7 Jul
2003
7 Jul
'03
7:44 p.m.
For those of you who missed the announcement in alt.sys.pdp8,
I've now almost completed the M220 version B schematic. It's
available at:
http://www.parse.com/~pdp8/pdp8i/m220b.html
The trials and tribulations of the PDP-8/I restoration can be
found at:
http://www.parse.com/~pdp8/pdp8i/restore.html
Plenty-o-dead 7474's in that one :-)
Cheers,
-RK
--
Robert Krten, PARSE Software Devices +1 613 599 8316.
Realtime Systems Architecture, Consulting and Training at www.parse.com
Looking for Digital Equipment Corp. PDP-1 through PDP-15 minicomputers!
8 Jul
8 Jul
12:30 a.m.
--- Robert Krten <root(a)parse.com> wrote:
For those of you who missed the announcement in
alt.sys.pdp8,
I've now almost completed the M220 version B schematic. It's
available at:
http://www.parse.com/~pdp8/pdp8i/m220b.html
Cool! Thanks! I have a few M220 cards that will eventually benefit
from your efforts (I borrowed them from a parts machine
to keep the
main machines running).
The trials and tribulations of the PDP-8/I restoration
can be
found at:
http://www.parse.com/~pdp8/pdp8i/restore.html
Plenty-o-dead 7474's in that one :-)
That's been my experience, too. I have replaced as many as 8 7474s
at a go to get an -8/L back on its feet. I don't recall replacing
any other chip, as a matter of fact.
-ethan
1:19 a.m.
Ethan Dicks wrote:
--- Robert Krten <root(a)parse.com> wrote:
7474's Dead d flops? whats the story on that?
Jim
For those of you who missed the announcement in
alt.sys.pdp8,
I've now almost completed the M220 version B schematic. It's
available at:
http://www.parse.com/~pdp8/pdp8i/m220b.html
Cool! Thanks! I have a few M220 cards that will eventually benefit
from your efforts (I borrowed them from a parts machine to keep the
main machines running).
The trials and tribulations of the PDP-8/I
restoration can be
found at:
http://www.parse.com/~pdp8/pdp8i/restore.html
Plenty-o-dead 7474's in that one :-)
That's been my experience, too. I have replaced as many as 8 7474s
at a go to get an -8/L back on its feet. I don't recall replacing
any other chip, as a matter of fact.
-ethan
10:03 a.m.
--- Jim Davis <jpdavis(a)gorge.net> wrote:
Ethan Dicks wrote:
Dunno. I can say categorically that they were failed chips. They
did not pass muster in a handheld TTL tester, and when replaced,
the PDP-8/L worked.
There was a mention on the list of a batch of 7440s that failed in
another M-series machine (might or might not have been an -8/L)
with the same date code.
Not sure why 7474s from the mid-to-late 1960s would be more fragile
than, say, 7400s. Perhaps the flipping and the flopping wears them
out faster than anding and oring? :-)
-ethan
That's been my experience, too. I have
replaced as many as 8 7474s
at a go to get an -8/L back on its feet. I don't recall replacing
any other chip, as a matter of fact.
-ethan
7474's Dead d flops? whats the story on that?
Jim
13 Jul
13 Jul
6:50 p.m.
Ethan Dicks sez...
--- Jim Davis <jpdavis(a)gorge.net> wrote:
:-)
In my case, the failure modes were as follows:
2 chips failed with: grounding the PRESET line caused the Q
to go high as expected, but when PRESET was left floating Q
went low. [DEC leaves the PRESET and CLEAR lines floating on
various modules, so I consider this a fair test].
1 chip failed with insufficient +5 on the Q (or bar-Q, forget
right at this instant) output. The measured output was something
like 1.6V.
Like Ethan sez, when these chips were replaced, things got better.
I think the "reason" might be that these chips were pushing the edge
of semiconductor manufacturing technology -- they are certainly one of
the more complicated chips from the early 74xx (all 14-pin only :-))
era. That's my theory...
