Got a tip for us?
Let us know
Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
Display brightness of my old iMac
- Thread starter zoran
- Start date
- Sort by reaction score
csdesign3
macrumors member
My external PSU is a 12v 4Amps and i am running the normal Chinese board Chinese inverter board(i don't feel my PSU too hot but its contained into a plastic case like a laptop adaptor), and i have a 12v 5 Amps just in case of the amperage is not sufficient. My only problem right now its time to test and give results (as an IT guy and a father of two child its very difficult to have spare time) but i will try this friday to make the test and post some photos.
I used the 12v from the PSU in my initial testing and it worked just fine. No difference from using the 12v from the LCD driver board. Both will work.
I chose to use the 12v from the driver board for three reasons:
1. I was cutting the 6 wires from the driver board anyways and the proximity of the step down module to the driver board in my layout made it easy to use one of those 12v wires
2. It lowers the power demand on my 13+ years old iMac PSU - might help it last longer
3. It spreads out the heat producing sources in the iMac
My wife used my display for a week (approximately 8 hours per day) without issues. The back of the iMac does get warm behind the PSU and inverter, but not so warm that it is uncomfortable to leave your hand on it.
However, just to be safe, I am going to install a small blower fan below the inverter and PSU just to ensure all my time and efforts on this conversion don’t go up in smoke…😀😎
csdesign3
macrumors member
Hi @SubDriver just as a recap, next friday when connecting stepdown converter and PWM modulator, its better to connect to the 12v rail from Chinese converter board or the PSU itself?
I think both are acceptable. Given that you are using a separate power supply brick, I think it is probably easier to use the 12v coming from the LCD driver board instead of from your power supply.
csdesign3
macrumors member
iMacConversionEnthusias and @SubDriver
My Draw setup dont work and even test the sugestion of taking 5v of BLO to StepDown module. both not working, the controller board make a click noise and the PSU turns off (tryied 12v4A and 12v5A). I think i might start looking into your solution of using original apple psu.
So sorry to hear it didn’t work. I’m thinking maybe the power supply isn’t strong enough to drive the original iMac inverter?
Or maybe the the power that is pulled from the 12v line to the step down converter prevents sufficient power from reaching the iMac inverter?
Did you also try the other method you mentioned above and feed the step down converter directly from the power supply? That would keep both 12v lines to the inverter undisturbed.
The wire colors for my mid-2011 iMac SD card reader are different than the colors coming from the card reader in this post. I’m gonna have work through some trial and error to figure out how to correctly connect it to a USB-A plug.
I am going to wait to add that to my conversion until after I get everything else figured out.
Hi Guys, my idea to take 5V from the BLO wire to power the step-down module did not work for me either. Not sure why.... But I got very good result (seen on the first image) by taking the power directly from the 12V power supply before the Chinese board is even powered. I do not use the PWM module as I am still waiting for it to be delivered. So here is the setup :
Chinese board - the model with the DP port.
External (Brick) power supply 8A
Original iMac inverter
Step down module powered from the 12V down to 3.3V going to the BLO of the original iMac inverter
PWM from the Chinese board directly to the PWM of the iMac inverter
Google Chrome Cast with Google TV plugged in the HDMI of the Chinese board (GCCwGTV)
I am doing all of these because the brightness of the Chinese board is not good enough and when I use the original iMac inverter the brightness improves a lot, but the inverter starts going very hot and I am afraid it won't last. Now it is still going hot but probably about half as bad as it was before the step-down module. So, I think the step-down module is definitely fulfilling its purpose. My external power supply is still getting hot which is weird because as shown on the second picture the current drawn is not near the 8A - it is below 1A.
The reason I decided to power the step-down module not from the Chinese board but directly from the 12V of the power supply is so that I do not load the Chinese board with additional power consumption it is not designed for.
Currently when I switch off the GCCwGTV the screen shows no image of course but it is clear that the screen backlight is still on. So, I have an idea to switch on/off the screen backlight either internally inside the iMac box with a little board with a small remote (I have purchased one already) or directly at the 220V with a smart WIFI socket and a smart WIFI button which I am using for various other automations around the house already. There are other solutions for the backlight on/off issue too, but I am not there yet to think about it.
I am starting to like the idea to install a small fan near the original iMac inverter inside the iMac box and control it automatically with a thermostat board inside the iMac box but will get to it later in the process.
Have a nice day guys.
