Date: Wed, 1 Oct 2003 20:42:18 -0500 From: Derek Morton <[EMAIL PROTECTED]>
I have found (at work) that if a GAL is overheated in the process of removal or installation the program can be corrupted. Whether or not the device is actually damaged I cannot say as I discard any device which is overheated (rather than have it act quirky or fail prematurely in the field).
How do you determine if it was overheated? Or was that in the case where you know what hte contents should be, and if what you read out doesn't match what it was programmed with, then you know it was overheated?
To program them you will definitely need at least one PLCC adapter. As I mentioned, if memory serves, both 16V8 and 20V10 devices are used on that card (although having it in front of you, you will know for certain) and the 20V10 is a larger device.
I think there's a "universal" PLCC adapter for this programmer which does all the PLCC sizes up to 84 pins, but I'll need to double check. Another possibility is to wire wrap a PLCC through-hole socket to straight pin headers and tell the programmer that it's looking at the DIP equivalent to the GAL. Trade time for money...
As for a GAL getting warm... It is possible that if the program became corrupted you could have had contention on one or more outputs, but realize that GALs consume a LOT of power (relatively speaking - even the quarter power devices), and the faster they run the more they use.
So it is normal for them to be warm bordering on hot in operation? The chip in question was a Lattice GAL16V8.
A PLCC device is just about the most difficult thing to remove you will likely find in an older mac. The most effective way to remove a PLCC is to use a SMD rework station with the correct size LCC / PLCC hot air tool.
I use Chip Quik. It is an alloy one melts into the existing solder which lowers the melting point. If one forms a bead on each edge of the chip which has pins, one can heat all the pins on that edge. Then by moving the soldering pencil back and forth between the beads (four sides on a PLCC) eventually you get all four sides hot enough to come loose at the same time. With the melting point lowered by the Chip Quik, I've found this safe (for the chip) and effective, until my experience with the GALs. But I don't really know for certain that they were heat damaged.
It is always possible to figure out the program in a GAL, but it can be VERY time consuming and tedious.
How would you do this? I was thinking, set up on a Proto-board with a 5V supply, momentary contact switch for the clock, switches to the inputs and LEDs on the outputs. Then run through combinations (256 for an 8 input GAL) and do some repeats of the same inputs to see if the output changes to test for whether there's a state machine implemented. Then (if it's just combinational) derive the logic using a Karnaugh map or software that solves a Karnaugh map, though I haven't any such software.
If it's a state machine, I guess I'd test to see how many of hte outputs are state machine outputs. If it's only one or two, then once the combinational outputs are solved, the state machines might not be too hard. If all the outputs are state machine outputs, I think it might be impossible in a reasonable amount of time.
A faster testing method might be to tell my chip programmer that it's looking at a 256 X 8 PROM or EPROM and ask it to read the contents. If I wire the address lines to the inputs on the GAL and the data lines to the output pins on the GAL, that should give me a file with the results I would generate above. I think. Does this sound feasible? Is this on the right track?
Whether or not it is worth your effort to play around with this project of yours is up to you to decide.
The first project I have in line are these old Outbound Laptops. These were early unauthorized Mac clones. Many people remember the Outbound Notebooks, but the Laptop predated them and is very cool in its way.
Anyway, there seem to be a fair number of the Laptops still around, but they came either with an internal hard drive or an internal floppy, not both. There was a connector that could be used for an external floppy drive and an external SCSI adapter (not at the same time). However, most of the laptops seem to be missing these accessories. If one's operating system or hard drive gets hosed there's no way to reload the laptop if you lack the external floppy drive.
The external floppy drive is a PC style floppy mechanism with a controller/interface card on the back. That interface card is not too complicated, except that it includes this one GAL (and a somewhat hard to find 37C65 and WD92C32). The SCSI adapter has the same issue. So, if I can read or discover the contents of these GALs I can make more of the external floppy drives to support the orphan laptops.
This isn't a money making idea, as the cost of the components is more than folks are likely to pay for the external floppies, but I want to ability to replace these things, because I like those old laptops. I tried hunting down some of the old Outbound people who might have the GAL program files, but had no luck along those lines.
I too love the old Daystar products... I am the proud (original) owner of an SE/30 specific 50 MHz PowerCache. A fine piece of engineering indeed!
Daystar made great stuff. I often wonder if they had one or a few engineers who were really good, or if they had a culture of fine engineering that inspired anyone who worked there. I'm curious about the folks behind their products.
Jeff Walther
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