16 Aug
2025
16 Aug
'25
9:02 p.m.
I have recently bought a DEC PDP-8/s. It hasn't been powered on for about
40 years before I got it. I cleaned it and did some repairs on it (glued
broken flip-chip handles, replaced all front panel lights, restored the
acrylic front panel to as new condition and built a new switch mode power
supply for +10V and -15V).
After testing each flip-chip individually for dead shorts on the power
rails I reassembled the flip-chips into the backplane and on power up it
shows signs of life, but has a number of problems I will have to debug and
fix.
Does anyone here have the original Engineering Drawings or good PDF scans
of the drawings?
There are reduced copies of the PDP-8/s Engineering Drawings in Appendix A
of the two PDP-8/s Maintenance Manuals on Bitsavers, but I have not been
able to find scans of the actual Engineering Drawings. Some details in the
reduced copies in Appendix A are not legible.
Thank you
Tom
16 Aug
16 Aug
9:20 p.m.
I forgot to say that my PDP-8/s has serial number 296 which means it uses
the "8k core module" which has only 4k core populated. Below serial number
200 the PDP-8/s were delivered with the "4k core module" which is somewhat
different in both backplane layout and electronically.
On Sun, Aug 17, 2025 at 12:02 PM Tom Hunter <ccth6600(a)gmail.com> wrote:
I have recently bought a DEC PDP-8/s. It hasn't
been powered on for about
40 years before I got it. I cleaned it and did some repairs on it (glued
broken flip-chip handles, replaced all front panel lights, restored the
acrylic front panel to as new condition and built a new switch mode power
supply for +10V and -15V).
After testing each flip-chip individually for dead shorts on the power
rails I reassembled the flip-chips into the backplane and on power up it
shows signs of life, but has a number of problems I will have to debug and
fix.
Does anyone here have the original Engineering Drawings or good PDF scans
of the drawings?
There are reduced copies of the PDP-8/s Engineering Drawings in Appendix A
of the two PDP-8/s Maintenance Manuals on Bitsavers, but I have not been
able to find scans of the actual Engineering Drawings. Some details in the
reduced copies in Appendix A are not legible.
Thank you
Tom
18 Aug
18 Aug
10:06 a.m.
AyAlthough I've never seen one in the wild, the 8/S has always intrigued
me. I would love to see a cycle accurate emulator of one. Wish I could do
it myself but that's way out of my wheelhouse.
RayRay the Emulation Guy
On Sun, Aug 17, 2025, 5:26 PM Tom Hunter via cctalk <cctalk(a)classiccmp.org>
wrote:
I forgot to say that my PDP-8/s has serial number 296
which means it uses
the "8k core module" which has only 4k core populated. Below serial number
200 the PDP-8/s were delivered with the "4k core module" which is somewhat
different in both backplane layout and electronically.
On Sun, Aug 17, 2025 at 12:02 PM Tom Hunter <ccth6600(a)gmail.com> wrote:
I have recently bought a DEC PDP-8/s. It
hasn't been powered on for about
40 years before I got it. I cleaned it and did some repairs on it (glued
broken flip-chip handles, replaced all front panel lights, restored the
acrylic front panel to as new condition and built a new switch mode power
supply for +10V and -15V).
After testing each flip-chip individually for dead shorts on the power
rails I reassembled the flip-chips into the backplane and on power up it
shows signs of life, but has a number of problems I will have to debug
and
fix.
Does anyone here have the original Engineering Drawings or good PDF scans
of the drawings?
There are reduced copies of the PDP-8/s Engineering Drawings in Appendix
A
of the two PDP-8/s Maintenance Manuals on
Bitsavers, but I have not been
able to find scans of the actual Engineering Drawings. Some details in
the
reduced copies in Appendix A are not legible.
Thank you
Tom
16 Aug
16 Aug
9:36 p.m.
Hi Tom
Grok tells me: “ Yes, the DEC PDP-8/S uses many of the same flip chip PCBs as the
original PDP-8 (Straight-8), particularly from the R-series Flip-Chip modules. Both
models rely on these standard R-series modules as building blocks for their
diode-transistor logic, though the PDP-8/S implements a serial architecture that reduces
the overall number required. ”
You should be able to find the R series schematics on line. If not, contact me on Brendan
at McNeill dot co dot NZ and I will share my PDF’s with you. I’m out of town for the next
couple of days.
Sent from my iPhone
On 17 Aug 2025, at 16:11, Tom Hunter via cctalk
<cctalk(a)classiccmp.org> wrote:
I have recently bought a DEC PDP-8/s. It hasn't been powered on for about
40 years before I got it. I cleaned it and did some repairs on it (glued
broken flip-chip handles, replaced all front panel lights, restored the
acrylic front panel to as new condition and built a new switch mode power
supply for +10V and -15V).
