Re: Firing up the pdt11

[Chris Zach via cctalk]

Assuming people are still interested I'm working on other, lesser issues 
now that the little thing works.


First thought: The interconnections between the CPU board and the IO 
board/memory boards are weird. Basically it's a plate, insulator, board, 
very odd spacer that provides interconnection, bottom board, insulator, 
plate, and the bottom hinge that holds the cpu board above the floppy 
controller board.


These interconnections are very sensitive to torque. Make sure all 
screws are snugged down and all the bolts on the bottom (6) secure the 
screws to the bottom hinges. Otherwise torque will cause the 
interconnection to be intermittent and you'll go crazy trying to 
troubleshoot.


Another odd issue: When I have the top CPU board vertical everything 
works fine. When I lower it, at about a 20 degree angle all hell breaks 
loose. The floppies no longer work, and the system drops into ODT. At 
first I thought it was the ribbon cable but that looks fine. Then I 
thought it was the sockets having poor solder connections so I reflowed 
them on the CPU board and the disk board. Still no. At this point I'm 
thinking it is noise from the CPU board affecting the disk controller board.


There is a short of shield made of a layer of plastic paper, then a 
layer of foil, then another layer of plastic paper that goes between the 
boards. However it's not grounded, and I think that's part of the 
problem. Any idea why there would be so much noise, and how to reduce 
it? All of the ground wires are installed and there are a lot of them in 
this thing.


C

Re: Firing up the pdt11

[Glen Slick via cctalk]

On Tue, Oct 13, 2020 at 2:29 PM Chris Zach via cctalk
 wrote:
>
> I do have a card around here called an RXV21 from Plessy or something
> like that, maybe it could talk to an RX01 drive and format the disks?
>

Several of the 3rd party controllers could low level format disks.

For example:
http://www.bitsavers.org/pdf/microTechnology/MXV21_floppyCtlr.pdf
http://www.bitsavers.org/pdf/sigmaInformationSystems/SDC-RXV21um_1981.pdf

Re: Firing up the pdt11

[Chris Zach via cctalk]

RX01 format is a standard IBM format used by many systems, including 
many CP/M ones, so it was possible to buy pre-formatted disks.  Maybe 
they came that way.


That may be it: The Elephant disk does say on the factory label: Single 
sided, single density, IBM compatible, 128 bytes, 26 sectors. So 
something like that will INIT on an RX01? Maybe that was it, if so weird 
mystery solved.


The other disks from Solarex are not looking good. Some of them have 
paper copies of directories, and they seemed to be using the FD: driver. 
Now I believe Solarex was running TSX on their systems, is FD: just 
TSX's way of saying DY? If not anyone need a bunch of 8 inch floppy disks?


Thanks for the help on this one. If the PDT really can't do formatting 
then maybe I'll just stick it back in the closet for another 20-30 
years. It's an odd duck, but a cute odd duck


CZ

Re: Firing up the pdt11

[Pete Turnbull via cctalk]

On 13/10/2020 22:28, Chris Zach via cctalk wrote:
Then I guess the question rattling around my brain is "How did I get 
this Elephant Memory systems disk formatted?"


RX01 format is a standard IBM format used by many systems, including 
many CP/M ones, so it was possible to buy pre-formatted disks.  Maybe 
they came that way.


I do have a card around here called an RXV21 from Plessy or something 
like that, maybe it could talk to an RX01 drive and format the disks?


Many 3-party controllers could.  Mine isn't a Plessey one, but it can do 
that - but mine connects to standard SA800-style drives, not an RX02.  I 
also have a Baydel F311 controller, which also can format disks and 
connects to standard SA800-style drives, but it only does single density.


--
Pete
Pete Turnbull

Re: Firing up the pdt11

[Chris Zach via cctalk]

> DEC controllers and DEC 8" drives cannot.  Not for any platform.
>
> Back in the day, DEC floppy users purchased pre-formatted floppies.
> If you had an RX02, you could "INIT" an RX01 floppy to RX02 use -
> essentially just rewriting the data portion of the sector to
> double-density (256 bytes per sector) and I _think_ it's possible to
> put it back.

Then I guess the question rattling around my brain is "How did I get 
this Elephant Memory systems disk formatted?" I know I didn't have an 
RX02 at the time, and I know DEC didn't do it for me as a favor. I know 
I bought a box of ten of them because I stuck the Elephant Memory 
Systems sticker on the front of my RM02 for good luck (I wonder where 
that drive is these days) I thought that is why I kept the PDT11 
around.


