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1  Hardware and U-Boot firmware / Hardware / Re: GuruPlug Server Plus Heat Problems on: May 31, 2010, 06:52:29 AM
You will improve your credibility if you speak about what you have actual experience rather than using hear say.
tinker, I'll take my lumps on Sheeva plug statements, since I've never owned one. It appears I was wrong, and I apologize for alluding to heat problems in the Sheeva plug. That's what I get for reading only a few unconfirmed posts on Sheeva.

I do have a guruplug, and can attest that it has huge heat problems. After leaving my huge heatstrap modified guruplug on for a number of days, it continued to get hot and then started to reboot. My next step is to add a fan to the setup. I'm totally disappointed with the guruplug, and will never buy a GlobalScale product again.
2  Hardware and U-Boot firmware / Hardware / Re: GuruPlug Server Plus Heat Problems on: May 27, 2010, 04:15:33 PM
Whatever direction works. I have a slight bias for fan air blowing directly onto the heatplate. Actual mileage may vary in practice. Doug
3  Hardware and U-Boot firmware / Hardware / Re: GuruPlug Server Plus Heat Problems on: May 27, 2010, 03:38:29 PM
Excellent mod. That should cool it enough to run. It blows air directly on the heatplate with a big fan.

The 1.3A at 5V translates to 6.5watts. That's nearly double the power dissipation of the Sheeva plug, which we already know had a marginal thermal design. No wonder the guruplug was DOA or should we say HOA (Hot on Arrival).

Doug
4  Hardware and U-Boot firmware / Hardware / Re: GuruPlug Server Plus Heat Problems on: May 27, 2010, 12:03:54 PM
If you need reliability and don't want to roll your own OS and thermal design, stay away from Sheeva/guru plug designs.  Doug
5  Hardware and U-Boot firmware / Hardware / Re: GuruPlug Server Plus Heat Problems on: May 27, 2010, 11:20:26 AM
A fan isn't required. One thing is certain. The existing guruplug design will not work. If you want it to work, you must cool it. Either passively like my big strap solution or with a fan. Your choice. Pick your poison, but pick you must. Doug
6  Hardware and U-Boot firmware / Hardware / Re: GuruPlug Server Plus Heat Problems on: May 27, 2010, 07:57:21 AM
Thanks for the picture and fan links. The fan is excellent. Make sure you think about air flow and ducting. Smashing the fan between the heatplate and PS shield with no airflow gap won't help much. Make sure there is a path for the air to flow.  If you could get the fan to suck air from the existing bottom case vents and blow it against the heatshield with the exhaust air flowing directly out of the case along the sides, that would be ideal. Doug
7  Hardware and U-Boot firmware / Hardware / Re: GuruPlug Server Plus Heat Problems on: May 27, 2010, 06:41:23 AM
The heat sources are the ICs on the bottom of a two board stack. The existing heat plate is attached to that bottom board. If you add a fan just below the heatplate, it probably will work. Give some thought to ducting of the air. Here's the component stackup with a good suggested fan location.

Top of Case with logo
Daughter board with LEDs on top side
Main PCB with most hot ICs on bottom side
Heatspreader - with heat tape connecting it to ICs, with bic pen type springs on the 4 corners pressing it to the main pcb
->Add 40mm fan here<-
PSU plastic shield
PSU
Bottom of Case - with AC plug

This means of course that your case needs to grow vertically - maybe 15-30mm. Add standoffs and longer screws, and maybe you can get the existing case back together with just a big gap for the fan and ducting. Post pictures when you finish this.

Doug
8  Hardware and U-Boot firmware / Hardware / Re: GuruPlug Server Plus Heat Problems on: May 27, 2010, 05:18:38 AM
I thought of that location for a fan as well. There are several problems with that location.
1. It is far away from the heat source. The daughter card sits just underneath that spot.
2. Where would the airflow go? Where would air flow in, and where would it exhaust? Will it increase airlow at the heatplate? I think not.
3. You won't be able to see the status LEDs.

But, it may be worth a try. Any airflow will help.

