• Please review our updated Terms and Rules here

What did I do to my PDP-8 today.

vrs42

Veteran Member
Joined
Nov 24, 2009
Messages
655
Location
Beaverton, Oregon
Sintered nylon parts are definitely very porous and prone to picking up all sorts of grime. I've had some luck soaking them in "floor finish" to create a finish that is less absorbent and easier to keep clean.

Now, if JLPCB would just fix their input filters to take all correct STL files...

Vince
 

gwiley

Experienced Member
Joined
Nov 12, 2021
Messages
115
Location
San Diego, CA, USA
Thanks for being pioneers on this trail - what did the parts cost?
The switch handles were only about $1.10 each on the two orders. The price differed by only a few cents. First order was for qty 10, second order was qty 21. Shipping from China varies a lot depending on how quickly you want the parts. I've seen it range from about 30% of the part cost for slow shipping to over 200% of parts cost for the fastest. It's still pretty inexpensive either way.
 

gwiley

Experienced Member
Joined
Nov 12, 2021
Messages
115
Location
San Diego, CA, USA
Sintered nylon parts are definitely very porous and prone to picking up all sorts of grime. I've had some luck soaking them in "floor finish" to create a finish that is less absorbent and easier to keep clean.
That's a clever ideal, I'll have to try it. Any brand or type in particular that you prefer?


Now, if JLPCB would just fix their input filters to take all correct STL files...
haha, yes! Fortunately, in one case anyway (DEC PCB handle), the correct STL file can be loaded into Microsoft 3D builder and written out again which appears then be correct in JLC's eyes.
 

DDS

Veteran Member
Joined
Sep 5, 2013
Messages
588
I'm not that familiar with the Ender 5. I have the Ender 3 Pro. I concur with what you're saying up to a point. Where I have been able to make my own decisions on dimensions, the parts I have printed in PLA have had adequate strength. Where I have had issues are with fine details like the pivot pins on your switch handles, or the "spear" locating pins on a Kryoflux enclosure that broke off while still being printed. Where you're constrained to the dimensions of a previously injection molded part, you need to go to a higher strength plastic, which as it happens, require higher bed and hot end temperatures, which the stock Enders just won't do. And while you can modify an Ender to print nylon, the initial price plus the cost of the mods put you up where the more advanced printers are priced.


P.S. Be advised that Nylon is very hygroscopic. So Nylon filament needs to be stored in very low humidity like in a "dry box." Longer print times might even require the filament be fed from a humidity controlled enclosure. Add the cost of the humidity controls to the price of the printer and pretty soon you're at the point where farming out the occasional Nylon print makes more and more sense.
 
Last edited:

DougIngraham

Experienced Member
Joined
Oct 2, 2019
Messages
464
Location
Rapid City, SD USA
Those parts look pretty good.

Tinkering with 3D printers is a hobby separate from 3D printing. I have not seen a cheap 3D printer out of the box that can make usable parts. My Creality CR-10 is a case in point. It is now a pretty good printer but with the upgrades it is now approaching $1000. I scratch built a Core XY which is quite good and can do about a 450mm cube but I have never needed that. It cost me about $1200.

For the PDP-8 paddles I would just fix them by using the drill guide I provided with a drill press and using acrylic rods for the pins rather than trying to print them. If you don't have all the paddles then you probably should print a whole set in colors that are close. The pins are fragile and really probably should be to avoid damage in an accident to the metal parts of the switches which are much more difficult to repair.
 

vrs42

Veteran Member
Joined
Nov 24, 2009
Messages
655
Location
Beaverton, Oregon
That's a clever ideal, I'll have to try it. Any brand or type in particular that you prefer?
Not really. The container I have is "Holloway House Quick Shine", but I suspect any mop-n=glo type product would do. Basically the idea is to get an acrylic polymer dilute enough to soak in, then dry onto all the nooks and crannies. It's also important not to use stuff (solvents) that would react with the nylon. I don't remember where I got the idea, but it was probably reading about 3D printing somewhere.

Is that tire wiping product similar? I haven't looked.

Vince
 

DougIngraham

Experienced Member
Joined
Oct 2, 2019
Messages
464
Location
Rapid City, SD USA
In the 3D printing universe, dipping prints into polyacrylic lacquer has become popular. I believe the approach is to hit the surface with sandpaper (400 grit), remove the dust and then dip. The sandpaper keys the surface. Those Nylon prints look like they might be porous which means it might be better to use a different material. My first thought would be to mix up a small batch of a thin very slow cure epoxy, something like West Systems using the clear hardener. Immerse the parts to be coated in the epoxy. Place the container with the immersed parts in a vacuum chamber and pump it down until all the air has come out of the parts. The epoxy will boil vigorously so use a tall container so it does not boil over. When the vacuum is released the epoxy will be forced into the voids in the part. Remove the parts and let the excess epoxy drain off. Wait the 24 hours for it to cure and you should have a good surface that will accept coatings (paint). I have tried coloring the epoxy but by the time you have added enough pigment to the resin it no longer behaves the way you want.

I have not done this to 3D prints yet but I have used this as a form of pressure treatment with wood. The epoxy has a harder surface than Nylon and will not allow water or grease to be absorbed.
 

vrs42

Veteran Member
Joined
Nov 24, 2009
Messages
655
Location
Beaverton, Oregon
View attachment 1244752
I've been trying to set up an HP1630G to look at the Omnibus. There's a fancy new memory/boot loader under there with a serial port implementation (the Atmel programmer's ribbon cable goes there). Boot and memory work fine, but not so much the serial port.

Alas, I'm out of pods on the analyzer, so I'll have to remap the pins to use every single available input. I also need to add a proper clock, so that the analyzer will actually take the samples at reasonable intervals. (Probably means a chip needs to be added to the protoype board to OR the TPn signals.)