I do have a card around here called an RXV21 from Plessy or something 
like that, maybe it could talk to an RX01 drive and format the disks?


Darn brain, there's a hole in it somewhere around this seemingly 
not-interesting fact. The disk though is still here, and is formatted 
RX01 with programs I wrote to it 30 years ago.


I did have an H11 computer, but it did not have the H27 disk drive, or 
at least I have no memory of owning one after looking at that one on Ebay.


In a practical sense, I really don't need to format anything anymore: 
The best use for the RX01 is to bootstrap BRUSYS so I can backup the 
EDSI disk with the TK50. Reading old disks is nice, but the first thing 
I do is create a .DSK image of them on a real disk. In theory it is 
handy to have a small capacity disk to do image transfers from SIMH 
using the PDP11GUI but now that I have Kermit up I can just transfer 
stuff that way


Anyone want a pile of old RX02 formatted disks? I'll trade them for a 
few RX01 floppies just to have and to make PD: bootable disks for all 
the MiniMINCs out there.



Back in the day, DEC floppy users purchased pre-formatted floppies.
If you had an RX02, you could "INIT" an RX01 floppy to RX02 use -
essentially just rewriting the data portion of the sector to
double-density (256 bytes per sector) and I _think_ it's possible to
put it back.


Hm. Well at least that makes disk alignments a lot simpler: If all the 
disks were originally formatted at DEC then interchange is pretty much 
guaranteed.


Ah DEC. Always wanted to get that last nickel from their user base.

CZ

Re: Firing up the pdt11

[Ethan Dicks via cctalk]

On Mon, Oct 12, 2020 at 7:15 PM Chris Zach via cctalk
 wrote:
> Well, the drive is working. Better...

Excellent!

>  I've heard that the RX02 can format an RX01, but can it?

Nope.

There were 3rd party controllers that could format 8" media in DEC
machines (DSD for one).

DEC controllers and DEC 8" drives cannot.  Not for any platform.

Back in the day, DEC floppy users purchased pre-formatted floppies.
If you had an RX02, you could "INIT" an RX01 floppy to RX02 use -
essentially just rewriting the data portion of the sector to
double-density (256 bytes per sector) and I _think_ it's possible to
put it back.

CP/M users could and did buy blank media and format it.

-ethan

Re: Firing up the pdt11

[Chris Zach via cctalk]

Well, the drive is working. Better.

Summary: The PDT11/150 needs to have resistors on the harness to the 
floppy drives to limit the current for the sector LED. Without it the 
LED will be "off" and you will get a quick 8 stepper motor clicks 
without any click to load the heads. Looks like the PDT uses the sector 
count signal to determine if a disk is in the drive, and if it doesn't 
see that it just fails with a quick braaap!


And after trying a 47 ohm resistor (marginal) and a 22 ohm resistor (no 
luck at all) it turns out you want to use around 67 ohms of resistance 
for best results on the sector led. I didn't have any 67 ohm resistors, 
but I did have two 140 ohm resistors, so putting those in parallel gave 
me 70.


Drive PD1: now boots, reads disks, and seems kind of happy. I still need 
to clean up the whole board and put this harness in the drive, but at 
least it's running with two floppies again.


On the bad side (and something to think about): My memory must be in 
error: I can't format RX01 floppies with the PDT11. I recall that the 
PDT would literally rewrite the sector information along with the actual 
data track on each write (why) but this is not enough to format or init 
a blank disk apparently.


Which is odd, because I have a few Elephant Memory systems floppies that 
still work and obviously *are* formatted for RX01/PDT. But I never owned 
an RX02 so how did I get these formatted in the first place?


On to the RX02 again I guess. I'm going to put this pdt11/150 back 
together and start thinking about how to format floppies. I've heard 
that the RX02 can format an RX01, but can it? Certainly not with an 
RXV11 controller, I'll need to either find an RXV21 or get a Unibus 
pdp11 working so I can use this RX21 controller someone graciously lent 
me (or find my Quniverter and try that, but that would be 
stupid-complicated).


Which could be interesting: I have two Unibus pdp11's: My 11/05 (which I 
think only has 24kw of core memory anymore) and my 11/24 (which I have 
never gotten to work right and doesn't have any memory boards). Quick 
question to end this thread: Can an 11/24 come up to ODT without any 
memory? I've never seen anything on the serial ports.

