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Strand 520i - No DMX Output on Output 2

#1 User is offline   trolley01 

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Posted 06 April 2012 - 07:27 PM

Hi,

Got a Strand 520i and just putting in a show. Went to plug it all in - using all 4 outputs for convenience. Plugged in all 4 - set the outputs on the desk and went to test and got no activity on the second output.

Went back and checked all my connections - plugged the cable from output 2 to output 1 and every fixture on the chain works perfectly. Checked that I had enabled the output for the right range - and it is.

Even if I plug in an alphapack with a short cable directly into the back I do not get a DMX activity light. Plugged it into output 1/3/4 and worked first time. Almost like something has blown and stopped it working.

Had a quick look under the hood for any obvious fuses, etc on the outputs and nothing.

Any suggestions on what might be causing this much appreciated! Have managed to get round at the minute by doing a quick bit of re-wiring but would like to get sorted.

Thanks!

#2 User is offline   DrV 

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Posted 07 April 2012 - 12:48 AM

The DMX goes via some 3 pin 0.1" connectors immediately under the XLRs. These are usually made with insulation displacement connections and may be causing a problem. You could try swapping DMX2 with DMX1 to see whether the fault moves. Looking in the back this would be the right hand connector on the top row and the one to its left. (They are labelled DMX1 and DMX2 on the PCB).

Next place to look is the flexistrip cables which run from the output panel to the main board. Check that these are inserted fully and squarely.

Another possibility is that one of the protection diodes on the output panel has gone short. These are hidden behind the flexistrips and you'd have to check them with a meter. The 3rd and 4th from the right are for DMX2. If one of the associated resistors just above them is open this would cause the same problem. These are all surface mount.

After that you are down to the 75176 chips on the main board and these are surface mount too so not really a field fix (although not impossible). You'd have to get the whole CS card out to replace them.

Dave

#3 User is offline   trolley01 

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Posted 07 April 2012 - 08:29 AM

Thanks for the quick reply.

Checked the insulation displacement connections by switching outputs 1/2 and the problem moved. Flexistrip cables were all secure - pulled and cleaned out with some air duster just to check.

I metered the diodes and the resistors, and the 3rd/4th diodes and resistors are both open.

Do you know where I might be able to get hold of a schematic for the connector board? I can then whip it out and do a quick replacement of those components

Alternatively I guess I am looking for a replacement connector board?

#4 User is offline   DrV 

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Posted 07 April 2012 - 10:36 AM

View Posttrolley01, on 07 April 2012 - 08:29 AM, said:

Thanks for the quick reply.

Checked the insulation displacement connections by switching outputs 1/2 and the problem moved. Flexistrip cables were all secure - pulled and cleaned out with some air duster just to check.

I metered the diodes and the resistors, and the 3rd/4th diodes and resistors are both open.

Do you know where I might be able to get hold of a schematic for the connector board? I can then whip it out and do a quick replacement of those components

Alternatively I guess I am looking for a replacement connector board?


The diodes should appear open as they are actually Transient Voltage Suppressors (TVS) which are electrically a bit like a pair of back-to-back zeners. Each one has one end connected to chassis ground and the other end to a DMX line. If you get a nasty voltage on the external lines they are supposed to conduct to stop it getting to the chip. The resistors are in series with the DMX lines to limit the surge current to something manageable. If the resistors (which should be 4R7) have gone open then it looks as though the TVSs did their job and the external spike has blown the resistors open. I don't know exactly which TVS is used but they are an SMB package and would need a stand-off voltage of about 12. These would do the job. If you are certain that there is nothing nasty around you could just short out the resistor positions and remove the TVSs to check whether it works but DON'T leave it like that as the main PCB will be unprotected. If you do decide to test it that way then make sure that you are using a properly earthed dimmer pack and run it from the same socket as the desk.

If I were doing this I'd just put a scope on the bottom end of the resistors to see whether there was DMX present.

Hope this helps
Dave

#5 User is offline   trolley01 

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Posted 07 April 2012 - 03:22 PM

Thanks again Dave.

I have access to another 520i, so think I am just going to switch the two connector boards and see if the problem moves. I'm not sure my nerves would cope with the way you suggested! I don't own a scope either - only a multimeter.

Have you any idea what value of resistor might be being used? I can't quite see it without taking the board to pieces first.






#6 User is offline   DrV 

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Posted 07 April 2012 - 03:40 PM

View Posttrolley01, on 07 April 2012 - 03:22 PM, said:

Thanks again Dave.

I have access to another 520i, so think I am just going to switch the two connector boards and see if the problem moves. I'm not sure my nerves would cope with the way you suggested! I don't own a scope either - only a multimeter.

Have you any idea what value of resistor might be being used? I can't quite see it without taking the board to pieces first.



They are 4r7 (4.7 ohms) as I said above ;)

Edit to add: If you find that the fault is indeed on the connector panel then PM me and I'll give you a repair quote if you like - it's small enough to post in a jiffy bag.

Dave

This post has been edited by DrV: 07 April 2012 - 03:43 PM


#7 User is offline   trolley01 

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Posted 07 April 2012 - 04:04 PM

View PostDrV, on 07 April 2012 - 03:40 PM, said:

They are 4r7 (4.7 ohms) as I said above ;)


Sorry - you did indeed!!

Thanks for the offer - I will let you know.

#8 User is offline   trolley01 

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Posted 10 April 2012 - 10:22 PM

Just an update - had the desk apart today as I had some time.

Replaced the two resistors with new, and the output works perfectly.

Thanks very much for your help.

Craig.

#9 User is offline   DrV 

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Posted 11 April 2012 - 09:12 AM

View Posttrolley01, on 10 April 2012 - 10:22 PM, said:

Just an update - had the desk apart today as I had some time.

Replaced the two resistors with new, and the output works perfectly.

Thanks very much for your help.

Craig.

That's good news. Did you check the functioning of the TVSs? It is possible that these have been damaged and are no longer protecting the main board against transients. To check them you need to

1) disconnect the flexistrips going from the panel to the main board and make sure they can't touch anything.

2) connect a power source of about 20-24v THROUGH A 1k LIMITING RESISTOR beween each DMX pin and the metalwork of the back panel.

3) check the voltage between the DMX pin and chassis.

The voltage should be clamped at approx 15v. If it goes above this then the diodes are not protecting the rest of the circuit and need to be replaced.

Dave

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