Thank you for all the suggestions. I’ll be away from the machine for couple more days but will get back to troubleshooting it when I get back. From earlier tests I believe I tested swapping the 6502 (will try that again anyway) from another machine. Now that I tried the PET, I did switch the power on and off and I did see the whole screen filled with random characters. Then it goes blank (just as it should) but then it goes to the blank screen with the single reversed ? on screen. It’s always on the same spot, and also I noticed that the random characters were identical every time. If this helps any. — Ville L. > William Levak <wlevak@SDF.ORG> kirjoitti 16.7.2016 kello 5.54: > > > > There is a diagnostic tool for the PET. It clips on the 6502 with jumpers on the user port an keyboard. It is very good at diagnosing addressing logic and memory. > > > On Wed, 13 Jul 2016, William Levak wrote: > >> >> 320351 is from a 2001N or early 4000 with 9 inch screen. Check the voltage regulators. This machine uses 4116 dynamic RAM. These early RAM were not reliable. Can you swap them around and get a different result? >> >> >> On Fri, 8 Jul 2016, Ville Laustela wrote: >> >>> Hello all. >>> I am finally returning to this project, now equpped with a brand new Hakko FR-300 desoldering gun so replacing IC’s is a now really fast and easy. >>> Since last time I have removed all the ROM’s and checked those, all Ok. >>> The two 74LS244, are those the chips UC3 and UB3, right next to the 6502? Or the UE9 and UE10? >>> Small print I had not noticed before: my board is 320351 (ftp://zimmers.net/pub/cbm/schematics/computers/pet/2001N/320351-6.gif) >>> — >>> Ville L. >>>> Check also the 74154. This is the bank select logic. >>>> William Levak <wlevak@SDF.ORG> kirjoitti 2.11.2013 kello 6.48: >>>> Since the video logic appears to be working, I would suspect the system ROMs. If you have already swapped them out, the next thing to look at would be the 2 74LS244 bus drivers for the ROMs. If you have access to a multichannel triggered oscilloscope, you can check them in circuit. Otherwise, you would have to replace them just to check the possibility. They seldom survive being unsoldered. >>>> On Fri, 1 Nov 2013, Ville Laustela wrote: >>>>> Hello all. >>>>> I posted the following thrue http://cbm-hackers.2304266.n4.nabble.com -site but that didn't seem to work (message shows on the website but apparently not in the mailing list itself) so I'll repost this now here. Sorry if this gets double-posted. >>>>> -- >>>>> I had my PET-2001 with me at SAKU (Finnish Amiga Users group) 2013 meeting some weeks ago (photos here: http://koti.kapsi.fi/~myrjola/photos/digital/saku_2013/index.php) running a small BASIC- demo I made. After being running several hours without any problems, suddenly the machine halted. >>>>> Since that all the machine gives out is a reversed ?- mark on screen (see here: https://www.dropbox.com/sh/90jl2zx2qi8lc27/uZUFNHoDJT). This appears identical in every boot. If I reset the machine (by quickly turning mains switch off and back on) I can see screen filled with random characters, then it blanks (like during normal reset) but goes to the ?-mark screen again. As you can see in the photo, most of the bigger chips have small heatsinks installed and all electrolytic caps on the board were replaced earlier. >>>>> I have tried re-seating all socketed chips but still no go. Only chips running more than warm are the two MOS MPS 2114 chips (warm to touch but not as hot as fe. shorted RAMs I replaced in a 64C once). >>>>> Any ideas how to proceed from here? I have a working CBM 8032 from where I can borrow chips for testing. >>>>> -- >>>>> Best regards, >>>>> Ville >>>>> >>>>> Message was sent through the cbm-hackers mailing list >>>> wlevak@sdf.lonestar.org >>>> SDF Public Access UNIX System - http://sdf.lonestar.org >>>> >>>> Message was sent through the cbm-hackers mailing list >>> >>> Message was sent through the cbm-hackers mailing list >> >> wlevak@sdf.lonestar.org >> SDF Public Access UNIX System - http://sdf.lonestar.org > > wlevak@sdf.lonestar.org > SDF Public Access UNIX System - http://sdf.lonestar.org Message was sent through the cbm-hackers mailing listReceived on 2016-07-19 18:00:03
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