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Oberlehrer

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Everything posted by Oberlehrer

  1. Oberlehrer

    Video Output Frequency of Macintosh LC - 25hz??

    As I said I will be able to make detailed tests only after I got it recapped. It might well be that you are correct about this. My experiences come mostly from a (recapped) IIsi (same timeframe albeit different video subsystem) which is behaving somewhat strange in the video department. I'm using dip switch adapters for the IIsi and I have made the following observations: - adapter set to VGA/SVGA: none of my monitors work - adapter set to 640x480: two monitors work (a Panasonic PanaFlat LC50S and a NEC Multisync), the third one doesn't get any signal (or isn't able to process the incoming signal) There are no other apparent issues with the video system. Interestingly on my Performa 475 both adapter settings and all three monitors work fine...
  2. Oberlehrer

    Video Output Frequency of Macintosh LC - 25hz??

    LC arrived. Dead power supply, logic board probably needs a recap too. But it boots in general. Tests will have to wait after I got everything in order.
  3. Oberlehrer

    Video Output Frequency of Macintosh LC - 25hz??

    I'm not sure about this. My experiences with a IIsi are similar: adapter and monitor work with a different computer, adapter works also with the IIsi and a different monitor. Perhaps there is a sync signal that somehow differs. Anyway, I'll be getting an LC soon (condition unknown) and will run a few tests.
  4. Oberlehrer

    Mac LC and DB15 to VGA adapter problem...

    Not sure if it is "working" in the complete sense. (Please correct me if I'm wrong.) That the floppy gets ejected immediately seems to indicate that the LC is not booting from the hard drive. Hence it's waiting for a bootable floppy - which the floppy in the movie obviously isn't. If it were actually booting from the hard drive the floppy would either not get ejected at all (if it was readable) or only after interaction (I think there would be a dialog box if it should get formatted or ejected). So it seems that the mainboard might work somewhat but the hard drive might have problems. Have you tried a bootable floppy? Again, I might be wrong about this.
  5. Oberlehrer

    Mac LC and DB15 to VGA adapter problem...

    Yes, the "Pomeranian" part gave this away somewhat. Anyway, I've recapped a IIsi, a Performa 475 and an SE/30 so far; so if everything else fails it would at least not mean shipping the machine around the globe... Another thing: I think without the VRAM upgrade the LC supports only 512 x 384; not sure if the NEC will play nicely with that. I know that the NEC can do 640x480 without a problem.
  6. Oberlehrer

    Mac LC and DB15 to VGA adapter problem...

    Dresden, Germany. If you were located in Zgorcelec or Jelenia Gora...
  7. Oberlehrer

    Mac LC and DB15 to VGA adapter problem...

    Just out of curiosity: Roughly where in Poland are you located?
  8. Oberlehrer

    Mac LC and DB15 to VGA adapter problem...

    I don't think I've seen such an LC "in the flesh" myself so far; the ones I've seen always had the (unused) cutout for a second floppy drive. So it seems Apple made a case revision at one point. I'm only mentioning this since you talked about buying a second case which seems to be constructed different. Make sure that the parts are really compatible. Other posters will probably know more about the different LC revisions.
  9. Oberlehrer

    Color Classic II without audio

    Having separate digital and analog grounds is not uncommon where I come from; no idea if this is also done with the Classic II though. Usually those are then tied together at a single point in or near the power supply (unless there are also separate supply lines for digital and analog IC's). Perhaps that point where the grounds are tied together is missing.
  10. Oberlehrer

    Apple "mistake? video 512 x 342 vs. 512 x 384

    3 - 6 - 12 - 24 - 48 - 96 - 192 - 384 - 768
  11. Oberlehrer

    Apple "mistake? video 512 x 342 vs. 512 x 384

    Another thing worth considering: The Apple II had a vertical resolution of 192 pixels - exactly half of 384...
  12. Oberlehrer

    Apple "mistake? video 512 x 342 vs. 512 x 384

    1024x768 is a standard resolution; 512x384 is exactly half of that...
  13. Oberlehrer

    Mac LC and DB15 to VGA adapter problem...

    I think the 191 is very similar to the 190. NEC had always good compatibility. So I guess it SHOULD work if the computer outputs a correct signal and the adapter is working.
  14. Oberlehrer

    Mac LC and DB15 to VGA adapter problem...

    I'm using a switchable third-party adapter.
  15. Oberlehrer

    Mac LC and DB15 to VGA adapter problem...