Re: Firing up the pdt11

[Chris Zach via cctalk]

Curiouser and curiouser

On a lark I got a 47 ohm (actual reading 50.1 ohms) resistor from the 
box, put it on the anode supply line of the sector pulse LED on the 
drive that is in the PDT11 (not the one with the blown LED) and hooked 
it up to the power supply.


With the resistor in I fired up the supply, set the voltage to 3v, and 
checked the current. Now the LED only draws about 30ma measured at the 
supply instead of over 120ma without the resistor. So, different.


Then I put this assembly into the actual PDT11 circuit: Now when I check 
voltage at the resistor point I see 1.9v across the diode instead of 5v. 
And when I put a disk in the PDT11 does drop the solenoid down and tries 
to "read" the disk (but fails, but it is 8 slow failures, and not 8 fast 
ones). So I think the LED is now "lit".


Then I looked closely at the wires on the actual floppy drive to board 
interface. I see on the *other* plug (the one that runs the track zero 
detection) that there *is* a small resistor in line on the harness 
itself. Haven't checked the value but I'm guessing it's 68 ohms or so. 
But there is no similar resistor on the line to the sector pulse LED. I 
just checked the broken drive, same deal.


Maybe they "forgot" the resistor on the sector pulse LED? They didn't 
put it on the board or I wouldn't see +5 with the LED lit. More 
interestingly maybe the actual disk assembly for a PDT11 is 
*deliberately different* from an RX01 so you would have to order the 
"right" specific part. I don't know; I haven't taken apart my RX02 to 
see if that resistor is in line on the disk drive itself for either of 
these.


It could also have been an oversight, I'll check the top disk to see if 
the resistor is visible. Maybe the LED works at full +5v brightness for 
awhile, then opens at +5 but is still closed at lower voltages and lights.


This brings up another issue: As these are soft-sectored, does the 
amount of light the LED produces matter? Maybe my LED+resistor is bright 
enough to trigger sector pulses, but they are now not where the data is 
anymore? How critical is sector pulse alignment for an 8 inch floppy drive.


This is progress, and this is interesting. I wonder how deep this rabbit 
hole goes...


CZ



On 10/12/2020 11:11 AM, Tony Duell wrote:

On Mon, Oct 12, 2020 at 4:04 PM Chris Zach  wrote:



In a 'real' RX01, each sensor LED (track 0 and index) has the cathode
grounded and the anode connected to +5V via a 68ohm series resistor.
If you measure the voltage across the pins with the LED disconnected
(or if the LED is open-circuit) with any reasonable meter, it'll read
5V. The meter will not draw enough current for the resistor to drop a
noticeable voltage.


Ok, that makes sense. Is the resistor on the board or on the drive wire
harness somewhere?


I'm pretty sure it's on the PCB.



I'll jumper the disk 0 sensor into my test board here (actually just the
extender board from another PDT11) and see what the voltage looks like,
then compare it to the same spot on the second drive.


I'd look at the voltage on each pin of the LED in the 3 other sensors
(index and track 0 for both drives)

-tony

Re: Firing up the pdt11

[Tony Duell via cctalk]

On Mon, Oct 12, 2020 at 4:04 PM Chris Zach  wrote:
>
> > In a 'real' RX01, each sensor LED (track 0 and index) has the cathode
> > grounded and the anode connected to +5V via a 68ohm series resistor.
> > If you measure the voltage across the pins with the LED disconnected
> > (or if the LED is open-circuit) with any reasonable meter, it'll read
> > 5V. The meter will not draw enough current for the resistor to drop a
> > noticeable voltage.
>
> Ok, that makes sense. Is the resistor on the board or on the drive wire
> harness somewhere?

I'm pretty sure it's on the PCB.

>
> I'll jumper the disk 0 sensor into my test board here (actually just the
> extender board from another PDT11) and see what the voltage looks like,
> then compare it to the same spot on the second drive.

I'd look at the voltage on each pin of the LED in the 3 other sensors
(index and track 0 for both drives)

-tony

Re: Firing up the pdt11

[Chris Zach via cctalk]

In a 'real' RX01, each sensor LED (track 0 and index) has the cathode
grounded and the anode connected to +5V via a 68ohm series resistor.
If you measure the voltage across the pins with the LED disconnected
(or if the LED is open-circuit) with any reasonable meter, it'll read
5V. The meter will not draw enough current for the resistor to drop a
noticeable voltage.


