Scanner will not switch on

[Lucky Luke]

Hello, I hope that this thread is the correct one, as it is rather difficult to classify my problem.

I have a Umax Astra 6450 scanner. Although it is quite old, I suppose, it is not frequently used. Over the last month or so, although the scanner itself worked with no trouble, the line-switch between the mains socket and the power-jack for the scanner would not switch off — to get the scanner to shut down, I had to pull out the power-jack.

Then, for a short period, the switch started to work again. Then it failed again. So, I bought a new switch, and today I installed it. However, now, the switch does not start the scanner's ON light, at all (whereas the old switch did not switch the scanner off).

I have put a new fuse in the plug that goes into the mains. I have tested the relevant socket by plugging a fan into it, and the fan works. I have plugged the scanner mains plug into another socket that works with other appliances, and it still does not switch on. With a neon screwdriver, I have touched every terminal in the new switch with its cover off. The neon does not light up.

Of course, it may be that the scanner is finished, but if so, why does the neon screwdriver not light up?

This is a total bafflement to me. Can anyone offer any useful advice? The photo shows the type of power-jack that plugs into the back of the scanner (if that is of any use, which I doubt). The diameter of the jack-plug is about 6mm.
In hopes of some help,
L.L.

 

[SFK]

Okay - so you have a computer scanner.
This has a mains plug, that goes to a black box (or incorporates a black box) that converts the voltage from 240V AC to some lower voltage. This outputted lower voltage is in a smaller wire, and you have put this lower voltage wire into an inline 'lamp' switch. The lower voltage wire then comes out of the inline switch and into a barrel plug (power jack) that goes into the computer scanner.


Can you show us a picture of the inside of the switch with the wires you have connected to it?

Can you tell us if there are any markings on the wire? (A white line shows polarity and I am worried you have crossed them over).

(Otherwise, as a test remove the switch. And rejoin the wires without a stitch. twist the wires that have no line down them together, and twist the wires with a line down them together and see if the scanner works.)

SFK

 

[JohnD]

It would be very interesting to see inside that switch you recently added.

I have a feeling the two wires have been crossed over.

 

[Lucky Luke]

Okay - so you have a computer scanner.
This has a mains plug, that goes to a black box (or incorporates a black box) that converts the voltage from 240V AC to some lower voltage. This outputted lower voltage is in a smaller wire, and you have put this lower voltage wire into an inline 'lamp' switch. The lower voltage wire then comes out of the inline switch and into a barrel plug (power jack) that goes into the computer scanner.


Can you show us a picture of the inside of the switch with the wires you have connected to it?

Can you tell us if there are any markings on the wire? (A white line shows polarity and I am worried you have crossed them over).

(Otherwise, as a test remove the switch. And rejoin the wires without a stitch. twist the wires that have no line down them together, and twist the wires with a line down them together and see if the scanner works.)



SFK

It would be very interesting to see inside that switch you recently added.

I have a feeling the two wires have been crossed over.

It would be very interesting to see inside that switch you recently added.

I have a feeling the two wires have been crossed over.


John D.

Thanks for the observations, folks. The matter of polarity did cross my mind when I put the new switch in, but I thought that it would not matter. I shall certainly try what you have suggested, but I am receiving a visitor today, and will not be able to come into my "den" again, for a couple of days. He is due shortly, so I need to log out and prepare for his arrival. I shall post a photo of the inside of the switch, but I clearly remember that no polarities are shown anywhere.
Your feedback is much appreciated. Thanks!

As a postscript, I have to tell you that my guest-to-be has been delayed and will not arrive until tomorrow. As soon as I knew this, I twisted the wires as you advised, and the switch worked. I was under the impression that polarity did not matter in a case like this. I must have been lucky with the wires when fitting the first switch, as the trouble did not occur. with that one. (However, it also gave me my false impression about polarity.) Once again friends, thanks indeed for your comments.
With kind regards,
L.L.

 

[BS3036]

Let's hope the scanner had power input protection!

 

[Lucky Luke]

Let's hope the scanner had power input protection!

It seems to be OK (I switched it on and off, twice). Re power input protection, you've lost me there — which is very easy to do. Could you add something to make this oaf more cautious in future?
L.L.

 

[SFK]

Power Input Projection...
Your low voltage wire has say 0Volts on one wire and say 12Volts on the other wire.

Your scanner is expecting 12Volts and 0Volts at the correct points in its circuit board.

And on your barrel plug that might be 12V on the inside conductor of the barrel and 0V on the outside conductor of the barrel.

If you swap over the voltage so the 0V gets 12V and the 12V gets 0V then some items on the circuit board will instantly fail and never work again.

Some circuit boards are made to protect against this from happening (with electronic devices called diodes) by stopping the reversed voltage at the very start of the circuit. Some circuit boards do not and they will be broken by a reversed voltage.

You were lucky, Luke, that your scanner was design well.

Have a look at to the black box, on the scanner. It may have an image of a circle and dot with voltages next to them. That shows you the expected polarity of the barrel plug (ie which surface is 12V and which is 0V).

SFK

 

[Lucky Luke]

Power Input Projection...
Your low voltage wire has say 0Volts on one wire and say 12Volts on the other wire.

Your scanner is expecting 12Volts and 0Volts at the correct points in its circuit board.

And on your barrel plug that might be 12V on the inside conductor of the barrel and 0V on the outside conductor of the barrel.

If you swap over the voltage so the 0V gets 12V and the 12V gets 0V then some items on the circuit board will instantly fail and never work again.

Some circuit boards are made to protect against this from happening (with electronic devices called diodes) by stopping the reversed voltage at the very start of the circuit. Some circuit boards do not and they will be broken by a reversed voltage.

You were lucky, Luke, that your scanner was design well.

Have a look at to the black box, on the scanner. It may have an image of a circle and dot with voltages next to them. That shows you the expected polarity of the barrel plug (ie which surface is 12V and which is 0V).

SFK

That was quite a chunk of typing to do, my friend, and I appreciate the trouble you went to to tell me all that. Thank you! Yes, it does seem that have avoided a disaster only by good luck.
With kind regards,
L.L.