Need to test a small board

[nervis1]

This is a 422 board, connects to a serial 232, and converts to 422. I'm having problems with comms and it may be this board. I have a multimeter, but I have no idea where I should have continuity and where I should not.

Can someone give me some ideas about how to test this board?

[gar]

051204-1413 EST USA

nervis1:

Provide a circuit diagram. What power is required for this board, and how are the +/-12 v for RS232 generated? 12 v is nominal, in some cases it might be +/-5.

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[nervis1]

Don't have a circut diagram. I have no idea what voltages it runs on. It connects to a standard 10 pin PC motherboard serial com2 connector if that helps. Most 422s are 3 volts but some of the older ones were 5v, don't know what this one is.

It's circa 1997 and I can't find any info on it on the web, obsolete I'm guessing.

[nervis1]

http://chaokhun.kmitl.ac.th/~kswichit/Rs422/Rs422.pdf


Found this may help?

[gar]

051204-1709 EST USA

nervis1:

Several suggestions: Use your camera without flash so have have diffuse lighting. Research some fundamental items --- find out what typical voltage levels exist on an RS232 connector, what are the default states, what can you do to change these, circuit trace your board and create your own schematic, get datasheets from the original manufacturer ( TI, Motorola, Signetics, National, Intel, AMD, and so on ), study these sheets for the characteristics of the parts on your board. Some times Mouser is a quicker way to get to a datasheet.

The RS232 connector you are referencing is a 9 pin female D connector, not a 10 pin, there is no 10 pin D connector made. There are no pins on an IBM 9 pin serial connector that are power pins. A self powered adapter, which apparently is what you have, derives power from the signal lines. These lines in many cases limit the available power. For example each output line of the 1488 RS232 driver limits at 10 ma. I did not quickly find the quiesent current at 5 v required by the 75179 with no load on the 422 side. The 120 ohms terminating resistor on the 422 schematic is a substantial load. In many cases 422 or 485 does not require any terminating resistance, depends upon line length. At 4000 to 8000 ft we use 249 ohms.

The schematic you referenced in your third post does not help much. Is the 75179 used on your board? The chips are not readable in the photo.

Before asking questions such as you presented you need to do more investigation on your own. A question like you presented only works if you connect with someone else that has exactly the same board and is intimately familar with the details you are asking about.

Do not assume I am giving you a difficult time, but I am trying to help you solve your own problem, and others in the future.

In a final exam I had at one time the regular professor, A. B. Macnee, was absent and in his place was the head of the department, W. G. Dow. There was a question on the test that I thought was inconsistent.

Almost all our tests were open book, on the honor system, and without any professor present. The lit school did not do things this way. I went to Dow's office to ask about this question and his only response was to tell me to describe what I thought the problem was as my answer.

If you were to know Dow and his teaching techniques you would know he was a great teacher, as well as as a prominent researcher in electron tubes. In the real world vs a lot of classrooms you do not know the answer, you will not be given the answer, and you have to try to ask the correct question and probe for the answer.

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[nervis1]

Chief. Count the pins on the left side of the board. 10.

That connector goes to a ribbon cable that connects to a 10 pin connector on the mother board like I said. The serial port on the right is 9 pins.

The maker HMS does not list this product on the web.

Before asking questions such as you presented you need to do more investigation on your own.

So now I have to find the answer somewhere else before I ask a question on this board? You are joking right?

[gar]

051204-2042 EST USA

nervis1:

Sorry about the connector. Since that ribbon cable will normally connect to a 9 pin male you can take a cable with with a 9 pin connector and trace it to determine what pins on your 10 pin connector correspond to RS232 9 pin connector pins.

There is nothing wrong with asking questions, but you obviously did not want to do some very simple things that would have allowed getting some useful answers. Important is from where does the power to supply the 422 chips come. The easy and most reliable way is to know the chip part numbers, and look at the data sheets to find the Vcc pin, then trace your circuit and see where it goes.

Normal RS232 drivers will have unloaded output signal levels around +/- 10 volts. If you put a typical RadioShack RS232 tester on the RD232 output you will considerably load those outputs. For a 1488 the output impedance is about 300 ohms until current limiting takes over.

Common (ground) will flow thru from the RS232 connector to the RS422 and to the common pins of the interface chips. Easy to trace on the board and with an ohmmeter.

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[nervis1]

I have no idea what the chips are, I was thinking more along the lines of ....you should see 5v here or you should have continuity across here, or you could check for a burned up IC here etc.

Data sheets, W.G. Dow, who???? Have no idea what you are talking about Gar.

Guess I'm way out of my element here knowing nothing about electronics.

Lets just let this post fade to oblivion. It appears to have been a waste of time for both of us.

[abasir]

Can you get a magnifying glass and read the numbers on the chip. It appears to be from SIPEX, they make RS232/RS422 interface chip. The chip may be obsolete but the datasheet might still be available. It's going to be tough if we don't know what chip it is.

[smarbaga]

if your computers rs232 port is working fine just change the chips on the interface.
looks like you should see the power across the orange cap and probably gets its power from the rts signal. (10v)
or get a new 422 converter

[gar]

051205-0829 EST USA

nervis1:

Looking at your photograph it appears that the board does not use a 75179. I finally found the 75179 spec for quiescent input current (happens to be under drivers ) and the maximum value is 70 ma.

There are two 422/485 chips on you board. Probably one is used for transmit and the other for receive. Pins 6 and 7 on each chip appear to be the balanced output or input lines, and each appears to have a terminating resistor. This corresponds with the pinout on a DS3695 or DS3696. Also on the 3695/3696 chips pin 5 is common (ground), and pin 8 is Vcc (+5 v).

On your board the device that appears to be labeled C3 is probably the primary +5 bypass capacitor. The + end of this capacitor may show a short circuit to the pin 8 of both chips. And the negative end a short to the pins 5.

These chips could be similar to National DS3696. This chip I have and it has a quiescent current of 20 ma at 5 v with no load. No way could two of these chips be port powered from a driver like the 1488.

My guess is that this board was not designed to interface from RS232 to RS422, but rather to operate from TTL level signals from a UART and be supplied from a 5 v supply.

There is no evidence of any circuitry that would be required to obtain power from the data and handshake lines of an RS232 interface.

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[gar]

051205-1246 EST USA

nervis1:

Where did you get information that this board is an RS232 to RS422 interface?

Also it is very clear this is not an electrically isolated board.

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