Date: Fri, 5 Mar 2004 22:52:02 -0500 From: Fluxstringer <[EMAIL PROTECTED]> Subject: Re: [PCI] Unplugging ADB Keyboard ?
But I have known for a decade that there is always a chance of a short or static charge. This might blow the chip that controls the ADB I/O.
I have spare motherboards so I don't worry so much. And I always pull the plug out straight.
Pulling the plug straight out is little protection against damage. See below.
" Don't try this at home kids. We're professionals " 8*}}} Date: Fri, 5 Mar 2004 23:29:42 -0500 From: [EMAIL PROTECTED]
You've been lucky.
ADB is NOT designed to be hot pluggable in any way, ever.
Unplugging ADB devices when your Mac is powered-up runs the risk of electrical shorts. Doesn't matter which plug you pull or how you pull it. The shorts can damage the device (keyboard, mouse, etc) AND the computer's motherboard.
Unfortunately, shorts are not the only, nor probably the main cause of damage when hotplugging the ADB bus. If shorts were the only issue then one could hotplug with care and have few worries.
The bigger problem is that any circuit with inductance will generate huge voltages if the current in the circuit is suddenly cut off. Unplugging a cable in the middle of a signal would qualify. Apparently the ADB chip does not have great overvoltage protection (usually strategically placed diodes to sink the overvoltage). It doesn't seem like there'd be that much inductance in the circuit though.
Date: Sat, 6 Mar 2004 00:50:11 -0500 From: Fluxstringer <[EMAIL PROTECTED]> Subject: Re: [PCI] Unplugging ADB Keyboard ?
Dan if you know please tell us ;
Are they repairable or is it just more economical to trash them ?
Can a replacement chip be found or is this too obsolete ?
How difficult is the solder job. Is special equipment required ?
The ADB chip, named the CUDA chip by Apple is a custom chip for Apple. There is no source for them outside of salvaging them off of other old Apple boards. There are two versions as far as I can tell and I have not been able to find any difference in their functionality. In other words, I've switched them out on MBs and the machine seemed to still work just fine. The Apple part numbers on the chips are 341S0788 and 341S0060.
On the bright side, they are very common. They were used starting on Quadras (the P475, 476, Q605, Q63x etc. have them) and are present on all following machines through the Beige G3. PM7200 boards are often easy to find at haul them away prices and they're a source for the CUDA chip. If you watch the Ebay Apple Motherboards section you will sometimes find a lot of several Road Apple'y boards for sale which might each yield a CUDA chip.
Still, you have to kill another Apple board to get a replacement.
The chip is a 28 pin SOIC (surface mount). You don't really need special equipment to desolder it, but it takes a decent amount of skill. Using Chip Quik makes it a lot easier.
Jeff Walther
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