General Category > Lisa Troubleshooting and Repair
Edge Connector Replacement
fri0701:
Thanks for the suggestions! I'll definitely be picking some of these up.
While we're on the subject, recently I had an odd component failure in a 1.2A PSU - the transistor at CR21 "blew its top" and its case cracked in half (picture attached). I'd like to get a replacement... the schematics say this component is a "MPU131", which might be this: https://digitroncorp.com/Digitron/media/Files/Datasheets/MPU131-MPU133.pdf
I'm not sure where to find a replacement or appropriate substitute. Anyone have any ideas?
blusnowkitty:
--- Quote from: fri0701 on December 19, 2022, 11:01:21 pm ---Thanks for the suggestions! I'll definitely be picking some of these up.
While we're on the subject, recently I had an odd component failure in a 1.2A PSU - the transistor at CR21 "blew its top" and its case cracked in half (picture attached). I'd like to get a replacement... the schematics say this component is a "MPU131", which might be this: https://digitroncorp.com/Digitron/media/Files/Datasheets/MPU131-MPU133.pdf
I'm not sure where to find a replacement or appropriate substitute. Anyone have any ideas?
--- End quote ---
I have a spare 1.2A supply in my parts box; the original is a Motorola MPU131. Looks like that datasheet you linked matches Motorola's original datasheet: https://datasheetspdf.com/pdf-file/658833/Motorola/MPU131/1
The original datasheet says the transistor can be "programmed" with two resistors in the circuit. I'd assume if you find a replacement and drop it in, it will behave just like the original part. Looks like this place has a large number of NOS Motorola parts: https://smallbear-electronics.mybigcommerce.com/transistor-mpu131-programmable-unijunction/
Probably would be wise to find out why the original part exploded, though.
fri0701:
Thanks for the link!
--- Quote from: blusnowkitty on December 19, 2022, 11:18:39 pm ---Probably would be wise to find out why the original part exploded, though.
--- End quote ---
Yep, definitely true. It happened out of the blue, and it seems to have also damaged my CPU board. I've recapped this PSU and it's worked fine several times before, which makes it even more frustrating...
blusnowkitty:
--- Quote from: fri0701 on December 19, 2022, 11:41:19 pm ---Yep, definitely true. It happened out of the blue, and it seems to have also damaged my CPU board. I've recapped this PSU and it's worked fine several times before, which makes it even more frustrating...
--- End quote ---
I can't quite make sense of the 1.2A schematic, but it appears CR21 ends up touching 5, 12, -12, and 5v Sense. It also appears to touch transformer T4 which may be on the AC side of the supply? I hope that transformer isn't shorted and letting line voltage through.
sigma7:
If you are repairing a 1.2A PSU, this post from Patrick is required reading:
https://lisalist2.com/index.php/topic,290.msg2152.html#msg2152
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