Vince
I finally made some progress with this. After re-doing the LA setup a few times, I got output that was somewhat helpful. The system wasn't coming up properly, and I eventually determined that OS/8 wasn't getting loaded from SerialDisk correctly. (It isn't trying to load from the board I'm debugging, at least yet.) That suggested my board was writing DATA at an inappropriate moment, though I hadn't caught it doing so.

I found a bug where I was using the wrong polarity for PAUSE, so that I was writing DATA if the opcode was x11x, but *wasn't* an IOT. Fixing that causes the board to be properly passive when it isn't being addressed.

Vince
 

DougIngraham

Experienced Member
Joined
Oct 2, 2019
Messages
464
Location
Rapid City, SD USA
I am in Oregon for a couple of weeks and managed to drop by Vince's place. We spent part of the day getting one of his 8/a's running and I was able to demonstrate Console Serial Disk at 9600 baud through the M8316 Option 2 serial port.
 

thunter0512

Experienced Member
Joined
Sep 27, 2020
Messages
423
Location
Perth in Western Australia
Some time ago I bought a VR14L with extreme screen cataracts.

The VR14L appears to have come from a GT40 setup as on the back of the VR14L there is also a GT40 tag.
Unfortunately I don't have the associated PDP-11/05.

The leaking corrosive PVA glue oozing out between the CRT and the protective front glass had caused a lot collateral damage.
I managed to remove the protective glass, clean up the mess and reattach the glass to the CRT.

Other restorations intervened so I left the cleaned up, but fully disassembled VR14L in one corner of my lab.

Recently I slowly reassembled the VR14L and started a step-by-step checkout of the subsystems.
Power-supply and high-voltage supply all checked out fine.

Then I turned my attention to the two A225-YB Deflection Amplifiers.
Without any input one of the A225 drives the output transistors hard causing the VR14L to blow fuses.
The second A225 worked just fine.
I checked the component values near the output and noticed that some resistors were well above their tolerances. The 47 Ohm resistors R23, R25 and R28 are 59, 56 and 57 Ohm. The transistors Q3 and Q4 measured very similar to those on the good A225. Interestingly the bad board uses BD237/BD238 for Q3/Q4 as opposed to 2N4923/2N4920 on the good board. It may be that the transistors Q3 and Q4 on the bad board have been changed sometimes in the past, but the rework is very neat and professional.

I decided to setup an "out-of-circuit" test bed for the A225 using two current limited power supplies for the +/-21V and a signal generator for input to avoid frying the expensive power transistors and/or fuses. With a scope I should be able to probe along the signal path to figure out what is happening.

As usual none of the active components (transistors and op-amps) are readily available. :-(

I have then setup a small test bed for the A225 on my work bench.
I supplied power, input and load via an edge connector (2 current limited bench supplies for +/-21V power, programmable signal generator setup for 1V P/P sine wave, 470 Ohm load resistor instead of the deflection coil and a 0.5 Ohm current probe resistor).
This made it easier to compare the working A225 with the faulty one.
I was able to probe along the path of the input signal using a scope and finally figured out that Q2 (2N2904A) was bad on the faulty board.
I did not have a 2N2904A but instead used a similar 2N3467 and now both A225 behave the same and no longer cause the 10A fuse to blow.

Next I will try to get the VR14L fully operational.
Unfortunately it has a W684 (8-level intensity) instead of the W682 (standard intensity) used in the VR14 in my LAB-8/e.
I will have to figure out how to drive a W684 from the VC8E Point-Plot-Boards.

Has anyone tried to use a VR14L with a W684 together with the VC8E Point-Plot-Boards?

A further point of confusion is the G840 Light Pen Option in the VR14L instead of the G838 Fault Protection used in the VR14 in the LAB-8/e.
Does the G840 also provide the Fault Protection implemented on the G838 or is this feature missing when you use the G840.

Finally - is there any way using the Light Pen Option with a PDP-8/e?

Tom
 

thunter0512

Experienced Member
Joined
Sep 27, 2020
Messages
423
Location
Perth in Western Australia
There is description of how we replaced the PVA with a sheet of Lexan in our PDP-12 restoration blog.
I will never ever again try hot-forming Lexan over the protective glass that was glued to the CRT with PVA.
The last time I tried this on my LAB-8/e's VR14 the Lexan adhered to the glass and cracked it as it slowly cooled in the oven.
If you are concerned about imploding CRTs in a public environment, then it is better to mount a 6 mm acrylic sheet in the front of the display.
 

thunter0512

Experienced Member
Joined
Sep 27, 2020
Messages
423
Location
Perth in Western Australia
At long last I got my second VR14 fully working. This seemed to have belonged to a GT40 graphics terminal which is made up of a PDP-11/05 "controller" and the actual VR14 display.

At the moment it is hanging off my LAB-8/e running diagnostics, but the end-plan is to populate the two VC8E "point-plot" display controller PCBs I got made in China (JLCPCB) from Gerbers some time ago. I also already got all the components from Digikey/Mouser so it is just a "bit" of labour that is left. The VC8E is made up of the M869 controller and the M885 Digital-to Analog converter PCBs.

I plan to run the new VC8E boards in my newish PDP-8/e. The Lab-8/e already had the original VC8E controller boards.

The VC8E PCBs have been redesigned using currently available components by Roland Huisman. His GIThub repository with Gerbers, schematics, parts lists etc is: https://github.com/Roland-Huisman?tab=repositories

Here are some Photos:

IMG_20221003_174907825.jpg

IMG_20221003_174711762.jpg

IMG_20221003_174858918.jpg

Tom
 
Top