Transducer to track down source of high frequency noise in a PC - Page 1
Forum section: electronics / projects

author: cdev
author_rank: Super Contributor
timestamp: March 20, 2017, 03:26:24 pm
content: One of my PCs has developed a problem with a loud very very high frequency sound and so far none of the microphones that I've tried seems to be able to do what I want which is to be able to use it and maybe a small coil magnetic field probe of some kind to localize the source of the sound so I can address it. My guess is that its between 15 and 20 kHz.I have a PCB mount condenser mike with built in preamp which is currently embedded in an old project. I think I'm going to try that. Has anybody ever had this kind of problem and solved it? I spent a lot of money on super quiet fan for my PC and managed to do quite well there, so to have this suddenly crop up is kind of distressing.Suppose it is a coil or something on the motherboard, how can I address it? Would hot glue be good to dampen vibrations?

author: senso
author_rank: Frequent Contributor
timestamp: March 20, 2017, 04:04:08 pm
content: How old is your PSU?How old is the build?If over 1 years, have you cleaned and repasted the CPU/GPU already?

author: SeanB
author_rank: Super Contributor
timestamp: March 20, 2017, 04:10:41 pm
content: Quick and dirty is a piezo sounder with the electronics removed, and connected to a 1x scope probe. Solder ground to the disk, and use the bigger back metallisation for the centre. Should enable you to see the signal and locate it easily. Will be electrically noisy, so better wrap the back end and probe with some aluminium foil attached to the ground lead, and wrapped over with some black electrical tape. Ugly and looks like a bodge, but so long as the cavity works it is a pretty reasonable pickup. Going to be crap signal wise with cable capacitance and only 1M impedance, but should work long enough to find the whining coil. My bets the whine is either a cracked ferrite or dying cap causing this, or a ceramic cap that is piezostrictive with the applied current in it, or a bearing going on a hard drive or a fan.Don't forget to listen to the PSU, most common cause as well.

author: Twoflower
author_rank: Frequent Contributor
timestamp: March 20, 2017, 04:35:02 pm
content: OK, we're here in a EE related Forum. But how about the simple but working approach to narrow down the source by using a simple paper tube? Just hold to the ear and scanning the components.

author: cdev
author_rank: Super Contributor
timestamp: March 20, 2017, 04:37:00 pm
content: Its around three years old and yes, I reseated the CPU with new application of Arctic Silver ceramique, but the reason I had to do that is the primary CPU fan had developed an issue, so now its in the process of getting replaced. I turned down the CPU multiplier, maybe I should do that even lower.Thank you all for the tips, these are great things to know.

author: Twoflower
author_rank: Frequent Contributor
timestamp: March 20, 2017, 04:42:50 pm
content: Could that be the main board alarm warning you that the CPU cooler is at to low rpm? Some main boards has a build in piezo beeper for that purpose.Regarding the CPU-Fan problem: You should check the core temperature that you're out of critical areas. If you're under-clocking the CPU, lower the core voltage as well. It has a much higher impact compare to the frequency. Go down by just a few 10mV.

author: senso
author_rank: Frequent Contributor
timestamp: March 20, 2017, 06:06:47 pm
content: 3 years old, if you have any medium/high end GPU I would bet on aging PSU's caps causing the GPU inductors to sing under load, the cpu V-regs can also sing, but not so commom.Brand of the PSU/wattage/system specs maybe?