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External Floppy Shunt Settings

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I'm sure that this question has been asked many times but I'm having a hard time finding a concise answer. How should the shunt be set for multiple drives?

 

I recently acquired a lot with a floppy controller side car and two external drives. One of the drives was labeled "drive 2" but when I took them apart for cleaning and inspection, the shunts were set the same and the same as the one for the internal drive of my PEB. Side note: drive 2 was also missing the resistor pack for termination.

 

I'll include a picture for proof of what the shunt settings were, I would like to replace these jumpers with a dip switch for each just in case someone wants to revert what I'm doing now.

 

In the picture, the two on the left are my new drives (MPI 51 drives) and the right is my PEB drive (shugart 400L).20210503_212133.thumb.jpg.a86103ffb8a497f6f8408c0040ffa6d1.jpg

 

I would like to know what pins should and shouldn't be connected for each of my 3 drives. I read something about removing the HL jumper but not under certain conditions and so and and so forth. I got really confused. So as simply put as possible would be wonderful.

 

Thanks for the time and effort to read through/answer my question. Much appreciated, have a good day.

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Ds0 on drive1 ds1 on drive2 and ds2 for drive 3

 

 

From the manual of the shugart

.2.3 Drive Select 1-4

The SA400L, as shipped from the factory, is configured to operate in a single drive system. It can be easily

modified by the user to operate with other drives in a multiplexed multiple-drive system. The user can activate the

multiplex option by cutting the "MX" position of the programmable shunt located in IC location 20. This allows the

multiplexing of the 1/0 lines.

In a single drive system (program shunt position "Mx" open), the four input Iines (ORIVE SELECT 1, DRIVE

SELECT 2, ORIVE SELECT 3, and DRIVE SELECT 4) are provided so that the using system may select which

drive on the interface is to be used. In this mode of operation only the drive with the DRIVE SELECT line active

will respond to the input Iines and gate the output lines. In addition, the selected drive will load its read/write head

if program shunt position "HL" is shorted.

The program shunt, IC location 20, positions "OSI," "OS2," "OS3," and "OS4" are to be used to select which

DRIVE SELECT line will activate the 1/0 lines for a unique drive. For example, if the user wants the first drive on

the interface to be address 1, he must cut program shunt positions "OS2," "OS3," and "OS4," leaving "OS1" in-

tact.

The program shunt is AMP P/N, 435704-6. The shunt positions can be cut using AMP's tool P/N 435705. The

shunt is installed in a dip socket and, at the user's option, can be removed and replaced by a dip switch (AMP P /N

4435626-4) . The user may also choose to have the program shunts pre-programmed and/or color-coded b

Sent from my LM-V600 using Tapatalk

 

 

 

 

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Keep the HL (or HS on the MPI drives) shorted and then move the other short to the drive you want it to be: OS1, OS2, OS3 or OS4 on the Shugart or DS0, DS1, DS2, or DS3 on the MPI. Note that a TI controller (the one from TI, not a CorComp, Myarc, Atronic, or SNUG) cannot access a fourth drive (OS4 or DS3). The other controllers listed can access all four, but the quirk in the TI variant can sometimes surprise folks.

 

On the resistor pack, only the last drive in a chain should have it, so if you have drives two and three connected to the external port, only the last drive should have it. Note this means your internal drive will have the resistor pack and the last drive on the external chain will also have one.

 

One other note: when TI sold their external drives they also included little cards inserted into the connectors on the cables to move drive select lines around. If your drives work now with the original cables as drives 1, 2, and 3, you shouldn't need to change anything (just document the setup so you know what it is doing). In other cases, you will see single lines moved around in the ribbon cable which makes the same type of change. Note that a PC cable (with the multi-wire twist) will not work properly on a TI.

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The little interface card TI provided shifted the drive select lines. Thus you kept all drives programmed as the first drive, but the little card shifted the select lines between each drive. Thus the first drive saw the first select line, but the second drive got the second select line in the first position, and so on.

The more "normal" way is to route the select lines straight, and instead tell the drives which of the select line to look at.

I have two straight cables, one from the internal drive connector and the other from the external. That's from a card in the box, that is. Setting the internal drives as 1 and 2, the external two as 3 and 4 then works. My card is a CorComp, so it handles four drives.

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Thank you all for the replies. I made a little progress in getting these drives to work.

 

The setup I currently have is this:

 

the shugart internal PEB floppy with resistor pack, HL and DS0 jumped, by itself in the PEB with the stock cable

An MSI drive without resistor pack, HS and OS2 jumped, in the first enclosure, connected to the back of the TI controller card.

The second MSI drive with the resistor pack, HS and OS3 jumped, in the second enclosure, connected to the cable of the first floppy drive using the adapter card that came with the drives.

 

Using this setup, I was able to get the internal drive and the first external drives to work just fine. They will both format, save, and load programs from the other drive. For some reason I can't get the third drive to work. When I get back home (currently at work) I'm going to try to swap the two external drives to see if the cable is bad. I knew the internal drive was good so I swapped it with each of the external drives to test them, after a bit of work they both tested good and capable of saving and loading to disks that the other one could read. Any suggestions, aside from the cable being bad?

