SF314 Drive Failures - any pointers?

telmnstr · May 19, 2015

Some time ago I started to dig into the bad floppy drive that was stock in a ST Mega 2. At the time I thought the drive was a D357 as that is what is printed on the back of the metal cover. But now I've learned that it's identical to the wide button SF314.

Does anyone know any common issues with the drive? Looking at my way earlier post it seems to run okay once the heads are out of the home position, but when the heads are homed it just fails. Obviously if you physically move them out of home then it's going to run out of room and not be correct with regards to alignment.

As I recall I used an oscope and verified that the home position optical sensor is good.

I saw a prior post from someone saying the ribbon cable that runs to their heads had delaminated or crumbled, that doesn't seem to be a visible issue with the drive I have but I can't discount it. The flexible ribbon looks to be fine.

I know it's possible to sub a PC drive as long as it has the dumper (or do the ribbon cable hack) but I really want to keep the drive original or close to it. The machine looks so good :-)

I did find other cases of people with failing drives, so I figured narrowing down the issue might be useful and it would be a good thing to keep as many drives alive as possible.

The boards do have a good number of electrolytic caps on them. I saw information regarding a different model Atari drive having caps that go bad . Looks like there is 4 on the board closest to the ribbon cable and 8 on the spindle motor drive.

Also note, the wide button SF314 drive has no drive belt, it's direct drive.

telmnstr · May 22, 2015

Okay, so the plot thickens. I've figured something out. If the cover is off then the floppy drive seems to be working. But when I put the system back together, it quits working.

I was thinking this is because I had the floppy cable stretched out (drive unmounted), and that maybe there is a break in the wires in the floppy cable that runs from the motherboard to the drive. So I took another cable from a PC and cut it up, replaced the original one keeping it similar in length. I tested my cable replacement with the cover off and the drive worked. So Iput it all back together and it comes up with errors trying to access the floppy disk, like it did before I replaced the cable. The light kicks on when trying to access the disk then it just fails.

I'm at a loss, and it's crazy frustrating. Cold/bad solder joint due to stress on motherboard maybe. The drive is rigid enough that stress from being mounted shouldn't effect it. Ripple in power supply? I'm going to turn it off, and let it cool down all the way and test it to make sure it isn't heat related.

There is one modification that someone (or factory) has done with stacked chips and one pin on the 68000 chip being cut and jumper wires to the PCB and chip side (separated) on that cut pin. Strange stuff, not sure what it's for.