How do I format a floppy in Basic 2.0?

[Hugo Holden]

I then pulled all the IC's that are in sockets and tried again (just to see if it would clear the fault but it did not!)
Looking at the schematic for the board I 7414 inverter may be the problem but with this removed there is no change.
Both these tried without power to the drive.

I am now at a loss as to where to go from here as unless I an missing something with all these chips removed everything is isolated after the buffers.

Pulling IC's won't necessarily help with the diagnosis.

I'd have to check the schematic and the logic circuits, but pulling a 7414, will simply result in the inputs that the output of that IC is driving, achieving a high logic state (a TTL input assumes a logic high with nothing connected to it) and that logic state in conjunction with other circuitry could be incompatible with the drive to the GPIB bus lines being in a high or uninterfered with state.

If you could post your schematic of the bus interface of your disk drive, and make measurements of the 16 lines with the scope, or at worst a meter or logic probe, I could suggest where the fault might be, otherwise its guesswork.

I once attended a lecture by a prominent Neurologist who explained an interesting principle about trying to make a conclusion or a diagnosis, based on applying a lesion ( a defect or damage) in a complex system. He was mainly talking about early efforts in Neuroscience, to explain what anatomical locations in the brain were responsible for what functions, basically by damaging an area of the brain to see what the result was. But the methodology is completely flawed.

For example unplugging an IC from a logic pcb to check the effect, would qualify as a similar defective methodology (unless perhaps it was an open collector output type driving a shared bus). And then trying to draw a conclusion is pointless.

He gave an example of an Alien coming to earth, and trying to work out how an internal combustion engine works. In an attempt to find out what all the working parts did, the Alien started removing working parts from the engine one by one. After they removed a Piston, the engine started vibrating very badly. So they documented in their notes that the purpose of the Piston was to stop the engine vibrating.

 

[daver2]

On the schematic:

UB1 handles half of the data bus.
UB2 handles the other half of the data bus.
UD2 handles the bulk of the control lines.

It would be surprising (with UB1 and UB2 installed and UD2 removed) that the PET IEEE 488 test would fail on DAV and NRFD in this case

With all all of the devices installed 9and the power ON) can you check the voltages on the following pins just after a power-up condition, and before you have done anything:

UD2 pins 9, 10, and 11.
UD2 pins 13, 14 and 15.
UA4 pins 1 and 2.

Then run the PET IEEE 488 test until you obtain the error and perform the above voltage measurements again.

Post the results.

I do remember writing a long thread about testing this drive. It would probably benefit finding this.

You can drive each individual IEEE 488 line from the PET (and observe the readback) by using the appropriate PEEK and POKE commands. These can be ascertained from the book and test software. For each state of the signals, you can ascertain what the voltages are within the drive around the buffers.

Note that the ATN signal enables/disables the data buffers whereas the control buffer is always enabled.

The IEEE 488 bus is basically a "wired-OR" bus - so any driver can drag the bus signal(s) LOW - but all drivers must be HIGH for the bus signal(s) to be HIGH.

The key to testing this beast is to understand how the MC3446 buffers work and, therefore, how you can POKE the signals from the PET, how you can readback the signals via the PET (PEEK) and what the voltage measurements around the respective buffers should look like.

If the buffers are working, the problem must lie with the internal control signals. However, just removing ICs doesn't help if a logic HIGH causes the associated IEEE 488 signal(s) to become active!

@Hugo Holden SNAP!

Dave

 

[orac81]

Has it been established that the problem is in the communication between the pet and drive? In my view the first thing to do would be a program to send code (via the user command) to the ram in the 3040 that tests the CPU, RAM, ROM, but does not access the drive itself, just testing the computer and IEEE interface. If that works, then start trying the drive with those commands discussed earlier.

As said, pulling chips out probably doesnt tell you much.

Bit-rot in the ROMs is common on these old machines, which can lead to all sorts of odd symptoms.

 

[Hugo Holden]

You said:

As I now have the line buffers on sockets I tried the test program with all 3 removed (the ones in the drive)
The test program passed ok.
I then tried with one buffer and found it failed, It's the same with any one of the three buffers (only one at a time)
Its the same DAV and NRFD error each time.

