ATX power supply.

Sadly, it's there.

Reply to
Dave Plowman (News)
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Well yes, but this is a brand new one. CPC's finest. ;-)

I've ordered up a PCI network card from Ebay. Cheap enough not to worry if it's something else.

Reply to
Dave Plowman (News)

Any time I read something like that I'm reminded of the young guy who was 'instructing' a still newer guy in the art of fault finding, scoping signals in just-arrived equipment which had 'Busy' and 'Done' indicator lights. Both were lit, a frequent result of power problems, so I looked inside.

Turned out that an internal cable was visibly not plugged in.

He probably never forgave me for pointing this out!

Reply to
Windmill

ATX MoBos don't specify a -5v requirement. The original PC and AT PSUs all provided a -12 and -5 volt rail but the -5v was only typically used as a very low current biasing voltage source (micro-amperes). The -12v otoh was often used to supply dozens of milliamps, typically to power the RS232 line driver/receiver chips.

I guess that by the time the ATX spec was written, they realised how totally redundant a -5v bias rail had become when there was a handy -12v supply (usually with a half an amp rating) which could be used to provide any other negative bias voltages via a suitable analogue regulator incorporated into the adapter or on-board device to supply the micro- ampere or so bias voltage required. Basically, they simply dropped the

-5v out of the spec. The -5v pin still exists in the connector but simply as an unused pin.

Reply to
Johnny B Good

Would the network driver use -5v? If so, I could have a look for a reg presumably close to it and check the voltages round it. They tend to be big enough for me to change, unlike most SM components. ;-)

Reply to
Dave Plowman (News)

Actually, my remarks regarding the *original* ATX specification dropping the -5v rail weren't entirely true. I've just been looking at a customer's PC brought to me to sort out a startup problem which turns out to be the classic "Bestec Fry-up" fault (even though the PSU isn't a Bestec Branded model - it's a "RaidMax" model: KY-550ATX if anyone wants a 'Heads Up' to check that their 13 year 'Old Faithful' PC isn't in imminent danger of getting its MoBo fried). It turns out that this, and indeed a working spare, both sport the -5v (white wire) connection.

The faulty unit is actually equipped with a 20/24 way MoBo connector which makes the presence of the -5v rail all the more surprising. My similar vintage spare only has a 20 way connector but the existence of the -5v pin was still a surprise finding.

I think the dropping of the -5v was more related to the later ATX MoBo spec than to the PSUs (and by 'later', I mean a decade or so back when the manufacturers had long since unconscionably dropped 16 bit ISA slot support).

As for the possibility of a duff on-board 50 or 100mA rated -5v regulator chip, that's certainly worth checking out (although it's still likely to be an SMD chip - small but not *that* small compared to an SMD transistor, cap or resistor).

I couldn't say whether or not the PHY chip needs a -5v supply. These days, any -ve bias voltages are more likely to be generated on chip from the +5 or +3.3 volt rails rather than using a -5v regulator driven off of the -12v rail. However, "Nothing Ventured, Nothing Gained" so it might be worth spending 5 or 10 minutes (carefully) probing around any -5v smd analogue regulator chips you might be able to identify near to the PHY chip.

TBH though, I think your chances are pretty slim but it's always worth a quick look see to verify you're not missing an opportunity for a quick fix.

Reply to
Johnny B Good

Computer fixed. Replaced the power supply and got a PCI network card for pennies.

This isn't the first Azuz mobo I've had problems with. Is there a best make you can buy for home assembling a desktop?

Reply to
Dave Plowman (News)

Have looked at the original PS again -I've replaced it so not urgent.

And nowhere I can find sells 680uF 200v caps that are anything like the same physical size of the originals. All much larger in diameter and would be difficult to fit.

However, it was an OC Schottky diode. Replaced that and the PS now at least starts up. Not tried it in a PC, though.

Reply to
Dave Plowman (News)

formatting link

Reply to
alan_m

Only once per PSU thread, please :-P

Reply to
Andy Burns

Would you really expect a maker to fit those - and for it to have worked ok for several years?

Oh - they are 200v caps. Not 35v, which are much more common.

Reply to
Dave Plowman (News)

I've never heard of Azuz as a MoBo maker before. Do you mean Asus?

I've been using Asrock MoBos for the past decade or so ever since my "Trade Supplier" unconscionably dropped the Jetway Brand in favour of Asus, Asrock, Gigabyte and one or two others I can no longer recall.

Jetway were, imho, the best kept 'trade secret' in the world of MoBo manufacturers so it was with some reluctance that I started using Asrock MoBos just over a decade back. The choice was initially based on specifications and price (best bang for your buck - on paper at least).

Experience has proved that the 'on paper at least' "best bang for your buck" was also true in practice. I've never been impressed by the likes of Gigabyte and other "Well Regarded" makes and have been most

*unimpressed* by Foxconn (foxes who con money out of the likes of HP?), a manufacturer whose product I won't touch with a bargepole having had to try and repair HP branded PCs in the past using such unstable s**te.

My desktop PC's current build is based on an Asrock MoBo, as was the previous build. The NAS4Free box is also using a 5 or 6 year old micro ATX Asrock board (starting with a single core Semperon but now sporting a dual core Athlon 64). AFAIAC, they've not given me any problems over the past 5 years or so that I've been using them for.

You can check out the wiki on Asrock here if you want more info:

HTH & HAND

Reply to
Johnny B Good

Both the Asus (sorry) mobos I've had trouble with were more than 5 years old.

Perhaps I expect too much having a couple of Acorn machines still going strong at about 20 years old. ;-)

Reply to
Dave Plowman (News)

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