Service Forum

[jmwtzl]

I am modifying an old Nokia RS232/TTL data cable which uses a MAX232CPE.

The Nokia data cable is a "3rd party" device which is built into an "interface box" rather than the DB-9 plug so the circuit is very easy to access!!

I have checked out the circuit and it is very similar to Victors "driven" circuit so few mods are required. The only major difference is that 4 of the caps are 22uF (only 1 is 1uF).

I am aware that the official value is 1uF (or 0.1uF for a MAX232A).

Will using 22uF caps be OK?

Thanks

[victor]

1uF is the official value of the manufacturer too. with 22uF the charge pump frequency might be lower so I suggest you to replace it with the proper value, just to be sure. Also see the COM port wiring, I bet there's some difference too, Nokia uses M2Bus
_________________
Victor Voinea
ALLservice HQ, Romania.

[jmwtzl]

Thanks Victor - will replace the caps with 1uF.

Yes , the COM port is set up for RS232 TXD/RXD but mod is easy.

Apart from the 22uF caps, I just need to:
- switch a cap to pin 2 to 16 (instead of 2 to GND)
- remove diode from pins 12 and 15
- add the two 4.7k resisitors
- add the 2 diodes
- remove the 78L05 5v voltage regulator.

Thanks