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Broke my plotter's rs232 db9 female wires, need rewire help pls

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deliad

New Member
Hi,

I have a chinese plotter cutting machine which communicates via rs232 db9 port

Yesterday i accidently brike the connectors and with my bad luck the wires disconnected too.

This plotter is totally ubranded and the board inside doesn't have any model or brand written.

The board side of the db9 connector is 8 pin IDC ribbon cable

The only things that i know are:

1. The wires that were used on the db9 female connector are:
From the ribbon cable

Wire 1 RED -NOT USED

WIRE 3

WIRE 5

WIRE 6

WIRE 7

WIRE 8

The wires were connected to the db9 female NOT AT THE REGULAR STANDARD ORDER!

Plotter was used these communicate settings
DTR/DSR RTS/CTS

And the total wires that used are 5 wires

Its probably DTR/DSR RTS/CTS And ground

BUT, i dont know how to identify the what wire on the ribbon connects where on the db9 female, AND AGAIN, its not on the standard order.
 

Les Jones

Well-Known Member
Most Helpful Member
Does the ribbon cable go to an IDC DB9 connector or is the end of the ribbon separated and soldered into a normal DB9 connector ? If it is a IDC connector it should be possible to identify the ground wire which goes to pin 5. Is the connector that was damaged the one on the back of the plotter ot is it the one on the end of the cable from the computer that plugs into the back of the plotter ? I am not clear what you mean when you say "NOT AT THE REGULAR STANDARD ORDER"

Les.
 

deliad

New Member
Hi, you didn't got me

iv'e uploaded a video to youtube to explain better

 
Last edited:

Les Jones

Well-Known Member
Most Helpful Member
When you say that "NOT AT THE REGULAR STANDARD ORDER" do you mean that the signal definitions do not use the standard pins that they would use.
This is the standard pin numbers associated with each signal definition.
1 DCD Data Carrier Detect in
2 RXD Receive Data in
3 TXD Transmit Data out
4 DTR Data Terminal Ready out
5 GND Signal Ground -
6 DSR Data Set Ready in
7 RTS Request to Send out
8 CTS Clear to Send in
9 RI Ring Indicator in

If they are different can you say which pins you use for each signal.
Has the connector (At the plotter end) on the cable from the computer also been damaged. If it has not then we now the signals will use the standard pins at the computer end so by testing with a multimeter we can see which pins at the plotter end are used for each signal. If we could see the back of the connector that had the wires pulled of we would know which 5 of the 9 pins had been used. We should be able to identify the ground wire coming from the 8 pin IDC connector with a multimeter by seeing which one connect to the chassis of the plotter or to the ground pin on one of the standard ICs (4000 series or 74xxx series). We are then left with 4 pins to identify. Again with a multimeter we can identify outgoing signals. At this point we have a relatively small number of ways the 4 wires could be connected. Did you not get a manual with the plotter when you bought it ?

Les.
 

MaxHeadRoom78

Well-Known Member
Hi,


Wire 1 RED -NOT USED

WIRE 3

WIRE 5

WIRE 6

WIRE 7

WIRE 8


Plotter was used these communicate settings
DTR/DSR RTS/CTS

And the total wires that used are 5 wires

Its probably DTR/DSR RTS/CTS And ground

.
One is going to be GND, one is RX, you may or may not have a TX, being a plotter, so the remaining are handshake.
If it uses a standard LSI USART IC you may be able to trace the board socket pins to an IC in close proximity.
Max.
 

KeepItSimpleStupid

Well-Known Member
Most Helpful Member
Once you have identified ground and have measured the voltages from the plotter, that will give you some of the wires.

On a good note, wrong connections do no harm
 

deliad

New Member
thanks for answer everyone.

KeepItSimpleStupid - I was expect from you to answer me, thanks

have some questions:

1. do you actually say that i should see voltage on multimeter even the plotter is on standby? the voltages to the com port is constant??
2. how can i measure voltage with multimeter when i don't know what wire is positive or negative to other wire?
3. you say if i wrong with wires i cant damage something?? i don't think so , if you say that voltages coming from the plotter IDC Side.
4. please explain me in detail how should i recongnise them with multimeter - what voltage belong to what pin?

someone sort it for me.

thanks.

