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RichCini
December 1st, 2006, 07:06 PM
All:

I'm restoring two T2k HD machines and I have a questions about external hard drives.

Both machines have the HD controller with the connectors on the back. So, I grabbed a 20mb MFM hard drive and a set of cables. The control cable I have has a twist in it between the "C" (outside) and "D" (inside) connectors. I'm guessing that I use "D" and strap the drive for ID=2 (options are 1, 2, 3, 4).

So, I hooked it up that way and I couldn't format the drive. So, I tested it with other combinations of C/D connector and ID#.

Has anyone attempted this and if so, what's the right way to do it?

Thanks.

Terry Yager
December 1st, 2006, 07:32 PM
Yes, I've done it, but it's been a looooooong time...
IIRC, the T2K uses a straight-thru cable with the drives strapped as DS0 & DS1 (or DS1 & 2, as the case may be). The twisted cable is an IBM thing, which I'm not sure will work on the 2K. If it does, then both drives must be strapped to the second device select, and the drive at the end of the chain must be terminated.

--T

RichCini
December 1st, 2006, 08:10 PM
Yes, I've done it, but it's been a looooooong time...
IIRC, the T2K uses a straight-thru cable with the drives strapped as DS0 & DS1 (or DS1 & 2, as the case may be). The twisted cable is an IBM thing, which I'm not sure will work on the 2K. If it does, then both drives must be strapped to the second device select, and the drive at the end of the chain must be terminated.

--T

I knew that the cable twist was an IBM thing which is why I used the "D" connector which is straight-pinned, but I will double-check to make sure the stripe reaches the drive in the right place. The external HD is terminated and strapped for ID=2.

There is one jumper on the HD controller which is not labeled with anything useful. I don't have a manual for the board. Would you have one I could get a PDF of? In fact, if you have any of the add-in board manuals I'd be happy to scan them and create a little page on my Web site for them. It seems that there's next to nothing out there on the Web on the 2000.

RichCini
December 2nd, 2006, 06:55 PM
Yes, I've done it, but it's been a looooooong time...
IIRC, the T2K uses a straight-thru cable with the drives strapped as DS0 & DS1 (or DS1 & 2, as the case may be). The twisted cable is an IBM thing, which I'm not sure will work on the 2K. If it does, then both drives must be strapped to the second device select, and the drive at the end of the chain must be terminated.

--T

After re-reading this a few times I just realized something. How is a chain of internal and external MFM hard drives constructed? Electrically, are they like floppy drives where they sit in a chain? This would mean that I have to remove the internal hard drive to remove the terminator and leave the external drive terminated.

I think a manual for the HD controller would be a big help.

kb2syd
December 3rd, 2006, 05:05 AM
Just a thought, but CAN the 2000 handle 2 drives? Is it possible that it can handle either an internal OR an external, but not both?

Tandy did do some weird stuff, and the power supply is very under sized.

Terry Yager
December 3rd, 2006, 07:04 AM
The external drive has it's own power supply, and it jacks-in to the 2K via a single 50-pin connector, IIRC. Unfortunately, I don't recall ever having to bother with cabling, just plug & play, and it's s'pozed to work.

Have you tried disconnecting the internal drive to see if it will see the external one all alone?

--T

RichCini
December 3rd, 2006, 04:13 PM
The external drive has it's own power supply, and it jacks-in to the 2K via a single 50-pin connector, IIRC. Unfortunately, I don't recall ever having to bother with cabling, just plug & play, and it's s'pozed to work.

Have you tried disconnecting the internal drive to see if it will see the external one all alone?

--T

More experimentation. I pulled the power plug on the internal hard drive on the one machine and connected the external hard drive to the secondary port using straight-through cables. The external HD (a 20mb IBM drive) was jumpered for ID=1 (the lowest number possible). And, yes, I made sure the cables were oriented the right way (both sides have keyways or alignment pins).

I rebooted with a DOS floppy and used hdformat to prepare the external drive. After a moment, it complains that it can't write to the system sectors and the format failed. I can see the head positioner servo on the external drive and it didn't move at all. The external drive is a newly-refurbished and recertified drive so I'm confident it works.

I have a second T2K that's slightly older but in much better physical condition and I tried the same procedure on with similar poor success.

This means two things. First, having the internal signal cables connected makes a difference (don't think so, at least not in my experience) or there's some magic in using Tandon hard drives.

I know that Tandy did some crazy things but could they have somehow locked the controller to the specific model of hard drive?

Terry Yager
December 3rd, 2006, 05:55 PM
I know that Tandy did some crazy things but could they have somehow locked the controller to the specific model of hard drive?

Yes, they could have, and they might have, but I can't swear one way or t'other. I know that the original controller in my ol' Tandy 1000HD would only recognize a drive with 306/4/17. As you well know, they were famous for such shenanigans.

