fozzard@boulder.Colorado.EDU (Richard Fozzard) (02/16/90)
A question for you SCSI jocks out there: I recently got a Syquest drive (Ehman) that I only need occasional access to. Its fan is painfully loud, so I would like to leave it powered down when not in use. However, I cant do this since my SE/30 with internal Sony 40 meg wont boot if the SCSI cable is connected, but the external drive is powered down. Presumably, the termination resistors in the Ehman require power to work. Is there any way to terminate the SCSI bus correctly w/o powering up that damned noisy Ehman? It does have a 2nd SCSI (25-pin) connector on the back, and it is the only external SCSI device. If you really understand SCSI termination, a reply to the net would probably be widely appreciated, since to most of us SCSI termination is black magic. Thanks for any help - rich ======================================================================== Richard Fozzard "Serendipity empowers" Univ of Colorado/CIRES/NOAA R/E/FS 325 Broadway, Boulder, CO 80303 fozzard@boulder.colorado.edu (303)497-6011 or 444-3168
dan@chaos.cs.brandeis.edu (Dan Schwarz) (02/16/90)
In article <17008@boulder.Colorado.EDU> fozzard@boulder.Colorado.EDU (Richard Fozzard) writes: >A question for you SCSI jocks out there: >Is there any way to terminate the SCSI bus correctly w/o powering up >that damned noisy Ehman? It does have a 2nd SCSI (25-pin) connector on >the back, and it is the only external SCSI device. > That's really odd - most of the SCSI devices I have worked with that are internally terminated, did not require power when the computer was operating. One possible solution is to remove the internal termination resistors, then add an external SCSI pass-through terminator. These are generally available for the 50-pin centronics SCSI connectors, but I've never looked for one which uses Mac-standard 25 pin SCSI. Another solution might be to replace the noisy hard disk fan with a quieter fan., or add some kind of thermostatic switch to control the fan (there is such a device available to quiet noisy SE fans - it switches the fan on when the temperature reaches a certain level.) -- | And the men who hold | Dan Schwarz, MB 2926 Brandeis U. | RECYCLE YOUR JUNK | | high places/ Must be | I'NET dan@chaos.cs.brandeis.edu | SUPPORT EARTH DAY | | the ones to start/ |----------------------------------| tradetapes?mailme | | To mould a new reality/ Closer to the heart ... RUSH | FloydRushDeadEtc..|
chou@umn-cs.cs.umn.edu (Chih-Hsiang Chou) (02/17/90)
In article <17008@boulder.Colorado.EDU> fozzard@boulder.Colorado.EDU (Richard Fozzard) writes: >A question for you SCSI jocks out there: > >I recently got a Syquest drive (Ehman) that I only need occasional access >to. Its fan is painfully loud, so I would like to leave it powered down >when not in use. However, I cant do this since my SE/30 with internal >Sony 40 meg wont boot if the SCSI cable is connected, but the external >drive is powered down. Presumably, the termination resistors in the >Ehman require power to work. You're right. The terminating resistors, being connected to the Ehman's power supply, ground the SCSI bus if not powered up. > >Is there any way to terminate the SCSI bus correctly w/o powering up >that damned noisy Ehman? It does have a 2nd SCSI (25-pin) connector on >the back, and it is the only external SCSI device. The fix is to disconnect the terminating resistors from the Ehman's power supply and feed them power from the SCSI bus (pin 25). I had done this successfully, with authorization from Ehman's technical support, and have no problem so far (near a year). Whenever I need to use my Syquest drive, I simply power-up the drive, insert the cartridge, wait the motor to speed up, then use the SCSITools DA to scan the bus and mount the cartridge volume. No reboot needed. > >If you really understand SCSI termination, a reply to the net would >probably be widely appreciated, since to most of us SCSI termination >is black magic. > I have enclosed a copy of the procedures of my modification below for anyone who is interested in doing so. The modification is recoverable so you won't void your warranty. However, there are three things to note: (1) the drive I have is the early Ehman model in PC style box, but I doubt there is any significant change in the new model. (2) be VERY carefully about the power from the SCSI bus. The first time I did, I forgot to disconnect the terminating resistors from the Ehman's power supply, and I blew away a 1A soldered fuse and one printed circuit wire on my Mac II motherboard. :-( The repair will cost serveral hundred $$$ for a motherboard replacement, but I fixed it by myself anyway (less than $1 for parts). (3) do this at your own risk, no guarantee or responsibility is promised here. However, if you have a success, I do like to hear from you. --- Instructions for Terminating Resistors Change on Syquest Drive ------ 1. Disconnect the power cord and SCSI cable from the Ehman case. 2. Unscrew the 6 screws on the bottom of the Ehman case and slide the cover out. Mine is the old model (PC shape), your packaging may be different. 