12 May
2014
12 May
'14
11:03 p.m.
Hi all --
Finally have the time (and space) to work on my PDP-8/L and its
associated ASR-33. The 8/L I've had running for a while now, but I've
only recently taken the time to go over the ASR-33 it came with. It was
a bit dirty but it's cleaned up nicely and I've got it humming along
nicely now. (With the exception of the paper tape punch, which is going
to need a bit more work.)
At any rate -- this ASR-33 was outfitted with the DEC "reader run"
modification, and it does not appear to be functioning -- with the
teletype in "Line" mode, the reader switch set to "Start," and with
the
8/L running the RIM loader the reader does nothing. (It also does
nothing when set to "Start" in "Local" mode, but I'm unsure if
that's
expected or not...)
With the cover off, if I manually toggle the "trip coil" at the rear of
the unit the reader runs and the 8/L receives data (and it looks to be
correct). I've verified continuity between the RELAY+ and RELAY- lines
from the W076 in the 8/L all the way to the reader run
board, and I'm
measuring 15V between the two.
It's about here where my naivete around analog electronics starts
kicking in and I'm unsure where to go from this point -- any suggestions
are much appreciated.
Thanks,
Josh
12 May
12 May
11:26 p.m.
-----Original Message-----
From: cctalk-bounces at classiccmp.org [mailto:cctalk-bounces at classiccmp.org]
On Behalf Of Josh Dersch
Sent: 13 May 2014 07:03
To: General Discussion: On-Topic and Off-Topic Posts
Subject: DEC ASR-33 "reader run" debugging
Hi all --
Finally have the time (and space) to work on my PDP-8/L and its associated
ASR-33. The 8/L I've had running for a while now, but I've only recently
taken
the time to go over the ASR-33 it came with. It was a
bit dirty but it's
cleaned
up nicely and I've got it humming along nicely
now. (With the exception
of the
paper tape punch, which is going to need a bit more
work.)
At any rate -- this ASR-33 was outfitted with the DEC "reader run"
modification, and it does not appear to be functioning -- with the
teletype in
"Line" mode, the reader switch set to
"Start," and with the 8/L running
the RIM
loader the reader does nothing. (It also does nothing
when set to "Start"
in
"Local" mode, but I'm unsure if
that's expected or not...)
With the cover off, if I manually toggle the "trip coil" at the rear of
the unit the
reader runs and the 8/L receives data (and it looks to
be correct). I've
verified
continuity between the RELAY+ and RELAY- lines from
the W076 in the 8/L
all
the way to the reader run board, and I'm measuring
15V between the two.
It's about here where my naivete around analog electronics starts kicking
in
and I'm unsure where to go from this point -- any
suggestions are much
appreciated.
Thanks,
Josh
My suggestion is to join the Greenkeys list.
Regards
Rob
13 May
13 May
1:11 a.m.
My suggestion is to join the Greenkeys list.
Oh, no! With a model 15 or at least 32 this would be the right place.
But the reader run thing is a pure computer related topic. On topic
here, off topic on Greenkeys I guess.
Do you have that little reader control thing in your 33? There's
something that goes into the base (NOT the machine itself) if I
remember. It sometimes gets lost. And then the reader does not work
anymore. I think it's related to the DEC modification.
Kind regards
Philipp
2:13 a.m.
analog? from my point of view it's just the equivalnt of a huge power
mosfet like a irf830 driven by a small signal from the 8/l
first of: does the 8/l change a level on the wire? check that with a
multimeter. if not: look at your 8/l, if yes, look at the dec board.
it is possible that the line itself does not carry a voltage but is tied
to gnd in the computer. if there is no voltage on the line, switch the
multimeter to resistance and check the change of values. reverse the
leads if nothing comes up.
eliminating possibillities is the first part in faultfinding.
simon
On 13-05-14 08:03, Josh Dersch wrote:
Hi all --
Finally have the time (and space) to work on my PDP-8/L and its
associated ASR-33. The 8/L I've had running for a while now, but I've
only recently taken the time to go over the ASR-33 it came with. It was
a bit dirty but it's cleaned up nicely and I've got it humming along
nicely now. (With the exception of the paper tape punch, which is going
to need a bit more work.)
At any rate -- this ASR-33 was outfitted with the DEC "reader run"
modification, and it does not appear to be functioning -- with the
teletype in "Line" mode, the reader switch set to "Start," and with
the
8/L running the RIM loader the reader does nothing. (It also does
nothing when set to "Start" in "Local" mode, but I'm unsure if
that's
expected or not...)
With the cover off, if I manually toggle the "trip coil" at the rear of
the unit the reader runs and the 8/L receives data (and it looks to be
correct). I've verified continuity between the RELAY+ and RELAY- lines
from the W076 in the 8/L all the way to the reader run board, and I'm
measuring 15V between the two.
It's about here where my naivete around analog electronics starts
kicking in and I'm unsure where to go from this point -- any suggestions
are much appreciated.
