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Model A1200 with 2.16 or 2.33 GHz Core 2 Duo processor

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Diagnostics expertise required re:- LED and potential fault finding?

Hi.

I had a hellish day yesterday. For weeks now, my Mac had started to overheat so I installed smcfancontrol and ran CPU fan at full tilt. It helped a lot. Coming back to mac in the morning I was sometimes seeing 15C. It freezes at around 40C.

Lately, I have been working and the screen goes grey from the top down with a message in many languages telling me it has to shut down.

So I stripped it and checked GPU and CPU as per your excellent guide. Brilliant resource. Many thanks for being there.

It's a 7300 on this model and the chip looks a bit bluish like it has really overheated.

Bear in mind, after a period of cooldown, it was restarting and working fine until it would shut itself down again.

The thermal paste was hard so I scraped it off, cleaned and re-applied.

All fans and ducts are clear. No real dust to speak of. In general, quite a tidy internals.

I put it back together (several times). I realised I'd left CPU sensor cable off.

Anyway, to get to the crux of the matter.

LED's.

I cannot remember the exact order of events leading to the current status.

I had it at a stage yesterday where 3 lit and remained lit but white led was steady. I then removed logic board to check thermal paste. It had spread over some transistors on the GPU. I cleaned it off again and re-applied a little less but sufficient.

Put it all back together again.

Now it starts. When power button is pressed LED's 1, 2 and 3 light. 3 goes off straight away and white light stays steady.

This normally boots to desktop within 25 seconds.

It is operating normally as smcfancontrol spins up the CPU heatsink fan at 32 seconds in but white LED stays on.

My concerns are:-

1) I am running this with cover off. Does iSight camera need to be plugged in to send a signal that it is working to enable screen to be switched on? It doesn't seem to make any difference to LEDs.

2) Why would GPU, logic board or LCD suddenly not work where it was fine before? I have been very careful handling all components.

3) If I buy a Mini DVI to VGA and connect secondary monitor, will it work if fault is purely LCD? I never like to assume but I am guessing it will.

4) Money is very tight at present. Do I go with GPU first or logic board? The LED info I have seen on here suggests GPU first (most expensive component).

5) Will this board run a 1Gb Nvidia MXM chip or am I restricted to a 7300/7600GT GPU?

6) This may seem a stupid question but I have had it to pieces so many times. I simply do not want to take it back to bare bones again. Got down to 8 minutes on strip down! Is it possible that I have left a cable off which would give these LED symptoms. I guess not but...

Apologies for the long description but hopefully it is detailed enough to help you to help me.

I am getting desperate with this.

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@Grumpy Greyhound, post an image of the broken component as well as its location. that will help us to identify what it is and what its purpose it. May help you in getting your computer back.

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@oldturkey03

Thanks for that. I have had a quick search on how to upload an image but it is beyond me. It talks about Media Manager, takes me to Dozuki and this and that.

Can I not just host an image on image shack or similar and link to it?

Here goes trying a link:-

[URL=https://imageshack.com/i/p9ttSvbSp][IMG=http://imagizer.imageshack.us/v2/800x600...][/IMG][/URL]

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1, No - if you're 100% that it's only the camera cable you left unplugged.

2. That's the way of electronics - most work until sudden catastrophic failure (there's no grinding noise or smoke as with bearings or other mechanical components). Handling can stress cold solder joins to failure... reassembly problems can often lead one to "think" or "believe" that all connectors are "good" when closer reexamination finds connectors misaligned, not snapped or locked in.

3. Yes - if the fault is the GPU or logic board you'll get no external video. This is a common troubleshooting technique to determine where the display issue begins.

4. Before you jump see this answer. It may be easier to find a complete good logic board than a replacement GPU (can't be just any GPU) that will work.

5 - no direct knowledge to answer that question. I can say that you are limited to GPUs that were OEM for that model... otherwise you'll have EFI and extensions (aka driver) problems.

6. White screen hangs while the video card and display are communicating have often been traced to either HD problems or System Folder OS problems (corruption of files). A shift boot, or booting from some other source may confirm or deny a HD/OS cause for white screen hang.

If this answer is acceptable please remember to return and mark it accepted.

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OK.

Plot thickens.

Graphics card back and no joy.

Noticed that there is a crushed SMD capacitor which repair guy appears to have reflowed. it has shorted as it is giving a continuous tone when using ohmmeter. Others give a reading.

A friend advised me to desolder it and remove.

This has helped. LED's 1, 2 and 3 are now lit but still no video on screen and external monitor does not display.

Should I have GPU board reflowed by a professional company who I know have some serious kit and are ISO9000 certified.

They have offered to replace SMD capacitor for £33 but I don't want to spend money unnecessarily if that will not resolve it.

i am concerned first place I sent it to were not as experienced.

Can anyone advise further please?

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machead3 - many thanks for your answer.

It clearly boots to desktop as when I pressed a key it bings through the speakers.

I have stripped it again and submerged the GPU in Isopropyl Alcohol and given it a good scrubbing with a toothbrush and dried it off with a hairdryer.

Now. I noticed that I had incorrectly installed the brace on the back and tightened it up tight. It was sitting on top of some transistors!!! Not as careful as I thought I was. This is a good tip to watch for when anyone reassembles these.

I had assumed, stupidly, that the dirty side of the brace was on the outside because it would naturally tarnish because of dust and dirt but it was a plastic isolation coating. I am pretty sure I did not install the brace incorrectly every time.

I cannot see any cracks and have now sent the GPU for a reflow with a professional company. A lot of people online recommend reballing over reflowing so we'll see how it turns out. For my sake, I hope it is successful.

I spoke to one guy today in the UK who is selling NEW OEM Apple GPU for £249 and he reckoned he has sold 15 this week. I doubt there are that many people repairing these in the world a week with genuine parts let alone the UK so I declined his 'kind' offer to relieve me of good money. The whole unit isn't worth that.

If reflow fails, I will cannibalise it for parts in a bid to help others repair their units.

This guy trying to sell me a new GPU said the early white Intel iMacs are the best in terms of resolution. I am sure they cannot be as good as any later model. Why would Apple reduce the quality of resolution?

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