Date: 2006-07-06 13:07:45
Op Do, 22 juni, 2006 7:28 am schreef William Levak: > On Wed, 21 Jun 2006 email@example.com wrote: > > >> Hi, >> >> >> I've tried to find a short on the PCB but have not found it yet. >> > > What I meant was that one of the IC's is shorted internally so that when > both bits 8 an 9 are high, the chip malfunctions. This could be one of the > IC's controlling addressing logic, or one of the RAM chips, or one of > the ROM chips. > >> I got 6540 ROM's and 6550 RAM's on the board. >> >> >> ROM part numbers (I hope this is the number below the MPS6540): >> >> >> H1 = O19 5078 A >> H2 = 013 4478 A >> H3 = 015 2878 A >> H4 = 016 4478 A >> H5 = 012 2978 A >> H6 = 014 4178 A >> H7 = 018 4378 A >> >> >> A2 = 010 2678 A >> > > This is Basic 1 with the revised $C000-CFFF ROM. This version has a > built-in diagnostic. You put a diagnostic connector on the user port and > on the keyboard connector and disconnect anything on the cassette ports. > You then turn on the computer and it runs the diagnostic and displays the > result on the screen. It usually displays at the top of the screen, so > you should be able to run it. When it finishes successfully, it turns on > the red LED on the system board. > > User port diagnostic connector: > (Looking from the back of the computer and numbering from left to right) > > > Connect top 2 to bottom 2 > top 3 to bottom 3 top 4 to bottom 4 top 5 to bottom 5 to top 11 top 6 to top > 7 to top 8 > top 9 to bottom 9 top 10 to bottom 10 > > Keyboard diagnostic connector: > (Numbering from one end to the other with the key at 19) > connect 1 to 9 to 17 2 to 10 to 18 > 3 to 11 > 4 to 12 > 5 to 13 > 6 to 14 > 7 to 15 > 8 to 16 > > > > firstname.lastname@example.org SDF Public Access UNIX System - > http://sdf.lonestar.org > > > Message was sent through the cbm-hackers mailing list > > Hi all, I made some progress on my 2001. After hours of trying to understand the workings of the video system and checking almost every pin with my oscilliscope I found a wierd signal. There was a (digital signal) that had three levels GND, 2,5 Volts and 5 Volts. This was the vertical sync signal. I disconnected all the pins on the IC's in this signal and connected them with wires so it didn't use the PCB. And yes video is restored. Now I'm gonna search for the short. Results on my page: http://www.xs4all.nl/~lagendr/Diverse/PET2001.htm Greetings Richard Message was sent through the cbm-hackers mailing list
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