• Hello, Guest! Welcome back, and be sure to check out this post for more info about the recent service interruption and migration.

SE30 SCSI Termination conundrum

mst3k

Member
I could use your expertise.
I’ve acquired an SE30 with an issue. It has 8mb of ram and boots easily from the floppy drive.
However, the hard drive is not recognized. I’ve pulled the hard drive and it works fine with my SE.
Ive tried several known ’good’ hard drives on this SE30 but none are recognized. Ive tried them on the external and internal connections. I’ve tried a scsi2sd drive and a blue scsi. Nothing is recognized. ScsiProbe 3.5 sees the motherboard at ID 7 but nothing else. It also reports ‘no termination’ on the computer. I’m assuming this is a motherboard problem? Maybe a blown fuse on the scsi connector?
I’ve tried replacing the ram and using different configurations. I’ve tried different HD setup programs.
what am I missing?
Thanks!!
 

Unknown_K

Well-known member
The termination needs to be on the HD (jumper to enable it and 3 sets of terminating resisters on the bottom PCB side of the OEM drive).

What OS is on the HD?

There is a 1A fuse in the SE/30 connecting pin 26 on the internal 50 pin scsi cable to 5v (should be a 1N4001 diode in line as well).
 

mst3k

Member
Thanks for the reply! The drive that came with the SE30 has 7.5.3.
The test drives have 6.08 and 7.
To my knowledge all of the drives are terminated correctly. I've looked at the original drive specs online and the terminating resistors seem proper, plus my SE recognizes the drive (if that matters)
If it is a fuse, is it simply a matter of replacing it on the motherboard? (If I can find it). The fuse that I think might be the culprit is a 'resettable' fuse. I'm not sure how they 'reset'. I did see another post with a 1A 5V pico fuse that was replaced but the motherboard is supposed to be drilled for that one?
I'll double/triple check the termination on the HDD again. This has been maddening.
Thanks!
 

mst3k

Member
Sadly, no. I think that is the next step. I've never seen a SCSI bus failure before. I'm sure it happens but I keep thinking there is a simple solution.
 

ktkm

Well-known member
Try connecting an external SCSI device with termination. I have a recapped board that was very picky before I switched from an old “upside-down” Quantum to a SCSI2SD 5.1 with software termination. The only time it would boot where if I had an external CD-ROM connected.
 

MacKilRoy

Well-known member
Try connecting an external SCSI device with termination. I have a recapped board that was very picky before I switched from an old “upside-down” Quantum to a SCSI2SD 5.1 with software termination. The only time it would boot where if I had an external CD-ROM connected.

Certainly SCSI termination issues are voodoo. They were back in the day as well (not exclusive to SCSI2SDs and so on). I would suggest what you're saying, and if it still causes issues, I would recommend an internal ribbon cable with an extra SCSI connector on it, and a physical active terminator applied to the end of the bus internally. There never seems to be a complete solution for everyone regarding termination issues. Back in the day, some devices just didn't like being in a certain position on the bus, or together with another particular device. SCSI has always been a black magic to perfect.
 

mst3k

Member
OK, I disconnected everything. No internal, no external, no SCSI devices at all.
I booted with a floppy to System 7.5.3.
I ran, from a floppy, SCSIProbe 3.5.
The motherboard SE30 shows up as ID7.
A large flashing warning at the top of the screen says "BUS NOT TERMINATED".
I then attached a tested hard drive with proper termination to the internal bus and rebooted with the floppies again.
The exact same result "BUS NOT TERMINATED" and the drive was not recognized. It did not show up.
I then attached a MacSD to the internal bus and watched the flashing lights:
Power light was solid. Power to the device from the SCSI port was good.
The SCSI activity light was blinking good UNTIL the floppy disk with the '?' appeared on screen. Then no SCSI activity.
I insert a floppy and it boots immediately. I run SCSIProbe 3.5 and nothing. Just the motherboard at ID 7.
Sorry to be a pest here. I really am a novice and I'm using brute force to try and solve this puzzle.
Wouldn't a blown 'fuse' mean no power thru the SCSI bus? I have power.
Is there a SCSI chip on the board somewhere?
As per ktkm, I have ordered an internal cable with extra SCSI connector and a physical terminator.
As per MacKilroy, I am looking into recapping.
Why does a bare board show as SCSI 'bus not terminated?
Any other ideas?
Thanks
 

ymk

Well-known member
I then attached a MacSD to the internal bus and watched the flashing lights:

MacSD is powered from TRMPWR, so your fuse is good.

Which resistor configuration were you using?

In pull-up mode, voltage is routed from TRMPWR to all of the SCSI data lines to pull them up to about 2.5V. Without this, the data lines will drop down to around 0V, causing the BUS NOT TERMINATED message.

The other variable here is the macsd.ini configuration. Does it work correctly in your other Macs?

Also try swapping the internal cable since they can fail.
 

mst3k

Member
Thanks for the reply.
The MacSD is in pull up, as shipped, config.
It works on my other Mac just fine.
The internal cable was pulled from a working Mac and is OK.
I can’t figure out why anything I attach to the scsi bus is NOT id’d, except the motherboard.
And why the scsi bus shows ‘not terminated’ even with nothing attached.
 

ymk

Well-known member
SCSI devices (SE/30 logic board included) only drive the bus lines in one direction, toward ground. Termination must be present for the lines to rebound to a high state (around 2.5V). The MacSD in pull-up was performing that function. Many Centris, Quadra and PowerMac class machines have the same termination onboard, but the SE/30 does not. That's where the termination error message comes from.

The SE/30 does have a discrete SCSI chip and it's labeled on the board. Unfortunately, it's located next to three capacitors which often leak onto it. Look for corrosion on its pins.
 

MacKilRoy

Well-known member
I had a buddy who had a SE/30 that he wanted to get recapped. After recap, SCSI wouldn’t work. Turns out the Bournes filters were fubar on the board. A replacement of them got SCSI back up and running. It’s a long shot but if recapping doesn’t work and a known good device and cable don’t work, it may be that.
 

MacKilRoy

Well-known member
Thanks! I'm glad you enjoy it.



Aren't those related to the floppy interface? I didn't think they could bring down SCSI.

There are traces that run through SCSI as well. I believe they have something to do with scsi termination actually. I could be wrong.
 

mst3k

Member
OK, I got out the magnifying glass and looked all around the SCSI chip and caps.
Yup, this baby needs to be recapped. Plus, I found corrosion all around the SCSI chip to the point that it looks like one of the pins may not actually be connected to the motherboard. I'm going to clean this all up, get out the multimeter and start looking for faults.
I'll post the final results, but it looks like not a termination issue, not a fuse issue, just good ol' corrosion (or a failed chip).
Stay tuned and thank you to everyone who helped me out here!
 
Top