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power supply unit-IC5308-low output voltage

Posted: Sun May 22, 2011 4:57 pm
by efect2000
Hello, It's the second unit I have problems with a "stupid" switch MM1665AH.

In the input there is the 5,60v, output is lower than 3,7v, I install a diode between pin 8 and 1 (input-output) and then the unit works perfectly.
So, i bought a pair on them (10e each one, bought on a JVC service) and happy and does the same, the input is ok and the output is low. I bought on ebay one faulty with loading. There is the same problem, feeding the dvd unit with an external power supply everything works perfectly, so today I wanted to find out where te problem is, and found nothing. I have swapped IC IC5305 with 5308, then I have about 5 volts on both outputs, but the unit does not works, now I see they are not the same type, but first time I bought both 1665, and besides, I had 5 volts on each output.

Now I have installed a 1n4148 again, like the first unit, and it is working. The switching voltage is the same on both, and measured input is also good.

Do you know why is happening this, even with new Ic's?

Thanl you

Posted: Sun May 22, 2011 5:42 pm
by efect2000
solved, I changed C5340 and C5306 and it works fine now. I did'n thought before do it. I measured and C5306 is about 70uF... :oops: :oops: :oops:

thank you, and hope is useful for other people.

Posted: Thu May 26, 2011 10:19 am
by andywilks
Moral of the story.... It's always capacitors ! !


The voltage regulators require input and output capacitance to be able to control the output correctly. The faulty caps allow ripple on the lines, upsetting the regs.