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Repair Log… (1/6/11) - MPU3


Following on the repair thread, we now have 3 MPU3 boards that will jump start with T59 and R79 missing, but now the challenge is to get them to boot on their own.


T59 = BC172B (BC238) can be used which is itself obsolete but you can still get them.


R79 is a 470K resistor yellow, violet, yellow. T60 again BC238 will do for this.


T61 is more tricky. This is a ZTX510 (you can still get them but it takes a lot of digging).

Magik suggested BC328 as a substitute and this works.


This does not guarantee the board will board start however!


If it doesn’t more parts need to be changed...


Now change T57 and T58 again BC238 will do for these.


This should do it, but T56 may need doing as well this will either be a 2n5060 (RS do them 19p each) or a ZTX300 (ebay 31p) depending on the mod state of the board, you will need to use the right one.


Check RAM voltage on pin 9 and 18 not pin 9 and 10 like I did. It should be 5v or near. If you measure pin 9 and 10 you will get between 3.89 and 4.01v if the board is happy. If the RAM is dead 0.34v.


Replacement RAM is still available for these boards. I use 6514.


Keep the RAM happy by changing regulator caps 2200uF 25V and C40 which is a tantalum cap.