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  • Help with Sproggy

    Just finished putting the kit together. I was testing it and the +5 volt and +3.3 volt circuits work perfectly. The other circuits are messed up though and the LM2587 gets very hot very quickly. I get -3 or so volts on the -5 and -12 rails and i think about +3 on the +12 rail.

    Any suggestions?

  • #2
    remove the MBR340 and then check also check all diodes for polarity.

    Mastero

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    • #3
      wow that was a quick response. as always, you are right. after i posted i went back and checked for the polarity and the sa28a diode was in backwards. so it's fixed now. thanks, though.

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      • #4
        no problem!

        Welcome to the sproggy's world

        Mastero

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        • #5
          Ok new problem. I was installing heat sinks. I got them all on and checked the voltages again. The 3.3 line was reading 10.8. So i checked to see that the MBR 745 wasn't touching the heat sink. It seemed ok so I swapped in a new maxim 788 and had 3.3 back. But I didn't have the heat sink on it. So i then installed the heat sink on the new maxim and one more test: now 11.5 on the 3.3 rail.

          What happened? Did i fry both of the 788's? I connected it to the heat sink in exactly the same way as the 787 and the 5v rail is working fine.

          Thanks.

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          • #6
            Obi Mastero, you're my only hope!

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            • #7
              Hey buddy its a very common problem with the Heat sink and the MBR 745 . be 100% sure that it is isolated.

              What happens is when the 745 is not isolated then you get this problem even at times there is a very small contact at the 745 remove the 745 from the heat sink and then check .


              Mastero

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              • #8
                Removed the heat sink....still the same problem. I assume neither the 5v or the 3.3v would work if the MBR used within it is not isolated. so i swapped them. both mbr's work in the 5v track but neither work in the 3.3v track. When I replaced the 788 in the 3.3v track, the mbr still had its heat sink attached. The circuit then worked correctly and gave 3.3V. Then I installed the heatsink to the 788. That is when i got 11.5V again. Is it possible that i damaged the 788's when i was installing the heatsink?

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                • #9
                  This is a very simple problem but need to be carefully solved.

                  a) Check with a connective meter if current passes from the 745 To the Heat sink.

                  b) Remove all the heat sink from all the ic's

                  c) Check voltage again.

                  let me knw

                  Mastero

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                  • #10
                    All heat sinks removed. Still no resolution to the problem. Seems like the 788 isn't working.

                    I put a 787 where the 788 was and now i get 5 volts so this leads me to believe the 788 is the problem. what could i have done wrong when installing heat sinks to ruin the 788?

                    Just ordered 2 more 788's from maxim.

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                    • #11
                      i guess you just got your problem solved .. the 788 had gone dead due to the short with the heatsink.

                      replace the 788 and be care full with the heat sink next time ..

                      take care

                      Mastero

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