Logbook for pdp8.de

Logbook showing problems, defects, errors, and solutions. Maybe you're problem is allready solved - or at least described herein.
Last entry
  Date Description  
2003/01/05 Moving the pdp8/m and the TU56H but not the 19" Rack, RK05, Plotter, printer, and the Teletype to Berlin.
2003/01/07 First powerup, after 10 years.
Serial interface defective.
While hunting down the bug, step by step the machine dies.
At last the program counter doesn't count any more, also bit 9 of MD is 1 most of the time.
  Incrementing the PC doesn't work, because CAR_IN_L signal is failing.
=> chip E3 of module M8310 (DEC 8881) is defective and has to be replaced.
  Time consuming purchase of spare parts.
Neither DEC8881 nor standard TTL SN7401 or SN7438 (not pincompatible!) are still in production.
2003/03/06 DEC 8881 stolen from a pdp11 modul M795 to repair M8310. PC happily counts again.
  Error symptom on 1. G111 module:
Read access always yields in 0000.
Cause:
No Strobe signal
=> chip E8 of module G111 (SN74H11) was defective and replaced by a new SN74F11.
2003/03/11 Error symptom on 2. G111 modul:
Bit 9 stays at 1 level.
Cause:
Most probably the inhibit driver. Bug hunt stopped cause other G111 module works.
Wrong assumption. Inhibit driver was OK.
But transformer T10 had a bad soldering point (from a repair years ago), now after 15-20 years leading to failure.
After resoldering the 2. G111 module works again.
2003/03/14 Error symptom M8650 YA (modified for 9600 Baud):
No output, no input.
=> chip E21 of module M8650YA (SN7404) was defective and replaced.
Despite repair module does not correspond to input correctly.
2003/03/22 Error symptom M8650 und M8650 YA:
Input doesn't make its way to the AC (AC always reads 0000).
=> chip E17 of module M8330 (DEC 8881) was defective and replaced by another victim out of modul M795.
Both serial interfaces now work bidirectional.
2003/03/23 Powerup of DECtape TU56H drive.
Start of OS/8 from DECtape.
Unfortunately M8650 YA disturbs the DECtape action.
No problems with modul M8650.
=> Next debugging session for M8650 YA.
2003/03/26 Error symptom M8650 YA:
Serial interface responds to non IOT commands.
=> chip E14 of modul M8650YA (DEC5314 = SP314) is defective.
Searching for replacement!!!
2003/04/06 E14 provisional fix through the aid of a SP380 Piggybag.
2003/04/21 RK05, Teletype ASR33, Teleprint390 and transformer 220V -> 110V for CalComp Plotter moved to Berlin.
2003/04/25 Powerup of Teleprint390 resulted in short flicker of the lamps and blown fuses.
4 capacitors had shorts => 2 diods and 2 tracks on a pcb were blown.
2003/05/02 Replaced capacitors, diodes, and pcb tracks of the Teleprint390. Motor works.
Local works, papertape punch and reader also work.
Only linefeed just works once in a while.
2003/05/17 "Carving" of buffers for the print hammer (using an old rubber).
Seems to work fine.
2003/05/18 Reconfiguring serial interface M8650 Rev. D back to 110 baud, 2 stop bits.
Test of Teleprint390 with pdp8/m.
Works fine, but still problems with linefeed.
2003/05/30
2003/06/01
Reverse engineering of the schematic of the printer interface (for Logabax LX180) of unknown origin. This printer interface is 8 bits wide in contrast to the better known modules M841 and M8365 (LA180).
2003/06/16 Orginal rack (Cabinet H960-BC) fetched by freight company.
2003/06/23 Cabinet H960-BC arrived in Berlin and was cleaned and loaded on 2003/06/29.
2003/08/13
2003/08/20
Cleaning of RK05. Trying to get it to work with Plessey controller. Disk spins up and can be set to write protect per program. Plessey controller nevertheless always states BUSY.
Looks like Plessey controller is defective.
2003/08/27
2003/09/18
Development of a "plugin" to simulate a TD8E controller and a TU56 dual drive unit.
Simulator works with files in OS/8 format, like the ones David Gesswein has on his www.pdp8.net Web-Site ready for download.
2003/10/02
2003/10/06
Development of a low level variant of the simulator plugin above. With this version it is possible to format a virtual tape and it is not restricted to the OS/8 block format. It should also pass the DECtape diagnostics (not tested yet).
Unfortunately the file format is not compatible.
Therefore this version will not be available for download untill it is merged with the previous version..
2003/11/07 Reverse engineering of Plessey RK8E clone finished.
Modified the DEC schematics to show the differences to the original RK8E. For the schematics look at download area .
2003/11/14 Got another Teletype ASR33.
Thanks to Mr. Viets.
2003/11/24 New version of simulator finaly merged with the old one.
The new version also has a graphical front end.
2003/11/27 64 bit version of simulator for Solaris 9 on Sparc
2003/12/04 64 bit version of simulator for HPUX 11 on PA-Risc
2004/01/17 Linefeed problem of Teleprint 390 solved by removing,
cleaning, lubricating, and reinserting the linefeed function pawl.
2004/01/19
2004/02/08
Started to merge the two defective ASR33 into one working unit.
One unit has a broken carriage mounting screw.
The other one is untested and has at least a broken case.

