Hello Thomas, > Yes, it's a homebrew project. Which transistor provides negative voltqage? Sorry, it a positive voltage. I hope I didn't confuse you too much ! Many years ago the ZTX650 was used in the Sinclair Spectrum computer to generate -ve for memory IC's!!!. Changing Q5 2N2222 for a ZXT650 (its a proper switching transistor) did in my case increase the voltage produced. > I can't find any negative voltage supply in the circuit. The LED is a Red > type, right? Because different LED color has different voltage drop. I found that different red LED's had varying voltage drops. The brand new one I bought for the job didn't work, an old one out of the scrap box worked perfectly ! > > > I am still not sure how to make the DC/DC circuit to produce 21V. Try looking at the collector of Q5 on a scope, when it switches the ringing of L1 should produce a nice big voltage swing which is rectified and smoothed by CR4,C11,C10 to produce an input to the 78L12. Note the output of this is approx.13v due to CR3, R27. Hope this helps Steve > > > Thomas > > >From: Steven Allard > >Reply-To: pic microcontroller discussion list > >To: PICLIST@MITVMA.MIT.EDU > >Subject: Re: [PIC]: ICD does not run. Please help! > >Date: Wed, 6 Mar 2002 08:47:28 +0000 > > > >Thomas wrote: > > > > > I enabled debug mode option already, but it still doesn't work. When I > > > press the "self Test" button, it returns "Incorrect MCLR pin supply > >voltage. > > > Check ICD0x4". What does that mean? > > > > > > I don't know if the DC/DC circuit output has to be 21Volts as it says on > >the > > > schematic. When I probe at the input of the 78L12 regulator and I get > >only > > > 12.5V. Is this the source of the problem? Anything I can do? > > > > > > >Is this a homebrew project ? If so try replacing the switching transistor > >which > >provides the -ve voltage with a different one. I found using an old ZTX650 > >gave > >a much greater negative voltage than a BCxxx. If you are using old > >capacitors it > >might be worth checking their ESR, good caps are important. > > > >12.5v into the regulator is almost certainly not enough to power it (mine > >produces ~20v) - check the datasheet if you are not sure. > > > >I also had to choose the LED very carefully - its used as a voltage > >reference > >(poor design ?) several would not work, I seem to remember 1.2v volt drop > >across > >it is about right. > > > >Hope this helps > > > >Steve > > > >-- > >http://www.piclist.com#nomail Going offline? Don't AutoReply us! > >email listserv@mitvma.mit.edu with SET PICList DIGEST in the body > > > > > > _________________________________________________________________ > Send and receive Hotmail on your mobile device: http://mobile.msn.com > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email listserv@mitvma.mit.edu with SET PICList DIGEST in the body -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads