djrodderz Posted March 28, 2020 Share Posted March 28, 2020 Hello! Just wondering if I could get some help... I had just sold a Vic-20 and upon the buyer booting up the system the speed seems to be too fast. Could anyone shed any light on this please? This is the Video he has sent me of my system against his existing system. Regards DSCI1836.AVI Quote Link to comment Share on other sites More sharing options...
R.Cade Posted March 29, 2020 Share Posted March 29, 2020 I don't know what would cause it, but that is really bizarre! Do you know if the VIC was modified by someone in the past? Quote Link to comment Share on other sites More sharing options...
djrodderz Posted March 29, 2020 Author Share Posted March 29, 2020 Hey thanks for the reply. I don't believe so. I will open it up and take some snaps of the board when I get it back. Quote Link to comment Share on other sites More sharing options...
carlsson Posted March 29, 2020 Share Posted March 29, 2020 Ok, so both VIC-20's are PAL units which can be identified by the mislocated screen on Avenger. I wonder if the LM555 timer has something to do here, or if it would be a matter of a partly broken 6522 VIA where the timers don't work properly. Quote Link to comment Share on other sites More sharing options...
djrodderz Posted March 30, 2020 Author Share Posted March 30, 2020 Thank you for your reply. could that be cured with a change of the chip? Quote Link to comment Share on other sites More sharing options...
carlsson Posted March 30, 2020 Share Posted March 30, 2020 The VIC-20 has two identical 6522 chips that serve different purposes: https://vic-20.appspot.com/docs/viausage.txt Often but not always those chips are socketed so easy to replace one if it is bad. In theory you can swap the chips, which would cause other things to stop working, in this case I would think tape would stop working. Of course the question is how those timers are loaded, if it is due to other components or perhaps a corrupted ROM. Would the computer start up normally without a game cartridge, but with a very fast cursor? Quote Link to comment Share on other sites More sharing options...
djrodderz Posted April 1, 2020 Author Share Posted April 1, 2020 On 3/30/2020 at 5:55 PM, carlsson said: The VIC-20 has two identical 6522 chips that serve different purposes: https://vic-20.appspot.com/docs/viausage.txt Often but not always those chips are socketed so easy to replace one if it is bad. In theory you can swap the chips, which would cause other things to stop working, in this case I would think tape would stop working. Of course the question is how those timers are loaded, if it is due to other components or perhaps a corrupted ROM. Would the computer start up normally without a game cartridge, but with a very fast cursor? Ill boot it up again when I get it back and check. Thank you. I’ll update then Quote Link to comment Share on other sites More sharing options...
djrodderz Posted April 1, 2020 Author Share Posted April 1, 2020 (edited) https://www.ebay.co.uk/itm/362441076581 Would this suffice? Edited April 1, 2020 by djrodderz Quote Link to comment Share on other sites More sharing options...
carlsson Posted April 1, 2020 Share Posted April 1, 2020 As far as I can tell: yes, that Rockwell 6522 should work, assuming the fault really is one of the VIA chips. I could be wrong of course, but those chips are easy to short circuit and cause partial faults so not impossible that something happened. Quote Link to comment Share on other sites More sharing options...
djrodderz Posted April 11, 2020 Author Share Posted April 11, 2020 https://imgur.com/sOVhMTM Quote Link to comment Share on other sites More sharing options...
djrodderz Posted April 11, 2020 Author Share Posted April 11, 2020 I’ve opened her up. Seems the chip is in the top left but I can only find the one. Quote Link to comment Share on other sites More sharing options...
carlsson Posted April 12, 2020 Share Posted April 12, 2020 Both 6522 are located next to eachother in the upper left corner. I can't determine what is printed on the current chips but they should be equivalent. Quote Link to comment Share on other sites More sharing options...
djrodderz Posted April 13, 2020 Author Share Posted April 13, 2020 https://m.imgur.com/a/lCDf9ww Quote Link to comment Share on other sites More sharing options...
