• Updated 2023-07-12: Hello, Guest! Welcome back, and be sure to check out this follow-up post about our outage a week or so ago.

Centris 650 just arrived, and I have forgotten a lot of stuff. Dumb questions ahead.

kkritsilas

Well-known member
I just received a Centris 650 from a local surplus place that I actually found on eBay.

Machine appears to be a 1993 unit, and it is said to chime when powered up. From the outside, the plastic front and rear plastic covers have yellowed considerably (closer to orange, actually). The machine has 4MB RAM soldered in, a floppy drive, and hard disk and hard disk tray, as well as the CD ROM are not present. There is a NuBus ethernet card in the middle slot. i opened it up, and after a little bit of effort, was able to remove the inner metal work and power supply to get access to the motherboard. This was necessary in order to remove the PRAM battery, which remarkably showed no evidence of leakage, but I also think it was replaced at sometime, as it green and white, brand is SAFT, and it says 3.6V and Lithium on it, along with Made in France.

Now the questions (because my last 68K Mac was a IIVX, and I have forgotten a lot of stuff):

1. Without a HD, what is the easiest way to verify that the motherboard is OK? I think I should try to find a bootable floppy, preferrably with some diagnostics on it, or get an OS disk set (which I will eventually need, anyway). Is there a preferred diagnostics disk, or OS version? i haven't powered up the machine yet, as I don't have an ADB keyboard, and from what I remember, I need an ADB keyboard with a power button to start the machine.

2. The idea for this machine is to verify that the motherboard is OK, then get a SCSI2SD adapter with a 16-64GB uSD card. Can I make use of all 16-64GB of storage, and is there any disk size limitation imposed by the version of the various Systems? in other words, will
getting System 7.5 impose limitations on volume size, where System 8.1 will not? Or should I just try to get a tray and a rotating SCSI drive? Seems like the costs for either option are pretty close.

3. There are two unkown to me slots in the machine. One is inline with the outside NuBus slot, and is in front of it (towards the front cover) and looks like a card edge connector. The other is near the 72 pin RAM slots, and is slightly offset from the 4 RAM slots. What are these slots?

4. is there any place outside of eBay to look for the SCSI tray and drive, and/or a SCSI CD-ROM?

Kostas
 

3lectr1cPPC

Well-known member
I believe system 7 (or at least most versions of it) have a volume limit of 8GB. Yours being a 68k mac, it might be better to go with something even smaller though. Someone else will have to confirm.

On the motherboard - If it chimes and displays the question mark, most of the board is working. It's possible that other functions such as serial/adb/scsi/etc. may be broken, but this is highly unlikely. Being from 1993, you'll need to recap it for continued operation. The caps in 1993 machines go just as bad as earlier ones at this point, and having one working now means you have a good chance of escaping without having to do extensive repairs. For added reliablility, recapping the power supply may be in order. They go bad quite often.

Not sure on diagnostics, I've never heard it discussed.

Welcome to the forums, and of course, enjoy your mac!
 

alectrona2988

Well-known member
I do have a caddy loading CD ROM drive if you want it. Not sure if it works as I do not have anything to test it with...
As for the 2 unknown slots you speak of, that might be for VRAM.
Disk limitations? You can only run up to a 4GB partition if I recall. Anything higher and the system won't function properly.
That's all I can think of for now.
 

kkritsilas

Well-known member
Thanks to all for the welcome.

The two VRAM slots I think are placed together under the floppy drive (and I guess the CD-ROM if it was there). THere are a pair of them. The one connector is black, and is in line but forward of the last (closest to the case) white NuBus slot. The other is right next to the 4 72 Pin SIMM Slots. I suspect that one of them is a PDS slot, and the other a cache card slot? But I don't really know, as I don't recall either of them in my IIVX, or my Mac II that I had prior to my IIVX.

See this picture, I have circled the card slot with a thin red line:

C650_1.jpegC650_1.jpeg
 

mdeverhart

Well-known member
The slot next to the RAM slots is for a ROM SIMM, but your board probably has soldered down ROM. The slot behind the NuBus slot is the PDS (processor direct slot).

yes, the two slots under the drive cage are for VRAM SIMMs.
 

kkritsilas

Well-known member
Mdeverhart, thanks for identifying all the strange connectors.

Another dumb question: the 4 slots for the RAM take 72 pin SIMMs, correct? The 72 pin SIMMs come in two types, FPM and EDO. Does the C650 care which of the two types is used, as long as both are 80ns?
 

mdeverhart

Well-known member
Yes, 72pin, 80ns or faster (lower number, eg 70ns). You can install them one at a time, though apparently you can get a speed up from memory interleaving if you install them in matched pairs.

Everything I found said FPM, which matches my recollection, but I couldn’t swear to it.
 

volvo242gt

Well-known member
System 7.6 works well on these machines, if you don't need to run applications that require 24-bit addressing. It'll be quicker than 8.1, too. Since your board is the base version without the AAUI port for ethernet, you have a 68LC040 chip running at 25 MHz. I do have the regular 68040 I pulled out of mine. Also 25 MHz. That will at least give you the FPU. Converting my 650's board into a Quadra 650 board, with the slightly faster 33 MHz chip.