Cheers,
-RK
--
Robert Krten, PARSE Software Devices +1 613 599 8316.
Realtime Systems Architecture, Consulting and Training at www.parse.com
Looking for Digital Equipment Corp. PDP-1 through PDP-15 minicomputers!
Ethan Dicks wrote:
Dunno. I can say categorically that they were failed chips. They
did not pass muster in a handheld TTL tester, and when replaced,
the PDP-8/L worked.
There was a mention on the list of a batch of 7440s that failed in
another M-series machine (might or might not have been an -8/L)
with the same date code.
Not sure why 7474s from the mid-to-late 1960s would be more fragile
than, say, 7400s. Perhaps the flipping and the flopping wears them
out faster than anding and oring? :-) That's been my experience, too. I have
replaced as many as 8 7474s
at a go to get an -8/L back on its feet. I don't recall replacing
any other chip, as a matter of fact.
-ethan
7474's Dead d flops? whats the story on that?
Jim
14 Jul
14 Jul
12:33 a.m.
Robert Krten wrote:
<snip>
:-)
In my case, the failure modes were as follows:
2 chips failed with: grounding the PRESET line caused the Q
to go high as expected, but when PRESET was left floating Q
went low. [DEC leaves the PRESET and CLEAR lines floating on
various modules, so I consider this a fair test].
1 chip failed with insufficient +5 on the Q (or bar-Q, forget
right at this instant) output. The measured output was something
like 1.6V.
<snip>
That sounds like a design flaw. Even with TTL, unused inputs should be
tied to somthing.
What was the fanout for the Q /Q on the fried output?
Jim Davis.
21 Jul
21 Jul
1:11 p.m.
jpdavis sez...
Robert Krten wrote:
This was not in-circuit, this was in a test jig. I don't know what the
in-circuit fanout would have been, that would require massive amounts
of digging through the schematics :-)
Cheers,
-RK
--
Robert Krten, PARSE Software Devices +1 613 599 8316.
Realtime Systems Architecture, Consulting and Training at www.parse.com
Looking for Digital Equipment Corp. PDP-1 through PDP-15 minicomputers!
<snip>
:-)
In my case, the failure modes were as follows:
2 chips failed with: grounding the PRESET line caused the Q
to go high as expected, but when PRESET was left floating Q
went low. [DEC leaves the PRESET and CLEAR lines floating on
various modules, so I consider this a fair test].
1 chip failed with insufficient +5 on the Q (or bar-Q, forget
right at this instant) output. The measured output was something
like 1.6V.
<snip>
That sounds like a design flaw. Even with TTL, unused inputs should be
tied to somthing.
What was the fanout for the Q /Q on the fried output? 
8 Jul
8 Jul
4:48 p.m.
Jim Davis wrote:
<snip>
Good question! I've also chased down several bad 7474's in my Imlac,
and I suspect some bad 7474's on a
few HP 1000 series I/O boards I have down in the shop.
Is the 7474 a 'dog'? I've know a few TTL parts that were pretty bad,
mainly counters though. But a latch?
That's been my experience, too. I have replaced as many as 8 7474s
at a go to get an -8/L back on its feet. I don't recall replacing
any other chip, as a matter of fact.
-ethan
7474's Dead d flops? whats the story on that?
Jim
10 Jul
10 Jul
12:37 p.m.
On Tue, 8 Jul 2003, Bob Shannon wrote:
Jim Davis wrote:
This reminds me of a similar problem in the JC80 systems, where 74170
chips would fail more often than anything else. I'd sure like to know what
the cause of that was...
-Toth
7474's Dead d flops? whats the story on that?
Good question! I've also chased down several bad 7474's in my Imlac,
and I suspect some bad 7474's on a few HP 1000 series I/O boards I have
down in the shop.
Is the 7474 a 'dog'? I've know a few TTL parts that were pretty bad,
mainly counters though. But a latch? 
2:42 p.m.
Is the 7474 a
'dog'? I've know a few TTL parts that were pretty bad,
mainly counters though. But a latch?