carlsson Posted April 13, 2020 Share Posted April 13, 2020 (edited) Motorola ZC86068P? I understand that the Motorola MC6820/6821 may be similar to a 6520 PIA, but out of the search results I can find online, I don't see any that mentions a Motorola chip that is equivalent to the MOS/Rockwell/Synertek 6522 chips. (*) The leftmost chip is UAB1 (Keyboard-Serial), also known as VIA #2 which I believe is the chip to exchange. The one right to it (yours named ZC86068P) goes into UAB3 (Serial-Joy-User-Cass), also known as VIA #1. How does the computer behave when you boot it without a cartridge? Does it behave as expected, but the cursor blinks very fast? Does the keyboard read correctly? Did you have a chance trying to load something from a disk drive? From tape? (*) As a side note, it recently was posted by a Commodore alumni on Facebook that pretty much all second sourced chips - at least in the beginning - were manufactured by MOS but sent to Rockwell and Synertek to put their logotypes on them to satisfy the requirement of second sourcing CPUs and support chips. Possibly they went on to actually manufacture their chips a bit later on. Edited April 13, 2020 by carlsson 1 Quote Link to comment Share on other sites More sharing options...
djrodderz Posted April 23, 2020 Author Share Posted April 23, 2020 On 4/13/2020 at 10:28 PM, carlsson said: Motorola ZC86068P? I understand that the Motorola MC6820/6821 may be similar to a 6520 PIA, but out of the search results I can find online, I don't see any that mentions a Motorola chip that is equivalent to the MOS/Rockwell/Synertek 6522 chips. (*) The leftmost chip is UAB1 (Keyboard-Serial), also known as VIA #2 which I believe is the chip to exchange. The one right to it (yours named ZC86068P) goes into UAB3 (Serial-Joy-User-Cass), also known as VIA #1. How does the computer behave when you boot it without a cartridge? Does it behave as expected, but the cursor blinks very fast? Does the keyboard read correctly? Did you have a chance trying to load something from a disk drive? From tape? (*) As a side note, it recently was posted by a Commodore alumni on Facebook that pretty much all second sourced chips - at least in the beginning - were manufactured by MOS but sent to Rockwell and Synertek to put their logotypes on them to satisfy the requirement of second sourcing CPUs and support chips. Possibly they went on to actually manufacture their chips a bit later on. Thank you. I now have a replacement chip so can see what is going on. I will boot it up as is and see if the cursor is blinking too fast. Will then try and replace the chip and see if it continues. Thanks for your help... Will let you know 1 Quote Link to comment Share on other sites More sharing options...
djrodderz Posted May 9, 2020 Author Share Posted May 9, 2020 Ok I’ve change the chip and this is the result... https://youtu.be/uzgtRwWzJJk Quote Link to comment Share on other sites More sharing options...
carlsson Posted May 9, 2020 Share Posted May 9, 2020 Ok, it seems like the cursor is blinking at normal speed. Does it otherwise behave normally? Quote Link to comment Share on other sites More sharing options...
djrodderz Posted May 9, 2020 Author Share Posted May 9, 2020 It seems to be. Unfortunately I don’t have any software here to test it. You don’t think it’s a little fast? I wasn’t sure I might have to buy a cheap cartridge on eBay to test game wise. Thanks again btw Quote Link to comment Share on other sites More sharing options...
carlsson Posted May 9, 2020 Share Posted May 9, 2020 (edited) You may run a few benchmarks. Here are some inspired by the Rugg-Feldman ones from 1977. 10 PRINT"START":TI$="000000" 20 FOR K=1 TO 1000 30 NEXT K 40 PRINT TI/60:PRINT"END" It should report 1.11 on PAL (1.2 on NTSC). Add one row: 25 A=K/2*3+4-5 On PAL it should run for 9.8 seconds (NTSC 10.61 seconds). You could compare this with a stopwatch to verify that both the computer runs at expected speed, and that the TI timer (which comes from the VIA chip) runs as it should. Also I didn't catch if you ever responded to how the computer behaved at BASIC prompt before you replaced the chip, if the cursor blinked even faster or if it otherwise acted up. I take it you have no secondary storage peripherals like tape recorder, floppy drive etc to try and load software from. Edited May 9, 2020 by carlsson Quote Link to comment Share on other sites More sharing options...
djrodderz Posted May 15, 2020 Author Share Posted May 15, 2020 Thank you. I didn’t get the first bit come up as you suggest but after putting in line 25 it was around 9.8 seconds ... https://imgur.com/qJVyujA Quote Link to comment Share on other sites More sharing options...
djrodderz Posted May 15, 2020 Author Share Posted May 15, 2020 After initial 10-40 lines... https://imgur.com/SyNfQIU Quote Link to comment Share on other sites More sharing options...
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