PDP11/20 restoring

[pbirkel@gmail.com]

So I think that someone had the machine running in the past and dropped something ugly on the backplane when it was running...

I did that once (a long time ago -- 48 years I believe -- in a place far, far away) with a PDP-8/L while checking front panel bulb replacements. I was fortunate (a bit) in that the key backplane wire(s) smoked, thus giving me clear evidence of where to check for damage. I was able to scrounge replacement chips off of some junk/surplus boards from another manufacturer. I learned a lot about the circuitry in an 8/L that weekend (under great duress/stress!); thank goodness for quality DEC documentation. We had an AX08; the attached scope was quite convenient for checking signal levels.

 

[Roland Huisman]

Ups and downs... The machine was running but the DC-low circuit got fried in the H720F... Quite simple to repair. A diode and a DEC3009 transistor were broken. In these applications I just use new general purpose transistors. A while ago I also repaired a H720 and I remembered that the 3009B transistors had the pinout reversed compared to my replacement. No problem, I just placed it 180 degrees rotated.

Now a 3009B was broken again and I wanted to replace it with the same general purpose transistor. Check where CBE need to be... Hmm can't be right, now it is the same as the broken transistor. I had a spare H720 board so I checked it, and all the 3009B transistors were placed in the opisite position... :-? :!:

Now I wanted to be sure, I unsoldered a 3009B from both boards. And guess what... One is CBE and the other EBC.



So be careful when you think you are replacing a DEC transistor with an 'original' one. You might get fooled!

Regards, Roland

 

[jackrubin]

Fun! Were both marked with DEC numbers or was there any other way to identify the different types?
Measure twice, cut (solder) once!

 

[Roland Huisman]

Hi Jack,

One transistor has a Motorola brand printed on it with a date code I guess (M436) and EBC pressed in the housing.
The other has TI203 printed on it. No branding or TI means Texas instruments? No pin marking on the housing.
Both transistors have 3009B printed on it.

Regards, Roland

 

[Roland Huisman]

I have some other DEC Galway Ireland machines and now I see that the 11/20 were made in Galway Ireland as well... Does anyone know a bit more about the Galway factory? I'm very curious about what they actually did there. Did they make the boards and backplanes as well? Or was it just assembling with parts produced in the US?




Edit: There is even a website for the former Galway employees...

 

[Roland Huisman]

Finally a little demo with a tape drive :D That TC11 was a tough one to get back online...

 

[m_thompson]

That is the first TU56H that I have seen.

 

[Hunta]

That is the first TU56H that I have seen.

at work. Me too

 

[gnupublic]

Is the TC11 the counterpart to the TC08 for PDP8? Are you able to format tapes with it?
This is the only thing I'm still not able to do with my TC08.

Volker

(offtopic: one other video with TU56H: https://www.youtube.com/watch?v=LaX0po5hBJk )

 

[Roland Huisman]

I think the TC08 should be capable of formatting tapes too. Even the M868 is capable of formatting DECtapes. For the TC11 there is a special paper tape program to format tapes. You have to set switches on the front of the controller. Maybe there is a special paper tape program for the TC08 as well. Never had one, so never searched for that...

Edit: according the TC08 manual the DEC-08-EUFA-D paper tape should do the trick.
Vince has a newer version of it. dec-08-eufb-pb
https://so-much-stuff.com/pdp8/tapes/dec.html

 

[bqt]

Is the TC11 the counterpart to the TC08 for PDP8? Are you able to format tapes with it?
This is the only thing I'm still not able to do with my TC08.

Volker

(offtopic: one other video with TU56H: https://www.youtube.com/watch?v=LaX0po5hBJk )

The TC08 can format DECtapes. But if I remember right, there is a switch on the controller that needs to be set to enable formatting. And then OS/8 should have TCFRMT.SV (if I remember the name right), which does the work. I think it even tells you when to flip the switch.
Check the documentation.

 

[gnupublic]

The switch is the WTM switch (write time marks). It is used for the first pass of 4 passes that are done for formating a DECtape. At the end of pass 1 you have to witch it off again.
The program is either from papertape or OS/8. (There is also a absolut similar tool for usage with TD8E.)
My TC08 stopps the tape near the middle of pass1 and throws an error. This is the problem I have to find since about more than one year....

And Roland gets his machine ready in just some weeks! Congrats!

Volker

 

[Roland Huisman]

I've got a little present from a forum member. A MM11F memory backplane and a core stack which is damaged unfortunately. So I hope someone can help me to get the backplane complete again. I think it would be awesome to have one original memory module in this machine. So it would be great if anyone can help me to get it complete again.

But then I would need these missing boards. :

4x G102
1x G103
1x G225 (E) or G108 (FP)
4x G226
1x H207 or H210
1x M109 or M1091
1x M729 or M7290





Regards, Roland