As always, Gamba has an excellent point. Jos� should definitely inspect the socket and crt board. Those are more likely culprits than a crt fault.
And Gamba is also right about those 9" crts: They are extremely reliable. I've seen only one grid-to-cathode problem ever in a compact mac. It didn't cause any components to burn up, but it prevented the brightness control from having much effect, and the raster had lousy contrast and poor focus (it looked very "washed out"). Tapping on the crt neck as hard as I dared (with the thing powered up) didn't fix it. An old TV repair "hail mary" trick is to zap the grid-cathode with enough juice to vaporize the flake of cathode coating that generally causes these problems (the spacing between cathode and control grid is very, very small). Most of the time, this takes care of the problem permanently, and generally without damaging the crt. I charged up a 0.02uF, 1kV cap with the 500 or so volts available across the outer terminals of the focus potentiometer. Then, I quickly touched the cap's leads across pins 1 and 2 of the crt (with power off, and crt connector/board removed). A brief flash inside the neck, and it was fine. > It sure sounds to me like it's something like a grid-to-cathode short. > But I'm surprised if that is it. I've never heard of Mac 9" CRT failing > that way. They seem to be bullet-proof. > Im curious about what the fix is, and how permanent it is. > > Maybe he should check for a short outside of the CRT, i.e.,on the card, or > socket. > > Gamba > <http://home.earthlink.net/~gamba2> > > > Tom, if the Colour Classic community managed to get a CC analogue board > to you, is there any chance that you might be able to produce a > schematic, please? (It's a single sided board with tracks on one side > and components and wire jumpers on the other.) Stuart I would be happy to trace the schematic of a CC analog/ue board. It's one old Mac that I don't own, so I've had little experience with it. I do this as a hobby, though, which means that I do a bit here, a bit there, until it gets done. Tracing the classic Mac analog board took me a weekend, but many months passed before I got around to converting my chicken scratchings into a neat schematic, then another year or so passed before I wrote up any text to go with it. But if the kind folks on this list would tolerate partial (and potentially illegible) works in progress, I'd be up for it. Anyone with a spare CC analog board (working or not, but complete), please send it to my school address, below, and I'll start working on it. And if any of you have knowledge of any congenital defects of this model, please feel free to pass those on to me, too. -- Prof. Thomas H. Lee Center for Integrated Systems, CIS-205 420 Via Palou Mall Stanford University Stanford, CA 94305-4070 http://www-smirc.stanford.edu 650-725-3709 ph, -3383 fax -- Compact Macs is sponsored by <http://lowendmac.com/>. Support Low End Mac <http://lowendmac.com/lists/support.html> Compact Macs list info: <http://lowendmac.com/lists/compact.shtml> The FAQ: <http://macfaq.org/> --> AOL users, remove "mailto:"; Send list messages to: <mailto:compact.macs@;mail.maclaunch.com> To unsubscribe, email: <mailto:compact.macs-off@;mail.maclaunch.com> For digest mode, email: <mailto:compact.macs-digest@;mail.maclaunch.com> Subscription questions: <mailto:listmom@;lemlists.com> Archive:<http://www.mail-archive.com/compact.macs%40mail.maclaunch.com/> Using a Mac? Free email & more at Applelinks! http://www.applelinks.com
