Jump to content

benanderson89

6502
  • Content Count

    84
  • Joined

  • Last visited

Contact Methods

  • Website URL
    http://benanderson.homeip.net/

Recent Profile Visitors

The recent visitors block is disabled and is not being shown to other users.

  1. benanderson89

    Power Supply takes a while to reach full output voltage

    Thank you! I'll get those ordered.
  2. benanderson89

    Power Supply takes a while to reach full output voltage

    Do you know the part numbers for DP3 and DP4? I may as well buy all the parts. I have two new optos in a baggy in the garage so I may as well buy all the diodes and just replace everything in one shot if I have to spend the time setting everything up anyway.
  3. benanderson89

    Power Supply takes a while to reach full output voltage

    You know, I think I meant to replace that and never got around to it (partly because I couldn't find it since it's one of the small ones). I'll open the case tomorrow and test the diode. EDIT: Wait, no, the giant one with the heat sink. Why did I think one of the little ones? Yes, there was a lot of gunk around that area of the board and it'll absolutely be that diode I forgot to replace. I'll remind myself to order a part tomorrow.
  4. The Macintosh Classic I've been working on is now done. All the large electrolytic caps on the analogue board and the caps on the logic board were all replaced. Voltages measure stable and within spec from the floppy disk port. C2 on the CRT neck board was also replaced. However I've noticed that when the computer is left switched off for a long period of time, the voltage readings are very low, the screen is the wrong shape, it shakes violently and there's a chequerboard pattern. If you wait, the voltage eventually creeps up and it boots (but the memory check takes a while), wait even longer and the screen eventually returns to the correct shape and stops shaking. Anyone know what could cause such an issue?
  5. benanderson89

    Short when CRT board connected

    It doesn't, but there he is, churning away.
  6. benanderson89

    Short when CRT board connected

    Back from the repair shop! IT'S ALIIIIVE! Pins 1 and 5 are supposed to be together. 1 is G1 and 5 is ground of G1. A lad from the vintage television forums said that's what it's for. My actual issue was that two caps, the only two I didn't replace that were hidden under a massive gob of hot glue, had went open circuit. So there was a floating voltage to ground and no current to drive the CRT. End result is that the power supply protection circuitry kicked in. I still have a "shimmering" issue with the display after it's had a chance to warm up, so I think there's one more old cap that needs to be removed on that analogue board or I need to adjust the voltages just a tad. But either way, it works. I'll be ordering an SD2SCSI from Amiga Kit next pay day!
  7. benanderson89

    Short when CRT board connected

    Theres no short to ground in the brightness circuit so we can rule that out. The short is the tube itself.
  8. benanderson89

    Short when CRT board connected

    There's no shorts anywhere when the CRT is disconnected.
  9. benanderson89

    Short when CRT board connected

    The rest of the computer is fine - it's only the when the tube is connected that the low voltage side shorts. The short is on the pins of the CRT itself.
  10. benanderson89

    Short when CRT board connected

    1MB is installed on the motherboard since the Classic is basically a Macintosh Plus. This is what the screen scan in question looked like. It wasn't slow enough to see it draw; it was so quick I'm sure anyone with epilepsy would go into a fit. After switching off the machine and switching it back on, nothing happens. I've not ran tests on the tube inside my Classic since that's off in storage, but I've tested the tube I've had delivered. It's definitely not a heater short as the filament glows and everything holds nice and stable. No continuity or resistance between either the heater pins to anything else. The only short is Pin 1 to Pin 5, and as it turns out, my old and cheap meter is dying and there's actually a dead short, no resistance at all. The reading I was getting from my meter was it's own internal resistance (you get the same result touching the two probes together). So it's not G1-K, G1-H or H-K. G1-G2 short, perhaps? Here's the pin-out as seen from the back of the tube and labelled. It's basically the top and bottom pins that have a dead short together.
  11. benanderson89

    Short when CRT board connected

    This is the second tube I have that just got delivered from eBay, so yeah it needs a bit of a clean and pin 1 bent back into place.
  12. benanderson89

    Short when CRT board connected

    Looking at the neck of the tube, are you ABSOLUTELY SURE pins one and five are supposed to NOT have continuity? They look like one solid piece of metal from here (pins covered with blue and pink plastic commoned an outer sleeve around the cathode) I have a funny feeling I'm chasing yet another red herring (since I was told no pins except 3/4, the filament, should have continuity) and both my tubes are absolutely fine. Even so, I've used my little bench supply to test the heater filament and it holds nice and steady. Likewise I've blasted pins one and five with everything from 0.3A up to 5A in short bursts (whilst tapping the neck) and I think I've successfully blown some crap off of G1 as the resistance is now sitting comfortably at around 2ohm, which is about what it should be if old forum posts as far back as 1999 are any indication. I think on Monday I'll contact a local TV Repair man who's been in the business for decades. He'll be far better than me at tracing the analogue/sweep board and finding out where the actual short to ground is.
  13. benanderson89

    Short when CRT board connected

    Asked ye-olde reddit electronics sub for help. Old TV repair guy says he's confident it's a GK short. From what I can tell you basically just discharge a whacking huge capacitor between the two pins and it vaporises the debris off of the gun. Wondering how I could do that with what I have.
  14. benanderson89

    Short when CRT board connected

    P.S. Just checked, that's the wrong monitor revision, sadly. I have a Rev B with the slim connector on the yoke.
  15. benanderson89

    Short when CRT board connected

    Let me quickly call some local repair guys first. One is an old TV repair specialist that's been in the business for decades and he might still have his old CRT equipment. The other is more for vintage synthesizers but also has all the old equipment since I've had several vintage things repaired by them in the past (albeit mostly synthesizers but they've done TVs, too).
×