Path: utzoo!mnetor!uunet!mcvax!ukc!dcl-cs!bath63!pes From: pes@ux63.bath.ac.uk (Smee) Newsgroups: comp.sys.atari.st Subject: Disk problems (continued -- also, media-change) Message-ID: <2511@bath63.ux63.bath.ac.uk> Date: 9 May 88 15:26:58 GMT Reply-To: pes@ux63.bath.ac.uk (Smee) Organization: AUCC c/o University of Bath Lines: 87 (I have no way of knowing if this is of international or only UK interest. Still, wider distribution is probably better than narrow distribution, both since Cumana are available worldwide, and because other makers may produce similar drives.) I bought a Cumana 1-Meg disk drive (from a company called LAN) at the recent Atari show in London. Reasons for choosing this were: (a) the price was right; (b) the Cumana drive was fitted with its own internal power supply (unlike many current 3rd party drives which parasite off the joystick port for power); (c) I have a Cumana 1-Meg disk drive at work, and it works fine; and (d) LAN said the drive was ST-compatible. (Indeed, once you've gotten into the box and found the instructions, Cumana also say it is ST-compatible.) It isn't -- though it can be made to be. The problem: I took the thing home, hooked it up, and began some simple tests. It did not seem to recognize media change -- this was tested by the simple method of opening a window on the drive, swapping (or not swapping) disks, and pressing escape to force a redisplay. After some fiddling, I'd narrowed it down, and it was related to the write-protect state of the disks. If you removed a disk and put in a WRITE-PROTECTED disk, it would detect the swap; if you took out a WRITE-ENABLED disk and swapped in a different WRITE-ENABLED disk, it would not notice. (In full accordance with Murphy's Law, the absolute worst case. I didn't try WP->WE, by the way.) Not being shy, I opened the beast up. It contains, right next to the WriteProtect sensor, a second ('DiskInserted') sensor. A bit of experimenting confirmed that it does NOT report WriteProtected if there is no disk inserted. (The ST, of course, relies on the disk drive to report WriteProtected when there is no disk in, as this is how it detects MediaChange. {Question for Atari, of course, is, why didn't they use drives with 'DiskInserted' sensors, and use that to detect MediaChange?}) A look at the bottom of the PC board showed that both sensors went into the same three-contact plastic box (a double switch). Markings on this (tiny) switch box indicated that both switches were normally-open types, and that the centre terminal was a common terminal. So, I soldered a small bit of wire in, shorting the 'DiskInserted' sensor so that the drive always believes there is a disk in. (All this action occurs beneath the leads to the 'Active' LED, so is a bit tricky.) Works fine now; though I've probably voided my warranty. The point of all this, though, is that this is another possible cause of the 'directory window mixed up' problem. If you are sure that your problem is not identical disk serial numbers, you might want to check this. If you pull a disk out of the drive and put it back, and then hit Esc to force a redisplay, then EVEN IF YOU HAVE PUT IN THE SAME DISK, the drive should spin (and select light come on) as the ST has to read the header block to check the ID. If the drive does NOT spin, then the ST has not noticed the disk being removed -- which means the problem described above may apply. If you find your drive has this problem, you have two choices, I'd say: either modify the drive (or have it done by a repair shop) as suggested above; or try to return it for refund or replacement on grounds that it is NOT, in fact, ST compatible. NOTES: (1) This worked for me. If you decide to open your drive up and fiddle it yourself, I WILL NOT ACCEPT ANY RESPONSIBILITY if you muck it up. Make sure you are VERY gentle, and use a SMALL, LOW-LEAKAGE, soldering iron. Also note that you will almost certainly be voiding any guarantee if you do so. AND, if you do decide to mod it, MAKE SURE that you nobble the correct sensor switch. If you get the WriteProtect sense switch instead, by mistake, you will end up with a drive which (a) doesn't recognize disk swaps, and (b) thinks that all disks are write enabled. (2) (As noted) this DOES NOT apply to ALL Cumana drives. The one I use at work (bought about a year ago) worked fine right out of the box. The one I have at home (bought about 2 weeks ago) did not. Cumana drives, in our experience, are very reliable beasts -- but it is not clear that they (or someone doing the repackaging, perhaps) know what 'ST compatibility' is. Also, it MAY apply to some other makers' drives. A Brand A disk drive frequently really is a Brand B drive mech, with Brand C electronics, packaged in a Brand A box. The point is, if at all possible, make sure to see the drive working before you buy it -- testing is simple, as described above. Failing that, make sure that whoever you buy it from gives you a 'statement' that the drive 'is ST compatible' in whatever terms will allow you to use local consumer protection laws to return it if it has this problem. Cheers, Paul