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ADi T8053 LCD Color Terminal - PSU output high at startup

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    #21
    Re: ADi T8053 LCD Color Terminal - PSU output high at startup

    lack of load will cause overshoot.

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      #22
      Re: ADi T8053 LCD Color Terminal - PSU output high at startup

      Originally posted by stj View Post
      lack of load will cause overshoot.
      But it was doing it even when connected to the system...

      When I tested it yesterday, however, it didn't even start again.

      I did try forcing a start without load, 12v went to about 18v, then when mains power was disconnected, it made a tick-tick-tick noise (though I read this as common without load for some SMPS)

      But, can't remember if it did that last time. Dammit!
      "Tantalum for the brave, Solid Aluminium for the wise, Wet Electrolytic for the adventurous"
      -David VanHorn

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        #23
        Re: ADi T8053 LCD Color Terminal - PSU output high at startup

        coulnt you add a mov?

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          #24
          Re: ADi T8053 LCD Color Terminal - PSU output high at startup

          If the meter tests OK in another PSU - this could be because the other one is powering up slower. My meter overshoots 2-3 volts as well, however it takes less than a second to show the correct reading. Maybe there is something wrong with the PSU - but if it were REALLY wrong, at 18v it would have fried the computer already.
          Originally posted by PeteS in CA
          Remember that by the time consequences of a short-sighted decision are experienced, the idiot who made the bad decision may have already been promoted or moved on to a better job at another company.
          A working TV? How boring!

          Comment


            #25
            Re: ADi T8053 LCD Color Terminal - PSU output high at startup

            Originally posted by Th3_uN1Qu3 View Post
            If the meter tests OK in another PSU - this could be because the other one is powering up slower. My meter overshoots 2-3 volts as well, however it takes less than a second to show the correct reading. Maybe there is something wrong with the PSU - but if it were REALLY wrong, at 18v it would have fried the computer already.
            I have not seen my meter overshoot like this on many many ATX PSUs, the fact that this one is different suggests to me that the PSU is the cause.

            I think the PSU has something wrong, since it won't even power on again. Will test again with normal PSU and see if everything else is still working.


            It sounds as if you haven't read my previous posts, so to sum up:

            * 12v rail was over 22 volts at start when the thing was working last time
            * When it worked last time, everything did work fine, nothing blew up (Theory: PSU was known to be stupid, protection was built-in?)
            * Powering the system from a normal ATX PSU worked, so my idea that the PSU is made on purpose to do that and of the PC needing an extra kick to get started is probably untrue.
            * Capacitors on the outputs are 25v and 35v, BUT they do not appear to be original, so could be that they aren't supposed to be rated that high. (I think now, Perhaps the last person did that to compensate for the fact they weren't Low-ESR?)
            "Tantalum for the brave, Solid Aluminium for the wise, Wet Electrolytic for the adventurous"
            -David VanHorn

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              #26
              Re: ADi T8053 LCD Color Terminal - PSU output high at startup

              Or could the (possibly) previous 16v capacitors not handle 18-22v?

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                #27
                Re: ADi T8053 LCD Color Terminal - PSU output high at startup

                Originally posted by seanc View Post
                Or could the (possibly) previous 16v capacitors not handle 18-22v?
                That would have to be an even worse design choice, assuming of course that the overshoot was either intentional or (seemed) unavoidable as the result of a bad design.

                Wish I had another one of these things to compare it with too...
                "Tantalum for the brave, Solid Aluminium for the wise, Wet Electrolytic for the adventurous"
                -David VanHorn

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                  #28
                  Re: ADi T8053 LCD Color Terminal - PSU output high at startup

                  leaky opto-isolator on the 12v feedback maybe.
                  opto's used to fail a lot in old tv's

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                    #29
                    Re: ADi T8053 LCD Color Terminal - PSU output high at startup

                    @stj: Are you sure that optoisolator is for the 12v rail and not 5v/12v combined? The other two I know are for standby circuit feedback and FPO/PS-ON signal.

                    Also, I just saw this:
                    Originally posted by Agent24
                    I'm a bit wary of doing that though, low ESR where normal ESR is expected can cause problems too, right?
                    Bad caps can cause rails to overshoot. I'm begining to think those Jamicons and United Chemicons should be changed. Low-ESR caps would be helpful here. This PSU doesn't have big torroids on the outputs, so even slightly lower ESR caps shouldn't cause parasitic oscillations.