After testing each flip-chip individually for dead shorts on the power
rails I reassembled the flip-chips into the backplane and on power up it
shows signs of life, but has a number of problems I will have to debug and
fix.
Does anyone here have the original Engineering Drawings or good PDF scans
of the drawings?
There are reduced copies of the PDP-8/s Engineering Drawings in Appendix A
of the two PDP-8/s Maintenance Manuals on Bitsavers, but I have not been
able to find scans of the actual Engineering Drawings. Some details in the
reduced copies in Appendix A are not legible.
Thank you
Tom
18 Aug
18 Aug
10:46 a.m.
On Sun, Aug 17, 2025 at 12:51 AM Tom Hunter via cctalk
<cctalk(a)classiccmp.org> wrote:
I have recently bought a DEC PDP-8/s. It hasn't
been powered on for about
40 years before I got it. I cleaned it and did some repairs on it (glued
broken flip-chip handles, replaced all front panel lights, restored the
acrylic front panel to as new condition and built a new switch mode power
supply for +10V and -15V).
Hi, Tom,
I'm watching this thread with interest because I've had an -8/S for
years and haven't been able to do more than superficial work on it.
I'd love to see better docs emerge.
Mine appears to act like "Panel Lock" is always on. I've checked the
switch, it's not that, so it's likely to be whatever gate the switch
tickles.
The other major issue I have is relamping. I'm curious what you used.
The -8/S uses flying wire bulbs and the leads coming out of the glass
are quite brittle. Many of my lamps have broken leads. I was going to
attempt repair of as many as possible (I'm sure most of the filaments
are still good) but I definitely need a source of bulbs for ones with
burned-out filaments and/or unrecoverable broken leads.
I have dabbled with R-series logic in the past (I have some DF32
drives) but I am pretty much a novice with testing and repair of the
older modules.
-ethan
19 Aug
19 Aug
3:10 a.m.
Hi Ethan,
Relamping is relatively easy. I changed all the lamps in my front panel.
The lamps are readily available. I bought 100 of them from Digikey for
US$65.19 part number "CM2187-ND". Here is a link:
https://www.digikey.com.au/en/products/detail/visual-communications-company…
You can get these types of lamps much cheaper directly from China via
AliExpress, but unfortunately I did not find a 28V version. You might get
away with using the 24V version on AliExpress. Likely the difference in
brightness is not too distracting. Here is a link (but there are many
others):
https://www.aliexpress.com/item/1005004900146314.html
Select 5mm, 24V and a quantity 50 x 2 (100) and be prepared to spend less
than US$5 including shipping.
I bought these too, but have not actually tried them yet.
The engineering drawings would be very helpful. I am surprised that no one
appears to have scanned them yet. There are relatively cheap camera type
scanners available which can do the large format drawings. I use a Viisan
S21 with good results. A "real" large format flat bed scanner would
obviously do a little better, but very few places have these here in
Australia.
Tom
On Tue, Aug 19, 2025 at 1:46 AM Ethan Dicks <ethan.dicks(a)gmail.com> wrote:
On Sun, Aug 17, 2025 at 12:51 AM Tom Hunter via cctalk
<cctalk(a)classiccmp.org> wrote:
I have recently bought a DEC PDP-8/s. It
hasn't been powered on for about
40 years before I got it. I cleaned it and did some repairs on it (glued
broken flip-chip handles, replaced all front panel lights, restored the
acrylic front panel to as new condition and built a new switch mode power
supply for +10V and -15V).
Hi, Tom,
I'm watching this thread with interest because I've had an -8/S for
years and haven't been able to do more than superficial work on it.
I'd love to see better docs emerge.
Mine appears to act like "Panel Lock" is always on. I've checked the
switch, it's not that, so it's likely to be whatever gate the switch
tickles.
The other major issue I have is relamping. I'm curious what you used.
The -8/S uses flying wire bulbs and the leads coming out of the glass
are quite brittle. Many of my lamps have broken leads. I was going to
attempt repair of as many as possible (I'm sure most of the filaments
are still good) but I definitely need a source of bulbs for ones with
burned-out filaments and/or unrecoverable broken leads.
I have dabbled with R-series logic in the past (I have some DF32
drives) but I am pretty much a novice with testing and repair of the
older modules.
-ethan
27
days inactive
29
days old
5 comments
4 participants
participants (4)
-
Brendan McNeill -
Ethan Dicks -
Ray Jewhurst -
Tom Hunter