How to work out unknown PSU replacement

Adrian Graham binarydinosaurs at
Sat Nov 3 04:59:48 CDT 2018

> On 3 Nov 2018, at 01:27, Paul Berger via cctalk <cctalk at> wrote:
> Are you saying that there is a capacitor between input? output? of the 79L05 and the ground pins of the chips?  If so that would seem pretty normal as it is usually recommended that you have capacitors to ground on both the input and output side of a 3 terminal regulator.  Are the ground pins on the three chips you mentioned isolated from the ground of the rest of the board?

Hi Paul,

The trace goes from power socket to pin 2 of the 79L05 and a small value cap which is connected to the GND plane along with pin 1 of the regulator. Pin 3 goes directly to a decoupler then straight to those 3 chips which are isolated. Today I’ll break out the ’tin foil covered sponge’ method of tracing any other points on the board that I might have missed last night.

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