Power Supply: Fixed

By Anonymous -
Testing continued on the power supply. I borrowed a few 4Ω 255W resistors from the Power Systems lab so I could try and load test the supply.
     With four of these resistors wired in parallel we get 1Ω. Because of Ohms law this means we will get a 5A current from the 5V output. This would give about 25W of power, (P=V*I). 900W is more than enough to satisfy this.
The result of having the load was a drop in the output voltage. The 5V line dropped from its normal 5.07V to around 4.96V. I hooked the oscilloscope back up to measure the +8V and +5V lines as they power up.
Compared to before this was a much better graph. There is a much lower spike in the +5V output, it jumps to 5.8V and then quickly settles down to 4.8V to 4.9V (according to my multimeter). The power supply appears to be working just fine now. No more random tripping and no more burning resistors.

Next on the agenda: Powering up the machine and running a few basic tests. Posting a list of installed options.


Edit: I forgot to mention when I posted this that one other thing I did was reform the capacitor C5, which is the filter cap for the +8V line. I think that definitely helped to smooth out the +8V voltage spikes seen in the previous graphs. I have attached the schematic below for those interested. C5 is located in the top middle. You might need to right click and hit "view image" to zoom in.


Comments

  1. UnknownJune 7, 2017 at 6:08 AM

    The Living Computer Museum in Seattle has a lot of running DEC gear and may be of help in your restoration. They have extensive restoration experience. http://www.livingcomputers.org/

    ReplyDelete
    Replies
    1. AnonymousJune 7, 2017 at 6:39 AM

      Thanks! I will keep that in mind.

      Delete

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