Re: Agilent E4406A CPU Board Pulling down the power supply.
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Does it have any MLCC ceramic caps? Those are also prone to cracking and going short.
A $300 thermal camera is really handy to find stuff like this - could be a cap, could be a shorted fet in a switching voltage converter, could be a lot of common things, or it could be something really obscure.
The alternative to the thermal camera is mist the board with IPA - whatever is shorted and getting hot will evaporate the IPA fast - way faster than it evaporates from the rest of the board!
Hello,
I have got an Agilent E4406A VSA that the PSU is hiccupping due to a supply rail overload.
I pulled all the daughter boards and I get down to the CPU board + the front panel and that still causes Hiccup and green LED pulsing on the front panel.
I then pulled the CPU board and the fan control board as I know the unit should power up OK without it.
The PSU comes up Ok and the front panel shows a white blank screen so looks like the CPU board is pulling it down.
I pulled the CPU and started measuring with a DMM around the yellow tant SMD caps to look for a dead short.
Most of them show around 1 kOhm and above bar some that presumably are in parallel over several locations on the board and find they measure around 200 ohms.
Anyone seen / know of any issues to do with the CPU pulling down the power supply?
A little bit of history... I got this unit recently and it would not power on. The orange LED was on but no action from the power switch. Pulling the fan control board made the unit power up Ok and work. I ended up replacing 3 x 100 k SMD resistors after doing a measure. They were open circuit. The unit then worked for a while and was happy I had fixed it until the hiccupping occurred and got to where I am now with the fault.
Any ideas welcome..
Thanks,
Simon
ZL1SWW
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