In the case where you were trying just one of the "buffers", where you referring to the socket or the chip? I assume that, since the one controlling the NRFD and DAV, socket UD2 the one of interest, that you tried the three different chips independently in the UD2 socket with UB1 & UB2 sockets empty? Or did you mean that any of the three chips in any single socket regardless of which particular chip or socket, caused the fault ?

Possibly all three buffer IC's are defective. This is another thing about pulling parts, swapping them etc, it can get really confounding if there is more than one defective part. Unless you have a stock of known good ones helps a lot.

These buffer IC's have a high failure rate. They are not alone, in that there are other IC's that do the same thing on serial & parallel interfaces, in that they are types which interface with lengths of cable between separate devices. One reason is the cables when they are not connected and handled, charge up electrostatically, as they represent a capacitor for each conductor and a common. Then when they are plugged in there is an electrostatic discharge into the chip. It is worse for longer cables. On top of that, if one device being connected has a floating (not earthed) common and is hot plugged, there can also be a high discharge current when the cable is initially plugged in and the signal pins can make contact briefly before the cable shell, and that can kill the chips too. When I hot plug connectors (try not to do it too often) I always touch the outer connector shells together initially just in case.

Or as @daver2 pointed out there could be an issue with the internal control signals.

 

[oldcomputerdave]

He gave an example of an Alien coming to earth, and trying to work out how an internal combustion engine works. In an attempt to find out what all the working parts did, the Alien started removing working parts from the engine one by one. After they removed a Piston, the engine started vibrating very badly. So they documented in their notes that the purpose of the Piston was to stop the engine vibrating.

Point taken but at the time I was thinking maybe as it was easy to do I would see if it would give me a clue..

With all all of the devices installed 9and the power ON) can you check the voltages on the following pins just after a power-up condition, and before you have done anything:

UD2 pins 9, 10, and 11.
UD2 pins 13, 14 and 15.
UA4 pins 1 and 2.

Will do Dave but I have the boards out right now (see below)

In the case where you were trying just one of the "buffers", where you referring to the socket or the chip? I assume that, since the one controlling the NRFD and DAV, socket UD2 the one of interest, that you tried the three different chips independently in the UD2 socket with UB1 & UB2 sockets empty? Or did you mean that any of the three chips in any single socket regardless of which particular chip or socket, caused the fault ?

Yes any single one chip in any of the 3 (on the floppy board)

Possibly all three buffer IC's are defective. This is another thing about pulling parts, swapping them etc, it can get really confounding if there is more than one defective part. Unless you have a stock of known good ones helps a lot.

As I said before I have tested all the chips and they are all ok, This was my reason to remove them so I could use the tester.
I have also retested them to be sure I have not damage them myself.

Or as @daver2 pointed out there could be an issue with the internal control signals.

That brings me to this.

Before testing the board for readings, I thought as I now have the 3446 buffers on both the pet and the floppy drive in ic sockets I pulled them all and using the schematics check continuity on all pins between the pet and the floppy drive buffers.

All except one were ok.
The NRFD line is open circuit, So after removing the boards to try to find why I found the pet board is NOT as per the schematic.
I found the NFRD line goes to the output of a 7417 buffer with its input coming from pin 39 on the 6520 pia.
I found this by following the tracks and then confirming by testing continuity.

The board is as original with no modifications so maybe there are different versions to explain this ?
On the back of my board as part of the etched circuit board it says "PART NO 320350 REV B"
Has anyone come across this before?

Schematic I am using >>>


But I found I have this>>


Once I have an answer as to whether or not this is correct or not I can then refit the boards for the voltage tests.

Dave

 

[daver2]

The IEEE 488 PET book agrees with the schematic.

The test program for NRFD (Not Ready For Data) uses PEEK/POKE address 59456 (which is the VIA pins PB1 and PB6).

There is something wrong somewhere.

What is A9 pin 6 connected to then (the supposed NRFD MC3446 bus signal - mislabelled as NFRD) if your board has it sourced from somewhere else?

Dave

 

[oldcomputerdave]

It seems there is a numbering problem for the edge connector pin numbers between the pet and the drive schematics I am using.
This may well have been confusing me but I don't think that is the only thing that's wrong.

