RC2023. To restore a PC05 high speed punch reader and get my PDP11/10 booting basic on it

I have recently managed to get my PDP11/10 working and it is yearning for an I/O device

My challenge involves a number of parts
1. restore/repair a DEC PC05 high speed punch reader (The big bit)
2. Create absolute loader and PDP11/Basic paper tapes
3. Make an alternative detector to replace the broken PC05 reader array.
4. Install the M7812 interface card and possibly get it all into a rack
5. Boot write and save programs utilising the high speed punch/reader
6. If time permits I will try to get my VT55 working as the console.

I will be posting here as well as some of the videos on my restoration FB page.



This stage is just the preparation work. The repair and restoration will start tomorrow :slight_smile:

Finally I have been getting into the hardware. Cleaning the chassis and refurbishing the punch is up first.

Apology: It would seem that I can post my facebook videos but when I try to post the link for a set of photos from facebook it just puts up the header for my FB restoration page. This is annoying for me as well as for others I suspect.

I can’t turn back now sorry. lots of duplication so that it is up here in the forum.

With the front panel removed you can see the reader mechanism and switch block. The reader will be serviced later

With the punch removed it can be serviced. This will be shown in detail in the next video

One of the most important parts of the punch are these components. The die block, the punch pins and the one on the left which is the anvil for want of a better word. The anvil surface is finely ground and very precise so that clean holes are punched. In the case of mine it was a little rusty but came up well after honing the surface with an extremely fine oil stone.

The switch block had to be removed and the switch tops also removed so that I could straighten all of the metal parts. This punch must have been dropped or hit hard enough to bend them.

Here it is looking a lot cleaner but not yet ready for testing
The paper output guide was too rusty so it was wire brushed, sanded and resprayed. It will be the first of many.

This is the refurbished punch ready to go in. Watch the next video to see what was done.

The punch is installed but there’s more work before testing.

With the punch mounting plate flipped out you can see the drive motor and phase shift capacitor for it. It is important to note that this capacitor may have PCBs (Poly Chlorinated Biphenyl) oil inside it. PCB is a known carcinogen. If there is any evidence of leaking you should take great care in cleanup and replacement of the capacitor. Mine is clean and not leaking 🙂

That looks so much nicer.

The Chassis came up looking good despite the anodising being eroded in places.

Under the punch mounting plate hides this board which the logic board signals to turn the punch motor off and on. A low voltage side has a transistor driving a reed relay which provides electrical isolation. the reed switch operates a Triac to switch the 110V AC line. Watch out the power for this diverts through the front panel switch board even if there is no punch switch present


I have a PC09 to repair. Nearly identical to the reader/punch you have. The reader works OK, but the punch does not. I found that the pulse coil that makes the Punch Sync signal was open. I bought replacement magnet wire and will rewind the coil.

I am hoping that all the coils are ok and am proceeding with the rust removal and freeing up the parts that are seized due to the hardennd grease. Fingers crossed :slight_smile:

This sequence of short videos covers partial disassembly, repair and reassembly of the High speed punch mechanism. The work mostly covers unseizing gummed up parts, rust removal and honing various parts.

Here’s the final short video relating to the PC05 Paper Tape Punch. Very soon I will be moving to the reader and electronics restoration and repair.

The third video shows the yellow tape wrapped coil next to the counterbalance that I need to rewind.

Have you looked to see if the breakage is between the interconnect cable and the magnet wire? Sometimes unwrapping and removing the first layer reveals a repairable coil. Good luck with it.

The solder joint problem was unfortunately at the very inside of the coil. I had to unwind the whole coil to find it.

1 Like

My RetroChallenge 2023: General tidy up and reader repairs
The next set of videos will be on repairs and finally getting the paper tape reader up and running.This is the bit I have really wanting to get into.

My RetroChallenge 2023: General tidy up and reader repairs part 2

So… The reason my posting of this video didn’t work was that the AI that sanitised it interpreted my phrase "More Mucking around"as offensive language. My emphasis on the syllables was obviously misplaced. All fixed now :slight_smile:

My RetroChallenge 2023 is coming along nicely with some positive results with a homebrew collumated lightsource working well with the replacement detector array that utilises the BPW-17 photo trtansistor.

The light source is a little crazy as I found a bunch of red LEDs that ware designed to feed a light tube. They have a very small domed lens and a collar to hold the tube. I went full hack and linished them down so that they could be mounted at a one tenth inch spacing with one for every detector (9).

My homebrew light source:

The original reader array is shown here removed and the BPW17 replacements soldered in:

This little tool has been valuable in the making of test loops. The paper guide in the PC05 according to the service manual should be shimmed using three pieces of paper tape. This is to ensure that a splice will not bind when going through the reader

In this video you can see the CRO attached to a test point which summs all of the signals from the BPW-17 photo transistors. This allows for alignment of the detector, light source and the resting alignment of the energised stepper motor.

The idea is to have all of the data lines trigger as close to the same time as possible with the sprocket hole firing a minimum of 0.1 milliseconds later.

1 Like

My RetroChallenge 2023: Finally I have some success with the device interfaced to the PDP11.

1 Like

That is really spectacular repair work!


My RetroChallenge 2023: This video is a little out of order. It is an interesting little bug and my cleaning solution regarding the printed circuit boards is a little unique.

Sometimes very old ICs have been in such a bad environment that the tin plating on the legs have lifted and the steel pins rust beneath the plating. In some cases I have seen the legs corrode to the point of detaching from the IC.

Watch this to find out about the phantom sticky tape

My RetroChallenge 2023: I have finally proved the Punch, Reader and Interface.

In the next clip I will try booting the paper tape basic and load a basic program as well.

Hi all,

I apologize for any dissatisfaction with my posts. apparently non FB users can’t see my videos. I can’t see any way through at this stage


My Retrochallenge 2023: The final throws. This set of short videos covers the configuration of a period correct terminal and the struggle of actually using the system in an end to end cold start and loading of a basic program via the repaired/refurbished PC05 high speed punch/reader.

I apologise for non FB users, I genuinely thought that the videos would be visible to all. With any slack time I have available I may get them all onto youtube and edit all of the links but I am uncertain if I can fit it in.

Part 4 is missing as I have encountered either a rendering fault or a corrupt video but I think there is enough to have it all make sense.


These are the headers to the paper tapes I generated which were needed to complete the task

This is the printout of the binary loader read in through the ASR33 paper tape reader. This is only possible with the M9301 board installed as it has the console emulator as well as the unibus terminator. The line at the bottom “L 77744” loads the program counter and runs when the “S” command is issued. At this point the absolute loader is read in on the high speed paper tape reader.

In order for this to be possible there needs to be no line feed characters and at least four nul characters after each carriage return. That’s because In this configuration I actually have a carriage with inertia :slight_smile:

Here you can see the sign-on options “Verbose Mode”. The old command immediately loads the basic program via the high speed reader. You may notice some typos. They are not typos but sticky code bars in the ASR33 as it has been static for about 6 months and needs lube and excercise

hmm Once again something has sanitised my final video. The one that actually matters DOH!!! I will look into it

Last time I had this the AI thought my word mucking was inappropriate. This time I can’t find the word causing my video to be sanitised :frowning:
The offending HTTP states this (data-unsanitized-src="https://video-lax3-1.xx.fbcdn.net/v/t42.1790-2…)

I am well dissppointed. :frowning: