pinto_guy Posted November 23, 2020 Report Share Posted November 23, 2020 My current project from the Colby estate is to revive a MacColby (1st pic). When I first turned it on, I actually got a loud bong, and the usual floppy question mark, so I was elated (2nd pic). It took me a while to de-stuck the two floppy drives, and I could get everything going in record time. Alas, just as I put everything back together, two new problems popped up. One was an easy fix (one FDD stopped ejecting), but the other one puzzles me: the screen all the sudden turned black. Not the J1-solder joint-problem black, but more like a fuzzy bright zone at the top of the screen (3rd pic). Before I start doing the usual swaps and get the scope out, I thought I'd ask. Has anyone seen this ? Quote Link to post Share on other sites
bibilit Posted November 23, 2020 Report Share Posted November 23, 2020 Flyback tranformer ? common issue with black screen symptom. Quote Link to post Share on other sites
techknight Posted November 23, 2020 Report Share Posted November 23, 2020 Could be anything to be honest. youll have to troubleshoot it. Meanwhile, why in the heck would colby make such an abomination? the original Mac would have been smaller Quote Link to post Share on other sites
bibilit Posted November 23, 2020 Report Share Posted November 23, 2020 Quote why in the heck would colby make such an abomination? the original Mac would have been smaller Probably a reason, military or industrial requirement ? plus having a twin floppy management included... Quote Link to post Share on other sites
pinto_guy Posted November 23, 2020 Author Report Share Posted November 23, 2020 Thanks. The flyback crossed my mind, but I did have a pretty strong spark when I discharged the HV connecter to the CRT. Also, I do have a strong single point in the center of the screen after I disconnect J1. Anyhow, I'll start the detective work soon. It's most likely a problem in the vertical raster circuit. Yes, the twin floppy is handy. Turns out that the 128k LB has capability for two FDDs 9internal and external). The was Colby did it was to daisy chain both with one ribbon cable, and simply connect the FDD2 enable signal from the pin 17 of the external FDD connector to the second floppy via line 14 in the ribbon cable. Quote Link to post Share on other sites
pinto_guy Posted Tuesday at 09:49 PM Author Report Share Posted Tuesday at 09:49 PM Sorry it took a while. I actually banged my head hard on this one but I finally found the source of the trouble. The trimpot R55 was slightly bent, and the lead to one pole was broken. This trimpot adjusts the height of the video on the AB. This was not really visible to the naked eye, but only with a magnifier. I must have pressed on it with my fingers at some point, which led to the breakage. So everything works now, and it's a cute little machine. I took some video shots that I will edit and post on youtube at some point. Thanks all. Quote Link to post Share on other sites
EmmyOcelot Posted Tuesday at 11:25 PM Report Share Posted Tuesday at 11:25 PM Reminds me of the old word processors from Brother. That’s one nice machine! Quote Link to post Share on other sites
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