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+3 Power Supply
Posted: Thu Nov 23, 2023 10:36 pm
by krypdtocken
Hi
My +3 power supply has 10,9v on the 5v output.
T2 was shorted, replaced but no change.
The coils all show the correct AC voltage.
Any ideas?
Re: +3 Power Supply
Posted: Fri Nov 24, 2023 12:21 am
by 1024MAK
It’s normally T1, T2 and sometimes IC1 (the uA723N).
With T2 not fitted, T1 should be off, then the +5V should be at or near 0V. if it’s not, T1 is faulty.
Before changing IC1, keep in mind that it compares the reference voltage on pin 5 with the feedback voltage on pin 4. If either of these is too far away from the other, it will drive T2, and hence T1 hard on.
Hence a problem with the circuitry connected to pin 4 or pin 5 could also be the cause of problems.
There is a schematic
here. Keep in mind that not all units may be exactly the same.
Mark
Re: +3 Power Supply
Posted: Fri Nov 24, 2023 7:03 am
by krypdtocken
Thank you for the “pointers”, pin 4 showed 7.5v as I remember it.
I will dig a bit deeper tonight.
Kristoffer
Re: +3 Power Supply
Posted: Fri Nov 24, 2023 11:17 am
by 1024MAK
Pin 4 is feeding back a proportion of the actual voltage from the +5V line, if the +5V line is higher than it should be, the voltage on pin 4 should be higher than normal. Similarly, if the actual voltage from the +5V line is lower than it should be, the voltage on pin 4 will be lower than normal.
Mark
Re: +3 Power Supply
Posted: Sat Nov 25, 2023 1:44 pm
by krypdtocken
Hi
I removed T1 and measured it out of circuit and it’s OK.
Measured pin 4 and 5 as follows ,4, 7.5v and pin 5.7
I’m leaning towards a faulty IC1, pin 10 show 12.2v( not sure if that is a fault though)
Kristoffer
Re: +3 Power Supply
Posted: Wed Nov 29, 2023 6:56 pm
by krypdtocken
Conclusion, T2 & C1 failed.
I now have 5.00 v !
