Apple Disk II speed control board failure

2 posts / 0 new
Last post
gjbl's picture
Offline
Last seen: 4 weeks 1 day ago
Joined: Jul 28 2019 - 04:00
Posts: 7
Apple Disk II speed control board failure
AttachmentSize
Image icon disk2-speedcontrol1s.jpg286.96 KB

Now, here is something for real Apple2 experts  :-)
Apple Disk II - the diskette spin motor won't start, all other functions seem to be OK, but with floppy not spinning its hard to tell. The analog board looks OK, the "motor on" signal is generated, the motor itself spins when powered. I traced the problem to the speed control board (SCB), initially I suspected Q4 (the power transistor), but it looks OK, BUT ... Q3 is faulty!  There is no visible damage on the board, no signs of overheating, etc. It is rather rare that a low power transistor fails by itself... Working with the SCB is difficult, for example the cables to the motor are so fragile that they broke at solder joints after I had bent them a few times. So, should I assume a single transistor failure, replace it, solder everything up and hope for the best OR is it possible that the source of the problem is somehere else?

Cheers,
Greg

 

gjbl's picture
Offline
Last seen: 4 weeks 1 day ago
Joined: Jul 28 2019 - 04:00
Posts: 7
problem solved

Well, I got some priv messages, but all in all solved the problem myslef. Both Q2 and Q3 were dead. I replaced them with standard low-power transistors and the motor works! A bit of advice: Q2 and Q3 have a bit of an unstandard pinout (BCE) and with a quite dense packing on this board I would definitely recommend selecting BCE transitors. Second note: the solder joins of the cables to the motor (green, blue, red, yellow) were *extremely* fragile, they broke alost immediately when I started to move the board around...

cheers,

Greg

Log in or register to post comments