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The red+yellow are connected together and are the +5V, both blacks are ground. This is according to the following part of the schematic:

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J2, J3 and J4 are the 15 pin MATE-N-LOK connectors that accept the connectors from the backplane, and as can be seen 1+4 are +5v and 7+8 are ground.

Pin 2 is +15V, and pin 13 is -15V, useful to measure those voltages.

The main circuit breaker on the PSU

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To be able to test the CPU we need to act as if the key is moved to the LOCAL setting. This comes in on the PSU on connector J1 on the PSU’s motherboard: the blue Berg connector that can be seen in the picture above. Following the schematic and the signals it looks to me like the signal we need is called DC ON (L), which comes in from pin 5 of that connector. To be able to play with that we need something to do that:

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Testing the PSU

With all of this in place it is now time to start testing.. Add test leads in the +15V and -15V sockets:

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Switch on the electronic load to 6A constant current:

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And then switch on the power and switch the “DC ON (L)” switch.. We need to be quickish because there is no cooling of the PSU…

The PSU switches on (Yippee) and the electronic load shows:

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The voltages of the +15V and -15V rails are:

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These seem to be fine, but the +5V rails seems to be slightly high. It should be 5.1V +/- 0.1V, but I will assume this to be fine considering we will have loss on the internal wiring and we’re only pulling 6A of load (which is the minimum for this PSU).

It appears that this PSU is OK, so next task is to replace the PSU in my 11/44..