Decided to repair both and now - both work.

2004/02/06 Designed and build a simple RS232 to 20 mA converter to use the Teletypes with a PC.
2004/03/10 Preparations for VCFe 5.0 running at full load.
Then suddenly the Plessey 8K memory and the power control unit 861B failed.
2004/03/14 After the setbacks of the last days finally some good news:
Got my M8650YA back to working condition (tested up to 9600 Bd) due to a donation (SP314) of David Gesswein.
Outage of the power control unit was caused by a defective capacitor in the 24 V auxiliary supply.
Replacing it and doing some minor works on the reed relay brought the power control back to working condition.
The failure of the Plessey memory module seemed to be contact problems. After cleaning the contacts it works again.

Critical milestone for VCFe 5.0 now achieved:
For the first time I was able to transfer a tapeimage (build on the simulator) to a real DECtape and to boot the pdp8/m from it.

With this image I also was able to successfully test the CalComp plotter and the XY8E (M842) interface.

2004/04/06 Visiting the "Computermuseum der Fakultät Informatik" of the Universität Stuttgart.
Very impressive demonstration of the only LGP-30 known to be in working condition (compare 'Mel the Programmer').
2004/04/13 Moved my vt100 terminal, the matrix printer Logabax LX180 and the IBM MagCard Selectric (MC72) to Berlin.
2004/04/15 vt100 works without a problem. LX180 and MC72 must wait in the cellar.
2004/04/30
2004/05/02
Exhibited my pdp8/m on the VCFe 5.0 am 1./2. Mai 2004 in München .
A lovely event, in combination with seminars and the excursion to the Gesellschaft für historische Rechenanlagen was very impressive.
Next year I will be there again, but with a lighter exhibition.
2004/05/03 System racked again.
2004/05/05
2004/05/14
On the VCFE I got some hints from Gerd Schünemann and started debugging the RK8E again.

SUCCESS!!! OS/8 booted from the RK05 at 2004/05/14 for the first time after more than a decade.

A defective 7410 caused ERROR_CLR_L to be always active, thus fixing the state machine to the IDLE state.

While debugging the RK8E the vt100 dies with ROM 2 error.

