CDTV SCSI with SCSI2IDE bridge. Stumped.

[chiark]

Weird one this.

I have a CDTV to SCSI from W.A.W, CDTV ROM 2.3, KS 1.3 and 3.1.

For SCSI, I have a 7720u with an IDE->CF adaptor on it. It has a 3.5" drive power connector to 2 floppy power connectors (1 for the CF interface, 1 for the 7720 itself)

I'm splitting power to the CD-ROM in the CDTV from 1 to 2 3.5" power connectors.

The 7720/CF interface *ONLY* works when it is powered by a separate power supply, and attached to the external SCSI port. When connected to the internal PSU / external port, it doesn't work. Internal connector/internal PSU, nothing. Internal connector, external PSU: nothing.

A standard quantum drive works on the internal PSU and port perfectly.

It sounds like a grounding problem to me: any inspiration for how to sort it out???

Cheers,
nick.

 

[chiark]

No clues?

 

[rkauer]

Some ideas: check the voltage levels with all parts hooked in. Also check the same rails with no boards at all.

I bet the CDTV PSU is dropping a too low voltage at the +5V rail.

 

[Merlin]

^^^
Whut he said, or maybe the current is dropping off, due to the PSU being too weak.

Remember, C= weren't known for making overly powerful PSUs.....just enough was good enough.

 

[rkauer]

Another idea is adding a small (100uF x 10V) to the +5V line near the ACARD to smooth voltage ripple and helps things a little.

 

[chiark]

Checked the voltage throughout initialisation - both 12v and 5v are holding firm, unfortunately.

regarding the capacitor, should I connect that from 5v to ground to filter the supply?

 

[rkauer]

Yes, +5V to the positive lead of the capacitor, negative lead to ground.

 

[chiark]

Thanks. I also wonder if there's some way to isolate the ground, or do something along those lines, as it really strikes me that there's some problem with respect to SCSI ground vs PSU ground.

Even when the CD-ROM is disconnected I get nothing from the SCSI->IDE bridge...

I wonder if grounding the ground plane of the card to the CDTV might also help.

@Merlin: the odd thing is that there's more than enough juice from this PSU to run a 68030 and a Quantum 3.5" hard drive too! I can't see the acard taking more power than those two combined.