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Low volts, high volts: What's the differential, anyway?

HP 3000 disc devices have been through many generations of design. Old-timers out there tell stories of the 7933 units as big as today's washing machines, all to store a few hundred MB. Things have come a long way in disc technology since those units of the 1980s. Sometimes they've come along too fast to keep up with all the voltage details.

For an example, a recent question scrolled by the steady stream of advice in the 3000-L newsgroup:

I’m attempting to upgrade from 4.3GB drives to HP's 18GB drives (ST318404LC), on our Series 979.  I inserted the new drives into existing Jamaica-style disc enclosure units. I carefully plugged in the SCSI adapter from the enclosure into the drive, and then slid the enclosure units into the  Jamaica. They power up okay and go through self test in the Jamaica okay. But the paths of the 18GB  drives then do not show up in MAPPER.  Both the smaller and bigger drives are F/W SCSI, so cabling should be okay, right? What's going wrong here?

Chuck Shimada, a 3000 hardware expert who donated countless hours of configuration service to Interex during the former user group's conferences, had a quick answer. "First, you are trying to attach a Low Voltage Differential device to a High Voltage Differential interface.  This cannot work without an LVD to HVD adapter on each drive, or Parlan LVD/SE to HVD box between the last HVD device on the SCSI chain and the first LVD device."

Shimada had lots of detailed advice on how to manage the difference in volts on 3000 discs.

"I did check the IODEFAULT.PUB.SYS, and your Seagate ST318404LC drive is in the file. But what the file does not tell you is that HP puts a small adapter board on the end of the drive which does the LVD to HVD conversion.

"If you have the adapter boards on your old drives, you can try to remove them and attach them to the new drives. The boards are small (I am guessing 1-inch x 3.5-inch as the size). They are attached to the drives' original interfaces and have two pices of mounting hardware going to the case of the drive.

"I have tried to find a part number to order the adapter board, but no luck. There is no HP part number on the board and I can not determinal the actual manufacturer by looking at the board and chips.

"If you try to place your old drives back and they do not show up on MAPPER, you should check the fuse on the FWD card. It is a small micro fuse. It looks like a small lamp, it would be around the terminating resistor packs. You may have to use a Volt Ohm meter to check it. Just pull out the fuse; it has two pins on the bottom and is usually in a clear plastic case with the rating informaton printed on it (in extremely small letters).  You should be able to get a replacement at your local electronics store (Fry’s, Microcenter, Radio Shack and CompUSA don’t have it).  If after replacing the fuse, or the fuse checks okay and the old drives still don’t show up, then the FWD card is dead.  Note that the ST318404LCs may also be dead, their interfaces have fusable links on their interface cards. They are not user replaceable.

"I have had success in using the Paralan MH16A. This is an external LVD to HVD adapter.  I just connect it between the HP28696A and three Seagate 36GB drives, and it worked great.  The customer even said that his application was running faster. (They were on eight 4GB drives in a HASS.)

"There is also a company out there, Peripheral Imaging Solutions (www.pi-si.com), that seems to have found a way to do the LVD to HVD conversion per drive.  They are selling re-manufactured disk modules with new Seagate drives inside.  However, the module will not qualify for HP hardware support.  But they are very affordable, their 18GB is $350. They also have a 36GB and a 72GB module. The 72GB is $550. The last used 18GB module I purchased was $695."