Mike's PCjr Page

Greetings All,

In cleaning out some of my father's old junk (he was a lifelong IBMer), I've come across a mint IBM 3510 external SCSI housing configured with a single speed CDROM drive. I would love to hook this up to my PCjr via a Trantor / Adaptec APA-348 miniSCSI / parallel adapter which I also have.*

However, from what I can tell, the IBM 3510 does not employ a powered SCSI terminator. Something that appears to be required for the APA-348 to wake up and smell the coffee. One option would be to add a second SCSI device with a powered terminator at the end of the chain. I may do this, but I've already got an 8GB DOM on the jrIDE and a 2GB jrCART humming along just fine (plus my wife might pitch another "vintage" external enclosure out the back door, if it were to show up).

Has anyone ever added 5 volts to a SCSI terminator to give it power? Is this completely crazy? Can such a thing be done successfully?

Thanks in advance for your comments.
Ryan

*Yes of course I could use number of other CDROM options out there (from Micro-Solutions, etc), but where would the fun be in that? This thing is SINGLE SPEED and weighs 10 pounds!

I'm no EE, but I just did a quick bit of reading and I'm going to yell at you for even thinking about it!

Passive termination (the default for old SCSI) uses resistors in the terminator. The issue with them is that the power level on the TERMPWR line can fluctuate depending on how many devices are attached. Active termination basically adds a voltage regulator to ensure that the resistors are properly fed, regardless of how many devices are attached. See https://www.analog.com/media/en/referen ... dn034f.pdf for a good write-up.

Does the APA-348 really require active termination? It's a low-end parallel port device, so I doubt that it does. Some termination would be nice, and active should be better, but I doubt active is needed.

If your 3510 is like mine then you have two SCSI connectors on the back. One should go to the APA-348 and the other can take any terminator you can find.

Hi Mike,
Thanks for the reply. My 3510 has a passive terminator installed. I can definitely try an active terminator, they are plentiful on eBay. I came across the following info that made me think I might need more than just an active terminator (I was thinking that even an active terminator didn’t supply termpower), but will definitely try that.

Thanks,
Ryan

…
SCSIworks! 1.3 Compatibility List
…
CD-ROM Drives:
IBM:
3510* (CD-ROM I, CD-ROM II)
…
* These SCSI devices do not provide termination power, and therefore will not work with the APA-338 MiniSCSI, APA-348 MiniSCSI Plus or APA-358 MiniSCSI EPP adapters, unless daisy-chained with other SCSI devices which provide termination power
…

Ok, that makes it more clear ... you need a device that provides TERMPWR as the APA-348 does not. (There are limits to what it can siphon from the parallel port.)

My good PCjr setup before jrIDE was a Shuttle parallel port adapter with an external hard drive and a CD-ROM in a 2nd enclosure. I was not using the same SCSI enclosures though, and my devices might have been providing TERMPWR.

Try either an active or passive SCSI terminator first before trying to rig something up. At worst case you will have to add something to the chain to properly terminate the bus. Something tells me that just trying to inject voltage on that line can get complicated, especially when you start considering that you have two different power supplies involved.