Ok, that makes sense. Is the resistor on the board or on the drive wire 
harness somewhere?


I'll jumper the disk 0 sensor into my test board here (actually just the 
extender board from another PDT11) and see what the voltage looks like, 
then compare it to the same spot on the second drive.



The thing that puzzles me is why you read 5V across an LED that seems
to work on the bench. I wonder if a connection is open somewhere.


Not many places for the connection to be open: The LED most certainly 
did work and did provide IR light on the bench and in-circuit. Weird.


C

Re: Firing up the pdt11

[Tony Duell via cctalk]

> One is for the solenoid that lowers the pad onto the disk to allow
> reads/writes.
>
> One is for the sensor to detect track 1 (LED and detector)
>
> One is for the sensor to detect sector pulse
>
> One is for the servo motor that moves the head in and out
>
> One is for the read/write head
>
> One is for the 110v power to the drive motor itself that spins the belt
> and the disk via the center spindle.
>
> I did not move the 110v power wire because that is from a common harness
> between the drives and it's pretty obvious the disk is spinning. :-) The
> other five were switched between controller channel 0 and 1 (PD0: and PD1:)
>
> At this point I think I'm onto the sector pulse LED not working due to
> 5v being applied to it. Will be working on that more this morning with a
> better/more precise power supply.

Jumping in at this point...

In a 'real' RX01, each sensor LED (track 0 and index) has the cathode
grounded and the anode connected to +5V via a 68ohm series resistor.
If you measure the voltage across the pins with the LED disconnected
(or if the LED is open-circuit) with any reasonable meter, it'll read
5V. The meter will not draw enough current for the resistor to drop a
noticeable voltage.

Of course there is no reason why the resistor couldn't be between the
cathode and ground (with the anode connected to +5V). It's a simple
series circuit, the current is the same everywhere.

The thing that puzzles me is why you read 5V across an LED that seems
to work on the bench. I wonder if a connection is open somewhere.

-tony

Re: Firing up the pdt11

[Chris Zach via cctalk]

When you swap the cables (and keep the drives in place), do you mean
that you swapped the data connection **and** the power supply cable(s)?


There are six wire bundles and connectors that hook an RX01 floppy drive 
sub-module to the RX01 read/write controller board (or the PDT11 
controller board)


One is for the solenoid that lowers the pad onto the disk to allow 
reads/writes.


One is for the sensor to detect track 1 (LED and detector)

One is for the sensor to detect sector pulse

One is for the servo motor that moves the head in and out

One is for the read/write head

One is for the 110v power to the drive motor itself that spins the belt 
and the disk via the center spindle.


I did not move the 110v power wire because that is from a common harness 
between the drives and it's pretty obvious the disk is spinning. :-) The 
other five were switched between controller channel 0 and 1 (PD0: and PD1:)


At this point I think I'm onto the sector pulse LED not working due to 
5v being applied to it. Will be working on that more this morning with a 
better/more precise power supply.


CZ

RE: Firing up the pdt11

[Henk Gooijen via cctalk]

See below.

Van: Chris Zach via cctalk<mailto:cctalk@classiccmp.org>
Verzonden: maandag 12 oktober 2020 03:14
Aan: Richard Pope<mailto:mechani...@charter.net>; On-Topic and Off-Topic 
Posts<mailto:cctalk@classiccmp.org>
Onderwerp: Re: Firing up the pdt11

Well, by "location" I mean there are plugs on the controller board for
PD0 (typically called the "top" drive) and PD1 (typically the "bottom"
drive). My test swapped the cables so the top drive was using the PD1:
logic on the board and the "bottom" was using the PD0 logic. In that
situation the PD1: channel with the top drive worked so the problem is
not in the logic board.


Chris,
When you swap the cables (and keep the drives in place), do you mean
that you swapped the data connection *and* the power supply cable(s)?

Henk

Re: Firing up the pdt11. Dec put 5 volts on an LED?????

[Chris Zach via cctalk]

Maybe. The part number is partially missing, the drive itself has a part 
number of 70-13077-02, DEC badged. That maps to a print set of 
EK-13077-IP which doesn't seem to be anywhere online. Drat.


