Weird Cherokee PSU noise

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JacquesT
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Weird Cherokee PSU noise

Unread postby JacquesT » Fri Dec 15, 2017 5:17 am

So picked up a cherokee psu last night, it works, ran fine for about an hour, but it makes a weird warbling electrical noise.

Anybody have any idea what part might be the culprit? Noise is coming from the fan side. I can return it for a full refund, but if it's going to 'replace 1 dry cap' then I'd rather just do that myself.

I can't open it as that would break a warranty sticker...

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:Octane: wip build - Currently 2xR10000 250Mhz, 640MB RAM, SSI graphics, 18GB 10K RPM HDD. Lucent and HD fan mod.

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marshallh
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Re: Weird Cherokee PSU noise

Unread postby marshallh » Fri Dec 15, 2017 6:04 am

Mine made the same noise. I'm pretty sure it's just the PSU fan being pwm'd to a low speed - eventually it would heat up, go faster and go away. If you hook up the fan directly to a 12v supply it's nice and smooth but very loud and will cause a tornado.
Strobing harmonics are a tough problem to solve on fan controllers.

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Irinikus
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Re: Weird Cherokee PSU noise

Unread postby Irinikus » Fri Dec 15, 2017 6:37 am

Mine does the same thing. It starts out rather noisy while the fan is powered down to a low speed, but becomes quiet once the fan speeds up, as the power supply warms up.
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JacquesT
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Location: Somerset, UK

Re: Weird Cherokee PSU noise

Unread postby JacquesT » Fri Dec 15, 2017 11:08 am

Hi, this is not the fan. The noise starts when you plug a power cord in while the PSU is outside the Octane. Power cord -> relay click -> weird warbling noise. The fan doesn't spin up, it only spins up when plugged into the Octane.
:Octane: wip build - Currently 2xR10000 250Mhz, 640MB RAM, SSI graphics, 18GB 10K RPM HDD. Lucent and HD fan mod.

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GRudolf94
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Re: Weird Cherokee PSU noise

Unread postby GRudolf94 » Fri Dec 15, 2017 2:42 pm

Well, these PSUs are always on, even in standby. This means it's always rectifying AC into DC, and then PWM'ing a MOSFET to chop that up into AC again, then rectifying that once more to provide the actual DC output. Along the way, it has several capacitors for filtering and smoothing, and one could very well be the cause of the squeal/warble/whatever it is.

The thing is, without opening it up and making a visual inspection, it's very hard to tell the origin of said noise. If nothing turns out to be looking bad, then it's a matter of desoldering cap by cap and running them thru a capacimeter and ESR-meter, which is something not everyone has, and quite a pain in the rear.
:Indy: R5000@180MHz, 256MB, XL-24, IndyCam
:Indigo2: R10K@195MHz in broken teal case with broken purple bottom, XZ Graphics, missing: RAM, drives/sleds, case bits, PSU; awaiting completion [ATX PSU CONVERSION IN THE WORKS!]
misc: Some Sun stuff, lots of x86 crap, one MSX and a MSX2+, a ZX Spectrum clone, slotloader 400MHz overclocked to 500MHz! iMac G3

JacquesT
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Location: Somerset, UK

Re: Weird Cherokee PSU noise

Unread postby JacquesT » Sat Dec 16, 2017 3:24 pm

I've posted over at badcaps.com in the hope somebody can help. I opened it up today and I couldn't see any bulging / leaking bits, apart from 19 years worth of dust which I blew out. I did plug the power cord in, turned on the wall socket and used an improvised ear horn to listen for the noise origin. It came from the region of the Potter and Brumfield relay, well that is where the noise was loudest. That's not to say it couldn't be any of the components around it.

Image

What I also noticed was as soon as the workstation is powered on inside the Octane the noise dissipates quite a bit. So as soon as some serious current starts to flow things quiet down.
:Octane: wip build - Currently 2xR10000 250Mhz, 640MB RAM, SSI graphics, 18GB 10K RPM HDD. Lucent and HD fan mod.

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marshallh
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Re: Weird Cherokee PSU noise

Unread postby marshallh » Sat Dec 16, 2017 5:51 pm

Could be the inductors there then. Usually they're varnished in production to prevent ultrasonic vibration which causes squeaking noises in audible frequencies. Over time the coils may break loose and start to move a bit. Coil whine is annoying but doesn't mean anything's wrong.

Of course that doesn't mean you have zero bad caps in the power supply - but as long as things work I wouldn't worry too much.

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GRudolf94
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Re: Weird Cherokee PSU noise

Unread postby GRudolf94 » Sat Dec 16, 2017 9:21 pm

I just recalled I have a Sun Fire V40z with 2 dead PSUs (also Cherokees), one of them is constantly clattering it's relay, the other does this warble thing. I know the problem is in the circuit that closes the relay, and the noise comes from the relay coil making the armature vibrate (but not quite open/close). Might not be the same issue, just throwing it out there. I didn't get enough time to trace the fault more accurately, though.
:Indy: R5000@180MHz, 256MB, XL-24, IndyCam
:Indigo2: R10K@195MHz in broken teal case with broken purple bottom, XZ Graphics, missing: RAM, drives/sleds, case bits, PSU; awaiting completion [ATX PSU CONVERSION IN THE WORKS!]
misc: Some Sun stuff, lots of x86 crap, one MSX and a MSX2+, a ZX Spectrum clone, slotloader 400MHz overclocked to 500MHz! iMac G3

JacquesT
Posts: 370
Joined: Mon Jan 28, 2008 11:50 am
Location: Somerset, UK

Re: Weird Cherokee PSU noise

Unread postby JacquesT » Thu Dec 21, 2017 12:55 pm

I may try and replace the relay as a first step, then slowly start to replace the other components around the relay.
:Octane: wip build - Currently 2xR10000 250Mhz, 640MB RAM, SSI graphics, 18GB 10K RPM HDD. Lucent and HD fan mod.


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