--T

RichCini
December 3rd, 2006, 06:05 PM
The external drive has it's own power supply, and it jacks-in to the 2K via a single 50-pin connector, IIRC. Unfortunately, I don't recall ever having to bother with cabling, just plug & play, and it's s'pozed to work.

Have you tried disconnecting the internal drive to see if it will see the external one all alone?

--T

Ok, in one last test before my hobby night ended, I pulled the TM502 from one machine and connected it to the external port of the second. I strapped the external drive as ID=2 and tested it with both the terminator and without. In both cases it wasn't recognized as a valid drive, giving a "bad unit error".

After this process, I have to say that I find the T2k flaky to work with. I don't know whether it's design or that the machines don't ship well. With both machines about 10% of the time I can't get the right amount of memory to register if it's more than 256k and the hard drive subsystem works only about 50% of the time. I wonder if there's a fault in the design of how the card cage connects to the planar.

Most of the drive errors are "Bad unit error on drive XX" which, reaching back in my memory, means that the controller is active but the drive isn't resetting properly.

I'm going to read the service bulletins tomorrow to see if anything jumps out at me. Also, I noticed in one of the Computer Catalogs that the external HD system for the T2K is the hulking external HD that's used with the Model III/IV. I wonder if there's something special in there that the HD controller expects rather than directly connecting the controller to the drive itself.

RichCini
December 4th, 2006, 06:43 AM
Ok, in one last test before my hobby night ended, I pulled the TM502 from one machine and connected it to the external port of the second. I strapped the external drive as ID=2 and tested it with both the terminator and without. In both cases it wasn't recognized as a valid drive, giving a "bad unit error".

After this process, I have to say that I find the T2k flaky to work with. I don't know whether it's design or that the machines don't ship well. With both machines about 10% of the time I can't get the right amount of memory to register if it's more than 256k and the hard drive subsystem works only about 50% of the time. I wonder if there's a fault in the design of how the card cage connects to the planar.

Most of the drive errors are "Bad unit error on drive XX" which, reaching back in my memory, means that the controller is active but the drive isn't resetting properly.

I'm going to read the service bulletins tomorrow to see if anything jumps out at me. Also, I noticed in one of the Computer Catalogs that the external HD system for the T2K is the hulking external HD that's used with the Model III/IV. I wonder if there's something special in there that the HD controller expects rather than directly connecting the controller to the drive itself.

I pulled a copy of the schematics for the 5mb Model 4 hard drive (master unit; I don't have a copy of the 10/20/35mb manuals) and compared the drive interface to that of a standard MFM drive. On the control cable, there's one signal that's not standard (pin 2, RWC; HDSEL8 in the standard) and on the data cable, pin 7 (12v trigger to power-on slave units) and pins 9/10 (TCLK; "reserved" in standard). There are also a few signals swapped in the 50-pin cable versus the 34-pin control cable.

Given this, maybe the 5mb master unit is unique to the III/IV and when buying an external drive for the T2k, you buy a "slave" unit that has a special cable to activate the electronics (pin 7 connected to +12v).

Do you have a catalog number of an external drive for the T2K?

kb2syd
December 4th, 2006, 07:59 AM
Do you have a catalog number of an external drive for the T2K?

I've looked through the canonical tandy parts list and there are no drives listed as specifically being secondary for the model 2000. I have also looked at the 1984 and 1985 catalogs. No mention of the secondary hard drives for the 2000 in them.

I have several of the secondary hard drive boxes. They are just enclosures, power supplies, and they use a relay to turn them on. They sense the 12v you mentioned earlier and power op the unit based on this signal. I can open one up and tell you if any of the pins are reveresed, or if there are any other obvious oddities. Do you want pictures too?

Kelly

RichCini
December 4th, 2006, 12:36 PM
I've looked through the canonical tandy parts list and there are no drives listed as specifically being secondary for the model 2000. I have also looked at the 1984 and 1985 catalogs. No mention of the secondary hard drives for the 2000 in them.

I have several of the secondary hard drive boxes. They are just enclosures, power supplies, and they use a relay to turn them on. They sense the 12v you mentioned earlier and power op the unit based on this signal. I can open one up and tell you if any of the pins are reveresed, or if there are any other obvious oddities. Do you want pictures too?

Kelly

An inside picture would be good, thanks.

Also, I remember a reference in the 1985 or 1987 catalog to a specific cable assembly for the T2K to the external hard drive. Have you seen one of those? I wonder if it takes the 34-pin and 20-pin MFM data and control outputs from the T2K controller and combines them into the 50-pin connector used on the "master" hard drive or if the process was for Radio Shack to sell just the "slave" unit.

