My Altair 680 has achieved the position of primary attention on
my workbench. All of the ICs are socketed. Not having seen
power in over 20 years, I did not trust the power supply as far
as I could throw a bus. I pulled all of the ICs, attached dummy
loads (automobile bulbs) and powered up. Sure enough, there was
AC all over the place (where there should have been DC). I
replaced all of the electrolytic caps and that got rid of the AC
but some of the voltage levels are very wrong, at least as compared
to what is written on the schematics. The worst offender is just
off the "plus" side of the full wave bridge (BR-1). It should be
nine volts but is actually at 11.5. This makes what should be the
main five volt rail a little more than 9 volts... the far side of
VR-1 (a 7805). The wave form coming off the transformer is really
ugly not a smooth sine wave. I hate power supplies. I don't really
understand, looking at the schematics, what this transformer should
be doing. My guess is that it should be making a nice nine volt,
60 cycle AC sine wave with each of the two outputs 90 degrees out
of sync? What could be wrong with a transformer that it would
produce something like:
bent and very squared off at spots? My scope shows nice clean 120
coming into the transformer. How do I figure out a part number for
a replacement transformer?
I believe you are correct Tony. It looks like dropping values into
the TMA-11 registers
while the processor is halted does not work.
I had forgotten that I have a 873-YA bootstrap loader installed which
can boot from
a TM11 tape drive. I located a backup tape that was built using
Rollin. I booted
>from the tape and I did get the Rollin command prompt on the console.
So it looks
like the tape drive is in fact working.
You are also correct that if the RK05 works (it does), the grant
signals should be
good up to the RK11 controller.
My PDP-11/05 system with 32kW (28kW usable) now has a working RK05 drive
with RT-11 v2C with MUBASIC and a TMA-11/TS03 tape drive. Once I hook up my
ASR33 teletype, I will have an authentic 1972-ish system. Later, I
will begin work
on my PDP-11/20. That system was installed in Sept/1970.
Many thanks to all who helped sort out my issues.
Sun Aug 7 12:06:09 CDT 2011 Tony Duell wrote:
>> To test the tape drive, I used the programmer's console on my PDP-11/05 to
>> issue a read command to a mounted tape. When I issued a read command by
>> depositing a command into the TMA-11 command register, the tape advanced
>> slightly and then stopped. The 'Bus Grant Late' error was set in the TMA-11
>> status register. The status register did indicate the controller and tape drive
>> were both ready. No data was read in.
> Were you toggling in commands on the front panel with the CPU halted? I
> seem to remmber that some PDP11s will not handle bus requrests / NPRs if
> the processor isn't running, and thus if you try to operate such a
> peripheral in this wa, you will get a 'late grant' problem. It's better
> to enter a short program from the panel and run that. All the program
> needs to do is deposit the correct device command word in the right I/O
> location (you can set up all the other values -- the address, word count,
> etc -- from the panel) and loop either until the device indicates the
> command has completed, or just loop forever, and you can halt the program
> after a suitable time and examine device registers, memory ,etc.
>> The read command was issued while the processor is halted.
>> This particular system did not originally have any external devices hooked up
>> to it.
>> Beginning at the processor, the system has the following components installed:
>> KD11-B PDP-11/05
>> LS11 line printer card (connects to a Centronics 101A printer)
>> MM11-U 16K x 16 core memory
>> MM11-U 16K x 16 core memory
>> RK11-D RK05 disk controller
>> (See http://www.iamvirtual.ca/collection/systems/minis/PDP11-10/Boards.html
>> for details)
>> The BC11 cable leading to the TMA-11 controller is put on the Unibus
>> out connection
>> at the last slot of the RK11-D controller.
>> Based on previous posts from others, I suspect I don't have the processor grant
>> set up correctly.
> My first question is 'Does the RK05 work correctly?'. The RK11-D is an
> NPR device too, so if its's working, grants must be getting as far as
> that. If the're then not getting to the tape controller, there must be a
> fault either in the cable between those devices, or a fault in the RK11-D
> itself (I have had a device that failed to pass on a grant, I think one
> of the bus driver ICs had fialed. It was an easy fix, anyway...)
