in the same IDE cable as before, no matter the cable order/positions. The jumpers remained like before so the problem's elsewhere. Checked with multiple IDE cables, same behavior. With both plugged in, the BIOS recognized the HP drive although misspelling its name, and the Asus one was never recognized at all. I even got a "bad slave drive check/fail" on boot or something like that, referring to the HP. If I plugged them one at a time they recognized correctly and worked absolutely fine. I only ever use the Asus one so I left the molex connector on the HP just to hear it start while turning on the PC as I'm used to the sound, and disconnected its IDE. Clearly something's not right here but I'm all out of solutions, plus it really could be worse. I'm sure the PSU caused this quirk in some way to one of the drives or maybe both, but I have no clue.

5. Plugged everything else and now it's fine, with a new floppy drive of course. The case is significantly heavier now which is a testament to the new PSU's components when compared to the Premier's killer PSU.

In conclusion, the Premier LC-300-ATX killed one floppy drive and caused a slight quirk with the IDE secondary connections. As a beginner my lack of knowledge made in my head installing a new modern ATX PSU much more complicated than it is. I didn't even know modern PSUs came with floppy connectors, let alone 2 or more molex connectors, plus the adapters that you can add with no problem!

So to anyone who still has old ATX PSUs from the Premier brand, or even just old ATX PSUs in general, I highly recommend you remove them and get some modern ones asap. I was very lucky in the sense that it only caused me slight issues, but I'm definitely not willing to risk it again.

Thank you as always to everyone for all the help and replies, always learning thanks to all of you!

I've recently build a new PC for a friend and was genuinely surprised to see its brand new PSU still had floppy power and molex connectors.

It's good to hear it cost you 'only' a floppy drive. It could have costed you much more. It's much lighter because of all the missing stuff inside, hence gutless wonder 😋

Concerning your lack of knowledge, I've been in those shoes. Back when I just started, I had basically no idea what I was doing. I was taking apart computers I found dumped on the streets or stuff I was gifted somehow and I can give you one tip: Google everything. See something printed on your card? Google it.
Just google everything that might seem even remotely interesting to you.

People's past experiences can be quite valuable, though should not be taken as an absolute truth but instead it will often point you to the right direction.

And this is really a good tip for anyone out there who lacks the experience, google everything and read a lot. Read forums, old manuals, yes also wikis, old reviews maybe, perhaps someone posted something on youtube about it, you can learn a lot doing this especially if you're new to the hobby.

Had this PSU, worst I ever saw. I've never had courage to run it. Opened it, it was really bad. Everything cheap, lots of stuff missing. It was also lightest power supply out of all I had and passed through me (about 30 pieces).

You dont have to dump every old PSU. I have old Nexus from 2003, heavy as hell (1990grams), running good. (its Nexus NX3500) I've stuck with old OEM Fortrons. Have like 7 of them, all are heavy, good inside, and running for 2 years in retro PC without any problem. You need to opened PSU before use, it cannot have capacitors in bad shape, and PCB needs to be in good shape. It has to be at least middle quality PSU (Antec, Fortron FSP Group). It needs to weight over 1300-1400 grams, at least minimum. (better be in 1500-1900 gram range).

I provide picture of that Premier. It's in original LC form. (Premiere will be rebranded L&C I think). Most crappy PSU I saw. (weights 920grams! What a joke) The other ones are lowend too, but
even that Mercury was slightly better (still bad, dont even try to run PC with it). The only one, that is at least decent on lowend spectrum is that Frontier Power. Working good for hours and hours (I was using him for testing the motherboards at beginning when I didnt have more power supplies).

I wonder if with "L&C" they tried to trick people into thinking it's an LC-Power brand, which is rather ok.

W.x. wrote on 2023-06-19, 08:33:

Had this PSU, worst I ever saw. I've never had courage to run it. Opened it, it was really bad. Everything cheap, lots of stuff […]
Show full quote

Had this PSU, worst I ever saw. I've never had courage to run it. Opened it, it was really bad. Everything cheap, lots of stuff missing. It was also lightest power supply out of all I had and passed through me (about 30 pieces).

You dont have to dump every old PSU. I have old Nexus from 2003, heavy as hell (1990grams), running good. (its Nexus NX3500) I've stuck with old OEM Fortrons. Have like 7 of them, all are heavy, good inside, and running for 2 years in retro PC without any problem. You need to opened PSU before use, it cannot have capacitors in bad shape, and PCB needs to be in good shape. It has to be at least middle quality PSU (Antec, Fortron FSP Group). It needs to weight over 1300-1400 grams, at least minimum. (better be in 1500-1900 gram range).

I provide picture of that Premier. It's in original LC form. (Premiere will be rebranded L&C I think). Most crappy PSU I saw. (weights 920grams! What a joke) The other ones are lowend too, but
even that Mercury was slightly better (still bad, dont even try to run PC with it). The only one, that is at least decent on lowend spectrum is that Frontier Power. Working good for hours and hours (I was using him for testing the motherboards at beginning when I didnt have more power supplies).

Agreed. I've run a lot of my old rigs using FSP PSUs as that's what was quite common and relatively cheap (FSP as a brand didn't have the same reputation that Antec/Zalman/etc brands had) and of pretty good build quality (particularly any FSP PSU that had heavy 5v lines was usually a good one, later ones I find are perhaps a bit more debatable though still not trash).
I at first used the '300W' Premier PSU for my Celeron 400 build, but I got all kinds of instability when I tried to network it (I already knew this PSU was of dodgy make but I had very few PSUs at the time. My Celeron 400 was basically my first completed build ever). This was fixed when I upgraded it with a ±250W FSP PSU.

Any particular thing you watch out for concerning the PSU PCB?