My Centris 650 Wont boot

[Mycatisbigfoot]

Ok this is what happend,

I was on my Power mac g4, just copping disk 7 for os 7.6 ( to a floppy)
and my 650 just went off and wont go back on, The computer needs a new system but that is all i know now, But when it did go off, My apple vision was pluged in to the computer,
I have tryed dirfrent combos of hard ware, from that I have also unpluged the strange cd drive on the and the hard drive, but still nothing,

I would like to get this computer going,

I do have a pc power box, and i can wire so if some one send me the wireing I can test another power box to test.
I have also took all of the chips out and put them back in, I tell you I have more problems with towers then All in ones,

[Hrududu]

I bet its the power supply. I've got a Centris 650 also, and its basically the same as a Powermac 7100. I'll see if the power supplies are interchangeable.

[electroshock]

I bet its the power supply. I've got a Centris 650 also, and its basically the same as a Powermac 7100. I'll see if the power supplies are interchangeable.

Agreed, the PSU was my very first thought, too. The C650 was the first Mac I personally paid out cash for and that was a real solid workhorse. Definitely worth reviving.

[MacTech68]

So when you attempt to turn it on using the button at the rear, nothing at all happens?

1. remove the keyboard and mouse (and all other peripherals) and try the power button on the back.

2. try removing the mains power for about an hour. If it powers up after that, then there is possibly a resistor that needs replacing.

3. check the battery on the main board. If it reads below about 3.4 volts when fitted, remove it. Leave it without the battery for a day or two and try again (without the battery). The battery is located under the CD/Hard Drive cage.

Note that the power button at the rear can be turned 90 degrees to keep it pressed in. Make sure it isn't being locked in the "on" position (though this feature is normally used to make it power up after a power failure).
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[velocityg4]

I bet its the power supply. I've got a Centris 650 also, and its basically the same as a Powermac 7100. I'll see if the power supplies are interchangeable.

They should be. Since all throughout that case style I believe the motherboards could be swapped. As that was the method always advertised in MacWorld.

So I think that the IIvi, IIvx, Centris 650, Quadra 650, PowerMac 7100's and a few Performa's can be swapped. Though I think the 68030's used 30pin simms I don't quite remember if the IIvx I used to own was 30 or 72 pin.

[richardtj]

from recollection, there's a slight difference between the 650/610 and 6100 power supply pin outs- more pins. Think the same would go for the 650 and 7100. There's a glass fuse within the PSU of older 68040 macs from recollection- slow blow 3.5 amp fuse that may have gone. You may want ot take a look at that if all else fails!

[velocityg4]

Here is some info I found on what normally goes wrong with these PSU's.

Aztec Powersupply
There is a problem with some Aztec Powersupplies where the 5V trickle voltage circuit goes bad over time. The +5V.TRKL supply voltage for the power-on circuit, as fed to pin 10 of the (Macintosh IIcx/IIci/650) powersupply connector, is in the Aztec power supply generated on the top PCB (95402 A) with a circuit that (a.o.) consists of C34 (33 nF), Q5 and Q6 (transistors) and D15. This circuit forms a sawtooth oscillator (sawtooth voltage on C34), the output of which is fed to the transformer T4, in order to galvanically separate the trickle supply from the mains (the sawtooth generator is on the primary side !). The function of D15 is to compensate a voltage (junction) gap, but this compensation is critical, unfortunately. Therefore, the oscillator can end up in a stable, non oscillating state (minimum voltage over C34) and consequently no AC voltage on the secondary side of T4. Simply superimposing a trickle voltage (5 V, > 5 mA) on pin 10 of the power supply connector (or the ADB connector) does not work, because signals from the sawtooth oscillator are used in other places of the supply as well. The solution to the problem is to replace D15 by two silicon (signal) diodes, connected in series, thus doubling the voltage gap to 1.2 Volts. In that case, there is no stable non-oscillating state possible. In order to end up with (approximately) the original frequency (roughly 17 Khz), it might be considered to change C34 to 39 nF, but the value is by no means critical. The change, though simple and very cheap, requires some experience with electronics and at least a soldering iron. Please note that the primary DC voltages are high (hundreds of Volts) and remain present some time after the supply has been disconnected. Disconnect the computer, open it and remove the power supply (directions can be found on the internet). Remove the fan (latches on the bottom side). You may choose not to disconnect the fan, since the lock of the power connector (on the lower PCB) is hard to reach. Open the power supply by removing its top cover (two screws) and remove the top insulation sheet. Remove the two screws with which the top PCB is fastened, pull it (a little) towards the rear and lift it. Unplug the mains connector from the top PCB (lock is on the down side !) and rotate the PCB far enough to see D15. Unsolder D15 (entirely) and connect it in series another (similar) diode. Remount the duo and reverse the above steps (put everything together again). The startup of the IIcx/IIci/650 after this modification is always certain, but the startup delay depends on temperature. The colder the machine, the longer the delay.

http://68kmla.net/wiki/Macintosh_Quadra_650