Tarbell is making me insane

Wow, a lot to go over here... Rich, if you have any problems with your drive I might be able to help you after this exercise! : ) I'm hooking the 3.5" drive power cable directly to the output of the 7805 on the tarbell, which is getting its power from an 8v switching power supply. The power is nice and steady at 4.95v. The only thing I haven't done is made sure the case is grounded. Some drives had jumpers for that, but mine doesn't. So it could be either way. The tarbell card I have doesn't have any one shots for data separation. The read data line goes into a L74 (Dual D Edge Triggered Flip Flop), then goes into a LS175 (Quad D Type Flip Flop with Direct Clear). There are two LS161 (Synchronous 4 Bit Binary Counter) that are hooked up to parts of the LS175. There are is a XOR gate and two NAND gates. I'm not sure what is going on at the moment, does it seem like that pile of parts could be implementing a PLL? I would think a PLL would be more complex than that. I'll at least make sure all of the edges match up (Read data vs separated clock and data) I hope I find something obvious. I should at least see a difference between the two tarbell cards (reliably bad vs somewhat bad). I have a 4FDC Cromemco? It uses a 1771. I might be able to use the tarbell driver to boot off of that. Is anything known about that card as far as being better or worse? The two 3.5" drives and the 5.25" drive I have don't do anything with the ready/disk change line at all. BUT, I know the Sony 3.5" drive doesn't generate index pulses until the drive speeds up (I think that is what its doing). With a TEAC 235HF drive it takes 694.053ms for the drive to generate sector pulses AFTER the drive was given a "Motor Enable" signal. Even though the head was NOT at track 00, the drive didn't signal that status until 491.221ms after given a "Motor Enable". So the drive seemed to spin the motor up, tell the controller it was not at 0, and then start issuing index pulses. That is probably how the 3.5" disk is getting away without a ready line. The older drives probably generated index pulses regardless of if the drive is ready or not. These newer drives with more brains must not make index pulses unless they are ready. On my second kenbak build I had a problem. First I tested all of the ICs (digital only) but didn't find any problems so I started swapping them all. About 3 hours after testing it started working, but then stopped. I found a cold solder joint. Pushing around and bending the boad "fixed" it. : ) So I fixed the joint and reinstalled all of the old chips. : ) The main reason I swapped the 1771 was because I think I read somewhere that its a very static sensitive part and of all of them the most likely to go out... I will replace the sockets with machine pin sockets. The tarbell is treating the 3.5" disk drive as that TM100 tandon SSSD drive. The data rate recorded to the drive is 8.07us per bit. I'm getting 123916 bits a second, which doesn't seem to match anything I remember... My drive is a new from sony. I've made formatted and written to HD disks with the HD hole covered. This same drive reading the same disks does not always read. I don't know if its the tarbell's fault or not. The silly tarbell issues a "IN" to a "wait" port and the tarbell keeps it in a wait state until the 1771 is good and ready. Kind of makes debugging hard if the tarbell doesn't decide to stop waiting. ; ) The datasheet for the 1771 says "Upon receipt of the Read command, the head is loaded, the BUSY status bit set, and when an ID field is encountered that has the correct track number, correct sector number, and correct CRC, the data field is presnted to the computer." Is that the sector read code you are talking about? One of those first bytes? The data sheet says that the 1771 is capable of reading the entire track as one big sector. Maybe I should try to make a routine to do that. I don't know of any other way to get that code since it isn't part of a normal read. At least we both have a ZPU and both have one with the 2MHz switch. So that eliminates the CPU card one shots from the reliability question. Right? FP? That was part of a quote from him. Its not my board. I do have pictures at: http://www.stockly.com/forums/showthread.php?t=325 Its a regular Rev 0 card with some modifications. The biggest modification is the lack of one shots. It uses an 8224. I imagine he got this info from a vintage place somewhere because his work looks very well planned out. Or maybe he just planned it out good! I've read that HD (1.44MB 3.5") disks with tape over the HD hole aren't exactly a DD disk. Something about the track width being narrower because of the smaller head in an HD drive? BUT, the DD (720k 3.5") disks were formatted to 40 tracks 18 sectors, 128 bytes a sector using an HD drive. So the DD disks wouldn't have a wide track width to begin with. Are there really physical media differences between DD and HD that would keep a HD disk from being used as a DD disk when in a HD drive? The HD drive should be able to read the narrow track written on what it thinks is a DD disk, right? Is the magnetic material of an HD disk significantly different? Most of the information I've read about mixing media is in reference to DD disks being written in an HD drive and then becoming unreliable in a DD drive. I've also heard about people who add holes to disks to make a DD disk an HD disk, which probably works for them better than my tarbell works for me... : ) Thanks! Grant