What does the internal disk drive do? On 64s and SX-64s that black-screen, the first thing I look at (after fuses, etc.) is the PLA. -- --------------------------------- personal: http://www.armory.com/~spectre/ --- Cameron Kaiser * Floodgap Systems * www.floodgap.com * ckaiser at floodgap.com -- You've become useful again. -- "Die Another Day" ---------------------------

On Thursday 15 June 2006 06:14 pm, David Vohs wrote: When you say it "shows nothing" do you mean that the screen is as if it's not even powered up? Completely blank? This is a common problem with C64s. First thing you want to check is the power supplies, make sure that there's +5V where there's supposed to be, easiest place being at the corner pin of pretty much any of the logic chips. Do you have a scope? A logic probe if not? Find the PLA chip, it'll be a 28-pin DIP, mostly marked with the number 906114 though sometimes the generic 82S100 will be on there, and I'm not 100% sure if the SX64 machines may have used a variant on that or not. There will only be two 28-pin parts in there, and the other one is the 6581 SID chip (or variant, possibly). Scope (or probe) four pins on each side at the end opposite the notch. Pin 14 is ground, so you want to hit 10, 11, 12, 13, 15, 16, 17, 18. Each of these pins should show a high level, or a pulse, but none of them should be stuck low -- if one is it'll cause this symptom. I've also seen some that would only go "halfway up", where a scope would show two levels, ground and about 2.5V or so. This could be the PLA or it could be the chip at the other end of that enable line. If that doesn't turn anything up, scope the data bus. Easiest way I found to do this was to hit pin 2 of each of the ram chips, but I don't recall how easy that was on the SX, it's been a really long time since I've seen one. Again, you're looking for a logic pulse there, a line that's stuck low will kill the machine and give you the blank screen symptom. Unfortunately, so will a number of other problems, any number of other chips could short a bus line to ground and the only way to track them down sometimes is to pull them out and see if the line shows normal transitions after that. The company seemed to have *no* consistency whatsoever when it came to what was or wasn't socketed, though, which makes it even more fun. I used to buy my sockets 50 at a time and the smaller 14- and 16-pin ones 100 at a time for sticking them in there once I'd unsoldered a chip, because those boards weren't robust enough to take unsoldering more than once. A couple of other notes, on c= stuff in general-- bad ram can get HOT! This got bad enough that I found a little thermister that I stuck in the end of an old pen barrel with a bit of wire and a dual banana plug to give me a homebrew temperature probe. Burn your fingers, that can... The other applies much more to c64s than the SX, since they used those stoopid potted "brick" power supplies. A bad PS that went overvoltage (and they often did because that potting compound did NOT let the heat out) was usually a good machine-killer, often taking out the RAM first. Which is when that temperature probe came in handy. As well as the little box I built with a couple of switches and some resistors that'd let me put one of those under full load and meter both the AC and DC sides. :-) The SX wasn't anywhere near as prone to those problems, though. Good luck with it, and feel free to email me if you have any further questions on this or maybe need any parts (though I'm not sure about PLAs, since somebody has already asked about those and I've gotta do some digging :-). -- Member of the toughest, meanest, deadliest, most unrelenting -- and ablest -- form of life in this section of space, a critter that can be killed but can't be tamed. --Robert A. Heinlein, "The Puppet Masters" - Information is more dangerous than cannon to a society ruled by lies. --James M Dakin