Transistors and Flybacks and Rectifiers, Oh My (BU406)

[trag]

So, since Wally pointed me at Dalbani, who actually have the compact Mac flyback transformers in stock (I now have ten), I've been toying with the idea of putting together an analog board repair kit. These used to be available from various sellers way back when. I'm not sure there's enough demand left to make it worthwhile, but at this point it's a fun exercise to research it.

I went back to dalbani and looked up the BU406 transistor. They have four or five line items ranging in price from ~$.40 to ~$.90 in quantities of ten or more.

Anyone know the difference? Dalbani doesn't do useful things like providing datasheets or even really technical specs, unless I'm simply overlooking the links.

I wouldn't worry much and just assume different brands but there seem to be some transistors that folks have called BU406 which aren't actually up to the specs needed to make the display work right.

BTW, the flybacks look nice. The rubber/plastic of the suction cups is sweating some kind of sticky goo, which is something plastics do when they get old. But the suction cup isn't all that essential.

So, any insight? Buy one of each and test them out in a compact Mac?

 

[wally]

There are so many ways things can go wrong it makes your head hurt to think about it. I see Motorola used on my reference SE/30 analog board for the Bu406 horizontal switch application. So that vendor is likely a safe initial order choice. But I think testing to see if the raster has any strange irregularities is necessary also. Sometimes modern parts can be too good (switch too fast) and cause unwanted effects. One way to go is trying the three name brand vendors line item ($1.18 qty 1) first in your initial tests. If they test ok, you are done, cost to order and test all the others exceeds savings for your limited production run. All the other lines have unknown or uncertain vendors that seem more risky even if you were lucky enough to have all the test equipment and time to run qualification testing on all kinds of stuff including collector breakdown, leakage, and switching times, checking to see if they met the spec sheet requirements.

 

[H3NRY]

It seems odd to think of repair kits for early Macs, considering that 5 years ago you couldn't give one away, and Goodwill had stacks of them for $5. At the time I figured there were enough of them that like Model T Fords, there would be plenty to go around for the next 50 years and they would never become rare or expensive. The difference is we didn't used to recycle stuff, and a worthless Model T just sat out behind the barn or quietly rusted in a junkyard. Now we actively destroy obsolete stuff, so things really DO become "rare" pretty quickly. Also modern electronics have "time bombs" which will certainly disable them like electrolytics, and custom chips which go out of production with the particular model.

 

[trag]

It seems odd to think of repair kits for early Macs, considering that 5 years ago you couldn't give one away, and Goodwill had stacks of them for $5.

Yes. I used to go to the UT surplus property auctions in the 90s when they still had computer equipment and there would be lots containing twenty or thirty compact Macs.

They were everywhere.

Making the repair parts more accessible would cut down on the amount of cannibalization. I think that would be a good thing. It seems like the two parts that are now unobtainium as "new" parts are the adjustable inductor on the analog board, and the CRT. Apparently the same CRT was used in a bunch of security monitors, so you'd think there'd be a pile of them out there somewhere.