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Pre SE Analog Board Q1 and Q2 Transistor Replacements
Posted by: superjer2000 on 2018-09-16 18:39:29
I'm looking for suitable replacements for Q1 and Q2 on my 128k Analog Board.

The parts are MPS-U01 and MPS-U51 (2A, 10W transistors, NPN and PNP, respectively).  These parts aren't made anymore and I have googled and googled and can't find any obvious substitutes.

1) Has anybody out there replaced these two transistors and if so, what did you use?

2) Any idea what might be a suitable replacement?  Would these work?  (Just looking at the NPN versions, each of these options has a corresponding PNP version as well).

https://www.google.ca/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=2ahUKEwjE6q-L88DdAhW3IDQIHYbODAcQFjAAegQICRAB&url=https%3A%2F%2Fwww.mouser.ca%2FProductDetail%2FCentral-Semiconductor%2FCEN-U07%3Fqs%3DAjE1biBnhWNczfSdd%2FihpA%3D%3D&usg=AOvVaw3rHKRVlz4JydithHFkZYO4

This transistor seems to be a pretty good match, but the Emitter Base Voltage is 4V versus 5V.  I have no idea if that's an issue.

Another option, in a different package might be:

https://www.mouser.ca/ProductDetail/Central-Semiconductor/2N4895?qs=RS415aRcUaGnkmsE5YLl3w%3d%3d
Posted by: superjer2000 on 2018-10-07 20:31:27
I ended up replacing the MPS-U01 and MPS-U51 transistors with CEN-U07 and CEN-U57, respectively, (Modern replacements for MPS-U07 and MPS-U57) and everything is working great.  

This was for a Mac 128k analog board that wasn't working properly.  The prior owner indicated the machine turned off one day and smelt like smoke.  He kept it off and stored it for 30 years until I bought it.

I  didn't see any visually burned or damaged components and I just swapped in a Plus power supply to get the machine going.

I turned my attention back to this analog board and rather than try to troubleshoot it  I replaced every  non-film and non-ceramic capacitor (except for the two y capacitors which I did replace), these two transistors U01 and U51, CR2 and CR3 diodes, the optoisolator (U3), BU406, a couple of resistors that browned when I ran the power supply without load and did all of the Mac repair and upgrade secrets upgrades (CR1, CR5, CR20, CR21, removed upper RMI shield).  The Mac fired right up, the screen is rock solid and voltages are perfect after initial adjustment.  I'll post a Mouser parts list on all of the parts I replaced in case somebody wants to upgrade their board.  I bought enough parts to do 10 boards so I'm going to do the upgrades to my Mac Pluses, 512ks and other 128k unit. I will say though that this is a lot more work than a motherboard recap or an SE/30 analog board recap with ATX power supply conversion.  I think it probably took me five or six hours in total. 
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