Tandy 2000 FDC chip question

[falter]

I have a Tandy 2000 that will not boot. It gamely tries to read disks (which seem to be good), but basically on boot it will just move the head up towards the center of the disk, stop, then move it further, then stop.. and just keep going until it reaches the top and then keeps trying to go beyond that.

I found it had a bad FDC9216 (tested in my T1000). However I'm wondering about the big FDC chip -- on schematics it says it should be an 8272a, but the part number on the chip is 8040272. The only thing I can find on google is a reference to a Tandy part number 8040272, which in the tandy parts list is a 675a, which is what the T1000 uses.

Does anyone know what chip the T2000 is meant to have, and if there is in fact any difference? I have a spare 675a, but don't want to risk it if it's not the right one.

[Chuck(G)]

"...in the tandy parts list is a 675a"

No, it's a NEC D765A, also known as the µPD765A, cross-licensed with Intel as the i8272A; licensed to other manufacturers as well (e.g. Zilog Z0765A).

40 pin DIP, standard floppy controller for the PC. Pretty much all the same and common as dirt. I'd be surprised if yours was defective. They just don't fail very often.

[falter]

Doh.. Typed me numbers backwards. Thanks for the catch and the answer Chuck!!

[falter]

Darn.. that wasn't the issue. Oh well. Was hoping for a quick win there. At least I know the main FDC chips are good. I *think* the drives are okay, although I haven't found a way to test them outside the T2000 yet. I wonder if they'd be recognized as 720k 3.5 in a standard PC?

I put the T2k boot disk in a 1.2mb drive in another PC and can see all the files there.

[tipc]

add the Rockwell 6765 to the list of alternate part #'s. Actually I replaced the R* with the 8272a from a tandy 2k. I don't think I tested it the other way around. I imagine it would work thought.

[Chuck(G)]

Again, it's all the same chip--just different foundries. The only thing to be really aware of is the non-A parts--they have a much longer start-of-track PLL sync time, which was subsequently found to be excessive and can limit your ability to recover some "alien" formats.

[Chuckster_in_Jax]

I have a Tandy 2000 that will not boot.

This is a very common problem with the Tandy 2000. I have a couple of these with the same issue. Have also seen some on Eb@y listed with the "won't boot" issue.

I have yet to see any listing of someone having success with this issue.

[kb2syd]

My guess is that the ROM is corrupted. The 2K does not have a BIOS on board, it loads it from the disk. The ROM is pretty simple too, set up the FDC and load contents from disk, then execute.

I would dump it and compare it to some of the ones available online.

[falter]

Many thanks.

The problem seems to be eerily similar to the issue I had with my Tandy 1000. In that situation, a bad gate in a 7432 (I think) was preventing the drive from actually trying to read the disk. A bad output on the FDC9216 meant the computer couldn't read anything the drive presented so it carried on like this 2000 does.. repeating the same operation over and over again but never really reading anything.

The FDC9216 was definitely bad.. I swapped it into my 1000 and immediately it wouldn't boot again. But putting a good one into the 2000 has only resulted in the drive motor being periodically engaged with the head creeping forward each time it is engaged until it reaches the dn of its track.

It's hard to know if the drives have some fault here too. I don't know if you could get a more standard PC to use these given they are 720k?

The only thing I can confirm is that with a 1.2mb drive in a standard PC I can read the original boot disk supplied with the computer.

[tipc]

Those drives are not for vanilla pc's. We plugged one into my friends 1000tx in oh 1987 and it wouldn't boot. There's a dd variant that was installed in the Leading Edge Model M / Sperry HT PC. Can't speak to that.