With both boards removes an all buffers pulled and testing directly between the boards this is what I get >>

Pet A9.....connector pin...Drive UD2
Pin............(pet number)....Pin

2................6.................................6
6................7.................................2
10.............8 ...............................14
14............11...............................R3 + R5 + UA3-pin 1
nc ..............5................................10

The cable I am using between the pet and the drive is an original commodore branded moulded both ends one.
This is the schematic I am using for the drive>>

 

[oldcomputerdave]

Sorry the last line should be>

74ls17 pin 6 >>>edge connector pin 5 >>> drive UB2 pin 10

The pin numbers on the drive schematic don't match what I am getting by testing maybe I have the wrong schematic for my 3040 drive.
The pet and the drive schematics seem to use different pin numbers and I can't seem to decipher what is going on.

To clarify this is what I get in reality (tested)

Pet A9 Pin / connector pin (pet schematic) / Drive UD2 pin (tested not the one on the schematic)

2 ----------6----------------------------------6
6-----------7----------------------------------2
10----------8----------------------------------14
14----------11---------------------------------R3 + R5 + UA3-pin 1
7417 pin6---5---------------------------------10

Dave

 

[Wreck]

Point taken but at the time I was thinking maybe as it was easy to do I would see if it would give me a clue..



Will do Dave but I have the boards out right now (see below)



Yes any single one chip in any of the 3 (on the floppy board)



As I said before I have tested all the chips and they are all ok, This was my reason to remove them so I could use the tester.
I have also retested them to be sure I have not damage them myself.



That brings me to this.

Before testing the board for readings, I thought as I now have the 3446 buffers on both the pet and the floppy drive in ic sockets I pulled them all and using the schematics check continuity on all pins between the pet and the floppy drive buffers.

All except one were ok.
The NRFD line is open circuit, So after removing the boards to try to find why I found the pet board is NOT as per the schematic.
I found the NFRD line goes to the output of a 7417 buffer with its input coming from pin 39 on the 6520 pia.
I found this by following the tracks and then confirming by testing continuity.

The board is as original with no modifications so maybe there are different versions to explain this ?
On the back of my board as part of the etched circuit board it says "PART NO 320350 REV B"
Has anyone come across this before?

Schematic I am using >>>

View attachment 1287829
But I found I have this>>

View attachment 1287830
Once I have an answer as to whether or not this is correct or not I can then refit the boards for the voltage tests.

Dave

Hi,
Just out of curiosity; did you remove the board from the chassis? If so, did you ground the board as recommended by a service manual I found?

Joe

 

[oldcomputerdave]

Just out of curiosity; did you remove the board from the chassis? If so, did you ground the board as recommended by a service manual I found?

Hi Joe,
If you mean taking precautions for static discharge then yes I did.

----------------------------------------

Well it gets stranger and stranger!!!!

After convincing myself it was a wiring fault somewhere between the buffers,
This is after removing Ic's for testing (many times), removing and refitting both boards (also many times)
I decided to put it all back together and do the voltage readings on the buffers.
Nothing has been replaced or changed but on powerup the test program passes ok even with the drive connected!

I am not going to complain but I would like to know what I must have done to "fix it".

Now the drive responds to commands but still doesn't read or write disks.
I have already cleaned the drives and heads and lubricated the moving parts.
I think at least one of the drives has a faulty head.

Testing pin to pin resistance one head is open circuit.
Does anyone know what readings I should get?

Its progress even if it still doesn't work.

Dave

 

[daver2]

Is it possible you installed the cable connector at the PET end the wrong way round?

The connector should have a plastic polarising key installed, but (9 times out of 10) this key is missing, giving you the 'opportunity' to install the connector the wrong way around.

Dave

 

[oldcomputerdave]

I know what you mean Dave and the key is indeed missing, But I know thats not what is was as it was the first thing I checked when I first had the problem.
I labeled the connector "THIS SIDE UP"

Thanks once again for all the help Dave,

Now its a problem with the drives maybe I should start a new thread on this subject.

Dave

 

[daver2]

Most of what I was reading made no sense at all (to be honest), so I am just as surprised as you now you have some sense out of it.

All I can think of is that there is a bad connection, solder joint, or something else that was wrong (e.g. a reversible connector that was the wrong way round) - and now it is ok?

I think there is a Commodore manual somewhere stating what the head resistance readings are for various manufacturers disk drives.

Dave