Centris 650

[John8520]

My first "real liberation" in quite a while. This was at the flower shop where my Mom used to work, sitting in a pile in the office where it went unused for many years. A few months ago, the shop closed down (thankfully my Mom found a much better job soon after) and just this morning the secretary called us to see if I wanted it, and of course I did!

It's in amazing condition, has the main system unit, apple design keyboard (the mushy mexican one unfortunately) ADB mouse II, Apple High-Res RBG monitor, imagewriter II, and an Epson ActionLaser 1100. Aside from the IW II, which is yellowed and stickered, it's all in perfect condition with only light scuffs and residue, easy to clean off.

Upon opening the case, the Centris' specs are as follows:

- It's the higher end model, complete with a full 040, AAUI, and 8MB onboard RAM

- Has one 32MB stick of RAM

- No NuBus cards :/

- Two VRAM modules, two chips, 256kers?

- Quantum ProDrive LPS, 230MB

- Manual inject HD FDD

- 25Mhz 040

Despite all this awesomeness, it doesn't boot. Neither the power button on the keyboard or the back of the case invoke any sort of response at all, no clicking, humming, anything like that. I know the power source is good cause it starts up the monitor just fine. When it was last powered up in 2003 it worked fine and got online via a modem, maybe something happened since then? The Q700/IIcx PSU looks almost compatible; is it? I'd love to get this thing up and running, it's so nice!

Oh, right, pictures! http://picasaweb.google.com/john8520/Centris650

 

[Bunsen]

Try the motherboard battery.

 

[John8520]

It's dead. Does it need a working one?

 

[wood_e]

Yeah you need a new one! Quadras/Centris models are picky when it comes to their PRAM batteries. I thought my 605 was dead...

 

[iamdigitalman]

what do you mean by a mushy mexican appledesign keyboard? I have stacks of these things, all perfectly platinum, and they all feel pretty solid. I like the appledesign keyboard, dunno why it gets such a bad rep.

-digital

 

[John8520]

Dang, that's a serious bummer. I guess I'll start looking around to see if I have any good ones, at least my SE and 700 work with dead ones. Hopefully that fixes it, at least.

 

[John8520]

what do you mean by a mushy mexican appledesign keyboard? I have stacks of these things, all perfectly platinum, and they all feel pretty solid. I like the appledesign keyboard, dunno why it gets such a bad rep.
-digital

There are two versions, Mexican made and Thai made, the Thai ones have a much more tactile feel than most of the Mexican ones. I have four Thai and two Mexican, this is certainly true for all my boards.

 

[iamdigitalman]

interesting. I guess I will have to start looking though mine then, I have a couple dozen of them, one of them HAS to be thai. However, they all came from the same place...

I know the one I was using for the last couple years on my B&W felt a little mushy. Plus once I took it apart, the spacebar never went back on again, so it's raised up on one side. I asked on a google group on how to take one apart properly, but I never got any replies.

-digital

 

[Bolle]

i bet you got an aztec PSU in your centris... theres a pretty common problem with these PSUs. the circuit that generates the 5V trickle voltage goes bad over time.

i got this from a IIci related site some time ago after some heavy archive.org digging... (IIci and 650 PSUs are the same btw )

The (Aztec) trickle problem and its solution. The +5V.TRKL supply voltage for the power-on circuit, as fed to pin 10 of

the (Macintosh IIcx/IIci) power supply 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

with another (similar) diode. Remount the duo and reverse the above steps

(put everything together again).

The startup of the IIcx/IIci after this modification is always certain,

but the startup delay depends on temperature. The colder the machine,

the longer the delay.

You have gained the US$ 15 of a new supply (if available !)

 

[John8520]

Yes, it is an aztec PSU! Well, it looks easier to just pop in my q700 PSU as it does to rip that thing apart and fix it, but it's certainly something I'll look into.

 

[JRL]

Brand new PSU:

link

 

[Christopher]

what do you mean by a mushy mexican appledesign keyboard?

The mexicans filled the keyboards wth refried beans :O

 

[John8520]

Ok, I have a RAM question:

It has one 32MB in the slot, and of course the 8MB onboard. I went through some old PC stuff and found two more 32MB sticks, but nothing else matched. I read that the 650 is one of the macs that works better with matched pairs, so I wonder:

Do I get better performance with three 32MB sticks, one of them being unpaired, or with two 32MB sticks, both being paired?

 

[Temetka]

I think you would get a better performing system with a ton of RAM. It is probably not your main rig and therefore do you really want to hunt up a set of interleaved RAM, or just slap a boatload in and take the negligible performance hit you might incur?

If it were me, I'd max the sucker and never look back.

 

[John8520]

Yeah, that's the current plan. Though I /would/ like another 32mb stick! I might have another hiding in the shadows, if I didn't send it off with those LCIIIs...

 

[Bolle]

there is nothing like interleaving on the 650. you wont get anything from putting matched simms in there - besides more memory at all

 

[John8520]

Lowendmac says there is:

RAM: 4 MB or 8 MB on motherboard, expandable by 128 MB using four 80ns 72-pin SIMMs; motherboard had 4 SIMM slots which can be filled individually but should ideally be filled in neioghboring pairs to take advantage of interleaved memory; can use 4 MB, 8 MB, 16 MB, and 32 MB SIMMs

 

[Bolle]

hmmm... didnt know that. but should this be true? some apple technotes on taht would be nice. I got 4 exactly teh same 32MB simms in mine but would be nice to know if its worth something.

 

[madmann]

I would pull the simm chip and put the new battery in.

once you get it going stock start upgrading!!

I thought you had install them in pairs. ie 16 bit simms each so you need 2 for 32 bit addressing.

i know this is true on my 7100

in old mac 2 it was 4 at a time ie 8 bit simms x 4 = 32 bit