[cctalk] Re: Rainbow H7842 PSU Fault

-----Original Message----- From: Rob Jarratt <robert.jarratt(a)ntlworld.com> Sent: Sunday, April 30, 2023 9:35 PM To: 'Wayne S' <wayne.sudol(a)hotmail.com> Cc: rob(a)jarratt.me.uk; 'General Discussion: On-Topic and Off-Topic Posts' <cctalk(a)classiccmp.org> Subject: RE: [cctalk] Re: Rainbow H7842 PSU Fault Looks like the one I used is an L7812CV, which has a looser tolerance. I am going to have to order some tighter tolerance parts. > -----Original Message----- > From: Wayne S <wayne.sudol(a)hotmail.com> > Sent: Sunday, April 30, 2023 7:42 PM > To: Wayne S <wayne.sudol(a)hotmail.com> > Cc: rob(a)jarratt.me.uk; General Discussion: On-Topic and Off-Topic > Posts <cctalk(a)classiccmp.org>rg>; Rob Jarratt > <robert.jarratt(a)ntlworld.com> > Subject: Re: [cctalk] Re: Rainbow H7842 PSU Fault > > The CT version is 4%, the ACT is 2%. > > Sent from my iPhone > > > On Apr 30, 2023, at 11:37, Wayne S <wayne.sudol(a)hotmail.com> wrote: > > > > Spec sheet for the 7812 shows 2 versions - 4% and 2% tolerances. So > > the > voltages your measuring are within the 4% part. Maybe you do need the > 2% one. > > > > Sent from my iPhone > > > >> On Apr 30, 2023, at 11:26, Rob Jarratt via cctalk > >> <cctalk(a)classiccmp.org> > wrote: > >> > >> I think I have found a possible cause, but not too sure what to do > >> about it if I have. > >> > >> I had to replace the 7812 regulator that supplies Vstart. The new > >> one has an output that seems to vary between 12.2 and 12.4V. The > >> 7812 on the good PSU outputs a steady 12.1V. I think that is enough > >> to cause the E3d comparator to turn the comparator off and allow > >> its output to > float high. > >> > >> I suspect I may have used one with a wide tolerance rather than a > >> narrow one, or just have a bad one. It should be a genuine part as > >> it came from CPC Farnell. Not quite sure why the output varies on > >> the bad > one though. > >> > >> Regards > >> > >> Rob > >> > >> > >>