Products > Test Equipment
HP3577A 5Hz-200Mhz VNA Teardown
precaud:
Those are good points, Berni.
I've used series resistance to lower the operating voltage and fan speeds before. But with that approach, pressure would scale down proportional to the speed reduction. Not generally a problem if circulating air in a large, open enclosure. But after looking at the various cooling paths in the 3577, I'm thinking that isn't a good thing in this case. The power supply components probably wouldn't be affected by it; that air path is direct and open. But pressure is needed to push air through the small holes in the bottom of the card nest, and out the holes in the top panel of the cards.
That's why the Sanyo fan looks attractive; it generates the same pressure as the stock fan, with only a little less airflow.
Probably the best move to reduce cooling requirements is to swap the crt out for one of those nice LCD displays. Hard for me to justify that cost though, as long as the crt is still working...
Berni:
Well the static air pressure can also have a big effect on the noise of a fan too. In my homebuilt x86 NAS project i was trying to cool it all by drawing air trough the small case using a 120mm fan, but no matter what fan i used i could never get it to run near silent while also pushing the required amount of air trough it. Eventually i ended up grabbing a dremmel and cutting out the hole pattern where the fan mounts and blows trough so it was now a wide open hole, this finally solved it and got the noise level down to where i wanted it, now the harddrives are louder than the fan when all of them spin up.
So the restrictive air path could also be one of the things that is making the fan loud, or making turbulent noise as air makes its way trough the restrictions.
Oh and looking at the datasheet for the HP 3577A it claims it uses 450VA max, so that's indeed quite a power hungry instrument, ofrcouse the real power use in watts is likley quite a bit lower, but i think its going to be quite difficult to cool without making a lot of noise. The big ass HP 8566B Spectrum analyzer i have has a power consumption of 650 VA, sounds like a hair drier with the powerful fans and yet still gets pretty hot.
precaud:
Yes, you may be right. I've had similar experience.
That's why I was asking for feedback from someone who has successfully reduced the noise by replacing the fan.
bson:
I'm trying to install a NewScope-5 in mine, but can't for the life of me get the CRT out. The instructions say "on the HP3577A there is one additional screw on the bottom right that needs to be removed" but I have no idea where this screw is. I've removed every screw that I think can hold it, but it's not budging. There are two screws on the bottom back, one on the right, one on the left that attach to a captive bracket, but that's two screws and the left one is inaccessible without pulling the assembly partway out. Just removing the right one won't help. So I'm at a loss what f*cking screw I need to remove... I don't care to keep the CRT, it's going in the trash anyway, so at some point I'll just start ripping stuff out from the top until I can disassemble enough to pull the tube out from the front. But I'd rather not make a mess. Has anyone else done this already and know where this one additional screw is?
Edit: nvm, it's not at the bottom right but at the top right and looks like it's only holding the top PCB onto the cage. It's not. There are also two screws under the right side adhesive cover holding the display by the bezel. After removing those it slides out.
precaud:
The crt ass'y slides in on a "shelf". Look down at the bottom of the rear of the crt unit, you'll see one large-ish screw that secures it to the shelf. I bet that's the one.
Did you swap out your fan yet?
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