Doug

9  Hardware and U-Boot firmware / Hardware / Re: GuruPlug Server Plus Heat Problems on: May 27, 2010, 04:33:27 AM
You can make this device into a "plug computer" in the current form factor, but you can't violate the laws of (thermal) physics. The problem is that there is too much power dissipation in the ICs with no good thermal path to ambient. To keep this form factor, the thermal design must be improved significantly. There are several good posts from me and others in this thread suggesting solutions that might fit roughly within this form facter.

An excellent discussion on thermal resistance and ICs can be found in this pdf file. http://www.ixysrf.com/pdf/switch_mode/appnotes/1aprtheta_power_dissipation.pdf

Another excellent reference is from Maxim. This article discusses power MOSFETs,  but the principles are the same for any IC. http://www.maxim-ic.com/app-notes/index.mvp/id/1832

The heat strap I added, is probably an overkill in size, but I wanted to make sure I solved the problem. Even with that massive heatsink, the legs get very warm to the touch - about 100F at extremities. Using a digital cooking thermometer I measured 113F (45C)  touching the thermal tape attached to one of the ICs. The junction temps will be quite a bit higher than that.

Have fun designing your own case to solve this thermal problem.  Smiley

Doug
10  Hardware and U-Boot firmware / Hardware / Re: GuruPlug Server Plus Heat Problems on: May 26, 2010, 07:31:42 PM
Here are the detailed photos of my modified guruplug server plus with ruler for reference.
Assembled stack.



Stack from ethernet side


Underside of stack



Heatplate IC side view with heat-tape



Motherboard Hot ICs - 4 RAMchips, CPU, GigE-phy, Samsung



Daughtercard top view


Doug
11  Hardware and U-Boot firmware / Hardware / Re: GuruPlug Server Plus Heat Problems on: May 26, 2010, 01:51:25 PM
It will be late tonite due to a business dinner, but I'll post guruplug disassembled board photos with rulers & dimensions. I think you are right about a daughter card. Doug
12  Hardware and U-Boot firmware / Hardware / Re: GuruPlug Server Plus Heat Problems on: May 26, 2010, 01:32:37 PM
I'm not at home, but my memory is that there is no daughter card for the guruplug. So the sandwich is as follows:

Top Case
Main PCB (LED's on top side, most ICs on bottom side)
Heatspreader - with heat tape connecting it to ICs, with bic pen type springs on the 4 corners pressing it to the main pcb.
Aux Cooling block (in my case only)
PSU plastic shield
PSU
Bottom Case - with AC plug

The spreader is nearly the same size and shape as the Sheeva spreader. However, they added a 1/2" extra in one corner to cover the gig-E phy. See my photo in previous post.

Doug
13  Hardware and U-Boot firmware / Hardware / Re: GuruPlug Server Plus Heat Problems on: May 26, 2010, 12:41:27 PM
Also, I seriously doubt if a driver issue will cause or fix the heat problems. If there is a low power operating mode, it might improve thermal issues when idle, but then what if you want to use the device at full capacity? You still have the heat problem.

Thomasb has the right solution. Don't buy the guruplug or sheeva plug unless you want to make major mods to the thermal design yourself. Also, be prepared to make major OS surgery as well.

Doug
14  Hardware and U-Boot firmware / Hardware / Re: GuruPlug Server Plus Heat Problems on: May 26, 2010, 12:29:51 PM
varekey - I have not put much load on the unit yet. All I have connected is WiFi and 1 Gig-E port. With my mods, so far, it has not rebooted in 72 hours. Doug
15  Hardware and U-Boot firmware / Hardware / Re: GuruPlug Server Plus Heat Problems on: May 26, 2010, 11:22:29 AM
I think the guruplug has a pretty efficient power supply. When I disassembled the unit after running it until it overheated, the PS felt cool, while the heatplate felt exceedingly hot. That convinced me that the issue was IC dissipation not inefficiency of the power supply. That said, since the heatplate butts up against the powersupply safety shield, the shield actually blocks heat in. If you remove the PS, then there will be a slightly better path for the heatplate to radiate heat out.

Doug
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