Other logic board

My Mac says the date is 1904 (or 1956) and keeps resetting itself to that date when I turn it off.

You have a dead, or missing, PRAM battery.

There were three different types of PRAM batteries used in Macs. The Plus (and earlier Compacts) used a 4.5V alkaline battery that is very similar in appearance to a AA battery. The Eveready part number for this battery is 523. Equivalents are ANSI 1306AP, IEC 3LR50, NEDA 1306AP, Panasonic PX21, and Varta V21PX.

The 57x, 58x, 63x, and later Macs based on their motherboards used a 4.5V square battery, Rayovac part number 840 or 841.

Most other Macs used a 3.6V, 1/2AA lithium battery, which is readily available at many vendors.

Some people have had marginal success with using 3V CR2 lithium batteries designed for cameras, but Apple doesn’t recommend this for one simple reason: they tried it and it wasn’t sufficient. The early SEs and Mac IIs had 3V batteries in them and Apple received many complaints that the PRAM was resetting itself spontaneously after a year or two of use. They traced the problem to the 3V batteries and from that point on, used 3.6V batteries instead.

What other logic boards will fit my Mac as an upgrade?

Mac logic boards come in a number of basic designs, or form factors. Form factors are named after the first computer that comes in that form factor. Logic boards of the same form factor will physically fit in each other’s cases. An * indicates minor modifications may be needed to fit this board into a prior case or vice versa.

Logic board form factor “128” is common to the 128K, 512K, 512Ke, and Plus*.

Logic board form factor “SE” is common to the SE, SE FDHD, and SE/30.

Logic board form factor “II” is common to the II, IIx, and IIfx.

Logic board form factor “IIcx” is common to the IIcx, IIci, Quadra 700, IIvx/P600, IIvi, Centris/Quadra 650, and Power Macintosh 71xx*.

Logic board form factor “Classic” is common to the Classic and Classic II/Performa 200.

Logic board form factor “LC” is common to the LC, LCII/P40x/410/430, LCIII/P450, LCIII+/P46x, and Q 605/LC475/P47x. Note: if moving an LC II or higher motherboard into an LC, the LC’s fan and speaker will have to be replaced with those from the motherboard donor machine. The LC uses a unique fan and speaker housing that is physically incompatible with the later motherboards.

Logic board form factor “IIsi” is unique to the IIsi.

Logic board form factor “Q900” is common to the Quadra 9xx series and Apple Workgroup Server 9150.

Logic board form factor “Color Classic” is common to the Color Classic/P250, LC5xx/P5xx (with exception noted below for 58x machines), Macintosh TV, and Color Classic II/P275.

Logic board form factor “C610” is common to the Centris 610 and 660AV, Quadra 610 and 660AV, and Power Macintosh 61xx*.

Logic board form factor “Q800” is common to the Quadra 8xx* and Power Macintosh 8xxx prior to the 8600. Worth noting: the Q800 motherboard is nearly identical to the Q650 motherboard with the only difference being a couple of resistors on the board.

Logic board form factor “Q630” is common to any Macintosh 63x or 640 machine, LC 58x/P58x, Power Macintosh 5xxx/P5xxx, and all Power Mac/Performa 6xxx-series (with exception noted above for 61xx machines).

Can I use another Mac’s power supply to replace/upgrade the one in mine?

The power supplies for Macs generally follow the logic board form factors given above; i.e., computers which share a logic board design generally share a power supply as well. There are a few exceptions, most notably in the 8xx(x) series machines.

Why doesn’t my Mac have any video output when I hook up a monitor?

The Quadra 605 and its LC and Performa variants (LC/Performa 47x) will fail to output a video signal when the PRAM battery dies (or if no PRAM battery is present, or if it’s inserted the wrong way). A workaround is to turn it on with the power switch in the back, quickly turn it off, and turn it back on. While it isn’t known for sure why this works, speculation is that a capacitor on the video circuitry is charged by the PRAM battery and flipping the switch allows the capacitor to charge without discharging as it normally would on startup.

The Centris 610 and its later variants (C/Q 660AV, Q610, Power Mac/Performa 61xx) will also fail to output a video signal when the PRAM battery dies (or if no PRAM battery is present, or if it’s inserted the wrong way). There is no known workaround for this problem; you’ll have to replace the battery.