BTW, I tought to buy 8 pin IDC to RS232 DB9 but it doesn't exists, as the connectors for this connection (from pc to plotter) is not standard wiring order.
 

KeepItSimpleStupid

Well-Known Member
Most Helpful Member
(3, 4) OK. sorry, but I expecting stuff to go iteratively somewhat. I worked with RS232 since the mid 1970's. I had the benefit of an RS232 Breakout box. Something like this with the adapters makes it CAKE! The voltmeter method makes it MUCH harder.

When you connect a receive to a receive - nothing bad happens except it doesn't work. Note here: http://www.ti.com/lit/ds/symlink/sn75188.pdf is a typical driver chip. Note a 300 ohm resistor and diodes to the + and - supply. This is basic protection. It would not like all of it's output shorted to ground, but to each other is OK.

You have to find ground. Inspection or an ohmmeter to ground. Usually it's a solid connection to chassis ground and power supply common. Re-check with the diodes mode to make sure there are no diodes in your ground connection. Even if you don't initially find ground, you can measure the voltages with respect to chassis.

You also need to know if the device is a DTE (Terminal) or a DCE (Modem). If you know ahead of time great.

Here: https://en.wikipedia.org/wiki/RS-232 is the RS232 pinout, but not the IBM PC version. Note that you have voltages for assertion and a device side.
You have genders and crossover cables, so it makes it more complicated.

If you can get a breakout box, it really makes it easier.

Because they have SIDES, and it used DCE and DTE then you can look at these signals as "the device has power". Inputs won;t have any voltages on them. RS232 chips used to handle +-25 V; modern devices use +-12-15 V

If you can tell the plotter to ignore RTS/CTS all the better.

get ground
The next easy one is DTR/DSR or CTS/RTS. Some devices used to really mix up the signals back in the day.

If you only had 5 wires, you have Rxd, Txd, ground and normally RTS/CTS, but remember they are all relative to a DTE/DCE.

RTS/CTS and one of Rxd/Txd are generally not strictly needed. What I mean is, RTS/CTS is hardware flow control and Rxd/Txd are used for communication back to the Plotter driver. So, you can get a small file to plot with only 2 wires. Large files might plot somewhat. Without the other Rx/Tx there is no error communication back to the driver.

==

Ideally, you should have the standard gender 9 pin port on the PC and the reverse gender on the plotter and a straight-thru cable. So, this information,ground, the five signals used and the voltage readings, we have enough info to start.

So, except for a single short to ground, any pin can touch any pin on the PC or Plotter side without damage. You only have one ground pin.

As I understand it, only 5 wires are connected. Knowing which pins have remnants would help too. All good information.

==

Here http://www.electro-tech-online.com/threads/serial-rs232-cable-help.147785/ is a VERY SIMILAR thread.
 
Last edited:

spec

Well-Known Member
Most Helpful Member
Hi deliad,

I tought to buy 8 pin IDC to RS232 DB9 but it doesn't exists, as the connectors for this connection (from pc to plotter) is not standard wiring order.
You can get around this problem by separating the ribbon cable wires. Then get a standard solder-bucket connector and solder the wires to the connector in the order you require, using Keep's procedure in post #8 above. It is good practice to put small sleeves on the wires before you solder them to the connector. Then just slide the sleeves down over the solder joints. If necessary, you can make some sleeves by pulling the copper conductor out of a short length of ordinary wire.

spec
 

KeepItSimpleStupid

Well-Known Member
Most Helpful Member
Another thing you can do after watching the video is:
There is likely one or two RS232 driver chips. From that part number you can get the datasheet and trace the wires back to determine which wires receive and which wires drive.
Since you have 5 wires, you likely have only on RS232 driver.

That would really help.
 
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