Looking at Wikipedia these seem to be in TO-18 metal cases. Maybe they 
are Gallium Arsenide LEDs?


However if it was current limited then running it up to 9v should not 
have killed it. Is it possible one can drive an LED hard enough to get 
it not to light after awhile at 5v levels but still have it light at 
lower voltage levels?


This should be simple to test with the other non-working drive: Put a 47 
ohm resistor in series with the LED and see if it works. If so great, 
I'll ECO the other drives. If not then I can replace this with a 
standard IR LED, put in a damn resistor, and get it online again.


Still, it means the track zero LED can't be far behind assuming they did 
the same trick. Hm. Need to do more research.


CZ

On 10/11/2020 11:50 PM, Doug Jackson wrote:

Could it have been a 5V LED with integral current limit?

That would explain the odd behaviour.

Kindest regards,

Doug Jackson

em: d...@doughq.com 
ph: 0414 986878

Check out my awesome clocks at www.dougswordclocks.com 


Follow my amateur radio adventures at vk1zdj.net 

---

Just like an old fashioned letter, this email and any files transmitted 
with it should probably be treated as confidential and intended solely 
for your own use.


Please note that any interesting spelling is usually my own and may have 
been caused by fat thumbs on a tiny tiny keyboard.


Should any part of this message prove to be useful in the event of the 
imminent Zombie Apocalypse then the sender bears no personal, legal, or 
moral responsibility for any outcome resulting from its usage unless the 
result of said usage is the unlikely defeat of the Zombie Hordes in 
which case the sender takes full credit without any theoretical or 
actual legal liability. :-)


Be nice to your parents.

Go outside and do something awesome - Draw, paint, walk, setup a 
radio station, go fishing or sailing - just do something that makes you 
happy.


^G ^G ^G ^G ^G ^G ^G ^G- In more laid back days this line would 
literally sing ^G ^G ^G ^G ^G ^G ^G ^G






On Mon, 12 Oct 2020 at 14:33, Chris Zach via cctalk 
mailto:cctalk@classiccmp.org>> wrote:


Ok, this is weirder: I put the "bad" floppy drive on the bench and
started to take a look at it. First I checked the LED (yes, it's an
LED). With a bench voltage of 1.5 volts and a 100ma draw it lit up
nicely in the IR (detected by phone camera, so nice they can see the
light) and the photo transistor also seemed to work fine (at the sector
hole resistance went from infinite down to about 500 ohms). That's
good,
so what is wrong?

I noticed I could crank the LED higher current-wise to 150 ma and the
voltage was still <2 volts. Interesting. Then I hooked a break-out
harness to the pdt11 to see what kind of voltage it was putting out to
the LED.

It's putting out +5v whenever the unit is on. Maybe it's current
limited? To check I hooked up the drive's plug to the breakout to see
what the LED was seeing.

+5v. And even weirder, the LED was not lit.

What the heck is going on here?

So I put the LED on the bench for a bit of a destructive test.
Disconnected the PDT11 from the breakout cable, hooked up the power
supply, turned up the voltage and the LED came on, then went *off* at
around 3v. At 5v it was dead off, no IR light as measured by the
camera.
Turn the voltage down, and it comes on again. Up and it goes off.

And unfortunately at 9v it died (CRAP!) as I turned up the current
limit
Yes, I forgot to set the voltage limit on the power supply, my bad,
I am
boo boo the fool...

But this is weird: It looks like DEC put an LED in there with no
current
limiting, and a straight +5 volts. And the LED is always on at this
high
voltage? With no current limiting resistor? This does not make sense,
but the volt meter don't lie. I'm going to check the working drive to
see if it is limiting the voltage somehow. I'd say there was a resistor
in the LED assembly limiting the current, but if that's true my
cranking
the voltage to 9v should not have blown it up, and it should not
turn on
at low voltages then off at 5v.

Maybe the solution is to insert a resistor in series with the second
drive at around r=e/i or r=5/.1 (100ma) or 50 ohms.

Does this make any sense?

C

Re: Firing up the pdt11. Dec put 5 volts on an LED?????

[Doug Jackson via cctalk]

Could it have been a 5V LED with integral current limit?

That would explain the odd behaviour.