2004/05/14 Reverse engineering of the Plessey RK8E clone updated.
2005/02/12 vt100 still dead, M8650 YA dead again.This time defective parts are level converters MC1488 (E32), MC1489 (E17) and a 7474 (E29) flipflop.
2005/02/17 Got exciting email, two pdp8/e racks available including three RK05 and a TU56M with TC08 controller.
2005/02/17
2005/03/28
Preparing to get the two new racks. Date for truck and crew is cleared. I will get them at 2005/03/29.
2005/03/29 Moving the two new machines from "Wüllenweber" Highschool of Bergneustadt to Berlin.
It's time to thank all the helpers (Marcus Bilatscheck, Frank Borowski, Dennis Hahmann, Gunnar Heiden, Ronald Kopfer, Thomas Neuber, Guido Roock, Stefan Rupp, Kai Sotong) for carrying the machines up to the fourth floor.
My special thanks go to Mr. Walter Pohl of Wüllenweber High for giving me the chance to aquire these machines.
2005/03/30 First dive through my "treasures" -I'm happy like a child in a candy store :-)))
There is everything: dozens of interfaces, complete docs (even for the plessey ones), cables, test extenders, spare parts, Media (floppies, tapes, decpacks).
Simply dreamy!!!
2005/03/31 Cleaning pieces, filling racks.
2005/04/01 Start of restauration - Light bulbs for pdp8/e.
2005/04/02 Replaced defective light bulbs in TC08 panel.
2005/04/04 First tests 1 CPU, TC08, 1 of 2 TU56, 2 of 3 RK05J are OK..
2005/04/05 RX01 dual floppy moved to my pdp8/m rack, because of empty space.
Now the pdp8/m can be used as copystation between DECTape, RX01 Floppy and DECPack.
2005/04/06
2005/04/08
CPU and one 8KW memory module of "homebrew" pdp8 are defective. Errors localized on M8300 and G111.
Faulty component on M8300 replaced. A DEC 8881 (E2) was defective. The CPU now seams to work.
2005/04/09 The demotape I created for the VCFe 5.0 got device handlers for TD8E, RK8E and RX8E.
So it can be used to copy between tape, floppy and decpack.
2005/04/09 Defective componemt on G111 was a SN7474 (E4). After replacing all three pdp8s now have 32 KWords Memory.
Connected both new working RK05Js (2 and 3) with BC11 cable.
A test with "Homebrew" pdp8/e fails while single RK05J works with "original" pdp8/e.
After swapping drives and CPU moduls it shows, that the M8310 module of the "Homebrew" pdp8/e is the faulty part.
Bootstrap works but after that this module shows strange behavior.
2005/04/11 Start to check contents of floppies:
Pascal Compiler,
Fortran Compiler,
MACREL, LINK,
OS/8, OS78, RTS8,
Games, ...
2005/04/12 Start to update german part of website, first preparations for VCFe 6.0 VCFe 6.0 am 30. April / 1.. Mai 2005 in München VCFe 6.0 at 30-April 2005 / 01-May 2005 in Munich.
2005/04/17 DECTape TU56H gives in, tape only moves in forward direction. Replaced 7400 on BC05 - it's OK again..
2005/04/18
2005/04/19
Floppies and DecPacks saved to PC. Many read errors on some DecPacks.
2005/04/20
2005/04/23
TU56 defective bipolar motor run cap replaced by two antiparallel connected electrolytic caps. Now both drives of the new TU56 work.
2005/04/24
2005/04/29
Booting from TC08/TU56 only works with one combination of the new M8300/8310 CPU boards. OK M8310 of "Homebrew" pdp8/e is still defective.
Created Pascal and Basic Floppies for VCFe 6.0.
2005/04/30
2005/05/01
VCFe6.0 stil a very interesting event. Seeing known faces, even reckognized some visitors. Gerd Schünemann showed his pdp8/L and his pdp8/s. Met Tore Bekkedal from Norway and even the german TV (ZDF) send some pictures of my pdp8/m.
2005/05/02
2005/05/10
Show items moved into the racks again.
2005/05/10
2005/05/13
A closer inspection of the "smart" dual serial interface modul from MICO revealed bipolar PROMs for the OMNIBUS interface, a Z80 CPU, two PIOs, two SIOs and a CTC.
2005/05/15
2005/05/17
Revived he M8650 replica (soldered with a hammer). There was a defective 7474 (E29).
2005/05/23
2005/05/28
Debugged the "Homebrew" M8310. Maindec PDP8/E Instruction Test 2 revealed the error. After GTF link was always cleared. Looping on IOT test 9 helped to find the defective 7400 (E42). the defect used to clock the link register much to often.
2005/05/26 A gift from Gerd Schünemann improved the printing quality of my Geveke ASR33. At the VCFe6.0 he gave me an replacement for the brocken stud on my print carriage. Many thanks for that.
Now I only have to get rid of the linefeed problem.
2005/11/16
2005/12/12
Manfred Reich informed me about a pdp8 clone made in the GDR.
According to Mr. Reich the "Kleinsteuerrechner" KSR 4100 was used by Carl Zeiss Jena for the Zeiss scanning electron microscope ZRM12 and tthe Zeiss exposure unit ZBA10.
Thanks for this interesting Information.
2005/11/26 Got another package from Mr. Pohl. It was full with cables and front panels. Again many thanks.
2005/12/18 Finally added some pictures about the new systems and from the VCFe.
2005/12/23 To my surprise Remo Vogelsang gave me the great honour to send me a few SP380, SP384, SP314 and DEC8881s. Many, many thanks. I am very proud that one of the fathers of the pdp8/e/f/m got in contact with me.
to do Calibrating ASR33.
   
actual to do:
Searching paper and paper tape for teletypes and RK05 filter.
BLOG Most recent changes are recorded in the blog - only german language sorry :-(.