Hi again, I have made another video showing the grounding of the shift register (74LS165) pins 3,4,5,6,11,12,13 and 14. I previously thought it was pin 6 that had the same alignment, but now I have my doubts. Maybe it's pin 11. All the lines generated through grounding are very noisy except pin 11. There doesn't seem to be one pin that aligns perfectly! What do you guys think? http://web.me.com/lord_philip/other_computers/20012.html By the way, these photos and videos are shot off a small 7" LCD hooked up to a Matthew D'Asaro's composite video-out board that hangs off the video pins on the PET: http://home.comcast.net/~medasaro/6540rom.com/petvideo.html Phil On May 13, 2011, at 7:10 PM, Philip Lord wrote: > Hi again, > I played around with the board a bit again today. I tested all the 2316 ROM (901447), and found half were in fact dead. Either 00's or FF's. > In the end I just burnt a complete new set to 7x2716's. I was almost certain that it would fire up, or at least clear the screen this time. Anything actually...However the results are basically the same as before. Maybe the random characters are slightly better formed for some reason, but it's hard to say. > > So pin 6 of the 74LS165 goes to D7 on the CG ROM. I looked for obvious shorts but couldn't see anything. A more intense search will be needed. > > Ethan, I just spent the last hour going through your old emails about the fix...boy there was a lot! At one point you suspected one of the six 27LS244's but in a later email you possibly changed your mind. Here is what you said about the stuck bit. > > "I got the Fluke tester on that board- it has stuck bus bits - D1-D6 > tied together. It seems likely that it's something with 8-bits > through it, not merely 4, so it's more likely to be a PIA, CIA, or a > ROM rather than a 244 buffer or the SRAM." > > Not quite sure what the 'tied together' bit means...I was hoping you could explain your thoughts further. > > Cheers again > Phil > > On May 13, 2011, at 11:09 AM, MikeS wrote: > >> >> ----- Original Message ----- From: "Philip Lord" <random6000@mac.com> >> To: <cbm-hackers@musoftware.de> >> Sent: Thursday, May 12, 2011 9:42 PM >> Subject: Re: PET 2001 fix Part 3 - RAM/ROM board etc. >> >> >>> I didn't have a 5k resistor, so I used a 2k instead!!!!! >>> I grounded all the pins (3,4,5,6,11,12,13,14) and found that pin 6 had the lease effect. If anything it just slightly solidified the lines that were already there. All other pins created new vertical lines. >>> >>> Phil >> ----- >> Well, unless you can see a short or something unusual between pin 6 of B2 and the pin it connects to on the CG, I'd try replacing B2. >> >> Looks like there are problems elsewhere though if adding RAM in the lower four sockets didn't clear the screen and give you a prompt (or a reverse blank screen if the CG is out). Sounds like this PET is going to give you a hard time just like your PET64 ;-) >> >> m >> >> ********************************************** >> >>> >>> On May 13, 2011, at 10:07 AM, Philip Lord wrote: >>> >>>> Hi, >>>> I tried the step up transformer but that didn't seem to change anything. >>>> I just tried RAM in I7, I8, J7 and J8...again, no noticeable change. I believe Ethan had checked all these ROMs as good, but I guess that didn't stop the CG ROM from going bad somewhere in transit between US and Japan. >>>> I'll try the 5k resistor trick sometime today. I'll do this with the CG ROM removed so it'll be easy to see the lines. >>>> >>>> Phil >>>> >>>> >>>> On May 13, 2011, at 9:08 AM, MikeS wrote: >>>> >>>>> Hi Philip, >>>>> >>>>> If you get that vertical line with the CG completely removed it is almost certainly a bit stuck low in B2, the 74LS165 shift register, or a short somewhere on the PCB around it. If you have a 5K or so resistor you could try shorting each of the pins (3,4,5,6,11,12,13,14) to ground through that; each one should add a line and the one that doesn't is presumably already grounded internally or externally somewhere. You may well also have another issue, but I'd start by checking for a short and/or replacing that chip. >>>>> >>>>> BTW, if you have four good spare RAM chips why not install them in I and J 7 >>>>> & 8; if your ROMs are good that's all you need. >>>>> >>>>> Good luck! >>>>> >>>>> mike >>>>> >>>>> ----- Original Message ----- From: "Philip Lord" <random6000@mac.com> >>>>> To: <cbm-hackers@musoftware.de> >>>>> Sent: Thursday, May 12, 2011 4:30 PM >>>>> Subject: Re: PET 2001 fix Part 3 - RAM/ROM board etc. >>>>> >>>>> >>>>>> Hi guys, >>>>>> It's early here (5:06am), so please excuse the brevity of my message as >>>>>> I'll be going back to bed for a couple more hours after. >>>>>> >>>>>> I did change out the video SRAM as there were a few left over from the >>>>>> main RAM that were still good. Unfortunately this did not change the >>>>>> problem. Pulling the SRAM completely created a checkerboard effect, but >>>>>> there were diagonal lines strafing through the pattern. I'll test this >>>>>> again because at the time I didn't realize this was a valid testing >>>>>> technique. >>>>>> >>>>>> Pulling the CG ROM takes the image back to its original state, blocks and >>>>>> lines. >>>>>> >>>>>> One thing, late last night as I was briefly poking around with the logic >>>>>> probe, there seemed to be many places where I probed that slightly >>>>>> effected the pixel flicker. I didn't do much testing as it seemed a little >>>>>> random and inconsistent. So maybe as Mike mentioned, it could be a power >>>>>> issue. I have the board out on my desk hooked up to an original spare US >>>>>> PET 2001 transformer. Maybe there is some issue with it being a US version >>>>>> on 100v Japanese power. I think I have a JPN to US power step up converter >>>>>> somewhere, maybe I'll try to find that. >>>>>> >>>>>> Thanks again >>>>>> >>>>>> ZZZzzz... >>>>>> >>>>>> >>>>>> On May 13, 2011, at 4:31 AM, MikeS wrote: >>>>>> >>>>>>> >>>>>>> ----- Original Message ----- From: "MikeS" <dm561@torfree.net> >>>>>>> To: <cbm-hackers@musoftware.de> >>>>>>> Sent: Thursday, May 12, 2011 3:28 PM >>>>>>> Subject: Re: PET 2001 fix Part 3 - RAM/ROM board etc. >>>>>>> >>>>>>> >>>>>>>> Looks like the problem is mostly in the fifth character column; wonder >>>>>>>> if >>>>>>>> that's where the horizontal line was originally? >>>>>>> >>>>>>> D'oh! VERTICAL line of course... >>>>>>> >>>>>>> Message was sent through the cbm-hackers mailing list >>>>>> >>>>>> >>>>>> Message was sent through the cbm-hackers mailing list >>>>> >>>>> >>>>> Message was sent through the cbm-hackers mailing list >>>> >>>> >>>> Message was sent through the cbm-hackers mailing list >>> >>> >>> Message was sent through the cbm-hackers mailing list >> >> >> Message was sent through the cbm-hackers mailing list > > > Message was sent through the cbm-hackers mailing list Message was sent through the cbm-hackers mailing listReceived on 2011-05-13 15:00:08
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