General Category > Lisa Troubleshooting and Repair

Will the Lisa return an IO error without the "Lite" Interface Card

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friedboard:
- Correct, a 820-4033-A IO board but NOT the 820-4033-A2. Reading around I think this might be the Macintosh XL upgrade version for this board on the 2/5 that doesn't support a widget.
- a 2/5 chassis wiring harness, with 2 ribbon cables with 26 pin connectors in the drive cage (and no 20 pin connector ribbon cable)
- a stock lite adapter with no mods and wires
- Parallel, mouse, and 2 serial ports in the back

sigma7:

--- Quote from: friedboard on August 08, 2025, 06:57:00 pm ---- Correct, a 820-4033-A IO board but NOT the 820-4033-A2. Reading around I think this might be the Macintosh XL upgrade version for this board on the 2/5 that doesn't support a widget.

--- End quote ---

I'm not familiar with this: "the Macintosh XL upgrade version for this board on the 2/5 that doesn't support a widget" ... can you point to your reference(s) about this?

friedboard:
Yeah, I think it was just an old reference from a message board. Not sure how true it is: https://classiccmp.org/mailman3/hyperkitty/list/test-drb@ccmp.vtda.org/message/KETOQ33SNDARQS6WXYW766FULSTHSOVU/

sigma7:
Since this external posting from the typically very knowledgeable Eric Smith is bound to come up again someday, I'll try to clarify some of the potential confusion, without adding too much more confusion.

This is the referenced post:

https://classiccmp.org/mailman3/hyperkitty/list/test-drb@ccmp.vtda.org/message/KETOQ33SNDARQS6WXYW766FULSTHSOVU/


--- Quote ---Lisa I/O Card Question

eric＠brouhaha.com
13 May 2000 12:28 p.m.
"Wayne M. Smith" writes:
...
  I have a Lisa 2/5 with H8 ROM which has the following I/O card, no. 820-4033-A:
 http://home.earthlink.net/~wmsmith/_uimages/Lisa_IO_820-4033-A.jpg

This card works in a Lisa 1, Lisa 2 (no hard drive), and Lisa 2/5 (external profile).  It has support for two floppy drives, although that only works with Twiggy drives.  It does not support an internal hard drive.
...
  Some time ago I came across a different I/O card, no. 820-4033-A2:
 http://home.earthlink.net/~wmsmith/_uimages/Lisa_IO_820-4033-A2.jpg

That card works in a Lisa 2/10 or Macintosh XL.  It supports one 400K 3.5 inch drive (or 800K with Sun Remarketing's modified firmware), and one internal Widget hard drive.

The two cards are not interchangeable.  The Lisa 2/10 and Macintosh XL use a different backplane.  IIRC, the connectors are offset so that the old I/O card will only plug into the old backplane, and the new I/O card into the new backplane.  But even if I'm mistaken about that, I'm rather more certain that the cards aren't electrically interchangeable, since I've been looking at the schematics just recently.

Among other differences, the floppy drive motor speed control is done differently.  The old I/O card was designed to serially shift the motor speed control byte into the disk drive; when they upgraded to the 400K 3.5 inch drives, they had to add a "Lisa Lite" adapter card to convert the serial bits into a PWM signal.  The new I/O card generates PWM on the card.

The old I/O card had a socket for an AMD 9511 (or 9512) math coprocessor, which was never used by any production Lisa (or Macintosh) software.

The new I/O card instead has a footprint (but usually not a socket) for a Western Digital WD2001 DES crypto chip, which also was never used by any production Lisa or Macintosh software.

There are other minor differences between the two cards; I haven't bothered to track them all down.

Eric
--- End quote ---

The two varieties of the I/O Board are very much the same overall, except for the differences noted and the NiCd Battery and charger (1/5), missing on the 2/10 board (and ultimately removed from 1/5 boards due to leaking and corrosion).

The boards have the same shape and are mostly drop-in interchangeable in function. However there is a significant difference in the floppy drive circuitry, so simply swapping the boards will break floppy functionality (edit: this issue only applies to 400K single sided drives). If you don't try to connect / use the floppy in a mixed 1/5/2/10 Lisa, both I/O Boards will work.

Both varieties have nearly identical parallel ports, both supporting both ProFile and Widget drives. It is the variety of Motherboard that routes the parallel port either to the back panel or the internal cabling. A Widget can be installed in an external case with power supply and connected to the back panel parallel port normally used for a ProFile. A ProFile (or emulator) can be connected to the 2/10's parallel port cable in the drive cage originally intended for a Widget. The I/O Board doesn't know or care.

Since the internal chassis cabling is different for the 2/10 (with internal parallel port and 20 pin floppy cable) vs the 1/5 (with no internal parallel port and two 26 pin floppy cables), the two motherboard varieties have slightly different chassis card edge connector arrangements. However they are not sufficiently different to prevent connecting a motherboard to the wrong kind of chassis cabling.

So it is the Motherboard that determines whether a 26 pin cable in the drive cage is a parallel port or not... if the motherboard has a rear panel parallel port, then no internal cable is a parallel port. If the motherboard does not have a rear panel parallel port, then an internal cable is a parallel port. This is the case regardless of which I/O Board is installed.

Floppy drive support is the complication. The (edit: 400K single sided) 3.5" floppies require PWM for the motor speed control. The 2/10 I/O Board includes this, but the 1/5 board does not, so the 1/5 board requires the Lite Adapter. In addition, the 3.5" floppy drives have a 20 pin connector, so the Lite Adapter converts the 26 pin Twiggy cable to the 20 pin used by the 3.5" drive.

The final result is that an inconsistent/mixed set of 1/5 vs 2/10 boards and cables requires special attention and (edit: in the case of a 400K single sided drive) modifications for the floppy drive to work, and damage can occur if connected incorrectly, so it is best to avoid these unusual combinations if possible.

edit: grammar

sigma7:

--- Quote ---- a 2/10 IO board (3 large chips at the top left)
- a 2/5 chassis wiring harness, having 2 ribbon cables with 26 pin connectors in the drive cage (and no 20 pin connector ribbon cable)
- a stock lite adapter with no mods and wires
- a 2/5 Motherboard with Parallel, mouse, and 2 serial ports in the back

--- End quote ---

This combination will not result in a working floppy drive.

Edit: This combination does seem to work with 800K double sided Sony drives and the FloppyEmu (and likely other floppy emulators)


However, this combination does not work with 400K single sided Sony drives
Solutions:
1) Replace the 2/10 I/O Board with a 2/5 variety,
or
2) Replace the motherboard with a 2/10 variety, replace or modify the chassis ribbon cable so you have a 26 pin and a 20 pin cable, and remove the Lite Adapter,
or
3) Replace the Lite Adapter with a 26 to 20 pin adapter to suit the change in floppy wiring without adding any electronics such as are on the Lite Adapter,
or
4) Modify the Lite Adapter to work as explained in the LisaFAQ entry below (not recommended if you want to preserve the original components of the Lisa for collector purposes)

More info:
LisaFAQ: 3.8.3. Will a Lisa 2/10 I/O board work in a Lisa 2/5?
Topic: LISA card compatibility and interchangeable scenarios?

Once you come up with a configuration that can be made to work, then we can get back to investigating and repairing whatever damage might have occurred.

edit: corrected that only 400K floppy drive function is impeded

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