Subject:
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Re: U14 problem
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Fri, 15 Nov 1996 03:14:03 GMT
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Original-From:
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Fred G. Martin <fredm@media.mitSPAMLESS.edu>
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Viewed:
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1306 times
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Firstly, 19.9v is a normal unloaded voltage from a 12v DC adapter.
The reason: these common wall adapters are unregulated, and voltage
output varies inversely to current. I.e., if there is no load, the
voltage is higher than the rated voltage; if the load matches the
rated current, (500ma) you get the rated voltage; if the load is
greater than the rated current, you get less than the rated voltage.
From your description, I will guess that there is a short circuit on
the output side of the U14 regulator. With no power applied, measure
continuity (resistance) between power and ground (pins 28 and 14) of
the place where the RAM chip goes. It should be at least several K
ohms.
-Fred
In your message you said:
> I'm having a problem at stage 5.1 (memory power supply) of assembling my
> (first ever) Handy Board. The main and interface/charger boards have
> passed all tests up to this point.
>
> I've just installed C4, C5, and U14 according to the instructions. When
> I plug the DC adapter into the Handy Board (interface/charger board is
> completely out of the picture), I read about +.02 V where the memory power
> supply is supposed to come in, and U14 rapidly gets hot! I read +19.6 V
> at pin 3 of U14, and 0 V at pins 1 and 2 of U14. I tried a replacement
> for U14 thinking it might have been fried, but nothing changed.
>
> Any idea what might be going on here? I'm kind of surprised to see +19.6V
> coming in out of the power supply circuit, though I don't know if I should
> be. I thought this was supposed to be more like +12 V. I am using the
> Panasonic model KX-A11 DC adapter I received with my kit from Gleason
> Research (which is marked DC 12V 500 mA). The voltage measured at the DC
> adapter output itself is 19.9 V ! I have checked the board for obvious
> things like solder bridges or poor connections, but there are no such
> defects that I can see. I have the Handy Board schematics here as well as
> the assembly instructions, by the way.
>
> Any help in diagnosing this problem would be greatly appreciated!
> Thanks!!!
>
> -Troy
>
>
>
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Message is in Reply To:
 | | U14 problem
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| I'm having a problem at stage 5.1 (memory power supply) of assembling my (first ever) Handy Board. The main and interface/charger boards have passed all tests up to this point. I've just installed C4, C5, and U14 according to the instructions. When (...) (28 years ago, 14-Nov-96, to lugnet.robotics.handyboard)
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