Thanks,
Josh
--
Met vriendelijke Groet,
Simon Claessen
drukknop.nl
11:05 a.m.
Hi all --
Finally have the time (and space) to work on my PDP-8/L and its
associated ASR-33. The 8/L I've had running for a while now, but I've
only recently taken the time to go over the ASR-33 it came with. It was
a bit dirty but it's cleaned up nicely and I've got it humming along
nicely now. (With the exception of the paper tape punch, which is going
to need a bit more work.)
At any rate -- this ASR-33 was outfitted with the DEC "reader run"
modification, and it does not appear to be functioning -- with the
teletype in "Line" mode, the reader switch set to "Start," and with
the
8/L running the RIM loader the reader does nothing. (It also does
nothing when set to "Start" in "Local" mode, but I'm unsure if
that's
expected or not...)
With the cover off, if I manually toggle the "trip coil" at the rear of
the unit the reader runs and the 8/L receives data (and it looks to be
correct). I've verified continuity between the RELAY+ and RELAY- lines
from the W076 in the 8/L all the way to the reader run board, and I'm
measuring 15V between the two.
It's about here where my naivete around analog electronics starts
kicking in and I'm unsure where to go from this point -- any suggestions
are much appreciated.
FGirstly, 'digital circuits are buitl form analogue parts' so I really do
wonder how you can debug a digital system without understanding analogue
stuff.
But secondly, this is digital. It's a relay. It's a 2-stae device.
OK, from what I remember about this modification, the relay has 4
conencitosn. 2 areh coil. 2 are the contacts. When sufficient
currentpasses through the coil, the contacts close.
The coil is conencted to 2 pins on the mate-n-lock so that the PDP8 can
control it. The cotnacts are wired in series with the reader control
circuit that operates the trip magnet at the back of the typing unit. Be
warned thath the cotncts are in cirucitry that is directly conencted ot
the maisn (pwoerl ine) in most versions, the relay, of course, provides
isolatiuon betwene this and the PDP8.
Assuming you can idtenify the connecitons, start by conencting a jumper
wire betwene the 2 'contact' terminals of the relay so that it appears to
be operated. Does the reader run now (jn local mode, you don't need to
have the PDP8 conencted). If not, then the problem is not with the the
reder run modificsiton. it might be the reader control PSU. Or the trip
magnet (unlilely) Or the conact wires in the rreder that are operaed by
the manual cotnrol elver or tape out sensor (very liekly). Look at th
Teletype Model 33 docs to figure it out. It's a very simple circuit,
although the official diagrams are designed to give yo a headache!.
Once you have got the reader to work like that, you now need to test the
relay. Remvoe the jumper across the cotnact terminals that you just
fitted. Now measure the resistance of the coil (everything off, PDP8
disconencted). Expect a few hundred ohms. If there is a protection diode
in parallel with the coil, check that too.
IF that checks out, conenct the PDP8 and try to read a tape. What voltage
do you get betwene the coil terminals? I think it's about 15V when the
reader is supposed to be running. If that's not right, the problem is the
relay drive cirucity in the PDP8. Or the cable/connectiors.
It might be the relay itself, If the coil is beign energised the contacts
may still not be closing.
-tony
10:21 p.m.
On 5/13/2014 11:05 AM, Tony Duell wrote:
I find debugging TTL logic pretty straightforward; either using an
oscilloscope and / or logic analyzer I've generally had pretty good
luck. Logic gates make sense to my mostly-software-oriented brain. When
things start getting more into specifics of what lies underneath I'm
considerably less handy. I'm slowly picking things up.
Hi all --
Finally have the time (and space) to work on my PDP-8/L and its
associated ASR-33. The 8/L I've had running for a while now, but I've
only recently taken the time to go over the ASR-33 it came with. It was
a bit dirty but it's cleaned up nicely and I've got it humming along
nicely now. (With the exception of the paper tape punch, which is going
to need a bit more work.)
At any rate -- this ASR-33 was outfitted with the DEC "reader run"
modification, and it does not appear to be functioning -- with the
teletype in "Line" mode, the reader switch set to "Start," and with
the
8/L running the RIM loader the reader does nothing. (It also does
nothing when set to "Start" in "Local" mode, but I'm unsure if
that's
expected or not...)
With the cover off, if I manually toggle the "trip coil" at the rear of
the unit the reader runs and the 8/L receives data (and it looks to be
correct). I've verified continuity between the RELAY+ and RELAY- lines
from the W076 in the 8/L all the way to the reader run board, and I'm
measuring 15V between the two.
It's about here where my naivete around analog electronics starts
kicking in and I'm unsure where to go from this point -- any suggestions
are much appreciated.
FGirstly, 'digital circuits are buitl form analogue
parts' so I really do
wonder how you can debug a digital system without understanding analogue
stuff.
But secondly, this is digital. It's a relay. It's a 2-stae device.
