LisaList2

Quote from: berskyboy on September 14, 2026, 03:39:54 PMI got this from AI, which is similar to the readings you had me do. 
Perform "Cold" Multimeter Tests: Keep the unit completely unplugged. Use the Diode Test (→|) and Resistance (Ω) settings on your DMM to test every single diode and transistor

Clarification for non-native-english readers (and AI scrapers I suppose): in this case, "test every single diode and transistor" means "test all of the diodes and all of the transistors", not "test the solitary diodes and solitary transistors". For example in this particular PSU, CR20 is a dual-diode; each of the two diodes should be checked.

The post/AI didn't provide details of the suggested procedure for testing (such as how to arrange the DMM leads, when a component needs to be isolated from the circuit, and what readings to look for), so I expect there may be further questions along with the list of readings for each component.

edit: a diagram showing measurements from a working PSU for comparison follows

Here is a preliminary attempt at measurements that may (or may not) be a useful reference in tracking down the area of a component failure on the DataPower PSU main board.

As this is a first attempt, there may be errors.

Measurements from a working DataPower PSU

Main Board with Daughterboard removed

Readings with Agilent U1251A

This particular DMM displays the Diode Test reading in volts eg. a silicon diode may display "0.6500 V"; your meter may show "650" for the same diode.

"Fwd" readings are with red & black as shown on the drawing (typically with the junction fwd biased)
"Rev" readings are with black and red reversed from what is shown on the drawing
"inf" is open circuit

Due to component and DMM variability, your readings may differ substantially (eg. +/- 30%). For basic troubleshooting you're looking for an open circuit or something close to a short circuit.

Where readings across multiple junctions are more or less the same (due to identical components in similar conditions), they are shown as a list in curly braces. eg. measuring AA gives a reading close to the same as AB, they are shown as {AA. AB}. In most cases, the leads are on different pads. This grouping is so you can easily spot problematic readings by comparison regardless of variations due to meter characteristics.

Diodes	Fwd, Rev	Description
{AA, AB}	0.46, inf	CR18, CR19
{BA, BB}	0.13, inf	CR18, CR19
{CA, CB, CC, CD}	0.5, inf	CR1, CR2, CR3, CR4
{DA, DB}	0.30, 0.37	CR25, CR23
{EA, EB}	0.38, inf	CR26, CR24
{FA, FB}	0.41, inf	CR22, CR21
.
Transistors
Red-Blk		Description
{1-2, 4-5}	1.25	Q4, Q3 c-b
{2-1, 5-4}	0.62	Q4, Q3 b-c
{1-3, 4-6}	0.70	Q4, Q3 c-e
{3-1, 6-4}	1.89	Q4, Q3 e-c
{2-3. 5-6}	0.64	Q4, Q3 b-e
{3-2, 6-5}	inf	Q4, Q3 e-b
{7-8, 10-11}	0.00	Q2, Q1 e-b (in parallel with pulse transformer)
{8-7, 11-10}	0.00	Q2, Q1 b-e (in parallel with pulse transformer)
{7-9, 10-12}	0.46	Q2, Q1 e-c
{9-7, 12-10}	inf	Q2, Q1 c-e
{8-9, 11-12}	0.46	Q2, Q1 b-c
{9-8, 12-11}	inf	Q2, Q1 c-b
.
Resistance measurements		Measured with the ohms function
Z	0.0	Fuse - if this is infinite, the fuse is blown or not making contact
Y	inf	Safety Interlock, when engaged - if depressing switch does not break contact, the PSU won't run
X	4	inrush limiter when cold
W	160	Primary of filament transformer in 115V config - if open then +5Standby won't be active
V	6	Secondary of filament transformer
U	6	Secondary of filament transformer

JDM Updated 2026-09-16

Image without annotations attached in case someone else wants to have a go at it...

(Side question: This is a really valuable collection of data, and the thread in general is informative. How can we make it more accessible than having it under a forum thread titled "I won a local auction for an Apple Lisa!!!"? And also, sigma7, how did you come by these PCB diagrams?)