Mac SE/30 SCSI problem — #7

Post #7 by zuiko21

Source Forum	68kMLA
Category	Troubleshooting
Post Date	Fri, 6 May 2011 - 13:14
Original URL	https://68kmla.org/bb/threads/mac-se-30-scsi-problem.20046/

Post

Hi Trag, many thanks for your reply.

I would very carefully examine the area around the 53C80 chip for damage/corrosion from the leaking capacitors.

This makes a lot of sense... I remember seeing some greenish stuff on the 53C80's pins

(hmm... I think that pin is Vdd)

In other words check continuity from each 53C80 pin to the pin of whatever other component it connects to.

Yes, it seems the easier way to do it. Thanks for the advice.

The output side of the 53C80 should be fairly straightforward, as the pins should connect to the appropriate pins on the SCSI connector.

Will be the first to be checked... After further experimentation (with some abnormally excessive termination), SCSI Probe was able to sort-of-read the name of one of the disks on the chain. It said UUENTUM LT646W instead of QUANTUM LP240S -- that's the DB2 bit gone crazy!

But I'll eventually check every 53C80 pin. Should any connection show up as defective, I'll begin the (tedious) work of visually inspecting the board in search of the flaw...

If there's a schematic of the SE/30 logic board available get that and use it to check the 53C80 connections

Fortunately I have one! I can't remember the source anyway, I'll check later.

Ah, forgot about this. I have the 53C80 datasheet available here: http://www.io.com/~trag/DataSheet/Z53C80.pdf.

Thank you very much!

The D7-D0 lines probably connect pretty directly to the CPU data bus. The address lines and the other control lines may pass through one of the two VIA chips.

It's a surprinsing scheme... data lines come from the CPU bus, of course, but are actually D24-D31 (!). Address lines come from the bus also, but they're A4-A6. Both sub-buses are easily checked at the comfortable, large DIL pins of the Video ROM. Of the remaining lines, many are exclusively connected to the Glue chip.

The IRQ line almost has to.

Certainly -- VIA2's CB2 input.

Again, thank you very much for your help -- you're the real saviour of my SE/30! ;D

I'll be back with the results of the checkout. Cheers,