My Circuit cannot turn on all led

Thread Starter

ferdz

Joined Jul 17, 2021
12
Power dissipated as heat = (Input Voltage - Output Voltage)* Current.
No other reason.
hey bro i check the fuse switch and power supply and all its good but the circuit. cannot turn all the led? and may voltage regulator heating so much this is possibly a shortage?. sorry this is my first time. learning about electronics
 

Ian0

Joined Aug 7, 2020
3,752
Do you get 5V on the output of the 7805? If so, there is no short.
If the 7805 output is at zero, then there is a short.
If it is between 0 and 5V then it is overloaded.
 

Thread Starter

ferdz

Joined Jul 17, 2021
12
Do you get 5V on the output of the 7805? If so, there is no short.
If the 7805 output is at zero, then there is a short.
If it is between 0 and 5V then it is overloaded.
I check the lm7805 and the ouput is 5v
 

Irving

Joined Jan 30, 2016
2,308
Looking at the circuit (quite a complex pcb for a beginner) it has 12v AC transforme/bridge/2200u combo feeding the 7805 with approx 16v . On the output 2 X 555, 7474 dual jkff, 2 X 7447 decoder, 2digit 7seg display with 330ohm resistors, and 10 LED on 150ohm resistors. Max current draw if all are on is <400mA, but would typically be ~100mA (5 IC @ 5mA, 7 segments on @ 10mA)

7805 running withtypical push-on heat-sink dropping 11v@100mA would be warm to touch ~ 50degC but OK, at 400mA would be hot >100degC.

I'm guessing there's an assembly fault somewhere, but not a complete short probably. Chip in socket backwards? Solder bridge?

@ferdz have you fully checked every part is in correctly and there are no solder bridges where there should not be?

Maybe post some good hi-res pictures of both sides of your board.
 

Thread Starter

ferdz

Joined Jul 17, 2021
12
Looking at the circuit (quite a complex pcb for a beginner) it has 12v AC transforme/bridge/2200u combo feeding the 7805 with approx 16v . On the output 2 X 555, 7474 dual jkff, 2 X 7447 decoder, 2digit 7seg display with 330ohm resistors, and 10 LED on 150ohm resistors. Max current draw if all are on is <400mA, but would typically be ~100mA (5 IC @ 5mA, 7 segments on @ 10mA)

7805 running withtypical push-on heat-sink dropping 11v@100mA would be warm to touch ~ 50degC but OK, at 400mA would be hot >100degC.
I'm guessing there's an assembly fault somewhere, but not a complete short probably. Chip in socket backwards? Solder bridge?

@ferdz have you fully checked every part is in correctly and there are no solder bridges where there should not be?

Maybe post some good hi-res pictures of both sides of your board.
Yes sir i send a picture later
 

ronsimpson

Joined Oct 7, 2019
1,630
The transformer has too high voltage. I wish you had a 8 volt transformer. This will make the 7805 less hot. Please send a picture of the transformer.
 

narkeleptk

Joined Mar 11, 2019
545
You need to use more flux and heat on your solder connections, they are in pretty bad shape. Cleaning those up may help with your problem.
 

LesJones

Joined Jan 8, 2017
3,570
It looks like you have blobs of solder on the input capacitor to the regulator shorting the input and output of the regulator to ground. There is also a very large blob of solder on one wire shorting the regulator output to ground . The output capacitor also looks like it is inserted with reversed polarity. It would help if you posted the schematic with components numbered so we could say for example C1+ instead of input capacitor. Your soldering is so bad around the rectifier diodes that I can't see the tracks.

Les.
 
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