 

 

 

For anyone interested, the issues I had with the two external floppies I will explain:

 

The first one I tried made a clicking noise when it was trying to read or write to the disk but would give an error. I noticed the head was moving back and forth quickly but not very far. So, I moved the head manually to both extremes and it was very tight at both ends. After doing this a few times, it got loose and when I tried to read and write to the disk it worked perfectly.
 

The second drive I tested clicked (the head solenoid) and would give an error before clicking again (again, the head solenoid but turning off this time). The disk didn't turn at all so I turned the spindle with little resistance, the belt moved, but the motor was stiff. After turning it by hand a few times it was still tight but much better. So, I tried to load a program from a disk but it failed. However, the motor wasn't spinning very well. Without doing anything else, I tried to load again and it worked perfectly.

 

I then tested all three drives again without any problems.

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The cable probably isn't bad, but it is part of the problem. The adapter card is the issue. What you need is a cable with connectors to connect it to two drives. This cable must be wired straight through to all pins--no twists. The problem with the setup you have now is that the adapter card is moving the drive select line on you--and since you have your shunts set for a straight through cable right now, it isn't pointing the third drive to the correct drive select line.

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Thank you all for the replies. I made a little progress in getting these drives to work.
 
The setup I currently have is this:
 
the shugart internal PEB floppy with resistor pack, HL and DS0 jumped, by itself in the PEB with the stock cable
An MSI drive without resistor pack, HS and OS2 jumped, in the first enclosure, connected to the back of the TI controller card.
The second MSI drive with the resistor pack, HS and OS3 jumped, in the second enclosure, connected to the cable of the first floppy drive using the adapter card that came with the drives.
 
Using this setup, I was able to get the internal drive and the first external drives to work just fine. They will both format, save, and load programs from the other drive. For some reason I can't get the third drive to work. When I get back home (currently at work) I'm going to try to swap the two external drives to see if the cable is bad. I knew the internal drive was good so I swapped it with each of the external drives to test them, after a bit of work they both tested good and capable of saving and loading to disks that the other one could read. Any suggestions, aside from the cable being bad?
 
 
 
For anyone interested, the issues I had with the two external floppies I will explain:
 
The first one I tried made a clicking noise when it was trying to read or write to the disk but would give an error. I noticed the head was moving back and forth quickly but not very far. So, I moved the head manually to both extremes and it was very tight at both ends. After doing this a few times, it got loose and when I tried to read and write to the disk it worked perfectly.
 
The second drive I tested clicked (the head solenoid) and would give an error before clicking again (again, the head solenoid but turning off this time). The disk didn't turn at all so I turned the spindle with little resistance, the belt moved, but the motor was stiff. After turning it by hand a few times it was still tight but much better. So, I tried to load a program from a disk but it failed. However, the motor wasn't spinning very well. Without doing anything else, I tried to load again and it worked perfectly.
 
I then tested all three drives again without any problems.
Clean the head rails with isopropyl alcohol and lubricate them properly

Sent from my LM-V600 using Tapatalk

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12 minutes ago, Ksarul said:

The cable probably isn't bad, but it is part of the problem. The adapter card is the issue. What you need is a cable with connectors to connect it to two drives. This cable must be wired straight through to all pins--no twists. The problem with the setup you have now is that the adapter card is moving the drive select line on you--and since you have your shunts set for a straight through cable right now, it isn't pointing the third drive to the correct drive select line.

Is it possible to get them to work with the adapter that came with the drives? My system is very original with little to no modifications and I'd like to keep it that way. If I understand it properly, both external drives should be connected with the adapter but addressed with the same shunt setting?

 

12 minutes ago, arcadeshopper said:

Clean the head rails with isopropyl alcohol and lubricate them properly

Sent from my LM-V600 using Tapatalk
 

How should I go about lubricating the rails?

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A replacement cable is a perfectly normal period item--very few folks used the adapters for multi-drive systems. They just rolled their own cable, as it was much more stable that way.

 

You would also need two of the boards to set up a three drive system, as each adapter shifts the drive number down by one (by moving that wire down to the next lower drive's drive select line). The first board moves drive 2 to the drive 1 position, and the drive 3 to the drive 2 position, IIRC. It is also possible that your board is moving the drive 3 line to drive 1 (it is a long time (35 years) since I saw anyone trying to use these), as I think TI may have made two different adapter boards. . .

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Yep I sell a universal cable that works for external drives of either type125c11d4fd391d32fa4b8b02e8ac0802.jpg

Sent from my LM-V600 using Tapatalk

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9 hours ago, Ksarul said:

They just rolled their own cable, as it was much more stable that way.

Exactly what I did. Two cables, one for two internal drives, another for the two external drives. That's very special in my case, since I have the exernal drives in a separate box, so the external ribbon cable goes to a connector on the outside of that box. Then from the inside to the two drives.

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