Rs232 port not working

**kip** · 31-08-2008

I have an old phoenix apollo ci which i converted to an openbox some time ago but has been sitting in my loft for a few months now because i could no longer comunicate with it via my pc.. It works fine apart from this but is not much good to me like this.. I did a bit of research and found out the max232 chip was the likely cause, looking at the board though i can see 3 small chips below the max232 with 2F written on them and the track close to one of these has burnt out, does anyone know what the chip with 2F on it is? I have had a look through the maplin catalogue and can not see one. Also when i tried to buy a max232 chip in maplin they were much to big.. Are production chips smaller than what maplin can provide or was it just the wrong one? I am not to concerned about making a mess of this as i have since got another one, just thought i would have a play with my soldering iron.. Any help would be appreciated

**HB13DISH** · 31-08-2008

Hello kip,
A photo would help, especially with the Maxim Max232 to determine it's package size as it looks like you have it as SMT and not in a Dual-In-Line package. It is possible that this part is obsolete.
The other parts are hard to say without looking at the logo or shape.
Could be a capacitor, but 2F doesn't make sense.
If the new card is exactly the same, then please take a picture of that if the parts markings are shown better.

**HB13DISH** · 31-08-2008

The datasheet of MAX232 is attached here. See page 35/36 for ordering info and also the ds for package of 16-Narrow and 16-wide
Possible ordering part numbers
MAX232CPE in 16 pin Dual-in-Line (DIP)
MAX232CSE in 16 pin SMT SO-16 Narrow
MAX232CWE in 16 pin SMT SO-16 Wide

Just measure dimention E, if it is between 3.8-4.0mm, then your part is MAX232CSE
E between 7.4-7.6 mm > MAX232CWE

If it is a DIP, then MAX232CPE

Is the 2F shown inside a circle? If it is then this could be a logo.
Anyway the MAX232 uses at least four capacitors of 1 microfards.
I am only gussing that the 2F is probably a capacitor or you are not reading the symbol correctly. A photo might help.
Can you see any other such parts?

**kip** · 31-08-2008

In the bottom right corner is the max232 above the rs232 port and just above it are 3 capacitors and then the 3 chips
_http://i362.photobucket.com/albums/oo61/kip-photos/2007_0904Image0029.jpg

I could not focus in enough to focus on the chips in question but all they say is 2F.. You can clearly see the problem with this photo
_http://i362.photobucket.com/albums/oo61/kip-photos/circuitprobleminphoenix.jpg

I have been advised that the max232 chip may also be damaged by the official site for the openbox (i didn't tell them it was originally an apollo).. But would first like to know what the 2F chip is as this is quite obviously where the damage is.. I want to replace this first.. My Knowledge in electronics is limited to a city and guilds i did 18 years ago and things have shrunk alot sinse then, quite handy with the soldering iron though..

Thanks by the way for the quick reply

Please upload images, not link to them. Admin

**HB13DISH** · 31-08-2008

Can you tell me what is dimension E. This would determine what to order.
It looks like the wide SMT package, but I need you to measure it first.
As for the parts with the 2F marking, it is impossible to see and I am not really sure why do you want to replace them, unless you are absolutely sure that they are damaged.
You can try to solder a little piece of wire instead of the burnt PCB track. Just clean it first.
The big question is if you are able to solder a new MAX232 instead of the damaged one. If you have experience then an SO-16 is not that difficult.
But if this your first time then give it to a professional.
Please try to get a better picture around the parts with 2F marking. You might need a better camera.

**Llew** · 31-08-2008

2F is an SMT transistor. Problem is, it could be one of two types - NPN (BC850B)or PNP (2N2907A). Replace it with the wrong one and you'll kill it.

If you have a multimeter you can easily check what type it is (assuming at least one of them is OK).

Llew

**kip** · 31-08-2008

Originally Posted by HB13DISH

Can you tell me what is dimension E. This would determine what to order.
It looks like the wide SMT package, but I need you to measure it first.
As for the parts with the 2F marking, it is impossible to see and I am not really sure why do you want to replace them, unless you are absolutely sure that they are damaged.
You can try to solder a little piece of wire instead of the burnt PCB track. Just clean it first.
The big question is if you are able to solder a new MAX232 instead of the damaged one. If you have experience then an SO-16 is not that difficult.
But if this your first time then give it to a professional.
Please try to get a better picture around the parts with 2F marking. You might need a better camera.

I'm not completely sure the max232 is damaged, this has only been suggested that it might, i'm sure the transistor as Llew has suggested it is, is..I can see that it is damaged which might not be clear from the second picture.. I am not going to take this to a professional as it is cheaper to buy a new one(as i have), just wanted to see if i could fix it myself for fun.. i can't get my camera to focus any more (sorry for the link to image)

Llew, thanks for your reply also, i have a multimeter but have forgoten all but the most basic functions it can perform(can't remember the last time i used it).. Can you tell me what i can do to check what transistor it is.. thanks

**kip** · 01-09-2008

HB13DISH i have measured the max232 and it is as you say 3.8-4 mm dimension E.. Thanks this has been a big help in identifying the chip.. I think i have identified the 2F transistor also here h**p://www.fairchildsemi.com/ds/KS/KST2907A.pd .. do you think this could be it? I was also thinking that i could take another 2F transistor off the s-video module and replace it with the one that looks burnt out, i never use the s-video module so i could see if this would solve the problem

**HB13DISH** · 02-09-2008

OK. So the ordering p/n is MAX232CSE
If the part with 2F marking has three terminals in the SOT-23 package, as shown in the ds, then it could be KST2907A. (PNP transistor).
Personally I don't like ruining a perfectly good module, so you can either buy the same part from any parts shop and use that. (check Maplin, RS Components, etc).
But the problem is that it is SMT and you didn't say if you have experience with soldering small SMT parts.
You might find it easier to buy the same part with leads and solder that instead to the board. In this case use PN2907A.
There will be a lot of mechanical stresses on the borad, where the three pads are since the leads are strong. Would be best if you can solder the SMT package.
Good luck.

**kip** · 02-09-2008

My only experience soldering is from college some time ago and my last project was converting an old bsb dmac to d2mac (they used to sell kits for this). But no i don't have experience with such small components. You say they sell them with leads

I think your right about the s-video module, it was just an idea

.. I will let you know how i get on with this and thanks

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