Can you install System 7.5 using System 7 tidbits and disk tools?

A plain System 7.5 set of floppies ought to consist of something like seven (may possibly differ depending on language version) 1.44 MB Install disks (and some extra floppies, including Disk Tools). Is this not what you have? Do you have a special 7.5 version (such as floppy disks from a 7.5.3 download)?

A normal Install 1 disk would contain an Installer application. The Installer handles the unpacking of files on the following (six) disks. The procedure is to start the computer with Install 1 in the floppy drive, and then launch the installer. One can choose a Custom or an Easy Install. If Custom is chosen, it is possible to separately install things like a minimal system or a universal system for all Macs. One can also, for example, custom install the PC Exchange control panel for compatibility with PC-formatted floppies.

Try the usual things first. That is, resetting the PRAM (press the four keys Command, Option, P and R immediately at startup; hold down until a second startup tone has been heard), and later the aforementioned system startup with Extensions off. Try inserting the floppy several times.

Do you have access to Disk Copy 4.2 (http://download.info.apple.com/Apple_Support_Area/Apple_Software_Updates/English -North_American/Macintosh/Utilities/Disk_Copy/Disk_Copy_4.2.sea.bin)? If so, one could make an experiment. The idea is to try to read the floppy directly into an application. One would launch the Disk Copy 4.2 application (also known as Apple 3.5" Disk Duplicator, v4.2), then click on a Read Master Floppy button.

Post back if you need details about how to download, transfer and decode old Macintosh files. If yes, please let me know what you have to work with (such as other old Mac model with built-in floppy drive, PC with floppy drive, external USB floppy drive, etc).

You need PC Exchange if you want to read PC-formatted floppies (for example, when downloading onto a modern PC or Mac, and transferring files on PC-formatted disks via an external USB floppy drive). If so keep downloaded Macintosh files encoded (.bin or .hqx) or possibly just compressed (such as .sit) until on the LC.

In order to decode MacBinary (.bin) or BinHex (.hqx) or to decompress StuffIt (.sit), you will need a ready-to-use freeware utility called StuffIt Expander (version 4.0.1 or 5.5).

Earlier, with access to a Windows PC (capable of running a DOS program) with a floppy drive, the following was an option:

Prepare an empty PC-formatted 1.44 MB diskette via FORMAT A: in DOS or the "full" formatting option under Windows. Download the MACDISK.EXE file from http://rrzs42.uni-regensburg.de/macintosh/files/macftp.html . Run the MACDISK.EXE (DOS) program on the Windows PC. Follow the instructions on screen. The result will be a Mac-formatted (sic!) floppy that can be used in a Macintosh computer. This floppy contains a Stuffit Expander installer.

Unfortunately, the web address does not appear to be active any more.

Generally speaking, archive.org can sometimes be useful when searching for information on older web pages.

If you have an Apple/Mac user group in your country/area, someone there might be able to help you with a working copy on floppy of StuffIt Expander 4.0.1 or 5.5.

User Groups - Apple

With access to all the seven floppies Install 1 to 7, you should be able to start up from Install 1 and carry out the installation. Try the Easy Install to begin with. If this does not work, please post back.

Glad to hear that the System 7.5 installation was successful.

First of all, in order to avoid any accidental and unwanted erasure, it is not a bad idea to lock (write-protect) the floppy. Old floppy disks can sometimes lose information. Alignment differences between floppy drives can also appear. Is it an original floppy, or has it later been copied (backup)? An 800K (2DD/DSDD) or 1.44 MB (HD) diskette? The same result with Extensions off (Shift key depressed at system startup)?

I mean to reset PRAM and then start up with the Shift key depressed, with an empty floppy drive. Only then, insert the floppy (repeatedly, if required). The idea behind the Disk Copy 4.2 experiment was to at least try to avoid a dialogue box in Finder.

Yes, you would get exactly the same dialogue box if you as a mere test insert a PC-formatted floppy, providing that you do this after having started up with Extensions off (otherwise, the PC Exchange control panel would be active, making the disk appear with a PC icon on the Desktop). This means that the LC is not able to recognise the file system on the floppy. Unfortunately, in the case of the games floppy, it probably means that the disk is more or less damaged (perhaps somewhat/partly demagnetised). We cannot rule out that an attempt to read the floppy in another old Mac would be possible, though.