Luckily the Wombat motherboards (the ones found in the Centris/Quadra 650 and Quadra 800 machines) typically have tantallum capacitors preinstalled, so recapping will likely be unnecessary.

Floppy drive will likely need a cleaning and a relube job, and probably adjustment of the zero track sensor to get it to read/write to a disk. I also wouldn't be surprised if the eject motor gear is stripped.

Drive-wise, I'd probably do a 2GB or a 4GB SD card with either the RaSCSI, BlueSCSI, or SCSI2SD adapters. If the latter, partition it into two 2GB volumes so System 7 or MacOS 8 is happy.

That said, it might be easier to just get a 1GB Quantum Fireball (or similar) drive and mount it to a IIvx/650/7100 hard drive sled. It'll be big enough to hold the OS install, plus whatever applications and other files you save to it.

For a CD-ROM drive, either grab the one that Nick is offering you, or another Apple-branded CD-ROM drive (that way the "C" key booting trick works). If you need the mounting rails, I have a spare pair that I don't need. I also have an extra caddy that I used with my previous Centris 650. Current machine has a 4x tray loader that came out of a AppleCD 600e case that was missing its power supply, so I have no need for the caddy. You'll need to find a bezel. If you go with the stock style caddy loader, @slomacuser has a bezel that'll work.

RAM: Either FPM or EDO will work. I've used both. I currently have two 16s and two 4s in my machine. Since RAM isn't very expensive in the 72-pin variety, I may be upgrading mine to 128MB, for a total of 136MB. Which means the RAM I have will be available. That would upgrade your machine to 44MB from the current 4MB.

Keyboard-wise, stock was either the Apple Keyboard II (M0487) or the Extended Keyboard II (M3501). The latter keyboard does have the desired ALPS keyswitches in it (either the salmon orange or the cream colored versions, depending on how old the board is). The older M0115 and M0116 keyboards also work well, but carry a price premium, since keyboard builders like to buy them and salvage the keyswitches off them for their custom boards (or they'll modify the Apple boards to work with whatever system they're using. There's also the small Apple IIgs ADB keyboard - usually known by the A9M0330 model number. Again, ALPS switches. Mouse would usually be the teardrop ADB Mouse II.

To power on the machine, as long as the button is in place on the rear panel, you can use that to turn it on and off without a keyboard.
 

kkritsilas

Well-known member
volvo242gt, thanks for your thoughts. I will be sending you a DM/PM on the stuff you are offering.

I did manage to pick up an ADB keyboard locally, but it was a Power Computing branded keyboard. I also have a monitor adapter on the way, so that I can actually do something besides listen to the start up chime. It should be here in a week or two.

Finding real SCSI drives locally is a guaranteed no go. Macs, especially the early ones, were not real popular up here, so that source is dry. We don't use Craigslist up here, Kijiji is normally how used stuff is traded, and right now, there are exactly zero SCSI 1 anythings on it. I figured that if I am going to be buying any sort of storage, it is probably best to go with a SCSI to SD/uSD card so that it will be quieter, more power efficient, and I wouldn't need a sled because I could just put together an insulator of some sort for the back of the SCSI adapter card, and then attach it to the metal work with some double sided pads/tape, since it would be light, and relatively small. The smallest new uSD card I can find right now is a 16GB unit. I realize that I could just use 2-4GB of it, but it seems a waste not to use all of it.
 
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mdeverhart

Well-known member
The smallest new uSD card I can find right now is a 16GB unit. I realize that I could just use 2-4GB of it, but it seems a waste not to use all of it.
I wouldn’t worry about it too much. One, SCSI2SD, RaSCSI, and BlueSCSI all allow you to set up multiple virtual SCSI devices on the same card, so even if you limit the disk sizes for compatibility reasons you can use a big chunk of it. My BlueSCSI in my PowerBook Duo is set up to have 6x 2GB “drives”. Two, even quality 16GB cards are relatively inexpensive (I’m seeing < $10 on Amazon in the US, your mileage may vary).
 

kkritsilas

Well-known member
I can get SanDisk 16GB uSD cards for $CAD8.99, and Kingston Canvas for $CAD5.99. I'm going with one of them.

Just have to figure out if it works properly before proceeding. If so, I have a bunch of stuff to get for it (CD-ROM drive, RAM modules, uSD based SCSI adapter, VRAM modules, etc.). just have to wait on the monitor adapter to get here.
 

kkritsilas

Well-known member
Just wanted to follow up, and let anybody interested know that I have plugged the C650 in, and that I did indeed get a power on chime (more of a gong, really). The MacAlly keyboard LEDs flashed very briefly as well, and the rear fan spun, and was actually pushing a lot of air out, and the fan sounded good, even if it is a little loud by today's standards.
 

mdeverhart

Well-known member
Great! Glad to hear that it seems to be working! I have one as well, and they’re great System 7 machines. Fortunately, they don’t have electrolytic caps, so no logic board recapping should be needed.
 

kkritsilas

Well-known member
just a small follow up. The Mac to VGA adapter arrived today, and I was able to get video output to a Dell 24" Ultrasync monitor. I got the expected floppy icon with the blinking question mark (I don't have a HD or bootable floppy), so I am pretty confident that the machine is basically functional. Time to chase all the missing stuff.
 
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