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                      #30
                      Re: ADi T8053 LCD Color Terminal - PSU output high at startup

                      no i'm not sure - i dont have a schematic.
                      it isnt hard to trace the 12v line all the way back to the transformer to see what's on it though.

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                        #31
                        Re: ADi T8053 LCD Color Terminal - PSU output high at startup

                        I will give some new capacitors and opto-isolators a try when I do my next order from Farnell (or element14 as is it's now known - why, I have no idea, it was just fine, way to go confusing people for no good reason)
                        "Tantalum for the brave, Solid Aluminium for the wise, Wet Electrolytic for the adventurous"
                        -David VanHorn

                        Comment


                          #32
                          Re: ADi T8053 LCD Color Terminal - PSU output high at startup

                          I decided to revisit this with the intention of turning it into a self-contained DOS gaming machine.

                          I solved the power-on problem. Note how in the beginning I said the 5v standby was about 4.7v? I thought this didn't matter. Turned out one if the 5vSB filter capacitors was halved in capacitance and had high ESR. With even a tiny 100mA load the 5vSB was falling to 2.5v. But DMM too slow to show voltage dip when you press power button. Resolved the problem with a new capacitor.

                          I traced the board and find the feedback only monitors the 5v rail. 12v has no feedback. With the inverter unplugged the 12v sits at 16v. There's no ringing etc on power up. All clean. Just 'high' at 16v. When the inverter kicks in, it drops to 12v. It makes sense. You guys were right. Just an unregulated rail. I guess I chased a fault that doesn't exist.

                          Inverter runs from a TL494 and the panel has its own regulators. 16v won't bother either of them. Nor the audio amplifier which also runs on the 12v rail.

                          Now I just have to find out how to install DOS to a CF microdrive without a floppy drive...
                          "Tantalum for the brave, Solid Aluminium for the wise, Wet Electrolytic for the adventurous"
                          -David VanHorn

                          Comment


                            #33
                            Re: ADi T8053 LCD Color Terminal - PSU output high at startup

                            Originally posted by Agent24 View Post
                            I decided to revisit this with the intention of turning it into a self-contained DOS gaming machine.

                            I solved the power-on problem. Note how in the beginning I said the 5v standby was about 4.7v? I thought this didn't matter. Turned out one if the 5vSB filter capacitors was halved in capacitance and had high ESR. With even a tiny 100mA load the 5vSB was falling to 2.5v. But DMM too slow to show voltage dip when you press power button. Resolved the problem with a new capacitor.

                            I traced the board and find the feedback only monitors the 5v rail. 12v has no feedback. With the inverter unplugged the 12v sits at 16v. There's no ringing etc on power up. All clean. Just 'high' at 16v. When the inverter kicks in, it drops to 12v. It makes sense. You guys were right. Just an unregulated rail. I guess I chased a fault that doesn't exist.

                            Inverter runs from a TL494 and the panel has its own regulators. 16v won't bother either of them. Nor the audio amplifier which also runs on the 12v rail.

                            Now I just have to find out how to install DOS to a CF microdrive without a floppy drive...
                            Glad you found the issue with the 5v, it's surprising what a faulty cap can do.

                            With regards to the DOS issue, maybe consider DOSBox? It will run on top of any OS and most old games seem to play nice, although you might have to slow down the emulated processor for some games.

                            Comment


                              #34
                              Re: ADi T8053 LCD Color Terminal - PSU output high at startup

                              DOSBox still doesn't have the feel of a real DOS PC. When i used to have more time i did my own DOS Gaming bootdisk, to play all the stuff i was too young to play back in the day when that was the norm.
                              Originally posted by PeteS in CA
                              Remember that by the time consequences of a short-sighted decision are experienced, the idiot who made the bad decision may have already been promoted or moved on to a better job at another company.
                              A working TV? How boring!

                              Comment


                                #35
                                Re: ADi T8053 LCD Color Terminal - PSU output high at startup

                                It turns out you can copy the DOS floppies into a single folder on a bootable CD and run setup from there - provided you manually use FDISK first and format the drive yourself, otherwise the installer complains that it can't find floppy disk #1.

                                Microsoft logic!?
                                "Tantalum for the brave, Solid Aluminium for the wise, Wet Electrolytic for the adventurous"
                                -David VanHorn

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