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|01-17-2013, 10:33 AM||#1 (permalink)|
Join Date: Jan 2013
Location: South Korea
main board repair (LT1615) for mini cp
After resoldering a power cable, I fixed a connection between the power cable and RX board using glue. Today I tried to get rid of the glue from the RX board, and I found that two resisters are damaged. So I should replace the two resisters.
I found very helpful posting by zzyzx. (Thank you!)
Now I believe that I fully understood what I should do.
The two resisters are connected with LT1615 (or LTIZ)
So I should find R1 and R2 resisters and solder them.
Here, I have some questions.
1. In my case, the regulator is labeled by ph01, which is from the new RX board for mini cp.
Can I still use the same values of R1 and R2?
I could not find a datasheet for ph01.
2. According to the datasheet of LT1615, the switch (or output) voltage is determined by the following equation.
R1 = R2 ( Vout / 1.23 - 1) ==> 1.23 * (R1/R2 + 1) = Vout
Then, when R1 and R2 are 1M and 604k, respectively, we get 3.27.V
So, although I do not have those resisters, if the ratio of R1/R2 is 1.65, it will be OK, right?
For example, I can use 500K and 300K for R1 and R2.
(Vout will be 3.28V)
If I correctly understand, only the difference is the power consumption in R1 and R2.
3. It seems that R1 was missing before removing glue...
If I consider "R1 = R2 ( Vout / 1.23 - 1) ", Vout cannot be defined.
However, from 1.23 * (R1/R2 + 1) = Vout, Vout will be 1.23V.
I cannot expect what happen to mini cp in this case.
My mini cp did not have enough power, compared to the original one.
Do you think that if R1 is missing, the mini cp will not have enough power?