This reminds me of a similar problem in the JC80 systems, where 74170
chips would fail more often than anything else. I'd sure like to know what
the cause of that was...
3:20 p.m.
On Thu, 10 Jul 2003, Tony Duell wrote:
You know what happens when someone says impossible...
I just checked my parts bins, and I have *one* 7482, a TI part with a date
code of 7541. If you still want to replace your 7483 kludge, and know of
an economical way to get small things from the US to the UK, let me know.
Btw, what was the vintage of the old chip? Chances are one of the local
surplus places I visit from time to time has some 7482 chips in one of
their bins.
-Toth
This reminds
me of a similar problem in the JC80 systems, where 74170
chips would fail more often than anything else. I'd sure like to know
what the cause of that was...
I can remember replacing many 7474s in the RK11-C when I was getting
that going. Oh, and a 7482 adder, which was impossible to find [1]...
[1] I do mean _impossible_. I ended up using part of a 7483 that I stuck
to the flip-chip PCB dead-bug style and wired to the holes where the
7482 should have been. Runs fine...
5:16 p.m.
[7482 chip]
'Somebody these days claiming something is impossible is apt to be
interrupted by some fool doing it' :-)
[1] I do mean
_impossible_. I ended up using part of a 7483 that I stuck
to the flip-chip PCB dead-bug style and wired to the holes where the
7482 should have been. Runs fine...
You know what happens when someone says impossible...
I just checked my parts bins, and I have *one* 7482, a TI part with a date
code of 7541. If you still want to replace your 7483 kludge, and know of
an economical way to get small things from the US to the UK, let me know.
Actually, I got some 7482s a couple of years later. But I never bothered
to replace the kludge -- it works well, so I don't see any reason to pull
the card again. If it fails, I'll try one of the 7482s I have...
Btw, what was the vintage of the old chip? Chances are
one of the local
Around 1972, when the controller was made.
-tony
3:46 p.m.
--- Tony Duell <ard(a)p850ug1.demon.co.uk> wrote:
One of these days, I need to get my RK11-C up and working (I have a
working RK11D that's been used recently - I've had the -C since 1984
and haven't ever had the occasion to power it on).
I should probably build a KM-11 clone first.
-ethjan
> Is the
7474 a 'dog'?
I can remember replacing many 7474s in the RK11-C when I was getting that
going. Oh, and a 7482 adder, which was impossible to find [1]...
5:12 p.m.
One of these days, I need to get my RK11-C up and
working (I have a
working RK11D that's been used recently - I've had the -C since 1984
and haven't ever had the occasion to power it on).
I should probably build a KM-11 clone first.
You'll need it. Actually, it's useful to have _2_ of them, since there
are a pair of KN11 connectors with different signals on them.
Does anyone have the full lights panel for the RK11C? It's 144 LEDs or
bulbs that display the I/O registers, etc. I have the panel, but not the
right bezel for the RK11-C (I only have the DX11 bezel...)
Not particularly useful, but the blinkenlights sure look pretty....
-tony
6:06 p.m.
Hell yes, the blinkinlights are over half the point to vintage hardware!
When I built my HP1000 ATAPI (IDE) disk controller, the first job was
drilling 72 holes in the rack
mount front pannel for the LED's!
Turning that into a working disk drive was rather, well, secondary to
getting the LEDs blinking in a meaningful
way. I even tweaked my current limiting resistors to try to match the
LEDs brightness to those of the HP 2113
CPU, and use a real HP grey blank panel spacer so it would look 'close
to right'.
I gotta get .JPG of that machine on-line someplace....
Tony Duell wrote:
One of these
days, I need to get my RK11-C up and working (I have a
working RK11D that's been used recently - I've had the -C since 1984
and haven't ever had the occasion to power it on).
I should probably build a KM-11 clone first.
You'll need it. Actually, it's useful to have _2_ of them, since there
are a pair of KN11 connectors with different signals on them.
Does anyone have the full lights panel for the RK11C? It's 144 LEDs or
bulbs that display the I/O registers, etc. I have the panel, but not the
right bezel for the RK11-C (I only have the DX11 bezel...)
