Hi. All all head measures taken in the component itself or the connector? Thanks.

Hi I love this kind of drive, I am quite to solve a modification from a specific PC floppy to work into the SFD disk, I am not an elettronics expert but I have reached a very good point.
At this time my SFD unit is working even better with a PC unit than the original one, I arranged a bibolare bridge adaptor, and I am tring to fix head impedence adjustment, just to limit the energie to the haeds, I wish if you agree, to share some schematics and ask your help to close this project. I hope to full support the commodore comunity with my schematics and if you want with you help.
best regards Antonio

hi do you know the voltage draw on the 5v and 12v as i want to replace the transformer with a switching supply

Good day, Jani – I have an SFD-1001 that only wants to read the bottom side of disks. Disk rotation speed is spot on 300 RPM, I’ve cleaned the heads and aligned them to the point where the bottom head seems to read the best, but any time I try to read from the top of the disk the Red/Green LED flickers back and forth between colors, sometimes the head bangs into the end and eventually it gives up with an error. It will not format either, I get a “21, READ ERROR, 78, 0” every time and with every disk I’ve tried, even after degaussing. I notice when I scope the center tap of the R/W head that the bottom head gets regular ~9vdc pulses at regular intervals, which only change frequency while the head is moving. However I never see such pulses on the center tap of the top head. The schematic would seem to suggest the 7445 BCD Decoder as the control source for this voltage, either indicating that it is stuck outputting the voltage to the bottom head only or not being instructed to output voltage to the top head. Have you ever encountered this before, or scoped the head pins while the drive is in operation? I’d be very curious to learn what is “normal” for an SFD-1001 when reading data from the top head – should there be pulses present on the center tap pin?

Hi Jani, I set aside the SFD-1001’s for the time and have been working on an 8250 which is exhibiting the exact same behavior. What is even stranger is that for a while, both drives could format disks if I pulled the drive mechanisms (Micropolis) out of the chassis and set them on their sides. However, after cleaning the mechanisms, re-greasing the rails & worm drives and quietened down the drive spindles, I cannot for the life of me get either drive to move past the “23, READ ERROR, 78, 01, [0 or 1 depending on the drive]” error. I was very careful not to touch the heads as much as possible while cleaning. I’ve checked the drive speed on both, and all four R/W heads measure within 1.5 ohms of the corresponding coils from one to another. When I put my scope on the test points according to a maintenance guide I found, I can see the bottom head getting written to and then the data being read back from the head, but as soon as it finishes writing the sectors to the bottom head and switches to the top head, there is nothing on the trace but baseline noise. This would lead me to conclude that the head(s) are bad, but they both were working not long ago and are both now doing the exact same thing. Part of the trouble is that the same test point is used for both heads, so it is not apparent from the trace which head you are seeing. Contemplating this, I decided to swap the head connectors, so that the top and bottom heads would be reversed from the analog board’s perspective. This resulted in an immediate 75 FORMAT SPEED ERROR, further seeming to condemn the top head. I could accept this except for the fact that the coil resistances are practically indistinguishable from one head to another, top or bottom. It does not seem like any of the wires are disconnected from either r/w coil or the erase coil; the heads are spotlessly clean. I’ve verified that both top and bottom heads make good contact with the disk surface when the drive is loaded… This seems like a strange mode of failure for so many “top” heads – even from different manufacturers. I wondered if somehow the topside media was bad (I’ve been trying a variety of DS/DD disks from different brands, but they are all still old none the less). Since the 8250 does not use the index sensor, I flipped a disk and tried to format the “top” of the disk with the bottom r/w head. This also resulted in a READ ERROR at track 78, indicating that it successfully wrote to and read back from a full track of the bottom head but again failed on the first track of the top head. All evidence I’ve seen so far points to head failure, but I am having a hard time accepting that. I am now starting to wonder if somehow there is some component loose inside the heads, and setting the drives on their side allowed gravity to “help” correct whatever malfunction there is. I wondered if this might also indicate a loose connection, except that I have tried wiggling the head cable all the way back to the solder pads on top of the head and I cannot get the resistance reading to fluctuate; it does not seem to be a bad connection. Do you have any more ideas or suggestions on what could be wrong? I’m contemplating converting the 8250 into an 8050 and just using the bottom of both disks, if for nothing else but to test the rest of the mechanisms and ensure that they are aligned one to another and to other drives, but I really want this drive to run to the fullness of its capacity. 😐

Good morning, Jani. The head resistance reads within an ohm or two between each coil in the top head and the bottom head, but what I have found is that the actual core around which the coils are wrapped on the top head has been broken in every one of the drives that has this issue which I have inspected so far. I recorded a video of my removal of the RF shield atop one of the upper heads from a Micropolis 1106-IV (901012-G) drive from an 8250, and you can see the broken piece basically “flapping” loose, just above the side of the head with two different colors of coils. I am guessing that this is probably not repairable, but am now trying to find an alternate head or head assembly that could be used in its place as I have about 5 or 6 of these drives now which have this problem. They all work just fine when I convert them to single sided mode, with half of the usual storage, but I’d really like to restore them to their designed capacity. I’m even investigating the possibility of using one or both heads from a 3.5″ disk drive as their track width is only ~30% smaller than the track width of the 8250/SFD-1001 heads at 144tpi vs 100tpi, respectively. This has become a bit of an itch that wants scratching for me.

Hello!

I had a problem. My SFD-1001 is write to me when I using Performance Test:
Read error.
I set potmeter about 140 kohm, but the floppy not formatted completely for the disc. Sometimes end of center. My other SFD-1001 is working perfectly and I noticed the other sfd spinning faster than erly SFD.. But if set my speed too fast, then I got speed error message. What is the problem? Thanks.