3. Take a detail top-view look of the internal construction of the Ehman case with the opening of the Syquest drive facing to you. The Syquest drive is located at the lower right corner of the Ehman case. The power supply is at the left side of the case which has wires connected to the Syquest drive. There is also a ribbon cable which connects between the 25-pin SCSI port on the Ehman case and the 50-pin SCSI port on the Syquest drive. You may want to disconnect them temporarily to allow more working space. 4. The terminating resistors (two of them) are located at the back of the Syquest drive (left side, if you keep the top-view). Each of them is an array of resistors in a comb-like packaging. They are socketed in parallel. You should be able to remove the resistor one by one by gently shaking it while pulling it out. The +5V DC power is connected to the leftmost (again top-view) pin of each of the resistors. You may want to validate its existence by a voltmeter. 5. Now, if all is possible, find two new sockets which are identical to those on the drive. Insert the resistors into the new sockets with the leftmost pin open. I.e. first align the resistors with the new sockets, shift the sockets one pin to the right, then insert the resistors. See the diagram below: ________________ |______________| Terminating Resistor | | | | | | to pin 25 ___| of Ehman SCSI ________________ port on case |______________| New Socket ________________ |______________| Original Socket +5V from ____| Ehman power supply Next, insert the new sockets into the original sockets with the open leg on top of its original position. In the final view the new sockets are sandwiched between the terminating resistors and the original sockets. Be sure that the open legs do not touch the original sockets. Since I can't find the identical sockets, I home made one from another type of connector. I forgot the name. It's a long array of connector just looks like the terminating resistor. You may omit the new socket if you can bend the leftmost pin and don't have it touched with the original socket when you insert the resistor back. But for easy recovery to its original connection and shape, I chose to use the new sockets. 6. The +5V DC power from the SCSI bus is on the 25th pin of the Macintosh SCSI connector. Note that old models of Mac don't have this power line available. Since Ehman uses the same 25- pin connector, it's rather easy to find it. Simply connect a wire between the pin 25 of the SCSI port (a good place is on the small printed circuit board which connects the two 25-pin SCSI ports on the Ehman case) and the open legs of the terminating resistors. I wire-wrapped the connections instead of soldering it, for reason of easy recovery (in case I need warranty service). You may want to connect the wire first before insert the resistors back to the sockets. 7. Validate all the connections, then reconnect all the internal wires (if they were disconnected) and power cord. Don't connect the SCSI cable from the Mac to the Ehman case yet. 8. Turn on the Ehman's power supply (no cartridge inserted). Make sure there is no +5V coming up at the open legs. 9. Turn off the Ehman, connect the SCSI cable, then turn on the Mac. Make sure +5V is on the 25th pin and the open legs. Also make sure other SCSI devices such as the internal hard disk can boot up when the Ehman is off. 10. Turn on the Ehman, make sure everything is still OK. Now you can insert a cartridge and reboot the system (or use SCSITools to mount the cartridge). Make sure everything is doing fine. 11. If you have success at this point, congratulations. Otherwise, don't blame me. 12. Power off all machines. Disconnect all external cables if necessary. Put back the cover, screw it, reconnect all the cables, then your're done. That's it. GOOD LUCK!! P.S. I assume your Ehman drive is at one end of the SCSI chain, otherwise the terminating resistors should be removed completely. -- Chih-Hsiang Chou chou@umn-cs.cs.umn.edu Department of Computer Science University of Minnesota
dplatt@coherent.com (Dave Platt) (02/17/90)
