![]() ![]() U32 Pin 3 - Input to MC4044 Phase Detector (Soldered Into Board)Īnother point to note is that on Pin 2 of U31 (Other half of VCO that generates the Dot Clock). U19 Pin 17 - Output of VIC of PHI0 Clock (Not in Socket) ![]() AFAIK I know there is only 3 termination points on this line: I ended up pulling all my socketed chips (no CIA, CPU, ROMs, SID, VIC or PLA) and was just about to put 1 Mhz from my DIY signal generator into Pin 17 of the VIC socket when I said "let me check for some voltage there before I do this".įor some reason there is already a steady 1.6V on this line. but I can see why the eventually moved to the 8701, less guesswork in fixing clock issues. Yeah, it's an interesting piece of work that is for sure. In case it's of any use or simply for your enjoyment, here is a thermal image I took of the board after a couple of minutes of power: If anybody has some insight or suggestions on where to start looking more, it would be appreciated. I am hoping it's not the 6567 as they don't exactly go for pennies. I am having a hard time trying to figure this one because of the loopback/PLL nature of the circuit from the VIC-II, it is a chicken and egg problem for me. U19 (twice), U7 (twice), U32 (four times), Q7 (twice), U31, U18 and very unlikely U1 and U2 (already removed). If I take each one of the Diagnostic Manual tests and combine suggested replacements. Pin 4 of AV Jack (Composite) - 0.4V (No video signal) Pin 3 - U32 (loop input from VIC-II) - No clock & 0.15V Pin 39 U7- Normally 1 Mhz - BAD No clock, held at 0.3V Q7 Emitter - 0.16V (Not listed in Diag Manual, drops further when probed) ![]() Q7 Collector - 4.95V (Not listed in Diag Manual) Q7 Base - Normally 2-3V - BAD 0.4V (drops further when probed) Pin 1 - U7 - Normally 1 Mhz - BAD (Nothing) I could be wrong but I don't think it would hinder the clocking, which seems to be the first issue to tackle.įor diagnostics, I have removed the SID, CIAs and 3 Roms (U3, U4 and U5) to see if I can even get a decent black screen for the Dead Test cart to work, which it doesn't at this point.īased on the diagnostic manual on the clock system, here is what I have I pulled from the board (250407 Rev A): I haven't swapped the PLA (not sure how to test it as it sits) as I don't have one to replace one at this time, though I could build an EPROM one as a stop-gap. I get a somewhat black screen with wavy lines on RF, not sure if that is just interference or the ancient RF TV/Computer switch I have from the 80s. LED comes on, but no signal on composite. Using original power brick (with a C64 saver), voltage rails all test okay. Pulled the SID before first power up, just in case it had not been fried previously. When I popped it open, the last owner conveniently left a big screwdriver inside for me (not sure how they screwed it close), so I knew that this was not going to be a walk in the park. Picked up my first breadbin (thrift store) and of course hitting my first wall, of many I am sure, in getting it going. Decided to get back into the scene after foolishly giving away a C64C about 6 years ago. ![]()
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