Path: utzoo!attcan!uunet!bellcore!att!news.cs.indiana.edu!sdd.hp.com!hp-pcd!hp-vcd!neff From: neff@hp-vcd.HP.COM (Dave Neff) Newsgroups: comp.sys.mac.hardware Subject: Re: Mac IISi vs. HP DeskWriter = Fried Mac?? Message-ID: <1170008@hp-vcd.HP.COM> Date: 11 Dec 90 22:30:25 GMT References: <989@dvnspc1.Dev.Unisys.COM> Organization: Hewlett Packard, Vancouver, WA Lines: 101 Regarding the DeskWriter IO "problem": O.K., many people are missing the point so I will try to clarify a few things. I will explain the situation to the best of my ability. I am giving my understanding of the problem and this is not an "official HP statement" on the problem. The DeskWriter with AppleTalk detects a Mac problem because it automatically goes into AppleTalk mode when an isolation transformer (i.e. a PhoneNet connector) is sensed. Unfortunatly, the part that fails in the Mac causes the serial port to "look like" an LocalTalk isolation transformer is plugged in. Normally, the DeskWriter goes into AppleTalk mode iff there is a transformer. If there is no transformer, it goes into serial mode. Hence you cannot use direct connect AppleTalk (use a serial cable but turn on AppleTalk) with the DeskWriter. Surprisingly enough, there is actually no reason to really. If you have a serial cable run it in serial mode, if you need AppleTalk use AppleTalk connectors. Although the data transfer rate is higher on AppleTalk, there is no real throughput difference in most cases comparing serial with AppleTalk because the limitation of the printing is the speed that we can fire dots of ink -- not the IO. And turning AppleTalk on eats up RAM in the Mac so on a low memory (1 Meg) Mac this can actually lead to slower output on AppleTalk than on serial. Now as for the problem. Resistor packs on some of the Mac's serial ports can fail over time. This is NOT caused by the DeskWriter. When these fail, the DeskWriter "sees" an isolation transformer and goes into AppleTalk mode -- even though a serial cable is used. Hence there is a problem. It also appears that when the resistor pack fails AppleTalk does not work reliably via that port -- although serial will. Unfortunately the DeskWriter will always come up in AppleTalk on a failed port. Basically, once the resistor packs fail, the port no longer is following RS-422 impedance specifications and our automatic serial/LocalTalk sensing circuit interprets the impedance in a way that implies LocalTalk connectors. It is my understanding there is a quality problem with the resistor packs used in some of the Macs. I have also heard (rumor mode on) that HP's division that makes the LaserJet printers stopped using these particular resistor packs due to quality problems. What is the bottom line? Most people do not and will never see this problem. Those who do, often only see the problem on one of their two serial ports (since each port has a separate resistor pack) and can work around it by using the other serial port to print. If you do have a port that fails, you can try using that port in AppleTalk mode. To confuse the matter more, once your resistor pack fails, you can use direct connect LocalTalk (serial cable) since the printer will power up in AppleTalk mode. The printer may work in this mode, but error rates will likely be high (we have limitted data available about this particular senario). I know that above I said DeskWriter can't do direct connect LocalTalk, but weird as it may seen once you have a blown resistor pack you can :-). HP and Apple have given official joint statements concering the problem. I had not heard that Apple would only cover the repair if the computer had AppleCare support contracts, but I cannot speak for HP -- let alone Apple :-). However, this is my understanding of the situation: 1). If you have an old Mac there probably is not a problem. If your resistor pack is already blown the DeskWriter will not work in serial mode (and may not work well in AppleTalk mode), so you can either get your Mac fixed or return the DeskWriter. Having someone replace the resistor packs at the board level shouldn't be very expensive. However I don't believe the older Macs used the questionable resistor packs. The resistor packs are a part of what Apple calls the "de-glitch network" which is between the serial drivers and the actual external IO lines. I don't know much about the Apple service network, but it would seem to me that a board level repair in this case would be fairly simple and not too expensive. I'm sure someone will correct me if I'm wrong on this point :-). 2). To the best of my knowledge, the problem has only been seen on new Macs during the burn in period -- 2 days to 2 months after purchase. The resistor pack is blown and Apple has been fixing the board under warrantee. It is also only seen on a very small percentage of systems. 3). It is my understanding that Apple is using different resistor packs in most (if not all) Macs currently being built. This has been an unfortunate situation. We tried to provide a user friendly automatic sensing of the IO, and it has worked well in most cases. But from what I know about the problem and what I have heard in rumors and in previous postings people are over-reacting to a very large degree. To my knowledge, nobody has had to pay a dime to get the problem fixed. There may be some problems in the future as people who bought a new Mac and the restor packs blow but they don't know about it (since the ImageWriter will still work). If later on they buy a DeskWriter they would have a problem. If they don't want to pay to have their Macs fixed they could just return their brand new DeskWriter. I would not expect Apple to repair printers out of warrantee in most cases. I doubt that this is an exception -- but you would have to ask Apple about this. I hope this helps a bit. Apple has been very responsive with this situation and HP has truly appreciated the cooperation they have given us in explaining and fixing this problem. Dave Neff neff@hpvcfs1.HP.COM Disclaimer: Although I have tried to explain the situation as best I can THIS IS NOT AN OFFICIAL HP STATEMENT concerning the problem.