Lisa I/O board troubleshooting, and schematic weirdness from Mr Ian Primus on 2012-03-25 (lisalist1)

From: Mr Ian Primus <ian_primus_at_email.domain.hidden>
Date: Sun, 25 Mar 2012 20:28:41 -0700 (PDT)

I have been working at repairing a Lisa 2/5 boardset that was badly damaged by battery corrosion. I've been focusing on the I/O board first. I've managed to clean up most of it, and I had to replace RP4, and a handful of resistors and capacitors around the area. Overall, the board doesn't look too bad - the backplane bore the brunt of it, destroying the edge connector that the I/O board was plugged in to. I've desoldered the destroyed connector, but have yet to finish reassembling the backplane, so I'm testing boards in a 2/10...

So, I know that the disk interface cabling is different between the 2/5 and the 2/10, so I can't expect the floppy disk or the 2/10's Widget to work, so I have those disconnected. I am using the 2/5's CPU board, so I have the correct firmware to work with the I/O board.

I get a couple of beeps and error 51 on the screen. Now, I know that this relates to the parallel port VIA, so I've already tried swapping it - no change. I've started tracing the circuit, looking at the schematic I have, and... it's different. Now, I'd noticed weirdities about the schematic earlier - being unable to find D8, for instance. But this one is weird. It shows a chip, at U11E, supposedly a WD2001. Now, the chip at 11E is NOT a WD2001. It's a 29LS32. Furthermore, on the right side of the SAME PAGE of the schematic, the chip at U11E is correctly noted. What's going on here? Are these schematics I have for another revision? They're marked as Lisa 1 schematics (which should use all the same boards). I also have the the 2/10 schematics, and the same chip shows up. The only thing I can think of is that perhaps they mean U11*B*, which is an empty socket. What was supposed to go there, anyway? Was it this WD2001 chip?

So... I'm going to keep digging in to this, and see what I can come up with, but I really don't think this schematic matches this board. Another example, there is an R57 on the schematic that I can't find anywhere on the board. Any other pointers on troubleshooting the 51 error?

Also, are there schematics for the backplane board somewhere? This one has lots of corrosion and damaged traces, so I'm going to need to be able to trace it out to verify everything is correct.

Thanks!

-Ian

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