By the way, according to the technical bulletin I read, the external drive should be strapped for ID=2 and the terminator pack should be installed. This is what I've done. The only thing I can think of is that the external bus is flaky or something.

kb2syd
December 4th, 2006, 01:10 PM
The only thing I can think of is that the external bus is flaky or something.

Tandy flaky? Nah never happen ;-)

I think the only thing they couldn't make flaky would be pie crust.

kb2syd
December 4th, 2006, 05:20 PM
OK. I've gotten out my Tandy 2000 HDs, and a couple of secondary drives. Note that I have not TRIED any of this. Here is a picture of the internals of a Tandy 15 Meg secondary drive.

The drive is a Tandon TM503. It has a 20 pin data input and a 34 pin control pass through. The pins on the external connectors map 1-to-1 with the connectors on the drive.

Tandy tapped into two lines on the control cable to trigger a power relay. There is no on/off switch for these drives. This 12v goes comes from the interface on the model 2000. You will need to disconnect those two traces on the foil of the drive or the controller card or you may toast a plain drive.

I also took a look at the connectors on the back of the T2K. There are 3 external connectors on the 2000 HD interface card. Data and Control go to the external box WITH THE 12 V. If you're trying to drive a standard MFM drive, you must break this 12V line and the associated ground some how.

The 50 PIN connector duplicates the I/O connector on the model 3/4 line. Theoretically, this can be used to connect a PRIMARY external hard drive to the 2000, but I suspect that this will not work. Instead, this can be used to control other I/O driven stuff such as a clock calendar (if you don't have the mouse/clock card).

Hope this helps some. You have my contact info Rich if you want to chat for clarification.

Kelly

RichCini
December 5th, 2006, 06:27 PM
OK. I've gotten out my Tandy 2000 HDs, and a couple of secondary drives. Note that I have not TRIED any of this. Here is a picture of the internals of a Tandy 15 Meg secondary drive.

The drive is a Tandon TM503. It has a 20 pin data input and a 34 pin control pass through. The pins on the external connectors map 1-to-1 with the connectors on the drive.

Tandy tapped into two lines on the control cable to trigger a power relay. There is no on/off switch for these drives. This 12v goes comes from the interface on the model 2000. You will need to disconnect those two traces on the foil of the drive or the controller card or you may toast a plain drive.

I also took a look at the connectors on the back of the T2K. There are 3 external connectors on the 2000 HD interface card. Data and Control go to the external box WITH THE 12 V. If you're trying to drive a standard MFM drive, you must break this 12V line and the associated ground some how.

The 50 PIN connector duplicates the I/O connector on the model 3/4 line. Theoretically, this can be used to connect a PRIMARY external hard drive to the 2000, but I suspect that this will not work. Instead, this can be used to control other I/O driven stuff such as a clock calendar (if you don't have the mouse/clock card).

Hope this helps some. You have my contact info Rich if you want to chat for clarification.

Kelly

This is very helpful. Thanks. I'm hoping that I didn't toast either drive I connected to the external port, although I'm going to have to put a meter on the connector to see what's exactly on that pin. To isolate it, I'd put a piece of Scotch tape on the drive edge connector and trim it off on either side of the finger. Not permanent, but should work.

Now, even if 12v was on that pin, the MFM pinout shows the Head8 signal on it. Since none of the drives I have contain more than 7 heads (these Tandon drives were 3.2mb unformatted per surface based on the specs), which would mean that a 12.8mb (10mb formatted) drive has 4 surfaces. So, I should be OK.

kb2syd
December 6th, 2006, 12:48 AM
To isolate it, I'd put a piece of Scotch tape on the drive edge connector and trim it off on either side of the finger. Not permanent, but should work.

This method does work. I have several drives in service with this pin covered.


Now, even if 12v was on that pin, the MFM pinout shows the Head8 signal on it. Since none of the drives I have contain more than 7 heads (these Tandon drives were 3.2mb unformatted per surface based on the specs), which would mean that a 12.8mb (10mb formatted) drive has 4 surfaces. So, I should be OK.
On older MFM drives, I think this line was the write precomp signal. That being the case, maybe this could explain the problems you were having. With write precomp driven high it was on all the time.

Good luck.

RichCini
December 6th, 2006, 03:36 AM
This method does work. I have several drives in service with this pin covered.


On older MFM drives, I think this line was the write precomp signal. That being the case, maybe this could explain the problems you were having. With write precomp driven high it was on all the time.

Good luck.

I should re-read my own posts. Ignore what I just said about Head8. The 12v trigger signal is on pin 7, which is listed as "reserved" in the MFM interface pinout. Pin 2 is Head8 in the MFM pinout but Tandy has another signal on that pin (obviously limiting the interfaces use to those drives with 7 or fewer heads; probably 6 heads which is three platters or 19.2mb unformatted). The signal is RWC* which might be the precomp signal you mentioned.