KVM power supply.

Is definitely my week for computer related problems. Latest one is the KVM switch.

It's an Aten DVI/PS2 unit which cost quite a bit and looks well made - it's in a steel case.

Symptoms are it no longer works with only one computer switched on. Boot the second one and things do eventually all work. But the impression is it will eventually fail.

So on the principle it is usually a power supply fault I removed it and measured its incoming voltage under load on the bench - it uses a wall wart to provide the DC.

Measured at just over 4v.

Wall wart says 5.3v and 2.4 amps, and by the weight/size is an SMPS.

Using my bench top 5v 3 amp supply it works normally.

A new wall wart from Aten is 35 quid plus. ;-)

Anyone know where I can buy a suitable one at a sensible price? It doesn't have to be a wall wart.

Or I suppose I could just make a linear one?

Reply to
Dave Plowman (News)
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I have one, CS-1764, still OK after 9 years.

wall wart for mine says 4.0-5.5V 2.6-2.3A

I'd think any 5V 3A supply, would do e.g.

check the barrel dimension, or failing that a 3A USB charger with the uUSB plug cut off and solder on the barrel from your old wall-wart?

Reply to
Andy Burns

En el artículo , Dave Plowman (News) escribió:

It'll be the output cap. Crack it open (it'll almost certainly be welded shut. You can crack the seams carefully by squeezing them in a vice) and replace the cap. Use a good quality 105 degC replacement. Reassemble case with superglue.

Total cost about 50p.

The caps fail due to heat build-up in the case and no ventilation.

Reply to
Mike Tomlinson

Needs to be low ESR type for switched mode PSU output smoothing.

OTOH, if you just want a new one, does your bench supply say how much current it really draws? CPC have a good selection of switched mode wall wart PSUs, although 3A is going a bit higher than the cheaper ones will be rated for, hence wondering if the KVM really draws that much (15W).

Reply to
Andrew Gabriel

The KVM also acts as a powered USB hub for sharing peripherals to the connected PCs, so max consumption could be higher if using it like that, that just for switching keyboard, video and audio.

Reply to
Andy Burns

It was to be plan B if I couldn't find a reasonably priced replacement.

So I've done just that but had to cut it open.

It's actually a home made fixed 5v 3 amp supply - with no metering. But I can check later what the current draw is. Although might there be a difference between peak and average?

Having opened up the case and found the usual bulging cap, I might just put the guts back in a bigger case with some ventilation after repair - it doesn't have to be a wall wart here.

Reply to
Dave Plowman (News)

It's a PS2 type - not USB. As one of the computers is an old Acorn. No USB.

Reply to
Dave Plowman (News)

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just drill a bunch of 2-3mm holes in it

NT

Reply to
meow2222

How about a tenner from Rapid? Or probably cheaper still on eBay - though you might have to change the connector to match polarity and diameter of the KVM socket. My latest KVM is USB powered by the PCs that it serves and as such requires no extra mains.

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One feeble old PC isn't very keen on driving it on its own.

Not worth the effort a linear one tends to run a bit too warm for continuous use and life is too short to DIY wall warts. Mending them is possible if you can get into them and safely reseal again afterwards.

Dessicated high ripple smoothing capacitor would be my guess.

Reply to
Martin Brown

Quite a few of the PS/2 ones are too.

Reply to
Andy Burns

That really does tend to be a bit hit and miss with some PCs unable to source enough current to make the KVM behave itself. Bit pot luck...

Reply to
Martin Brown

All of my Aten units are powered by their PCs.

Or get an empty wall wart case...I have done that a couple of times.

Reply to
Bob Eager

Actually over 16 quid delivered - plus a mains lead.

I'd guess that this is a DVI KVM makes the difference - digits tend to take more current. And of course it's PS2 - dunno how much spare current they can supply.

I'd only make a linear one if I had all the bits lying around - which I do. Obviously with a suitable heatsink on the reg.

Good guess - it is just that.

Reply to
Dave Plowman (News)

The replacement arrived this morning and it's now working OK. In a much larger box with some ventilation. The on load voltage is 5.4v - but it worked OK with the temporary 5v one. Wonder why it's such an odd value?

Reply to
Dave Plowman (News)

En el artículo , Dave Plowman (News) escribió:

It's faulty, there isn't enough load on it to regulate properly, or it's an unregulated one.

The power probably goes direct to the ICs inside the KVM (in other words, there's no supplementary power supply on the KVM board.)

It should be 5v +/- 5%, so 4.75 min to 5.25v max.

I wouldn't be comfortable using it on equipment specified for 5.0v.

Reply to
Mike Tomlinson

But it says 5.4v on the original PS case. ;-)

When faulty it read just over 4v under load. Must admit I didn't measure the bench PS.

Reply to
Dave Plowman (News)

Not all logic is 5V +/- 5%. CMOS worked over a wide range and could even be biased to work as amps, etc. A usb device should be protected against odd voltages. TTL was +/- 10% AIRI.

Reply to
dennis

This last is true, +/- 10% was the standard operating tolerance for TTL. The +/- 5% for PSU rails was the means used to guarantee compatability between power rail voltages and TTL chip requirements in the face of inevitable volt drops between supply and devices (cable and circuit trace volt drops).

As you mentioned, standard cmos had a much wider operating voltage tolerance (3 to 15 volt, afaicr) depending on how fast you wished to operate the silicon. The cmos versions of the TTL family otoh, were specced for the same tighter 5v +/- 10% of standard TTL (mainly to meet speed specifications and retain compatability with existing TTL devices).

Reply to
Johny B Good

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