I have an "interesting" scenario:
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I bought an E8401A VXI mainframe from our favorite auction site to dabble in the world of test automation. It arrived incredibly dirty and grimy (it has no air filter), but powered on. I spent several hours blowing out dust and dirt, including the fan and power supply. It still worked fine afterward.
I then installed the first VXI card (E1405B Command Module) and let it run overnight - no issues.

The next day, a second card I ordered arrived and I installed it. When powering on with the two cards, the power went out within about a second. I removed the second card, and still, the unit was dead. No standby LED or any other sign of life.
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I figured the power supply had died on me.
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I contacted the seller, and they worked with me to send me a second unit (complete E8401A mainframe). When that arrived, it was even dirtier than the first one. But again, it turned on. I cleaned the power supply and put it into the first mainframe. It powered up fine but the PS fan was very noisy. So I used the one from the original PS.
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I installed the command module, no issues. I installed the second card (the one after which the first mainframe died), and still, everything was fine.
While all this took place, a third card I had ordered arrived, and I also installed it. Again, the unit powered up without issues! My hopes were going up that I had a fully functioning unit now.
I let it run for hours without problems.
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I then let it run overnight. Later the next morning, the temperature and fan LEDs were blinking, indicating overheating. This was strange since I had the unit next to an open window and the temperature had dropped into the low 60s that night. Within a ?few minutes, the mainframe shut down. For a brief moment, all LEDs on the front module lit, and then - dead.
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Hmmm … I disconnected the power cable, let it sit for a few minutes, and reconnected power. No signs of life, but after about 10 seconds, a loud "bang" from the inside. As bad as that was, it gave me some hope that it would be easy to identify which component had failed in such a spectacular manner. I open the power supply to investigate, and found - nothing! All looked good. No exploded caps or resistors as far as I can tell.
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My questions are:
? ? ? Has anyone had such a mainframe and experienced similar issues??
? ? ? Does anyone have a schematic of the power supply? I have the CLIP for the mainframe, but it does not include any details for the PS.
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One other interesting piece of information is a service note that indicates issues with a cap in the fan supply of these power supplies (). It doesn't provide further details other than a replacement part number for the PS.

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Thank you for any thoughts or tips.??
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Wolfgang
KI7PFX

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