Thinkpads Forum

A new Lenovo Desktop (ThinkCentre A50) exhibited some strange behaviour, and I am still having trouble explaining it to myself satisfactorily.

I set up this A50 in my working area at the client. CRT monitor video cable, sound cable to the output jack, ethernet cable, PS/2 keyboard cable, USB mouse, power cable. Set up the machine and it works.

I unplug all the cables, move it to the client working area, unplug the existing IBM Desktop (A30), plug in the new box. At that instant, I have used the PS/2 adapter on the Microsoft mouse and plugged it into the PS/2 mouse port.

The machine beeps irregularly three times or so and fails to start. I try several times. It is not going to run. Replace the existing IBM machine and it starts.

I cart the Lenovo box back to my working area, plug it all in, and it beeps again. Fails to start. Stare at it. Try again and it starts normally.

Same video cable, same Ethernet, same keyboard, USB vs PS/2 mouse, same sound cord, same power cord (*). It can't be the mouse, else the BIOS would come up and (possibly) complain. I did use two different power cables.

The power cable on the new box is a thick, heavy duty cable. Thicker, even, than some other IBM power cables. The power cable at the client area is a thinner monitor power cable (interchanged in a physical move by the client).

Now, I have posted lots in here about Ohm's law. Even number 18 wire will carry the current load of a 300 watt power supply for 3 feet.

Cart the machine back to the client work area. Plug it back in, but use the thick cable. Machine starts normally and runs well.

Can a heavy duty power cable (my guess is number 14 wire) make that kind of difference over 3 feet? I would have thought not.

In any answer, consider the following. GE (when I worked for them) made electric lawn mowers and supplied a 50 foot cable made with number 18 wire. That worked (although they cautioned not to bunch up the cable in a coil in one area because the heat in the cable could increase and melt the cable).
... JD Hurst

You could have a loose card, cable, or memory module. Try reseating everything inside.

I received a brand new PC that I had shipped to me. The video card came partway out of the AGP slot during shipment. When I plugged everything in, my monitor displayed "check cable". In a few minutes I found the problem.

Personally, I wouldn't think the PC would be that sensitive to input voltage to the point that a cable would make the difference. I assume when you say it failed to start, you meant you couldn't even go to the BIOS setup screen. Is anything showing up at all on the display when this happens?

GomJabbar wrote:You could have a loose card, cable, or memory module. Try reseating everything inside.

I received a brand new PC that I had shipped to me. The video card came partway out of the AGP slot during shipment. When I plugged everything in, my monitor displayed "check cable". In a few minutes I found the problem.

Personally, I wouldn't think the PC would be that sensitive to input voltage to the point that a cable would make the difference. I assume when you say it failed to start, you meant you couldn't even go to the BIOS setup screen. Is anything showing up at all on the display when this happens?

Reseating everything produced nothing because all was well-seated. Also, in my own area, the difference between no start and full start was just me staring at it (i.e., nothing).

And, yes, when I say it failed to start, I mean I could not go into the BIOS screen. Nada, nothing, except beeps. Strange, because I am back at the client this afternoon, and the machine in question is humming along just fine.

I agree with you, but that is the *only* thing I changed between numerous "no starts" and then perfect "full starts".

... JD Hurst

Perhaps the thicker power cable has ferrite beads or some other sort of ferromagnetic materials to control high-frequency noise riding on the AC power signal, or to control EMI/RFI. Maybe Lenovo used a cable like that since the switching power supply in that machine has some sort of issues with noise or reflections on the AC line... ?? Maybe without the "right" cable, the power supply becomes somewhat unstable??? Just a pure guess.

I don't think that the DC resistance of the conductors in the cord would make a difference, as you pointed out.

That is an interesting response. There may be something inside the cable.

In Coax cable, thicker cable provides higher speed. Signals travel at 80 percent the speed of light in RG-6 foam and at 67 percent the speed of light in RG-59 plastic. So from that point of view, thicker wouldn't seem to help. If something is inside (or if there is modest built-in resistance on the conductors (like scope probes)) then it could cause the issue.

I agree with you that pure DC resistance is not the issue. The cords are short enough that they could have small resistance to help absorb reflected impulses.

Thanks, ... JD Hurst