Kindest regards,

Doug Jackson

em: d...@doughq.com
ph: 0414 986878

Check out my awesome clocks at www.dougswordclocks.com
Follow my amateur radio adventures at vk1zdj.net

---

Just like an old fashioned letter, this email and any files transmitted
with it should probably be treated as confidential and intended solely for
your own use.

Please note that any interesting spelling is usually my own and may have
been caused by fat thumbs on a tiny tiny keyboard.

Should any part of this message prove to be useful in the event of the
imminent Zombie Apocalypse then the sender bears no personal, legal, or
moral responsibility for any outcome resulting from its usage unless the
result of said usage is the unlikely defeat of the Zombie Hordes in which
case the sender takes full credit without any theoretical or actual legal
liability. :-)

Be nice to your parents.

Go outside and do something awesome - Draw, paint, walk, setup a
radio station, go fishing or sailing - just do something that makes you
happy.

^G ^G ^G ^G ^G ^G ^G ^G- In more laid back days this line would literally
sing ^G ^G ^G ^G ^G ^G ^G ^G




On Mon, 12 Oct 2020 at 14:33, Chris Zach via cctalk 
wrote:

> Ok, this is weirder: I put the "bad" floppy drive on the bench and
> started to take a look at it. First I checked the LED (yes, it's an
> LED). With a bench voltage of 1.5 volts and a 100ma draw it lit up
> nicely in the IR (detected by phone camera, so nice they can see the
> light) and the photo transistor also seemed to work fine (at the sector
> hole resistance went from infinite down to about 500 ohms). That's good,
> so what is wrong?
>
> I noticed I could crank the LED higher current-wise to 150 ma and the
> voltage was still <2 volts. Interesting. Then I hooked a break-out
> harness to the pdt11 to see what kind of voltage it was putting out to
> the LED.
>
> It's putting out +5v whenever the unit is on. Maybe it's current
> limited? To check I hooked up the drive's plug to the breakout to see
> what the LED was seeing.
>
> +5v. And even weirder, the LED was not lit.
>
> What the heck is going on here?
>
> So I put the LED on the bench for a bit of a destructive test.
> Disconnected the PDT11 from the breakout cable, hooked up the power
> supply, turned up the voltage and the LED came on, then went *off* at
> around 3v. At 5v it was dead off, no IR light as measured by the camera.
> Turn the voltage down, and it comes on again. Up and it goes off.
>
> And unfortunately at 9v it died (CRAP!) as I turned up the current limit
> Yes, I forgot to set the voltage limit on the power supply, my bad, I am
> boo boo the fool...
>
> But this is weird: It looks like DEC put an LED in there with no current
> limiting, and a straight +5 volts. And the LED is always on at this high
> voltage? With no current limiting resistor? This does not make sense,
> but the volt meter don't lie. I'm going to check the working drive to
> see if it is limiting the voltage somehow. I'd say there was a resistor
> in the LED assembly limiting the current, but if that's true my cranking
> the voltage to 9v should not have blown it up, and it should not turn on
> at low voltages then off at 5v.
>
> Maybe the solution is to insert a resistor in series with the second
> drive at around r=e/i or r=5/.1 (100ma) or 50 ohms.
>
> Does this make any sense?
>
> C
>

Re: Firing up the pdt11. Dec put 5 volts on an LED?????

[Chris Zach via cctalk]

Ok, this is weirder: I put the "bad" floppy drive on the bench and 
started to take a look at it. First I checked the LED (yes, it's an 
LED). With a bench voltage of 1.5 volts and a 100ma draw it lit up 
nicely in the IR (detected by phone camera, so nice they can see the 
light) and the photo transistor also seemed to work fine (at the sector 
hole resistance went from infinite down to about 500 ohms). That's good, 
so what is wrong?


I noticed I could crank the LED higher current-wise to 150 ma and the 
voltage was still <2 volts. Interesting. Then I hooked a break-out 
harness to the pdt11 to see what kind of voltage it was putting out to 
the LED.


It's putting out +5v whenever the unit is on. Maybe it's current 
limited? To check I hooked up the drive's plug to the breakout to see 
what the LED was seeing.


+5v. And even weirder, the LED was not lit.

What the heck is going on here?

So I put the LED on the bench for a bit of a destructive test. 
Disconnected the PDT11 from the breakout cable, hooked up the power 
supply, turned up the voltage and the LED came on, then went *off* at 
around 3v. At 5v it was dead off, no IR light as measured by the camera. 
Turn the voltage down, and it comes on again. Up and it goes off.