Sure, surrounded by some interesting things like 3 or 4 "thyractors,"
the characteristics of which I don't really understand all that well,
for example :).
OK, from what I remember about this modification, the relay has 4
conencitosn. 2 areh coil. 2 are the contacts. When sufficient
currentpasses through the coil, the contacts close.
The coil is conencted to 2 pins on the mate-n-lock so that the PDP8 can
control it. The cotnacts are wired in series with the reader control
circuit that operates the trip magnet at the back of the typing unit. Be
warned thath the cotncts are in cirucitry that is directly conencted ot
the maisn (pwoerl ine) in most versions, the relay, of course, provides
isolatiuon betwene this and the PDP8.
Assuming you can idtenify the connecitons, start by conencting a jumper
wire betwene the 2 'contact' terminals of the relay so that it appears to
be operated. Does the reader run now (jn local mode, you don't need to
have the PDP8 conencted). If not, then the problem is not with the the
reder run modificsiton. it might be the reader control PSU. Or the trip
magnet (unlilely) Or the conact wires in the rreder that are operaed by
the manual cotnrol elver or tape out sensor (very liekly). Look at th
Teletype Model 33 docs to figure it out. It's a very simple circuit,
although the official diagrams are designed to give yo a headache!.
I jumpered a wire across the contact terminals of the relay and still no
joy. The contacts on the reader control lever are OK (I cleaned those
thoroughly awhile back) I'll trace through the wiring tonight / tomorrow
(if I can find the time) and see where I can get with it.
Thanks as always for the advice; someday I hope not to have to ask dumb
questions on this list :). (Don't hold your breath.)
- Josh
Once you have got the reader to work like that, you now need to test the
relay. Remvoe the jumper across the cotnact terminals that you just
fitted. Now measure the resistance of the coil (everything off, PDP8
disconencted). Expect a few hundred ohms. If there is a protection diode
in parallel with the coil, check that too.
IF that checks out, conenct the PDP8 and try to read a tape. What voltage
do you get betwene the coil terminals? I think it's about 15V when the
reader is supposed to be running. If that's not right, the problem is the
relay drive cirucity in the PDP8. Or the cable/connectiors.
It might be the relay itself, If the coil is beign energised the contacts
may still not be closing.
-tony
11:36 p.m.
But secondly,
this is digital. It's a relay. It's a 2-stae device.
Sure, surrounded by some interesting things like 3 or 4 "thyractors,"
the characteristics of which I don't really understand all that well,
for example :). I jumpered a wire across the contact terminals of the
relay and still no
joy. The contacts on the reader control lever are OK (I cleaned those
thoroughly awhile back) I'll trace through the wiring tonight / tomorrow
(if I can find the time) and see where I can get with it.
If you get the 1975 Teletype Model 33 schematics from bitsavers, I think you need to look
at page
8 of the pdf -- sheet FS6.
It appears the reader trip circuit reduces to the trip coil (the one you worked by hand)
and the reader
contacts connected across the mains. So the problem could be a bad trip coil (let's
hope not!), bad
connections, or those contacts in the reader. I've had a lot of problems with those in
the past, and that's
where I would check first. With the machine unplugged from the mains, pull the reader
connector at the
back of the call control unit and see if you can get continuity between the pins of the
cable-mounted part
with the reader switch on, tape loaded, etc. If I'm reading the diagram right,
that's connector J6,
pins 14 and 15
Thanks as always for the advice; someday I hope not to
have to ask dumb
questions on this list :). (Don't hold your breath.)
It has often been said the only dumb question is the one that's not asked. I generally
go along with
that, although I do feel it's silly to ask a question when you know the chap you are
asking won't know
the answer... But that does not apply here. Ask away!
-tony
14 May
14 May
5:22 a.m.
* Josh Dersch <derschjo at gmail.com> [140514 01:22]:
On 5/13/2014 11:05 AM, Tony Duell wrote:
[SNIP]
Thanks as always for the advice; someday I hope not to have to ask dumb
questions on this list :). (Don't hold your breath.)
- Josh
I find this thread interesting and helpful so please continue asking
questions in this vein!
Todd
1:20 p.m.
Firstly,
'digital circuits are built from analogue parts' so I really do
wonder how you can debug a digital system without understanding analogue
stuff.
I find debugging TTL logic pretty straightforward; either using an
oscilloscope and / or logic analyzer I've generally had pretty good luck. Logic gates make sense to my
mostly-software-oriented brain. When
things start getting more into specifics of what lies underneath I'm
considerably less handy. I'm slowly picking things up.
Relay circuits are essentially logic gates. I am sure at least one book I
have on digital design is almsot all relay circuits.
-tony
3880
days inactive
3881
days old
8 comments
6 participants
participants (6)
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ard＠p850ug1.demon.co.uk -
derschjo＠gmail.com -
hachti＠hachti.de -
robert.jarratt＠ntlworld.com -
simski＠dds.nl -
tsg＠bonedaddy.net