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I'll give that a bash sometime today! Thankfully I already have some compatible opto chips in the garage so I can just fish those out.

Hello again everyone! My Macintosh Classic is still being a pain in the backside. Today I replaced DP 3, 4 and 6 (though I've not done the opto isolator yet), and I'm still having issues. Screen shaking and taking a long time to reach a bootable voltage as per this thread from early October...

Thank you! I'll get those ordered. :)

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. :)

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...

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...

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

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...

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

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

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.

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...

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.

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...

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.

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

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...

It really is! It's infuriating because this is the last thing I need to do for my Macintosh Classic for it to work. ARRGH!

Replacement tube arrived and there's a short between 1 and 5 on this one, too. :( Looking at the pin out again I don't think this is a H-K short since pin 1 is G1 (it's linked to the software brightness control and is the top-most pin). I'm thinking it might be some debris lodged in there as...

Given its not working regardless it'll be no loss if it blows the grid, really. I'll see when the electrician is next in at the repair shop and I'll take it down.