And unfortunately at 9v it died (CRAP!) as I turned up the current limit 
Yes, I forgot to set the voltage limit on the power supply, my bad, I am 
boo boo the fool...


But this is weird: It looks like DEC put an LED in there with no current 
limiting, and a straight +5 volts. And the LED is always on at this high 
voltage? With no current limiting resistor? This does not make sense, 
but the volt meter don't lie. I'm going to check the working drive to 
see if it is limiting the voltage somehow. I'd say there was a resistor 
in the LED assembly limiting the current, but if that's true my cranking 
the voltage to 9v should not have blown it up, and it should not turn on 
at low voltages then off at 5v.


Maybe the solution is to insert a resistor in series with the second 
drive at around r=e/i or r=5/.1 (100ma) or 50 ohms.


Does this make any sense?

C

Re: Firing up the pdt11

[Chris Zach via cctalk]

Well, by "location" I mean there are plugs on the controller board for 
PD0 (typically called the "top" drive) and PD1 (typically the "bottom" 
drive). My test swapped the cables so the top drive was using the PD1: 
logic on the board and the "bottom" was using the PD0 logic. In that 
situation the PD1: channel with the top drive worked so the problem is 
not in the logic board.


However I may have figured out a clue: When I try to boot the pdt11 on 
the good drive (now PD0: again) with the door open the drive makes a 
quick BRAAP noise in the head positioning motor and it fails. It does 
not drop the head pad servo. When I close the door the drive clicks in 
the servo and boots away.


However on the bottom drive it always does the BRAAP regardless if the 
door is open or closed. So I looked at the spare 8 inch drive: There is 
no "disk present" switch or anything but there *IS* the sector lamp and 
CDS cell. So the big question:


Maybe the RX01/PD logic looks for the sector pulse signal to determine 
if a disk is in the drive? That would explain how the controller "knows" 
there is no disk.


And a bigger question: Is that an LED or a light bulb that lights up the 
sector pulse CDS cell (I can see the detector is a CDS, I recognize 
those from my 150-in-one Tandy days). If so maybe it burns out?


C


On 10/11/2020 8:17 PM, Richard Pope wrote:

Chris,
     I would like to get a clarification on this. Does either drive work 
fine in the PD0 position or does the drive that was not working in the 
PD1 position not work in the PD0 position? You said that the spare drive 
that you put in the PD1 position also does not work. I would try it in 
the PD0 position and see if it works or not. Would you please let me 
know on these items?

GOD Bless and Thanks,
rich!

On 10/11/2020 7:11 PM, Chris Zach via cctalk wrote:
I'm back to working on the PDT11/150 again, the bottom floppy is 
weird: It doesn't read rx01 disks, period. Top one is fine. So I tried 
swapping all of the connectors on the control board so the top one was 
PD1: and the bottom was PD0: Sure enough the top drive works fine as 
PD1: and bottom is still dead so it's a drive issue.


Pull the drive, put in a spare, button it up, and sure enough it still 
doesn't work. Any ideas?


Also I recall my MiniMinc/150 (which is in parts in my shed) had EIS 
and FIS, but this one only reports FIS. Did DEC make pdp11/03 
expansion chips that only had FIS?


C

Re: Firing up the pdt11

[Richard Pope via cctalk]

Chris,
I would like to get a clarification on this. Does either drive work 
fine in the PD0 position or does the drive that was not working in the 
PD1 position not work in the PD0 position? You said that the spare drive 
that you put in the PD1 position also does not work. I would try it in 
the PD0 position and see if it works or not. Would you please let me 
know on these items?

GOD Bless and Thanks,
rich!

On 10/11/2020 7:11 PM, Chris Zach via cctalk wrote:
I'm back to working on the PDT11/150 again, the bottom floppy is 
weird: It doesn't read rx01 disks, period. Top one is fine. So I tried 
swapping all of the connectors on the control board so the top one was 
PD1: and the bottom was PD0: Sure enough the top drive works fine as 
PD1: and bottom is still dead so it's a drive issue.


Pull the drive, put in a spare, button it up, and sure enough it still 
doesn't work. Any ideas?


Also I recall my MiniMinc/150 (which is in parts in my shed) had EIS 
and FIS, but this one only reports FIS. Did DEC make pdp11/03 
expansion chips that only had FIS?


C