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An Amazing Find for My Next Project -- iMac G4 20"

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The onboard microphone works (tested it with the speak search feature in Google Chrome) but a test recording I made plays back a consistent faint high pitched squeal in the background.


Interference from the upconverter? Thoughts?


https://www.dropbox.com/s/5pb9h1yl6fbuejk/test.m4a



Ersterhernd
 
I did that tonight as per your photo, MacTester. It gave an improvement for sure. I had no idea the GND connect was that easy to do.

Loaded elgato eyetv tonight and watched full screen TV on the 20". Not a single artifact.
Click to expand...

Cool! :thumbup:

Interference from the upconverter? Thoughts?
Click to expand...
Yes, I think so. You could disconnect the upconverter during the test record. Or from the CCFL inverter. If so, you could try to change the Picaxe PWM frequency >20kHz.

Is the microphone cable shield connected? (I'm not sure anymore if there is one)

MacTester
 
Hi Mactester, the PWM freq is already set to 25Khz. I read a post on DremelJunkies blog that stated it to be so. He must have been right because the LCD had an annoying flicker at 10khz.

That aside, I think the easiest solution to test this will be to shut the backlights off via the picaxe controller, do the mic test, then turn the lights back on.


Will try it later.



Ersterhernd
 
I read a post on DremelJunkies blog that stated it to be so.
Click to expand...
Can you give me the link to this post? Did someone other use a PWM controlled backlight in an iMac?

Gruss

MacTester
 
kiwisincebirth said:
Glad to see your hard work paid off. I suspected the EMI might be the issue. Differential signalling uses very low power, and does rely on the wires bing twisted, or shielded.

It is easy to forget the basics of shielding. My first 8 bit computer came in a plastic (only) case, If you placed an AM radio next you could literally hear your programming running, different programs would make different (and identifiable) noises. Some guy wrote a program to play "Happy Birthday" via any nearby radio.

The other tool at your disposal is to wrap the DVI plug, around the exposed wires with something like this.

http://solutions.3m.com/wps/portal/...cs/Products/Product_Catalog/~?N=7234470&rt=c3
Click to expand...


Kiwi, maybe it'd be an idea just to wrap the entire upconverter instead with a similar 3M product like this?

http://www.digikey.ca/product-detail/en/AB-5100 X 8.26"/3M5100D-1FT-ND/1630224

Your thoughts ?
 
ersterhernd said:
Kiwi, maybe it'd be an idea just to wrap the entire upconverter instead with a similar 3M product like this?

http://www.digikey.ca/product-detail/en/AB-5100 X 8.26"/3M5100D-1FT-ND/1630224

Your thoughts ?
Click to expand...
the reason to wrap the DVI display cable is it protects it from Any EMI that might be around. Wraping the up converter only stops EMI from the up converter, but what about the nuc motherboard itself. The nuc case itself has a metal shell to protect it, but also to prevent it from generating EMI outside the case.

You are blessed with an EMI tester (the dvi connector). Use it to test other components, like nuc, pico PSU, etc.

Also consider a sheet of aluminium on the base of the up converter, this may solve the problem. Depending on the type of metal the up converters heatsink is made of it may or may not also provide EMI shielding.

Just test with your dvi cable, and preferably ground the case of the up converter.
 
G5 Design According to Ive
GA-Z270MX-Gaming 5 |  i7 7700K |  GeForce GTX 650 Ti
G4 Cube Inspired Self Build
DQ77KB |  i3 3225 |  HD 4000
G4 Cube ReInvented
DQ77KB |  i7 3770S |  HD 4000
Kiwis 20" iMac i5
D54250WYK |  i5 4250U |  HD 5000
Tonight I really tore into the iMac to determine the cause of the artifacting on the LCD in OSX. I suspected up to this point that the culprit was the 12v to 24v upconverter. It turns out I was wrong.

I disconnected all of the following...

1. The PWM fan control (leaving case fan inoperative)
2. The PWM LED controller
3. The PWM brightness controller (connected Yellow Inverter wire direct to 3.3V)
4. The 24V upconverter (wired up the Apple iMac 20" PSU for the 24V)
5. Connected the original NUC 65W PSU to the NUC.

Upon booting to OSX, the artifacting continued exactly as before. Only certain shades of blue and black are affected by red or green flickering pixels.

Win7 boots just fine with no corruption.

I'm beginning to think this is an OSX Mavericks issue. Going to try an install of 10.8.5 Mtn Lion next, to see what happens. I intend to get to the bottom of this, one way or the other.


Ersterhernd
 
kiwisincebirth said:
Two things to try:
Disconnect Pico PSU
Ensure to put the NUC back into its shielded case.
Click to expand...

Hi kiwi, the nuc is in its case, except for a small hole I cut out for the sata cabling. Disconnecting the pico would be a lot of work because i still need 12v for the video, but doable.

I noticed that even in this disassembled state, if I move the 12v power wire slightly with my fingers, the artifacting changes either increased or decreased. It runs alongside the black & grey video cables up to my wiring connect to the DVI.

Very odd. I appreciate your input.


Ersterhernd
 
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