Checking on my Quadra 950

Quadra950 bezel close cc


It didn’t boot.

Compared to other Macs in my collection which have been in storage for a longer period (the LC II, for instance, or the Performa 630CD), I used this Quadra 950 for the last time around the second half of 2011, so it’s been a little more than two full years. Of course everything was working fine and, knowing I wouldn’t use it for a while, I stored the Quadra carefully, taking particular care in covering vents and other holes to avoid the excessive formation of dust bunnies.

Before connecting the Quadra to keyboard, mouse and display, I opened it to take a cursory look at the amount of dirt that accumulated inside of it since the last time I used it, but finding it rather clean overall, I went on and flipped the switch (actually I pressed the Power button on the keyboard).

The Quadra’s response: “KH-POP”, and nothing else.

Typically this beast of a computer, with a power supply capable of delivering 303 watts of maximum continuous power (you can, for example, connect an external display to the Quadra 950 PSU and the Quadra will power itself and the display), would make a sort of “KH-DUM” sound when powered on, followed by the spinning up of the various drives and the large fan mounted against the power supply. Instead all I got was a “KH-POP,” the power light would briefly turn on, and nothing else. The Quadra 950 has a security keyswitch on the front, with three positions: OFF, ON and SECURE. According to this archived Apple Knowledge Base article,

When the keyswitch is in the SECURE position, the ADB devices and floppy disk drive are disabled. For example, the keyboard does not generate characters, or the mouse moves but no menus can be pulled down. Also, when power is applied to the computer while the keyswitch is in the SECURE position, the computer automatically starts up.

Turning the keyswitch in the SECURE position made my Quadra 950 cycle in a scary loop of “KH-POP KH-POP KH-POP” — it was clear that the Quadra tried to power on but could not. A very faint burnt smell was not a good sign, either.

My first thought was: The power supply has bitten the dust, but I had my reservations. True, long periods of inactivity aren’t good for vintage Macs (or any computer, for that matter), but the Quadra 950’s power supply is considered one of the most robust, and I found it unlikely that it would give up the ghost this way. It’s just a feeling, of course, but something that happened later in my investigation may corroborate my instincts.

Cleaning out

I disconnected everything and started the cleaning process. I wanted to be as thorough as I could, and that meant removing the drive shelf and the power supply, then removing the large fan mounted on the power supply, inspecting each part and cleaning it gently. Then I removed all the connected NuBus cards and dusted them one by one; then I dusted the motherboard.

Power supply

As you can see, the power supply occupies a large part of the Quadra 950’s interior. In that empty space above it there’s the drive shelf (which I had already removed when I took the photo).

The amazing thing to note with regard to disassembling the Quadra 950 is how simple and straightforward it is. To remove the drive shelf I only had to remove two screws. To remove the power supply — just three screws. (Of course you also have to disconnect the various data cables and power cables).

Quadra950 inside motherboard

Here’s the Quadra without drive shelf, power supply, speaker bezel. I also removed one of the NuBus cards (the second from the top — I have four slots occupied of the five available) to be able to disconnect all data cables with greater ease.

This photo was taken before I dusted everything. As you can see, the Quadra was already rather clean inside.

The NuBus cards

For documentation purposes, let’s have a quick look at the four NuBus cards installed.

Asante Ethernet 2

1. AsanteFAST 10/100 NuBus Ethernet card by Asanté (Manufacture date appears to be 1996)

Paintboard TurboXL 1

2. Paint Board Turbo XL video card by RasterOps (Manufacture date appears to be 1993)

4 serial ports card

3. This one was hard to identify. It basically adds 4 serial ports to the Mac. After some digging, it appears to be either a Lightning or a Hurdler serial NuBus board manufactured by Creative Solutions, Inc. (“CSI”, as you can see on that label on the chip next to the large Zilog chip) in 1994. Here’s the related page from the original website (now archived).

Macintosh II PC Card

4. This one, instead, was very easy to identify. It’s a Macintosh II PC Drive Card by Apple Computer (part No. 820-0213-A). You can find more photos of this card here. It’s a rather old card (1987) that lets you connect an Apple PC 5.25″ floppy drive. I don’t have such drive — this card was already in the Quadra when I acquired it in 2003.

After the cleaning

After dusting and cleaning everything, I reassembled the Quadra and tried booting it again. And again, the Quadra’s response was “KH-POP,” just like before. But this time, since the room was darker, I could notice a spark on one of the NuBus cards every time I heard the “KH-POP” sound. I am not an electrician, but I’d say that this behaviour suggests that the issue may be on the motherboard (or on something connected to it, such as RAM chips or one of the NuBus cards, etc.) and not in the power supply. It looks as if every time I try powering the Quadra on, something creates a short circuit, interrupting the process. Perhaps a piece of dirt or a ‘dust bunny’ has lodged somewhere and I didn’t catch it, or a RAM chip has failed. Searching on the Web, I found someone having a very similar issue with his Quadra 950, but in his case the short circuit was caused by a pin of the main processor chip that he bent when he reinserted it after cleaning the motherboard. I haven’t touched any chip, and every RAM and VRAM memory stick looks firmly in its place.

I have already tried booting the Quadra after removing all the NuBus cards, but it went “KH-POP” again on me. Tomorrow I will try removing all RAM chips and even the PRAM battery, and see what happens.

I’m quite fond of this Quadra 950. I’ve used it on a regular basis from 2003 to 2006, and occasionally up to 2011. It’s the fastest 68K Macintosh I own (it has a Motorola 68040 CPU at 33MHz, two 400MB hard drives, and it used to have 28MB of RAM, which I expanded to 40MB by adding the RAM sticks I salvaged from the Quadra 700 when it died in 2005) and acted as a server in my vintage Mac LocalTalk network. I don’t want to give up on it yet. I’ve described the issue the best I can, so if you have any insight or suggestion, please do chime in — I’m all ears.


Quadra950 rear label


7 thoughts on “Checking on my Quadra 950

  1. Have you checked all the motherboard caps? That would be my first port of call, although I admit that wouldn’t explain the spark.

    I have an LC475 that I’m very attached to and dread the prospect of it not booting one day, but I guess that’s the risk we take with computers of this vintage! Hope you get your 950 sorted.

  2. Hi Alex! The motherboard looks clean as a whistle. At this point I’ll have to disassemble the Quadra completely, detach the motherboard from the case, and look on the other side of it. I too hope to bring this old beast back to service… I still have plans for it!


  3. Ah wait, I read you “2016 in review” where you mention not looking at your Quadra 950 dated,
    JANUARY 9, 2017

    I ask because I am thinking of buying one with the same symptom. Seller believes it’s the PSU as well.

  4. The PSU is the likely culprit. When I tried looking for a replacement months ago, all the options I found were a bit too expensive to risk a purchase which might or might not solve the problem. But one’s mileage may vary, of course.


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