improper project produces problems (iMac hack)

[tech-wreck]

so, i'm putting a computer together for my kids; nothing too hardcore, they'll only use it for youtube and minecraft. brief parts list:

MOBO: asus h61m-vs
CPU: pentium g620, stock HSF
GPU: GT240
RAM: mushkin 2GB 1600mhz (for now - borrowed this for testing)
PSU: FSP 300w mATX
CASE: this is where it gets interesting... i found a mid-nineties iMac on fleabay for a fiver, then set about it with power tools. cut up an old case for the motherboard tray and back panel, and crammed everything back in the case. most of it works...

problem 1: CPU temperature - over 50c when idling, 90+ under load. my pc has an identical heatsink/fan to this one, but sat on a 2500k that gets as hot under load as this one does when idle. (i use speedfan on both machines.)
i think this is an airflow problem, as it peaks at 'only' 80c with the bottom plastic cover off. looks like i will be dismantling it to cut another fan opening in the bottom tray. also, i think the psu fan needs to be flipped over so it exhausts up and out behind the motherboard tray instead of into the bottom of the case.

problem 2: built in speakers not working. the front audio jacks are working fine, but they come from a header on the motherboard. the speakers are the original ones fitted to the case, soldered onto the connectors from the donor monitor's speakers. these are plugged into the pcb with the volume control and power button. this is connected to the monitor via a couple of ribbon cables, and there is a separate audio in socket which is connected to the motherboard's audio out with a short 3.5mm audio cable.

so, it's either my soldering which has come undone, or the 'adjustments' i made to the monitor's pcb were a little too vicious, or the ribbon cables have popped out (they're hidden behind a metal shield), or the audio cable i found in a box of mixed stuff is no good.
or, i could have plugged it into the wrong hole, it's dark down there and i can't get many fingers in...

everything was going so well... then i switched it on.

i'll do a proper build log when it's fully working, but here's a preview:

 

[C12Friedman]

First I think we should address the PSU's airflow, the PSU will always exhaust out the back (unless the PSU's fan is removed and turned around). The PSU with fan up, (toward the open area of the case) can help in exhausting air from the case - there is a disadvantage though and that is that heat can cause a PSU to produce less power (why you sometimes see PSU marketing showing a temperature along with a wattage rating). I will suggest replacing the thermal compound on the CPU heatsink to attempt to address the heat there - also, check your CPU heatsink mounting to ensure all corners are locked down.
Audio issues... uh, er, I just don't know where to start there - how difficult do you think it would be to pull the CRT (looks to be a CRT in the pic) from the chassis? I think I'll suggest that route if it can help access your audio cables. Just curious, did you trace out the speaker wires or are you assuming you have no amplifiers/DAC's after the speaker connection at the PCB. I'm thinking you need amplification offhand (not positive here but my intuitive thought)

Hope it helps some

 

[tech-wreck]

First I think we should address the PSU's airflow, the PSU will always exhaust out the back (unless the PSU's fan is removed and turned around). The PSU with fan up, (toward the open area of the case) can help in exhausting air from the case - there is a disadvantage though and that is that heat can cause a PSU to produce less power (why you sometimes see PSU marketing showing a temperature along with a wattage rating). I will suggest replacing the thermal compound on the CPU heatsink to attempt to address the heat there - also, check your CPU heatsink mounting to ensure all corners are locked down.
Audio issues... uh, er, I just don't know where to start there - how difficult do you think it would be to pull the CRT (looks to be a CRT in the pic) from the chassis? I think I'll suggest that route if it can help access your audio cables. Just curious, did you trace out the speaker wires or are you assuming you have no amplifiers/DAC's after the speaker connection at the PCB. I'm thinking you need amplification offhand (not positive here but my intuitive thought)

Hope it helps some

i've just finished some tinkering, with mixed results. i opened the PSU and turned the fan over. it's mounted at the bottom of the case with velcro - i'm so glad i did that - so i'm hoping it'll now pull fresh air in through the vents in the bottom plastic panel. i'll fabricate something to divert the exhaust behind the motherboard tray later...
there is a 140mm fan at the top of the case, directly under the vent holes in the top plastic cover. is that enough? there's not really anywhere else to expel hot air from.
i'll have another go at the thermal paste, and make sure the heatsink is properly locked down. one of the two cores was a few degrees hotter than the other...

i'm enjoying all these 'learning experiences' 😉

and you may be right about amplification. after testing each part individually and found them all working, i connected them all back up and plugged the audio into a nearby laptop. powered the screen up and it worked, albeit very quiet, which wasn't so bad as for some reason i chose http://www.youtube.com/watch?v=wZZ7oFKsKzY as test material...

maybe it was so quiet because it was plugged into a headphone socket. i checked the speaker connections on the pcb with a multimeter; with the video paused or the volume wheel (on the pcb) down, it was 15mV, with the video playing and the volume up, 17-18mV. i'm no audio expert, but 3mV doesn't sound like enough to drive a speaker.
now i need to build a simple amplifier and frankenstein everything together. where's me soldering iron!

also, i forgot to mention in the OP that the ethernet connection stopped working, but after testing the bit i made (working) i have concluded that the cable i used to connect it to the router is fecked.

cheers 😀

 

[C12Friedman]

I would think with a 140mm at the top you should have adequate airflow. Other than the modified PSU, are there any intake fans or vents at all? I'm sorta thinking a few more pics may be of help (and give me something to drool over).
A few degrees temp difference between cores is normal, no concern there.
You'll get the audio figured I'm sure - sounds to be a fun, yet, frustrating project (sums up most all of mine) - can't wait for the build log

 

[tech-wreck]

I would think with a 140mm at the top you should have adequate airflow. Other than the modified PSU, are there any intake fans or vents at all? I'm sorta thinking a few more pics may be of help (and give me something to drool over).
A few degrees temp difference between cores is normal, no concern there.
You'll get the audio figured I'm sure - sounds to be a fun, yet, frustrating project (sums up most all of mine) - can't wait for the build log

you were right about the heatsink - it felt loose as soon as i got my fingers on it. now it's solid. and the numbers are fabulous


admittedly, these were taken while the computer was running in a bare chassis without all the plastic panels. i'll test again when it's reassembled. if it keeps under sixty degrees, i'm happy.


the PSU is the silver mesh thing behind the black mesh of the imac bottom tray. it sucks in through there and blows upwards. other than that, no intake fans. dropped the idea of cutting another hole in the tray, as that's where a lot of the cables are routed. instead, i'm going to leave the PSU fan blowing over both sides of the motherboard. unless that is a terrible idea. i don't know.

anyway, a couple of pics for droolage:



also, forgot to mention the BSOD/restart (repeat) issue when i put it back together. couple of hours reinstalling windows, drivers, programs etc., and then ten minutes to capture a HDD image. ten minutes i should have spent yesterday... isn't hindsight brilliant?