    The NEC I mentioned is a TFT, though. https://www.ebay.pl/itm/NEC-MultiSync-EA190M-19-1280-x-1024-250-cd-m-5ms-VGA-DVI-Weis-Silber/302801275915 Sure, that's twice as much as I paid for mine. Still not too bad.
  16. Oberlehrer

    Mac LC and DB15 to VGA adapter problem...

    I bought an old NEC EA190M a couple of weeks ago that also plays nicely with the IIsi. Those monitors probably cost close to nothing everywhere; I paid 15 € for mine.
  17. Oberlehrer

    Mac LC and DB15 to VGA adapter problem...

    Both the IIsi and the LC475 output at 66.7 Hz; and here that particular monitor works with the LC475 at 640x480 (and a PM8100 and a PM4400) but not with the IIsi. My guess is a different sync type.
  18. Oberlehrer

    Mac LC and DB15 to VGA adapter problem...

    I don't know if this is a question of adjusting or of monitor features. Sometimes certain older monitors work better with older computers than newer ones. I have an old Panasonic LCD monitor for such cases.
  19. Oberlehrer

    Mac LC and DB15 to VGA adapter problem...

    The Macs of that particular vintage are rather finicky as far as monitors go. I have a 19" monitor that works well with an adapter on my LC475 but not on my IIsi. Other monitors (even 19" ones) play nicely with the IIsi. The original LC and the IIsi came out at about the same time. Just a thought.
  20. Oberlehrer

    Performa 475 power problems

    So I got myself a cosmetically very nice Performa 475 without a hard drive and without VRAM. It doesn't really turn on and I'd like to find out if this is a power supply problem or a faulty logic board. When switching on the machine it clicks/pops continually from the speaker; the LEDs in the keyboard blink with the same frequency. All voltages are very low (roughly 50% of the nominal voltages). The power supply seems to work when not connected to the logic board; I'm getting +5.3V, +11.1V and -4.5V. The power supply is a Dyna Comp model; I don't know if the Performa 475 came with other supplies as well. My thinking is that a short on the logic board would probably only pull down one of the voltages (and not all three). Neither logic board nor power supply are recapped though both don't show signs of leakage. Any ideas?
  21. Oberlehrer

    Performa 475 power problems

    ...and as soon as my desoldering pump made contact with the power supply board I knew how wrong I had been about the caps probably not having leaked. A familiar smell permeated the air... Anyway, after recapping the power supply I got a chime; and with the "jumpstart" method I also got video. So far, so good. But of course I got one cap with the wrong height so the lid of the supply won't close. I'll probably recap the logic board as well while I'm at it.
  22. Oberlehrer

    Performa 475 power problems

    The Performa came without a PRAM battery. I was under the impression that without the battery it would chime but not produce any video; and that the "jumpstart" method would work for the missing PRAM battery (but not failing caps). I'm mostly irritated by the voltage breakdown; it's obvious that the computer won't boot when instead of +5V there are less than +2V. Anyway, a complete recap of both supply and logic board is probably in order.
  23. Oberlehrer

    SE/30 recapping: sound chip question

    My point was: Is there a (known) reason why both audio channels use different values and types (1u electrolytic vs. 0.1u ceramic)? Just being curious here.
  24. I'm currently preparing to recap a SE/30. First time for me so I'm taking some precautions. Now most electrolytics go from a voltage rail to ground, in fact nearly all of them. However there are a couple of electrolytics in the audio circuit as well. C3 and C4 are directly in the audio path so they're DC blocking caps (or coupling caps?). C5 goes from VREF for both sound chips to ground. I faintly recall that tantalum caps are not often used in the audio path so perhaps it's a better idea to stick to electrolytics here? What's got me stumped at the moment is C6 vs C24. C6 is 1u electrolytic, C24 is 0.1 ceramic. C6 goes from SND-R-A/D to ground, C24 from SND-L-A/D. So both essentially have the same function. So why the difference between those values?
  25. Oberlehrer

    SE/30 recapping: sound chip question

    Any takes on this? I'm about to order caps this week; I'll probably stick to electrolytics. The lifespan of modern electrolytics is hopefully a bit longer so there's a chance I won't have to do it again in my lifetime. Removing the old caps worked quite well; not a single pad lifted. I tried the "twist with pliers" method first but found it a bit unnerving. So I stuck to the "cut off the top" method that exposed the leads and the plastic part at the bottom. That part was so brittle that it was disintegrating with little force, leaving the leads on the pads. Those were easily removed then.
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