Not particularly useful, but the blinkenlights sure look pretty....
-tony 
12 Jul
12 Jul
12:31 p.m.
New subject: RK11-C Panel (Re: M220B (PDP-8/I) schematics available)
I think I may have an RK11-C bezel (no lights, just the panel with the silk
screen on the front, a fiber back with hole for the lamps.
Trouble is, I'm not sure I want to part with it -- someday I'd like to have
an RK11-C to go with my RK03's.
Jay Jaeger
At 10:59 PM 7/10/2003 +0100, you wrote:
---
Jay R. Jaeger The Computer Collection
cube1(a)charter.net
One of these
days, I need to get my RK11-C up and working (I have a
working RK11D that's been used recently - I've had the -C since 1984
and haven't ever had the occasion to power it on).
I should probably build a KM-11 clone first.
You'll need it. Actually, it's useful to have _2_ of them, since there
are a pair of KN11 connectors with different signals on them.
Does anyone have the full lights panel for the RK11C? It's 144 LEDs or
bulbs that display the I/O registers, etc. I have the panel, but not the
right bezel for the RK11-C (I only have the DX11 bezel...)
Not particularly useful, but the blinkenlights sure look pretty....
-tony
2:27 p.m.
New subject: RK11-C Panel (Re: M220B (PDP-8/I) schematics available)
I think I may have an RK11-C bezel (no lights, just
the panel with the silk
screen on the front, a fiber back with hole for the lamps.
Trouble is, I'm not sure I want to part with it -- someday I'd like to have
an RK11-C to go with my RK03's.
Oh, I wasn't expected to find one here. In fact it's not somethign I
_need_ -- the LEDs are just as pretty without the right bezel.
And yes, you do want to find an RK11C. It's one of the more 'interesting'
units to repair that I've come across....
-tony
17 Jul
17 Jul
10:55 a.m.
Tony Duell sez...
I can remember replacing many 7474s in the RK11-C when I was getting that
going. Oh, and a 7482 adder, which was impossible to find [1]...
More recently, I've had a lot of 74Hxxx parts (and yet more 7474s) fail in
HP98x0 calculators. I guess after 30 years I can't really moan...
[1] I do mean _iompossible_. I ended up using part of a 7483 that I stuck
to the flip-chip PCB dead-bug style and wired to the holes where the 7482
should have been. Runs fine...
Bzzt. Wrong. (First, you probably mean "_impossible_" :-)).
I just bought 5 of them for US$1.25 (or so) each from
Gateway Electronics. Along with spare 7453, 7460, 7440, etc. I think it's
something like "gatewayelex.com".
Cheers,
-RK
--
Robert Krten, PARSE Software Devices +1 613 599 8316.
Realtime Systems Architecture, Consulting and Training at www.parse.com
Looking for Digital Equipment Corp. PDP-1 through PDP-15 minicomputers!
Is the
7474 a 'dog'? I've know a few TTL parts that were pretty bad,
mainly counters though. But a latch?
This reminds me of a similar problem in the JC80 systems, where 74170
chips would fail more often than anything else. I'd sure like to know what
the cause of that was...
6:36 p.m.
> going. Oh, and a 7482 adder, which was impossible
to find [1]...
[...]
[1] I do mean
_iompossible_. I ended up using part of a 7483 that I stuck
to the flip-chip PCB dead-bug style and wired to the holes where the 7482
should have been. Runs fine...
Bzzt. Wrong. (First, you probably mean "_impossible_" :-)).
I just bought 5 of them for US$1.25 (or so) each from
Gateway Electronics. Along with spare 7453, 7460, 7440, etc. I think it's
something like "gatewayelex.com".
7838
days inactive
7852
days old
18 comments
7 participants
participants (7)
-
ard＠p850ug1.demon.co.uk -
bshannon＠tiac.net -
cube1＠charter.net -
erd_6502＠yahoo.com -
jpdavis＠gorge.net -
root＠parse.com -
tothwolf＠concentric.net