Max232 problem

[kyru27]

I've the following problem with a max232 chip:

If I connect Pin 13 from it to pin 3 of a DB9-connector I get -5,8 V in there which is on an appropiate range according to its datasheet (http://www.datasheetcatalog.org/datasheet/texasinstruments/max232.pdf), but the point is I get the same un pin 14 even if I have nothing connected to it which isn't even on a valid range.

I thought it was an internal short circuit, but if I swap the wires that are initially connected (Max 232 [pin 13] -> Db9 [pin 3] and Max 232 [pin 14] -> Db9 [pin 2] I get -5.8 on MAX232 pin 14 and 0 on pin 13, so it cannot be a short.

This happens even without the PIC working so it's not its fault.

This is the schematic, I've checked the connections and all are correct, so I might be missing something...

 

[ericgibbs]

hi,
Pin 14 is an output from the MAX.

The input pin 11 connected to the PIC is normally High, as the MAX is an inverter the output on pin 14 will be a -V which is Low.

Is this what you are asking.??

 

[kyru27]

Well, I think I should have explained myself better, sorry.

The main problem I have is that I'm unable of transmiting anything via RS-232, and, after analizing the circuit I guess the problem has to be that pin 14 is not doing the transmision as it doesn't change when the PIC is working (I have debugged the code and PIC is doing the transmision), in fact, according to the datasheet it's even working outside of range when I connect the DB9 to it ( if you look at the datasheet it should work at a minimum of -0,6 V (my Vs- is measured as -0,3) and I'm when I connect it to the DB9 pin it works far below from it, so, I guessed the problem had to be that so I'd have liked to know what might have been causing this behaviour to have it fixed.

But now if you tell me that this should be -V, that the voltage is correct there, then I guess the problem has to be another one.

Thanks.

 

[ronsimpson]

Your diagram does not show power and ground connected to the MAX232.

 

[kyru27]

Your diagram does not show power and ground connected to the MAX232.

Oh right... I uploaded an old one, anyway,they are connected properly to pins 16 and 15, so that's not the problem.

 

[ericgibbs]

Oh right... I uploaded an old one, anyway,they are connected properly to pins 16 and 15, so that's not the problem.

Hi,
Check the voltages on pin 2 and 6 , values are shown on this image

 

[kyru27]

Hi,
Check the voltages on pin 2 and 6 , values are shown on this image

Checked, but nowhere near to what they should be, 4.5 V on pin 2 and 0 now in pin 6, even though I even changed the 10 μF capacitor for 1 μF ones as shown in your schematic. -5,8 being still on pin 14, but anyway no transmision at all.

Thanks a lot anyway.

 

[be80be]

These chips are easy to mess up if you hook them up backward. And read the part number on the chip I got a whole tube of these and the first one I used wouldn't work I just new it was hooked up right. I spent a day fooling with it and guess what it was the wrong chip that came in a whole tube of nice new one's. It was a max. but the pinout was not the same as the ones I ordered and it didn't need the same cap layout.

 

[kyru27]

It has happened to me the same as be80be, it was another chip, similar but not the same... well that's solved at least.

Thanks a lot.