Getting Logic Analyzer 1650A/1651A to run

Unfortunately, I don't know anything about this particular unit, but I do know some things about floppy disks so maybe that can be of help.

The difference in terminology between mini and micro floppy isn't really relevant - different brands of disk sometimes exchanged these terms. What does matter is size. I presume it's a 3.5" double sided, double density (likely blue) floppy with one write protect hole (lower right) and no density hole (lower left) when holding the disk in the right orientation to insert into the drive.

If this is the case, then the 3.5" high density floppy disk (with a hole in lower left as well) isn't directly interchangeable with the one you have because the coercivity of the magnetic material is different, and it's likely the instrument itself only has a drive that understands double-density disks. You might get away with writing a copy of the floppy using a modern high density drive, by force formatting the disk to 720k in a proper MS-DOS environment, and using it read-only on the instrument however.

The problem with creating another floppy is that the zip archive on the site only has a bunch of files on it. If it needs any special format (e.g. non-FAT, certain boot sector requirements), then that hasn't been captured. I suppose it could well be possible to create another floppy by assuming FAT12 format and just leaving the files in the root directory.

However, the more likely issue is either the floppy you have has oxide shed over time (I've had many issues recovering Amiga disks of that day because of that issue - long article here: Project Kryoflux – Part 6: Dealing with Difficult Disks and Drives | Gough's Tech Zone) which can cause readability issues as well as a dirty drive head. How does it sound when starting up? If it keeps seeking back and forth, chances are, its head might be dirty or the drive may be bad and need to be replaced! The floppy disk may not be your only trouble! You might even need to crack it open to clean the drive and check the interface - if it's a regular 34-pin ribbon drive, finding a working 720k-only floppy drive is difficult, a high density drive may-or-may-not work. There are some USB floppy drive emulators (a bit hit and miss: Review: GoTek System SFR1M44-U100K USB 1000 Floppy Disk Emulator | Gough's Tech Zone) which you could replace it with provided you're able to image a correct floppy.

It may be salvageable, but I suspect you will need to understand a little more about floppy disks and floppy drives, and their formatting.

Thank you Gough, this makes me wanting to continue trying.

I recorded the sound of the floppy drive reading the disk, please have a look at the video http://youtu.be/LhBzWBMVpYQ

Maybe you can make some more conclusions?

Thanks for the video. It's clearly a 3.5" double sided double density floppy disk, so substitution of a 1.44Mb disk is not correct - even if the files are correctly written, the drive will not understand it.

This particular drive seems to be an original, old vintage drive. It does appear to be similar to a normal 3.5" form factor, and probably uses a 34-pin ribbon and standard power connector (but no idea whether it's jumpered for A: or B: operation). Replacement of the drive is a possibility, but double density drives are hard to find and likely to be problematic in the future. Replacement with high density drive may or may not work - you might try it as you might even have spare drives in older machines.

From the sounds of the video, the drive likely has a failed or misaligned track zero sensor. When you first power up the analyzer, and the drive receives power, it should make a short grunting noise, as the drive moves the head forwards and then backwards to find the track zero (i.e. outermost track). Your drive makes a repeated duh-duh-duh-duh-duh-duh-duh-duh-duh ... which suggests to me that an outer seek was done, but the return to track zero process was not successful. This is probably due to a failed, damaged or misplaced sensor. Alternatively, if the carriage itself is gunked up (needs lubrication), that could be another cause. A problem in the pin contact for /TRK0 logic connection could also mislead the analyzer into thinking the drive has not met track zero.

After the self-tests complete, and the drive spins up, you can hear the spindle motor seat with the floppy disk successfully and start turning the media. Then it sounds like it tried to perform a seek but didn't sound like it read much before the analyzer timed out. This may be related to the lack of track zero sensing causing the head to be outside its normal track position, thus reading "in-between" or completely blank unformatted area, and timing out on a lack of track marks.

The floppy disk doesn't sound squeaky, which is a good sign that it's probably okay as long as the media hasn't seen a strong magnet.

I would say that the drive, however, doesn't sound healthy. If you have another computer with a floppy drive, put the floppy on write protect mode, and see if you can make an image using a tool called Winimage. If you are successful, then the disk is okay, and the image can be copied to a USB 720kB floppy drive emulator to try and resurrect the system. However, fitting one will have lots of headaches (i.e. A: or B: jumpering, specific timing requirements) and may or may not work.

So this is a Philips LA but it deals with some cool options regarding replacing the floppy with SSD so may be very useful for you

https://www.youtube.com/watch?v=dk-aCr8sOIk&list=UUtiK8QrcCrsjDXpKzB1PO1A

Hope it helps a bit

Thank you for two very useful posts. I do have a modern USB floppy drive. I'm on Linux and tried dd if=/dev/sdb of=myfloppy.img command on a regular 1.44 floppy. It worked well, but both of the 720kB disks were unsuccessful, dd outputting 0 byte copied. Maybe I need to do this with an old drive also?

About the emulation, I have an extra Raspberry Pi laying around, maybe I could use it to emulate a floppy drive, but that will of course require a healthy image.

I think I will investigate if there's a working spare drive to buy somewhere and then look into the emulation options.

Many USB floppy drives only understand 1.2/1.25/1.44Mb high density formats. The former two are common in Japan, whereas 1.44Mb format is common on most IBMs. They will not read or write to 720kB double density disks properly, hence the requirement for a proper old machine and hardware floppy drive with hardware floppy controller under BIOS control. Or a hardware floppy drive under Kryoflux controller (which can read specialty format disks, e.g. Apple, Amiga, Commodore etc). It's one of the reasons why most floppy preservationists can't live without a special controller.

I haven't seen or tried anything, although I did hear of an effort to use the Raspberry Pi to emulate something like the Kryoflux by using high rate GPIO to sample the data output line from a proper old 34 pin floppy srive then decoding in software. They might have got it working although they did have issues with the length of DMA buffers and getting seamless readbacks from it, so emulation with a Raspberry Pi might noy be in the realm of possibility just yet.

Hi Gough,

Here's an update for you post your Gotek review.

The Gotek Floppy DIsk hardware makes it easy for one to build their own floppy disk emulator.

It's essentially an ST Micro ARM device that has an inbuilt USB host and bitbashes some I/O pins to emulate a floppy disk device.

[Note: A Floppy disk interface is nothing more than a set of open collector(or drain) logic signals]

Flashing the Gotek is easy - one can connect a USB-A male to USB-A cable male (an unusual configuration), hook it up to a PC and download a .DFU file using the standard STMicro download program.

Because the interface is serially streamed, the emulator is able to behave as you like from standard FM and MFM formats to GCR (Group Code Recording), others and even if you're prepared to write your own code - your own formats (RLL is a possibility).

The limiting factor of the formats available is the encoding and decoding performance of the microcontroller.

If the standard one is not fast enough it could be replaced with a faster one or a PSoC that can use UDBs (Universal Data Block) to transcode the datastream.

In addition to being a floppy disk emulator it can also be used as a conduit for floppy disk based systems to read USB sticks or to emulate hard disks.

The current firmware has a special mode where the user steps the floppy disk to Track 255 when all of a sudden the floppy disk emulation stops and a small set of LBA (Logical Block Address) based commands can access the USB stick's Logical Blocks.

As soon as the user steps away from Track 255 operation returns to normal.

You can also do handy mods such as replacing the 3 digit LED display with a graphical OLED display, add a rotary switch to more easily change disk images or make it act as multiple floppy drives.

Cheers

Compact