MAX232 over heating, even without any connection to controller

[burrow]

Hai,
i am having a max232 circuit that iam going to use for PIC TO PIC communication. and i found that max232 is overheating.
i tried removing all connections ( Input from pic and also RX TX output.. still its over heating
what might be wrong ?.. i double checked the circuit and circuit seems correct.

 

[FvM]

Wrong circuit or defective MAX232, possibly both.

 

[burrow]

Wrong circuit or defective MAX232, possibly both.

This is the circuit iam using

 

[FvM]

The schematic is fully correct.

 

[mrcube_ns]

Replace Max232!
It is defective for sure.
(I used MAX232 many times and never have problem with heating.)

Regards,

Mr.Cube

 

[Debasis Swain]

Your problem may solve after change the max232 ic, but according to your requirement you are going to communicate PIC to PIC. So, that's way you can do it without max232 by direct connect the TX-RX and RX-TX of both side.

 

[th3gr8]

Yea.. you don't need MAX232 for PIC-to-PIC communication .. MAX232 is just a voltage level converter .. PIC MCUs operates at 5V, so you dont need any voltage converter in between MCUs ..

 

[spudboy488]

But the OP never mentioned the distance between the 2 PICs. That might be why RS232 is being used.

 

[burrow]

yes, they are about 10 to 12m apart, thats why iam using max232 in between

 

[betwixt]

Double check you have the capacitor on pin 6 the right way around. It should have it's positive side to ground, despite the IC running on a +5V supply.

Brian.

 

[burrow]

Double check you have the capacitor on pin 6 the right way around. It should have it's positive side to ground, despite the IC running on a +5V supply.

Brian.

I checked it again.
a little more info..
i performed this test
"Put 5 volts into pins 10 and 11, then check pins 7 and 14 again. Should have about -10 volts output on each.
Put 0 volts into pins 10 and 11, then check pins 9 and 12. Should have about .6 volts output. "

once in a while this starts giving this right result and ic doesnt heat,, but after about 1 seconds the heating issue pops up again

- - - Updated - - -

I checked it again.
a little more info..
i performed this test
"Put 5 volts into pins 10 and 11, then check pins 7 and 14 again. Should have about -10 volts output on each.
Put 0 volts into pins 10 and 11, then check pins 9 and 12. Should have about .6 volts output. "

once in a while this starts giving this right result and ic doesnt heat,, but after about 1 seconds the heating issue pops up again

to be more precise, this is the test i performed
"

The following two tests check each "TTL in - RS232 out" converter.
Put 0 volts into pins 10 and 11, then check pins 7 and 14. Should have about 10 volts output on each.
Put 5 volts into pins 10 and 11, then check pins 7 and 14 again. Should have about -10 volts output on each.
If that succeeded, then check each "RS232 in - TTL out" converter. Connect pin 7 to pin8. Connect pin 13 to pin 14. This will be a "loopback test".

Put 0 volts into pins 10 and 11, then check pins 9 and 12. Should have about .6 volts output.
Put 5 volts into pins 10 and 11, then check pins 9 and 12 again. Should have about 4.5 volts output.

"

 

[burrow]

Okay here is the latest update.
i bought a new pair of max232. And i performed the above mentioned test in the breadboard( supplying 5v and looking for 10v ...)

and it seems to be working fine.
Now i just want to reconfirm the circuit on my pcb so that i wont burn any more IC'S

I have two PIC microcontrollers Say MCA AND MCB. my connection goes like this


TX OF MCA TO pin 11 of RS232(A)
RX OF MCA to pin 12 of RS232(A)

Pin 14 of RS232(A) goes to pin 13 of RS232(B)
PIN 13 of RS232(A) goes to pin 14 of RS232(B)

PIN 12 OF RS232(B) GOES TO RX OF MCB
PIN 11 OF RS232(B) GOES TO TX OF MCB


is this right ?

 

[betwixt]

That is correct. Don't forget to join the grounds together too!

Brian.

 

[burrow]

That is correct. Don't forget to join the grounds together too!

Brian.

Thanks.
Yea it will have common ground, actually it will have common power supply.

 

[burrow]

Finally its all working. Thanks friends..

 

[betwixt]

Well done!

Brian.

 

[burrow]

Hey guys problem is back,
one of the RS232 is starting to heatup.
not always. But once in a while it freezes and starts heating up ??

Can it be because some of the unused pns are left floating ?

 

[betwixt]

It shouldn't be a cause of problems but there is a remote chance that they are picking up signals from elsewhere (maybe the internal charge pump) and the rapidly changing output is causing a higher than normal power consumption. It will do no harm to ground unused inputs but you must leave unused outputs disconnected.

Brian.

 

[burrow]

I cant figure out the causes yet.

Some times the first max 232 starts heating, and sometimes the other one heats.. but if it starts working, it works as long as power is on, but after a restart the issue pops up again.

 

[paulfjujo]

hello,

Did you test if you have a potential difference beetween the 2 GND power supply of the 2 PICs
Make a measure , With open RS232 link , with an AC (and DC) voltmeter between PIN 5 (0V) of each DB9.
MAX232 overheating is an abnormal situation...
sometimes galvanique insulation must be used to avoid problem ... to dissociate the Gnd