Fat 40

[Gary C]

Ah damit.

Brushes now sat on commutator but motor still doesn't always start. Give it a flick and it will run but then after a few goes, it fails to start again.

Windings checked and one pair are shorted

Damn, I'm never going to rewind a multipole motor like this so its for the scrap. Time to find a spare drive.

 

[Gary C]

So, spare motor fitted and drive now runs and I can format, but as soon as I try to get a directory, it hangs with a drive light on.

I have another drive with these Micropolis drives and swapping the drives and the analogue card over, everything works fine. So the CPU board isn't quite working properly.

It does have a different ROM set but zimmers seem to indicate that thes can go with the pressed steel frame Micropolis drives.

So as I have three spare working boards (well, spare as they are in good drives) I might try some chip swaps.

Lots of chip swaps done and the only one that stopped my good board working was inserting the ROM at UK6

Now putting that back in the faulty board I get a flashing error code. The code appears to be 4 flashes, but thats listed as Unused ?

Is the code read as the number of red flashes ?

 

[Gary C]

This is going to turn into a disk drive diagnostic blog, oh well

I think one of the white sockets is defective as the drives diagnostic sometimes reports errors but a firm push on all the sockets usually fixes it, so they will have to all be changed, however

Drive responds to commands but wont write anything back.

Opening the error channel and doing an input shows 0 0 0 rather than 0 OK 0 0

Sending "UI" and reading the error channel, gives the same rather than 73 8050 CBM DOS 2.5 0 0 so it looks as if it isn't sending any data back on the bus.

Scoping the DI and DO lines, I can see DI's pulsing as expected but absolutely nothing on the DO's. All the DO's come from port B of the 6532 at UC1 but I know that cant be it because they have both been swapped with ones from a known good board. All the DO's are high at +5, but I notice that while the DI's pulse +5 to 0, the bus lines are pulsing +3v to 0v which is odd as thats sourced from the PET.

I wonder if the buffers are not switching, but that would mean two and why would the ports not pull down ? Of course the RIOT might not be being addressed but it works for input ok. Odd.

Humm.

Might need to write some diagnostics, Dave ?

 

[Gary C]

So what an interesting circuit.

The 6532 I/O ports run the IEEE through MC3446 bi-directional buffers which seems simple and straightforward, however the Not Ready For Data (NRFD) and Not Data Acknowledge (NDAC) aren't just simply run from the ports then through the buffers, but also by some discrete logic driven partially by the Attention signal (ATN) from the PET and the bi-directional buffer is hard wired as input (in which case, any signal on the D line is driven on the B & R lines). This must be because the IEEE-488 standard for response from a listener is to pull NDAC low within 14uS and I suppose the 6532 wasn't fast enough and it looks as if the circuit is an add on to make the initial operation work.

Having swapped the 6532's with a good board and the fact I am seeing no reply to data transfers from the disk but the disk is responding to messages sent to it, I'm assuming the transaction is getting stuck waiting for one of the signal lines to change. Checking NRFD & NDAC I can see that the disks internal RFD output to pin 11 of UD2 should be mirrored on pins 9 & 10 however I am not seeing anything on pin 9 so the MC3446 is suspect.

Hopefully that is stopping the handshaking but without looking at the software its a guess, but it is an actual fault and it is part of the handshake in this operation so its probably it.

MC3446's though are hard to get for a good price.

 

[Gary C]

New MC3446 fitted at UD2 and drive now responds correctly

One niggle left, drive 1's green light is now permanently on where it did respond before. Need to check the board to see if I have picked up a solder blob but at least its now functional.

 

[Gary C]

Ah, well. Drive 1 LED back to normal, odd.

 

[Gary C]

So edging closer.

With the new buffer chip, the drive responds to all commands and can read a disk but not format, which is strange at is was running the format before just hanging on the completion due to the handshake failure on the GPIB.

Swapped back to the known good digital board and it all works fine so its not the drives or the analogue board.

Now this board has also thrown flashing errors which go away with a bit of chip reseating so I might have some bad sockets (I know all the socketed chips are actually ok as they work fine in the good board). Gave the 6522 a squash in its socket and now its formatting fine.

This board has the white sockets which do seem to cause issues in some PET's and this drive has also suffered some corrosion so I think my next move is to replace the sockets with some good quality dual wipe ones. The drive light was being caused by a bad contact at pin 21 of UE1. Leg of IC cleaned and its working again, but I still think new sockets would be the way to go.

But on the whole its almost there. Quite fun, the 8050 is like a PET on steroids.

 

[Gary C]

Does anyone have a simple BASIC program to change the ID of a 8050 disk drive. I don't want to cut a pad or bend a leg but the M-W instruction I just can't seem to get to work.

Anyone ?

 

[Gary C]

Never mind

Found one, (I was putting a comma between each character)

However, still cant get CBMCommand to copy between devices

10 REM************************************
11 REM*
12 REM* CHANGE 8050 VER1.0 4/14/80
13 REM*
14 REM* THIS PROGRAM CHANGES THE 8050'S
15 REM* DEVICE NUMBER TO THE NUMBER THAT
16 REM* IS GIVEN BY THE OPERATOR. THIS
17 REM* CAN RANGE FROM 9 TO 15. THIS IS
18 REM* A SOFT CHANGE; THUS A RESET OF
19 REM* THE 8050 WILL CAUSE IT TO RESTORE
20 REM* TO THE HARD DEVICE NUMBER.
21 REM*
22 REM* THIS PROGRAM IS APPLICABLE FOR
23 REM* ANY 8050 OR 2040 WITH DOS 2.X.
24 REM*
25 REM************************************
99 PRINT"♥"
100 INPUT"OLD DEVICE NUMBER";DO
110 IFDO<8 OR DO>15 THEN100
150 INPUT"NEW DEVICE NUMBER";DN
160 IFDN<8 OR DN>15 THEN150
200 OPEN15,DO,15:REM COMMAND CHANNEL
210 PRINT#15,"M-W"CHR$(12)CHR$(00)CHR$(2)CHR$(DN+32)CHR$(DN+64)
220 CLOSE15
230 END

 

[Gary C]

Digital board fully functioning.

But the analogue board has a fault. I think its something in the Read/Write enable circuit. Getting nothing at the diff amp U2 during a read even though I know the heads on the drives are fine. As it happens with both drives, need to have a look at the common components.

Noticed that the output from the transistor array U5 is pulsing. Collector & base steady but the emitter is pulsing from 0 to ~7V and with the heads unplugged it just goes down to earth through a 12k resistor. So it looks as if its breaking down, odd. Its a quad pnp in a 14 DIL, Q2T2905 and there are not many about, same with the equivalent NTE2322, so I might have to take a risk with a China import

MPQ2907 looks like an equivalent on a brief check.

 

[Gary C]

Dont quite know how I thought the base of the transistors were steady, but the digital board does indeed pulse them on standby. Odd.

So its not the transistor array.

Back to basics I think.

Format a disk with the good analogue board then try to read it with the bad and see if I can see any data at the test points after the diff amp.

 

[Gary C]

Ah ha !

One of the video amps isn't working. NE592 on order.