Microwave oven circuit pcb

Thread Starter

MWaqas

Joined Oct 29, 2023
6
Hi there this is front and back of the circuit i really dont understand it the digital seven segment dosplay is not workinh theres a regulator ic 7905pi ic that i have removed the ic is not good i want to know how can i turn the segment on as the output of the ic is going to the vss pin 21 of programable ic . Also i don't understand qhy there are negative 12v rail
 

Thread Starter

MWaqas

Joined Oct 29, 2023
6
Hi there this is front and back of the circuit i really dont understand it the digital seven segment dosplay is not workinh theres a regulator ic 7905pi ic that i have removed the ic is not good i want to know how can i turn the segment on as the output of the ic is going to the vss pin 21 of programable ic . Also i don't understand qhy there are negative 12v rail
View attachment IMG_20231029_202939.jpg
 

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Thread Starter

MWaqas

Joined Oct 29, 2023
6
Btw i have removed kia 7905pi negative voltage regulator now from the traces i cant figure it out how this working on negative input and output going into the main controller chip 4 bit microcontroller which 47c044bn from toshiba .
And the removed regulator can been seen from the pads first pin is ground second was input negative and out put is going to pin 21
 

Dodgydave

Joined Jun 22, 2012
11,347
It looks like the circuit is using a Positive ground and Negative supply rail, of -5V for the chip, and -12V for the relays.

What is the problem with it?
 

Thread Starter

MWaqas

Joined Oct 29, 2023
6
It looks like the circuit is using a Positive ground and Negative supply rail, of -5V for the chip, and -12V for the relays.

What is the problem with it?
The problem is that it's not turning on ,
I want to know if there's a problem with the supply that's going through the negative regulator ( i mean if the regulator is not working) to the main ic , i want to know how can i jump start or give supply through externally to see if the display turns on so i can know that the problem will be solved by changing the regulator ic .
I want to know how can i test the regulator ic if it's gone bad or not and if then yes how can i supply the main controller ic i dont really know much of it i.e to the vcc pin of the controller and gnd so it turns on and powers the 7 segment display
 

Dodgydave

Joined Jun 22, 2012
11,347
So replace the regulator , and check the input and output supply, it should be around 12V input and 5V output, , something has caused it to blow there might be a capacitor that is faulty somewhere.
 

Thread Starter

MWaqas

Joined Oct 29, 2023
6
When i check it from multimeter the supply is coming but not going or outputting through regulator . As you can see accidently the pad is also ripped off a bit from where i have desoldered the regulator . I want to know if a supply of positive 5 volt will work if i connect it through the outpin pin of the regulator on the pad . As this is the negative voltage regulator , will the positive 5 volts work?
 

Dodgydave

Joined Jun 22, 2012
11,347
No it needs a -5V supply. Replace the regulator and it should give you the correct voltage, unless there's something else on the pcb that is faulty.
 
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