Summary: Can't clear ESP interrupts: check SCSI Term. Power Fuse

From: J Leung (
Date: Fri Oct 16 1998 - 12:03:46 CDT

There are only 2 replies to my question and the solution in our case was a
bad adaptor.

The following are the suggestions that I received over the net:

Thanks to: Harvey M Wamboldt & Marc Newman
1. First: If you do poke around the hardware, YOU MUST OBSERVE AT ALL
   TIMES proper static precautions and DO NOT touch the hardware with
   power applied.
   On 28 Sep 1998, J Leung wrote:
> Can't clear ESP interrupts: check SCSI Term. Power Fuse
   Sounds like it's telling you to look for a fuse for the SCSI Terminator
   Power. This would probably be a small device somewhere on the
   motherboard, probably near the SCSI connector. It may be soldered in
   place. Assuming you have a regular single-ended SCSI, you can check to
   see if you have terminator power on the SCSI bus by checking that you
   have 4.8 volts DC (or greater) on pin 38 of a 50-pin SCSI bus and on
   pins 17, 18, 51 & 52 of a 68-pin SCSI bus. If the fuse on the
   motherboard is blown, all is not lost. You may be able to get power on
   the SCSI bus from the external drive. You will need a manual for the
   drive (if it's a Seagate, you may be able to find one at telling you which jumper is which. SCSI terminator
   power can usually be provided from a hard drive by moving a jumper
   somewhere on the drive.
   Before you turn on the terminator power though, you should find out
   what happened to the fuse. You can sometimes blow drivers (or if you
   are lucky, the fuse) if you have too many terminators installed on the
   same SCSI bus. You should check the jumpers on all external drives to
   see whether their internal terminators are enabled or disabled, and any
   other devices on the SCSI bus as well. Remember, only use two
   terminators, one at each end of the SCSI bus. A lot of SCSI problems
   can be traced to having internal (built-in) terminators enabled when
   using external terminators at the same time. Another problem, far less
   common, occurs when different devices on the SCSI bus are connected to
   different power supplies. I once had two devices side by side with a
   50 volt difference in grounds between them. This can happen where
   grounds float, a common problem on a ship, and can also be caused by
   wiring problems, or where power is supplied from different sources
   (such as two backup generators). Other than on ships, this is a pretty
   rare problem. A few volts difference would be more than enough to blow
   Hope this helps,
2. Some SCSI devices, especially disks, have jumpers for internal
   termination. Unterminate your drive, it should work better.
Original Question
Hi, gurus! When the Sparc20 running Solaris 2.5 rebooted, it came up with
the following error message twice: Can't clear ESP interrupts: check SCSI
Term. Power Fuse We have the Sparcstation connected to an 8mm tape drive
and an external disk drive. Doing a probe-scsi reveals that the system
could reach/see its internal disk drive and the tape drive, but not the
external disk drive. Swapping another SCSI cable and/or terminator on that
external disk didn't seem to help. Does it mean that the power fuse of
the external disk drive needs to be replaced? Or what else could I check?
Regards, Janet

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