Two important pieces of information needed: 1- Does the Tapestry still work OK with batteries? If not, plan repair=20 options. If it does, don't mess with it! 2- IMHO, 4.5 volts is a little high for 3 alkaline cells. Brand new &=20 fresh carbon zinc cells would measure that. Measure the wall wart to=20 see if it is still ok. According to Energizer & Wikipedia 1.5 volts is nominal for both=20 types of cells. Hopefully, the wall wart died... On 1/23/2013 11:27 AM, William Bulley wrote: > According to RussellMc on Wed, 01/23/13 at 11:11: >>> This "enhanced" design has a serious failure mode - when it works at al= l, >>> and that seems to be unpredictable - it "runs" at an accelerated rate. >>> >>> Sometimes it doesn't light up at all! :-( >>> >>> How can this be? >> It seems very likely that you have higher voltage or spikes present. >> >> I'd expect that placing a large capacitor on the plug pack output would = help. >> >> Thought: Is plug pack definitely DC and not AC? (Unlikely) . > Not higher voltage (measured using DC multimeter) - stable 4.5 VDC... > > Spikes - can't say, have yet to use oscilloscope on the power rails... > > I thought of the large capacitor, but have not done so. Thanks. > > The wall wart or plug pack is stamped or labeled with 4.5 VDC... and > was ordered as such from DigiKey. It is definitely DC because: > > 1) the DC multimeter so confirmed > > 2) I specified 4.5 VDC when I ordered from DigiKey > > 3) the sticker/label on the wall wart or plug pack says so > > This is such a weird problem... :-( > > What bugs me is this: clearly the logic circuitry must have some way > (oscillator, bi- or multi-stable circuit, etc.) of "telling time", but > why would 4.5 VDC from wall wart or plug pack be so different from > 4.5 VDC from three AA cells - enough differenct so as to affect the > operating frequency of said oscillator? > > If the display was powered from AC mains, I could see how a logic > circuit could sense the zero crossings (for example) and use that > as a (relatively stable across six hours) time base. But since the > display is powered (as designed) from three AA cells, there must be > an internal time keeping device or circuit, yes? > > Or could they depend on the time constant of an RC circuit (with a > very large value of C)? Only tearing the tapestry open will give > me the anwser to this question. :-( > > Regards, > > web... > --=20 John Ferrell W8CCW That which can be destroyed by the truth should be. P.C. HODGELL =20 --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .