> -----Original Message----- > From: Jonathan Chapman <li...@glitchwrks.com> > Sent: 06 January 2022 13:00 > To: r...@jarratt.me.uk; Rob Jarratt <robert.jarr...@ntlworld.com>; General > Discussion: On-Topic and Off-Topic Posts <cctalk@classiccmp.org> > Subject: RE: Source for replacement caps in H744 regulators > > > One of the H744 regulators whines > > FWIW, none of mine are silent under load. If they're not being loaded (e.g. > on a test bench, with no dummy load, or if you have all the boards out) they > can whine excessively due to no minimum load.
I was testing with a 1R resistor, so drawing 5A of the rated 25A. The other two H744s did not whine, but this one does. I can try a bigger load, I think the best I may be able to do is 10A, possibly 20A. > > > it seems higher than the expected values printed on the meter > > Beware cheap test equipment. $client has a few of these Chinese handheld > LC/RLC meters, they're wildly inaccurate on some parameters, including ESR > on large electrolytics. We've got a proper Gen-Rad RLC Digibridge in the shop > to compare against. We couldn't figure out why some of their tuned filter > stages were failing QC at a much higher rate than expected. They were off- > frequency because the cheap meters were giving consistently incorrect > measurements when trying to match capacitors. > My ESR meter is built from a design by Bob Parker. I got it from someone in Portugal (https://evbesrmeter.pt/), so I don't think it is a cheap Chinese one. > That said, it's not like replacing them with new will *hurt* -- it just might > not > fix the whine. > > Thanks, > Jonathan
