Hi Folks, OT Linux-wise, but a lot of you are wise, hardware-wise, as-it-were-wise ...
1. I have an old desktop, whose on/off is mechanical (mechanical link from power button to switch in PSU). This link is now dodgy, and I often have to press it on/off several times before the power finally kicks in.
A possible solution, after running shutdown, is simply to switch off at the mains, leaving the power switch in the "on" state; and then, when starting up again, simply switch on at the mains. I.e. simply never switch the machine itself on or off.
However, I'm a bit concerned that the surge from switching on at the mains might not be good for the machine if it goes straight through to the PSU, rather than the PSU's own switch allowing it in from an already live mains cable.
Any comments?
2. If a TFT/LCD screen simply goes all white (every pixel bright white) when it's switched on, regardless of whether there's any input signel, does this indicate any particular type of internal problem which it might be worth probing for (by taking the back off and looking for, e.g., a loose chip/connection)?
Best wishes to all from the Scrapyard in the Fen Ted.
-------------------------------------------------------------------- E-Mail: (Ted Harding) ted.harding@nessie.mcc.ac.uk Fax-to-email: +44 (0)870 094 0861 Date: 24-Jan-07 Time: 11:04:06 ------------------------------ XFMail ------------------------------
The old AT style PSU's like these (with a mechanical on off switch) have no problem having the power disconnected/reconnected by pulling out the mains plug. All the mains switch is on these is a double pole switch in the mains supply anyway.
What I would recommend is that you disconnect power by switching off at the wall socket or by pulling the plug out of the wall rather than pulling the IEC (kettle) lead out of the back of the PSU. Those connectors have a bit of a tendency to arc under load and this could shorten the life of the PSU.
- If a TFT/LCD screen simply goes all white (every pixel
bright white) when it's switched on, regardless of whether there's any input signel, does this indicate any particular type of internal problem which it might be worth probing for (by taking the back off and looking for, e.g., a loose chip/connection)?
It is either a dud panel driver board (in which case it is probably beyond economic repair I am afraid) or if you are lucky it is a dodgy connection between the LCD and the driver board.
Make sure the power is off the screen and has been for at least an hour..only idiots and experts mess around with live equipment.
Inside the panel you should see a largish circuit board with a wide ribbon cable (of many pins) going to the actual panel itself. The board may be covered with screening plates which will need to be removed first.
Briefly ground yourself if you can..LCD's and the associated drivers are super static sensitive.
Check the security of the connections at both ends on this cable, usually the connectors are of the zero insertion force type and will have some sort of clip mechanism that retains the cable. Usually this is in one of the following forms.
The whole top of the connector (where the ribbon cable goes in) is a frame (usually of a different colour) that can be gently (and very little force is required, don't yank it) be prised up by a couple of mm..the cable will then slide out freely...reinsert cable as far as it will naturally go and push the frame down to lock.
The other type is more of a side entry type. These have a bar across the length of the connector where the cable goes in that hinges up to unclip the cable. same procedure as before..gently flick the "bar" up where the cable goes in and then remove.
It is not unusual for the release mechanisms of these connectors to be additionally secured with tape..do not try to cut the tape with a knife or by pulling at the cable...carefully peel it off. The cables are very fragile. Inspect the cable while you are doing this to check that it has not been snagged or otherwise visibly damaged.
Also there usually be a smaller PCB (or sometimes it is part of the main one) that has two thick'ish wires that also go to the panel. You can stay away from this bit as that is the drive for the backlight..and we know that works or the screen would remain black.
If the screen is the type that has mains going straight into it rather than being powered by a PSU brick then stay well away from the components near the mains socket even if the power is disconnected. there are capacitors there charged up with over 300VDC and they will bite you even after the unit has been unplugged for a while.
Sometimes you will encounter a multicore cable rather than a ribbon..you will in this case just have to carefully examine both ends to see how it is connected. In other cases the main board actually connects directly to a connector on the back of the panel, in this case simply carefully detach the board and re-attach it making sure all retaining screws are put back correctly.
Hope that helps Wayne
It's also probably worth mentioning that most LCD's carry a 3 year warranty and not everyone notices this so it if looks less than 3 years old or you can check the warranty status online via the serial number this may be worth checking first.
On 24-Jan-07 Wayne Stallwood wrote:
It's also probably worth mentioning that most LCD's carry a 3 year warranty and not everyone notices this so it if looks less than 3 years old or you can check the warranty status online via the serial number this may be worth checking first.
Many thanks for all the info, Wayne (this and previous mail)!
I knew I was asking in the right place!
Best wishes, Ted.
MODERATOR: PLEASE IGNORE PREVIOUS COPY OF THIS MESSAGE, SENT FROM WRONG EMAIL ADDRESS! -------------------------------------------------------------------- E-Mail: (Ted Harding) Ted.Harding@manchester.ac.uk Fax-to-email: +44 (0)870 094 0861 Date: 24-Jan-07 Time: 22:31:14 ------------------------------ XFMail ------------------------------
On 1/24/07, Wayne Stallwood ALUGlist@digimatic.co.uk wrote:
If the screen is the type that has mains going straight into it rather than being powered by a PSU brick then stay well away from the components near the mains socket even if the power is disconnected. there are capacitors there charged up with over 300VDC and they will bite you even after the unit has been unplugged for a while.
The backlight requires high voltages too, so either way watch those fingers.
Regards, Tim.
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ted.harding＠nessie.mcc.ac.uk -
Tim Green -
Wayne Stallwood