In article <17008@boulder.Colorado.EDU> fozzard@boulder.Colorado.EDU (Richard Fozzard) writes: > I recently got a Syquest drive (Ehman) that I only need occasional access > to. Its fan is painfully loud, so I would like to leave it powered down > when not in use. However, I cant do this since my SE/30 with internal > Sony 40 meg wont boot if the SCSI cable is connected, but the external > drive is powered down. Presumably, the termination resistors in the > Ehman require power to work. > > Is there any way to terminate the SCSI bus correctly w/o powering up > that damned noisy Ehman? It does have a 2nd SCSI (25-pin) connector on > the back, and it is the only external SCSI device. Yes, there is a way. It's not all that difficult. 1) Purchase one external SCSI terminator ($20 or so)... these are small blocks (about 1" thick) with a 50-conductor male Centronics plug on one side and a 50-conductor female Centronics jack on the other side. Also purchase one standard "Mac to SCSI peripheral" cable... male DB-25 on one end, and 50-conductor male Centronics plug on the other ($25 or so). 2) Open up the Ehman case. Find the internal termination resistors on the SyQuest controller board (probably 2 or 3 single-in-line or dual-in-line resistor packs plugged into the board near the 50-pin SCSI header). Remove the resistors with a small screwdriver; save for future use. Close the case. 3) Plug the DB-25 plug on the cable into the second 25-pin jack on the back of the Ehman case. Plug the other end of the cable (male) into the female jack on one side of the external terminator. 4) Cover the unused (50-pin male plug) side of the external terminator with black electrical tape, so that you don't short out the bus. Your SE/30 should now be able to boot correctly even if the Ehman is not powered up. The SE/30 provides terminator power (as do the SE and II series, but not the Plus nor (I believe) the Portable). Assuming that the Ehman case carries the terminator-power through to its second jack, the external terminator will receive power from the bus and will work correctly. There's an entirely different way to do this, which doesn't require an external terminator or extra cable... but it requires rewiring the Ehman case and/or the SyQuest interface so that the SyQuest's internal terminators can accept power from the bus if the SyQuest is powered down. This is not for the faint of heart, and I don't really recommend it... write for details if you absolutely need 'em. -- Dave Platt VOICE: (415) 493-8805 UUCP: ...!{ames,apple,uunet}!coherent!dplatt DOMAIN: dplatt@coherent.com INTERNET: coherent!dplatt@ames.arpa, ...@uunet.uu.net USNAIL: Coherent Thought Inc. 3350 West Bayshore #205 Palo Alto CA 94303
dplatt@coherent.com (Dave Platt) (02/17/90)
In article <1990Feb15.204213.29062@chaos.cs.brandeis.edu> dan@chaos.cs.brandeis.edu (Dan Schwarz) writes: > That's really odd - most of the SCSI devices I have worked with that are > internally terminated, did not require power when the computer was operating. Some drive-designers do a good job in this respect. For example, the Teac N50 streaming-tape drives have a very nice termination-drive circuit. Their internal termination resistors normally accept power from the tape drive, and also feed power out to the SCSI bus... but can also accept termination power from the bus if the tape drive is powered down. Other vendors are less generous. I've seen a number of external drives (e.g. the LaCie Cirrus) which would _neither_ provide power to the bus when operating (so that external terminators could be used), _nor_ accept power from the bus for their internal terminators (so that the terminators would work correctly if the device was powered off). If you have a peripheral of this sort in your system, and use its internal terminators, you MUST have it powered on at all times... otherwise it clamps the bus, and nothing will work. It's not always possible to pull the device's internal terminators and use external ones, either... these devices won't provide power to external terminators, and neither (alas) does the Mac Plus. The SCSI-1 specification forbids having powered-off devices attached to the bus... so these "unfriendly" devices are not really in violation of the spec, I think. I'd much rather buy devices that have a robust terminator-power circuit, however! -- Dave Platt VOICE: (415) 493-8805 UUCP: ...!{ames,apple,uunet}!coherent!dplatt DOMAIN: dplatt@coherent.com INTERNET: coherent!dplatt@ames.arpa, ...@uunet.uu.net USNAIL: Coherent Thought Inc. 3350 West Bayshore #205 Palo Alto CA 94303
whit@milton.acs.washington.edu (John Whitmore) (02/20/90)
In article <47013@improper.coherent.com> dplatt@coherent.com (Dave Platt) writes: > >The SCSI-1 specification forbids having powered-off devices attached to >the bus... so these "unfriendly" devices are not really in violation of >the spec, I think. I'd much rather buy devices that have a robust >terminator-power circuit, however! >-- There is a strong likelihood that the SCSI receiver circuits are diode-clamped to the power supply, so that a powered down SCSI device can act as an improper termination. Integrated circuits don't just have switches that turn "off"; they use diodes and ONLY WHEN POWER IS APPLIED AS DESIGNED do those diodes turn off. So, a powered down disk drive should be unplugged, regardless of whether it contains termination resistors or not. SCSI drive/receive chips will vary, and some varieties may be inert when powered down. Don't bet on it. I am known for my brilliance, John Whitmore by those who do not know me well.