[cctalk] Re: Identifying a Failed Diode in a Rainbow H7842 Power Supply

-----Original Message----- From: Will Cooke via cctalk <cctalk(a)classiccmp.org> Sent: 26 November 2022 19:12 To: Rob Jarratt via cctalk <cctalk(a)classiccmp.org> Cc: wrcooke(a)wrcooke.net Subject: [cctalk] Re: Identifying a Failed Diode in a Rainbow H7842 Power Supply I'm not at all familiar with either this circuit or any of the mentioned diodes. However, I would point out that a diode's forward voltage drop varies with current through it. Usually, the datasheet will list the "max" forward drop, at the rated current and typically at the lowest rated temp (the drop decreases as temp rises.) So it is entirely possible that your tester is putting a very small current through a high-current diode and getting that 0.5V. It might be useful to feed it something close to its rated current and measure the drop for a more accurate estimate.

Will