Attachments
Last edited:
csdesign3
macrumors member
Hi, the situation it's strange because both12v PSUs keeps turning of when connecting the Apple inverter and nothing lights up (4Amp and 5 Amp) maybe it's not sufficient.
In the same scenario, I changed to power lines for the stepdown converter from the 12v lines that feed the inverter to main 12v and nothing changes.
Checked everything many times the cables and connections are exactly like I have draw.
I have a working Apple PSU and the cables to follow your guide, just need to buy a push pull button, desperate to have a nice bright display men 😔
Yesterday after the failed testes I finally started to makes the holes for the DP, HDMI ports and USB Upstream ports
Attachments
csdesign3
macrumors member
If you don't mind wait a little, I already encounter your problem when converting mine to USB. But when converting I used super long wires to connect externally to the computer, right now I have a 7 port USB HUB inside of monitor to feed 4 USB ports at the back of monitor, iSight camera, SD card Reader and DD Driver. I have to cut my wires to a small size, when doing I can take a pic for you.
At the time I have find some info about the different color cables even from 2011 iMacs, but I have go hard way (multimeter) and connecting to a computer to see if gets detected.
Right now I'm in the middle of a revolution inside monitor 😄
I'm making tests for using the Apple Inverter, I'm drilling holes to put DP port,HDMI, etc .
csdesign3
macrumors member
I think I need to draw a more visual guide, your explanation using Apple PSU and Original Inverter it's a little complex to read and understand clearly. like we have done before, I will try to draw and get your validation. In the meantime I will help to document the color cables of the SD card and camera too
csdesign3
macrumors member
Attachments
@csdesign3 My best guess is the 5A power supply simply isn't strong enough to drive the iMac inverter plus the LCD driver board and other components. The success @iMacConversionEnthusias had powering directly from the power supply, which was 8A size, may be confirmation of this. I think your power supplies trip offline due to the large current draw.
Considering the original A1312 iMac power supply units were 300-310W units and there were 5 main 12V power feeds that come from it, each one of those individual feeds would theoretically be capable of carrying approximately 4A each (leaving some power for lower power lines from the power supply). Since the iMac inverter uses 2 of the 12V power feeds, that puts the maximum potential inverter current feed around 8A. (see the math below)
---------------------
300W/12V=25A total power supply capability
25A / 5 main power feeds = 5A per feed
Subtracting some power from these due to lower power lines from the PSU (e.g., SMB connections) leaves approximately 4A per each main power feed
---------------------
Good engineering design would mean the normal inverter power draw would be around 60-70% of the maximum. So that means nominal maximum current for the inverter would be approximately 5A.
The above analysis would make sense as to why @iMacConversionEnthusias had success with his 8A power supply and you did not have success with your 4A or 5A power supply. It would also seem consistent with some information that I have seen concerning conversion of the Retina 5K displays - they really push using 8 to 10A power supplies for those conversions.
What do you think? Everything above seems to make sense. I hope you are able to resolve it!
With respect to the current draw, I think the device in your picture is showing the AC current draw, not the DC current draw of your setup.
Comparing AC to DC current is tough, but DC current is usually near 3x the value of the AC current. This would put you near 2A for DC current using the AC current value shown on your meter. This still seems lower than I would expect, but is certainly closer to what reality likely is.
Yes, I agree. After I posted the message I realised that it is measuring the AC.
Initially I started my conversion with a 6A power supply and the overload or overheating build in protection was tripping every hour and that's when I decided to go to 8A.
I can and will measure the current after the PSU.
Another way of looking at it is that the AC power is
84.70 watts / 12V = 7.06 amps converted to DC.
csdesign3
macrumors member
I think i can borrow a 12v 6A for a quick test before buy a 8Amp external brick. It makes a lots of sense what you said about the power draw of the invert, i never think much about it, but yes the Apple PSU is very well designed and have high capacity per voltage line.
I will try to make today a quick test and leave feedback...
Hi, can somebody tell me how to wire the original HDD fan. I measured it and it seems to be good then I tried to connect it to 5V and to 12V with various combinations of suppling the V to the 4 wires. By the little I can see at the board behind the sticker I saw that the most right wire is VCC and the one to the left is GND and that's how much I could see. I read that 2 of the wires are for regulating the speed so I was thinking that if I short circuit them (the 2 most left wires) and supply the V to the VCC and to the GND wires it should work but it did not. Thanks.