With the help of various knowledgeable people on this list, it was
pointed out that
I did not have the connection to the tape drive controller in the
To test the tape drive, I used the programmer's console on my PDP-11/05 to
issue a read command to a mounted tape. When I issued a read command by
depositing a command into the TMA-11 command register, the tape advanced
slightly and then stopped. The 'Bus Grant Late' error was set in the TMA-11
status register. The status register did indicate the controller and tape drive
were both ready. No data was read in.
The read command was issued while the processor is halted.
This particular system did not originally have any external devices hooked up
Beginning at the processor, the system has the following components installed:
LS11 line printer card (connects to a Centronics 101A printer)
MM11-U 16K x 16 core memory
MM11-U 16K x 16 core memory
RK11-D RK05 disk controller
The BC11 cable leading to the TMA-11 controller is put on the Unibus
at the last slot of the RK11-D controller.
Based on previous posts from others, I suspect I don't have the processor grant
set up correctly.
I am currently reading several different manuals to get a description of how the
grant lines should be hooked up. I have read many descriptions of the
but I have not located information on where to use the Grant Continuity cards
or making changes to the wire-wrapped bus. In my case, I will need to make
changes to the bus, since I do not have any of the Grant Continuity cards ;-)
Am I on the right track to assume that the problem is likely to be
grant wiring, or should I be looking elsewhere?
Many thanks for any pointers!
I try to get my "new" PDP-11/34a back to live. I did a quick PSU test
today with dummy loads. All voltages, LTCL, DCLO and ACLO where OK so I
pluged in the logic boards. But the machine does not respond to the
knobs on the programmers console. Pressing HLT + CNTRL brings the
machine not to halt, but the "Bus Error" LED of the console lights up.
Grant continuity cards and NPR jumpers are in place.
It looks like I have the wrong bus terminator: There is a M9301-YF at
the CPU side and a M930 at the other bus end. It seems I need a M9302
in place of the M930? This would explain the bus error.
I took my scope to have a look at the ripple of the voltages.
Here is what I got on the second +5 V PSU:
X = 0.2 V / div ; Y = 2 ms / div
X = 0.2 V / div ; Y = 10 us / div
I get similar pictures on all voltages. Both +5 V power bricks (H7441)
show similar ripple as well as +15 V and -15 V.
There are spikes with up to 1.2 Vpp and it is clearly related to the
50 Hz lines frequency. This doesn't look that healthy. I had a look at
the BA11-K power distribution schematic. The two +5 V PSUs are
independent and run of different windings of the mains transformer.
I am a bit surprised to see about the same fault on all PSUs. I am no
SM-PSU expert, so I am now at the point where I have to ask for advice.
Paul Anderson <useddec at gmail.com> wrote:
> If the RK11-D in the last thing on the bus, remove the M930 terminator
> and place the BC11-A cable going to TM11 there, and then terminate the
> Unibus in the TM11. The RK05 can only be connected to another RK05
> (or RK03), or the terminator.
> I hope that solves your problems, and good luck, that's a nice system.
Thanks. I am using it as my test system before I tackle my PDP-11/20
Yikes! I checked the PDP-11 and the RK05. I am happy to report that both
survived the newbie torture test!! RT11 w/ MUBAS is still operational :-)
I never considered the fact that the bus inside the main system is so tailored
to the cards installed within them, especially on a slot by slot basis.
If I understand things correctly, the first RK05 drive cable is
attached to the bus
opposite the M7255 card. The RK05's are daisy chained together. The last
RK05 has an M930 terminator. In the main cabinet, the M930 terminator
opposite the M7257 card is removed and the BC11 cable leading to the 1st
slot in the TMA-11 is installed. The M930 terminator in the TMA-11 now
becomes the Unibus terminator. If the entire Unibus chain is <50 ft, then we
Are all BC11 cables the same? I see some with M919 connectors and others
PS. I am still looking for an installable RSTS-11 (version 4 or LESS) so I can
prep an RK05 drive under SimH where I can copy the image onto a real RK05
disk pack (I wrote some software to do this)
I'm trying to get caught up on my Physics Today collection
(no, I'm not, I just read the mag). There was an article in the
October 2010 issue, entitled "The Evolution of the Science Museum". I
think that article might be of interest to any of you who are in the
process of trying to make your collections publicly accessible.
Anyone who is interested, please contact me for details.
- Mark 210-379-4635
Large Asteroids headed toward planets
inhabited by beings that don't have
technology adequate to stop them:
Think of it as Evolution in Fast-Forward.