MDD only boots up when ADC monitor is plugged in

[ArmorAlley]

Hi all,

The answer to this question (as seems to be the answer to all MDD questions) is that the PSU is on the way out.

However, just in case it isn't, I'm posting to see if anyone else has had this problem and has found a solution.

I bought an MDD late last year with a beautiful Apple Cinema Display HD (in box too!). I bought it from the original purchaser and he had taken good care of it. I assembled it all and it works.

Yesterday evening I finally got around to plugging it into my HP LP2065 (1600x1200 LCD) and it wouldn't start. Bleh. I changed the PRAM battery. Nothing. I brought it downstairs assembled it again as I had done and it starts up with as loud a bong as ever. I plugged in another LCD monitor while it was powered down and both monitors came up on startup. I tried it with only the LCD monitor in the DVI port. Nothing. Merely a flash on the start button. Not even a bong. I plugged the ADC monitor back in. All OK.

I then stuck in a PCI ATi Radeon 7000 and put the LCD monitor into that. Starts up fine. I took out the ADC card (ATi Radeon 9000 methinks) that came with the MDD. Nothing. Won't start. I put the ADC card back in and plugged it in. Starts up fine.

Any ideas in getting it to boot up without an ADC monitor? The Cinema Display HD is a feckin' massive yoke.

Thanks very much

 

[ArmorAlley]

I came across this answer here: https://discussions.apple.com/thread/4274116?tstart=0

G4 MDD will only boot with ADC connected

There have been many similar threads to this one, but I have not found any which report a solution.

My problem.

G4 MDD Dual 1.42 that I have owned since new. Initially ran with 23" Cinema Screen HD, then with Samsung Syncmaster via DVI for several years, and then headless as a server.

Several years ago, I experienced the inability to boot problem (Power button lights, fans whir, and then stops). I gave up and stored the machine.

Recently, my Powermac G5 had display problems, and so I pulled out the MDD to see what was happening. It booted first time connected to the ADC Cinema display (which was the screen used by the G5).

Out of interest, I then tried booting with the DVI display, and the original problem occurred - no boot.

To summarise, the MDD works fine (stable, no software issues or kernal panics for long periods with 10.5. with the ADC display or ADC + DVI displays. It will not boot without the ADC display (only DVI connected, or headless)

I have done all of the usual - Pram reset, battery change, reseat memory, power lead out etc.

I have reached the same conclusion that Japamac reached in another thread - there is some loopback from the ADC which is compensating for a weak suppy in the MDD. However at the video card, there are no changes in 25V, 5V, or 3.3V lines when disconnecting the ADC, and all voltages are in spec. All screens and returns are commoned with or without the ADC. (Video card is original ATI 9000 XT Btw)

I have seen that this may be a front board problem, but the machine boots fine from front MDD button or Display button when the ADC is connected.

Any input would be appreciated

G4 MDD Dual 1.42, Mac OS X (10.5.

 

[Macdrone]

One MDD I have had that had the same type of issue was something to do with the power supply being weak and needing recap on the way it sees and understands standby 5volts and the 28 volts with the ADC monitor connected.  Full 28 volts is only used with proper video card and ADC display.  There is one full power USB port on the ADC port and I think that "tricks" the power supply for the 5 volts.

I hope that makes sense.

The next problem to occur is not being able to shut down without unplugging so be aware.

I hope that make some sense and am expressing it correctly.

 

[ArmorAlley]

Hi Macdrone,

Thanks for the reply. It has sunk in that the PSU will need to be fixed or replaced. I got the whole lot (MDD & Cinema Display) for the equivalent of $20 so I can't complain. It will just have to join the list of other things that need recapping. It's not as loud as I had been lead to believe though and that is a plus point.

 

[Macdrone]

The Rev A is not as load usually but more prone to death, the new fans in the later revs made it louder but last longer (as least thats what was mentioned somewhere i read)