Hallo Philip, > Are there any test I can do with a scope or logic probe > that could help me narrow down the bad ic? To be honest, in this case I have no idea. You already prooved that the video-RAM/CPU connection is OK. Which means that the trouble should be found in the circuit generating the image and especially the counter part. There are two weird things happening: - only the last three bytes of a row are copied to the next line - the counter "forgets" to increase after the first column <some hours later> A horizontal line is made of a border, the visual part and a border again. During the visual a counter reads out 40 memory places. The data is sent to a ROM which outputs the bits that have to be displayed. The only counters directly related with the video RAM are the two 74177s. and that's why I suspected them. But because there are borders, the 177s don't count continiously. So there must be a circuit that starts and stops the counting. And this circuit must count to 40 (20? 10?) in some way. What maybe looks like it is the circuit mid-left around parts of B5, C5, C6 and C7. Two things go through my mind: - The 74100 latches the address to be read by the video circuit. What if the circuit stops the latching too early (but the rest goes on)? At the next line the circuit starts with the too early latched address. - What if the circuit starts one bit too late with clocking the 74107/D5 and 74177 counters? My problem: I keep on encountering confusing things, like the combination at the top of the schematic of the vertical synv and the video on signal. I only can hope that the above ideas trigger someone elses mind to find a possible reason for the problem. -- ___ / __|__ / / |_/ Groetjes, Ruud \ \__|_\ \___| URL: Ruud.C64.org De informatie in dit e-mailbericht is vertrouwelijk en uitsluitend bestemd voor de geadresseerde. Wanneer u dit bericht per abuis ontvangt, verzoeken wij u contact op te nemen met de afzender per kerende e-mail. Verder verzoeken wij u in dat geval dit e-mailbericht te vernietigen en de inhoud ervan aan niemand openbaar te maken. Wij aanvaarden geen aansprakelijkheid voor onjuiste, onvolledige dan wel ontijdige overbrenging van de inhoud van een verzonden e-mailbericht, noch voor daarbij overgebrachte virussen. APG Algemene Pensioen Groep NV is gevestigd te Heerlen en is ingeschreven in het handelsregister van de Kamer van Koophandel Limburg onder nummer 14099617 The information contained in this e-mail is confidential and may be privileged. It may be read, copied and used only by the intended recipient. If you have received it in error, please contact the sender immediately by return e-mail; please delete in this case the e-mail and do not disclose it's contents to any person. We don't accept liability for any errors, omissions, delays of receipt or viruses in the contents of this message which arise as a result of e-mail transmission. APG Algemene Pensioen Groep NV is registered in the trade register of the Chamber of Commerce Limburg, The Netherlands, registration number: 14099617 Message was sent through the cbm-hackers mailing listReceived on 2011-05-19 14:00:02
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