Any other Mac that fails to output video likely has some sort of hardware problem. Try a known-good monitor or video card.

The single slot that looks like a SIMM slot on the Mac’s logic board

The ROM SIMM slot is found on many early Macs. It was used for a ROM update that superceded the ROMs on the logic board. If your Mac works fine without it, leave the slot alone unless you want a dead Mac. If your Mac won’t boot with the slot empty, you probably need a ROM SIMM (see note below). They are specific for each model of Mac and can occasionally be found on eBay. (These also make neat keychains if you have a spare one.)

Below is a table of ROM SIMM information for all Macs known to have a ROM SIMM slot:

⊞ table ⊞

Model ROM SIMM slot? Notes II No has solder pads for one IIx Yes required; no onboard ROM IIcx/ci Yes some later IIcx have only solder pads IIsi Yes very rare IIfx Yes required; no onboard ROM IIvx/vi/P600 No has solder pads for one SE/30 Yes required; no onboard ROM LC47x/Q605 Yes none known to exist Q/C660AV Yes some have only solder pads Q700 Yes none known to exist Q9x0 Yes none known to exist Q800 Yes none known to exist Power Macintosh x100 Yes –

It has been speculated that the early-production IIcx and IIsi models may have had an error in their onboard ROMs and the ROM SIMM is required to correct this error. On later models, it was removed because the error was fixed, and this is the reason for the rarity of the ROM SIMMs on these two models.

For Mac II-series machines with ROM SIMM slots, check to make sure the W1 jumper is removed (if a ROM SIMM is installed) or installed (if the ROM SIMM slot is empty). If the jumper is incorrectly configured, the Mac will look for a ROM where there may not be one and will not boot. If the ROM SIMM slot is empty and the W1 jumper installed and the Mac still won’t boot, make sure the onboard ROM chips are where they should be. If they are, try re-seating them.

What does that strange error code under the Sad Mac mean?

There are several combinations of letters and numbers - way too many to list here. However, Larry Pina’s Dead Mac Scrolls deals with some of them (mostly SE and earlier) and Apple has a reference, that deals with many of them as well.

Is there a good reference for my other 680x0 processor questions?

http://ftpmirror.your.org/pub/misc/apple/ftp.apple.com/developer/Tool_Chest/Testing_-_Debugging/Hardware_tools/Sad_Mac_Error_Codes_1.1.sit.hqx a reference, in MS Word format

What sort of processor upgrades can I do to my Mac without an upgrade card?

You can get a 68010 for your 68000-based Mac; the ‘010 is pin-compatible with the 68000 and should drop right in. You CANNOT put a 68060 into a 68040-based Macintosh; the ‘060 is not entirely compatible with the Mac ROMs or the ‘040 instruction set and would require a major rewrite of a good deal of software in order to work properly. The ‘020 and ‘030 are NOT pin-compatible.

The 68882 FPU is pin-compatible with the 68881 and should be used instead where possible. Socketed 68882s are most often found on dead SE/30 and IIfx motherboards and on Daystar Digital PowerCache cards. The 68LC040, which shipped in most Performa and LC Macs with an ‘040 CPU, can be replaced with a full ‘040 without the LC designation, thus adding an FPU to the previously FPU-less Mac.

Why does my Mac keep restarting when I shut down?

The Mac IIcx/ci, IIvx/vi, Performa 600, Quadra 700, Centris/Quadra 650, and Power Mac 7100 had a rather nice feature designed for ease of use as servers: the power button can be locked in the in position so that when the power is interrupted, the Mac will restart automatically. To disable this feature (rather annoying if you don’t want the computer running 24/7), simply take a flathead screwdriver and turn the power button in the back about a quarter-turn in either direction. The button will pop out and the Mac will no longer restart whenever it’s shut down.

What’s that J18 jumper on my LC475/Q605 motherboard?

With the jumper in place, your Mac will register a gestalt ID corresponding with the Q605. Without the jumper, it will register one corresponding with the LC475.

What’s that little red button on my Mac’s motherboard?

That’s the CUDA reset switch, which resets the PRAM if pressed. Don’t press it unless you’re prepared to deal with the consequences of an ordinary PRAM zap.