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dkjones96

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  1. dkjones96

    Color Classic VGA Mod. the CORRECT way

    I thought I'd add this little update. This mod seems to be working just fine so far on the Rev D board outside of a warm reboot sync problem that I can't trace. None of the ICs or resistors, outside of the really hot area below, get above ~115F so it shouldn't be drift or anything like that. Leave the machine off for a few minutes and it syncs right up and works for hours without a problem. It just seems to need shut down, not powered off, so the problem is unrelated to RF11. I upsized RF11 to a 3 watter and it runs at about 250F now but CF8 just runs hot I guess. That whole resistor/capacitor/zener diode area runs as long as the switch on the back is turned on so that electrolytic sits at about 65C(measured by attaching thermocouple). It's not comfortable to touch but well within specs, especially if you swap it out for a 105C during recap. Considering undoing the mod as I don't like the lack of clarity at 640x480 compared to factory resolution. To each their own!
  2. dkjones96

    Color Classic VGA Mod. the CORRECT way

    I have upgraded this guy to a Color Classic II logic board(couldn't stand the gimped stock CC performance) and with the 256K expansion I have 768K VRAM. As for screen distortion, it's the photo and I'll try to get a better one. I'm upping the dissipation rating of a resistor that is dissipating too much at the moment and when that is done I will get better photos. It does curve a bit at the top of the screen but it appears to be normal as it did it before on another analog board and is also something I notice in photos of other machines.
  3. dkjones96

    Color Classic VGA Mod. the CORRECT way

    Alright, RP6 needs changed out, you can only get 72V max with it as-is. Swap RP6 to a 752(7.5K) 1206 resistor and you are in business. Looks beautiful! I had only an 822 1206 available but it requires PP1 to be turned down all the way to get 84V. Only problem left is RF11 which runs over 300F as-is and when it's that hot you can't reboot or you'll lose sync and you have to shut down until the resistor cools and it seems to work fine again.
  4. dkjones96

    Color Classic VGA Mod. the CORRECT way

    So, I don't know if I was just imagining smoke or what but there wasn't anything overheated or burnt when I very thoroughly looked over the board. I did have a wiring error on my part but it was signal level and what caused me to have no screen before. It looks like I need to up the voltage a bit. I tried adding C26 from 1nF up to 5nF and all it appears to do is make the edges at the top and bottom extend to beyond what the horizontal deflection circuit can handle in the middle resulting in bad bowing and it makes the screen dimmer. It isn't a terrible aspect ratio, it is currently at 1.15 and I would like 1.33(4:3) It could be corrected by shrinking the vertical height but I would like it to take up more of the screen. I took a thermal camera image of the AB after it ran for a bit but forgot to bring it for posting this. Hottest I found was 165F at the big guy near RF19 and second highest was the 7.5K at RP61.
  5. dkjones96

    Color Classic VGA Mod. the CORRECT way

    Tried to do this mod on a revision D board and got smoke. Oops! I went with the 640x480 posting at Powercc.org. Here is a list of the parts mentioned to replace and what the Rev D board has: CL9 and CL10 - 3.3uF - Changed to 2.2uF and 1.8uF respectively. DL21 and DL22 - Changed to single 18V Zener at DL21(doesn't really matter as they are in parallel and the factory diodes are also 18V). RP6 - 5.6K - I left this alone as the site says 4.52 to 5.11 and I found a different, higher, value. RP8 - 15K - 33K RF14 - 236K - 216K RP23 - Unpopulated in Rev D - This is because a charge pump from the standby/crt supply feeds this circuit so I left it unpopulated since it only affects the logic supply. RL54 - 18R instead of 33R - Changed to 15R. RP61 - Already populated with 7.5K. RL62 - 47R - Changed to 100R. RL70 - 33K - 22K. J104 - Jumper - 10R. Sense line change is a bit more complicated. Revision D does away with J78 and J79 and there is a diode in that area. To make pin 20 connect as though it has J79 bridged you have to cut a trace from 20 to GND going towards the connector and run a jumper from 20 to 3. I have not figured out where the smoke came from but I will borrow the FLIR from work and see if I can find it. Nothing looked obvious though as I turned it off the instant I saw it. When I turned the computer on the CRT breifly got HV and then lost it resulting in the normal static crackle. Screen stayed off and blank while the computer itself proceeded to boot.
  6. dkjones96

    Classic 2 Speaker Port?

