2017-12-24 13:09 GMT+01:00 Noel Chiappa via cctalk <cctalk@classiccmp.org>:
> > From: Mattis Lind > > > Unfortunately I am not having any lutfisk this year. The rest of the > > family is not very fond of it. > > I"m glad to see there are _some_ non-crazy people there! :-) > > Anway, I can way top that - the tradition Bermudian Christmas dish is > cassava > pie: make that wrong (starting with raw cassava root), and it will _kill_ > you! :-) > > (Cassava root contains a cyanide precursor. That's what cassava root is > banned for human consumption in Japan. Somewhat ironic, the land of 'fugu' > banning it! :-) > After too much christmas food I spent some more time in the garage fixing the VT50/Vt52. The tip from Josh about the PROM socket was a good one. Replacing those together with the two ITT made 7400 chips I already replaced there were nice click sound when pressing the keys on the keyboard. Setting the terminal mode to OFF-line so that it loop-backed the serial signal gave a some kind of pattern on the video signal. But was it an OK signal or were there any more problems in the data path? Hard to tell without reassembling the entire terminal. But if the there actually are more faults in there I had to disassemble it again, fix and repeat. Instead I came up with a small circuit (well stole actually from the VT100 schematics) that generated a composite video signal from the TTL signals generated by the VT52 and feed it into an old Philips CM8533 monitor. https://drive.google.com/open?id=1nMq_N8tOcIauRmfHsVKMUJ_AUymoFiu7 Yes! All the logic seems to work just fine. So now I can quite confidently reassemble the thing and test the last step. HV generation, Horizontal deflection and CRT. Since the terminal appears to work I also dumped the firmware out of the four bipolar PROMs. http://storage.datormuseum.se/u/96935524/Datormusuem/VT52/124A9.HEX http://storage.datormuseum.se/u/96935524/Datormusuem/VT52/125A9.HEX http://storage.datormuseum.se/u/96935524/Datormusuem/VT52/126A9.HEX http://storage.datormuseum.se/u/96935524/Datormusuem/VT52/127A9.HEX @Fritz: You don't need to get a dump of the PROMs in your terminal. I think the ones I have is in pretty good shape. > > Noel > BTW. Comparing the VT52 and the HP2640 I worked on previously is like comparing a Skoda with a Mercedes or something. Single layer circuit board made of some cheap material (pertinax?) versus double sided gold plated boards. Very simple quite hardwired architecture versus generic microprocessor based design with a back plane bus. Was it just that DEC wanted to be as cheap as possible? The predecessor VT05 had four standard quad sized boards in a small backplane. /Mattis