    Since I have to crack the case again for the installation of a new system fan, because the original is loud an annoying and low-speed quiet fans are awesome, I was thinking about 'installing' a speaker grill in the side like the later revision Classic 2s have. Is it worth it? Sound doesn't seem too bad as is. If someone could do a rubbing of the factory grill on graph paper and get a bit of the nearby case seam for reference it should be pretty easy to drill the appropriate holes in the right spots. I've tried searching for such an image and haven't had any luck.
  7. dkjones96

    Macintosh Classic II Blues... :/

    Is there static on the front of the screen when you start up the machine? If so, your HV supply is working so that rules out at least the flyback and high voltage stuff. Play with the contrast pot a bit? Maybe a bad connection? It should be 5V logic for video and I can't imagine the system would boot without that. I know it sucks with the speaker there but you should really try to get more of that capacitor goo off the board. Canned contact cleaner can work. The electrolyte can slowly eat away at traces and such on the board so getting off the stuff that leaked can help you avoid possible future troubles. The two red marked areas are the areas of highest priority, I tested a couple from the other positions on the board and it was fine. In fact, out of all 20 or so caps only two had leaked and they were both in the low voltage area on the right and both of them had phenolic bottom caps vs rubber.
  8. dkjones96

    John's Classic Restoration Thread

    Very nice! Makes me second think not retrobrighting my Classic 2 and its associated keyboard and mouse...
  9. dkjones96

    Color Classic Power Supply Issue

    I've posted this on another forum but I hope someone here has seen this before as it has been a long 4 weeks of trying to troubleshoot this. I got a Color Classic and when it arrived I was able to plug it in, hit power, and it fired right up. Only issue I saw with it was that it was an RB monitor instead of RGB but since I planned to go through a complete recap I wasn't all that worried about troubleshooting the monitor. I shut it down, pick up my daughter from school, and when I get home to fire it up again it acts like someone shorted the power supply. Hit power and it blinks the led, chirps, and shuts off. Alright, time to replace the caps. I replace all of the capacitors in the analog board and the motherboard and it does the same thing. Hit power and it blinks. Maybe a bad cap job on the mainboard? Pulled it and it sits there constantly chirping and the HDD does not spin up. It acts exactly like a switcher supply that has been shorted on the output, however, it have that problem as troubleshooting has determined . It appears that the power supply thinks it is unloaded, even with an LC 550 motherboard and stock HDD installed. If I place another diode and 62 ohm resistor in series with DP15 and RP34 between the feedback winding of the supply transformer and pin 6 of the TDA4605 the computer operates, without this in place pin 6 falls below 7.25V and the supply shuts down because of the discontinuous output. Boots, runs, doesn't seem to have a problem, but the supply is loud as it is running at about 3KHz vs the almost 100KHz of the HV supply and the low frequency causes distortion on the CRT. The TDA4605 is running in discontinuous mode as though it is unloaded. Link to pin 8 scope trace shows how the HV supply runs continuously like it should but the LV supply does one giant pulse. When loaded it adds pulses like it should but it is still discontinuous. This is a pic of the supply being heavily loaded. It continues to regulate and seems to be getting necessary feedback. I've compared the startup of both supplies and I can't find anything blatantly obvious as wrong. I've resoldered every component related to the bad supply, checked capacitors and resistors and I've checked the transformer for issues and come up with nothing. I've swapped the TDA4605 and optical isolator from both supplies and nothing changed. For about 7ms on startup the supply oscillates normally like it is supposed to and once the rails get up to 12v and 5v it switches to discontinuous mode for however long it runs thereafter. Has anyone seen this before? Any ideas of where to look?
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