intermittent Imaging failure on unit 1

Hello, I have a QMDI 46-4 with 22mill impressions on it. Recently I had Imaging problems on unit one only. The other units all complete imaging correctly but unit 1 will either stop in mid imaging and or image incorrectly (as in a plate that looks like noise), and sometimes it does not even begin to start imaging. The plates on unit 1 still seem to image completely and correctly about 30% of the time. None of the Imaging modules show any errors in the GUI.

There are no errors on SF 62 ever. I've swapped the logic board from unit 1 to unit 2 and noticed no differences. I noticed that the cable from the backplane board to the imaging module that controls diodes 9-16 had 4 of the 64 wires spliced so i assumed that was the issue even though it has been that way for a long time and the splices appear to be ok. I replaced that cable with a new one and the problem changed. After the new cable was installed diodes 1-8 would image a total solid all the way down the plate. So I thought that maybe that cable was actually the one that was flawed and I put the new cable in that position. After putting the new cable in the first position and putting the old cable back in the second position I got it to image 5 plates completely and correctly in a row, but then the problem came back, where is stops imagining before completion.

The only options I can think of is that both cables are intact bad or that the problem is the backplane board itself. I have not swapped the power board on unit 1 as I've not heard anyone suggest that as a possibility so far.

The cable swapping does seem to dramatically affect the results but has not solved the problem.

I don't understand why if the issue was in the cables or the imaging modules why it would be causing problems on both halves of the plate, unless the cables or modules not work independently from each other. I don't see how the backplane board would have an issue that only affects unit 1 either.

I must be missing something as I'm out of ideas here. Does anyone have any suggestions for what I could look into next?

Thank you

It is possible the backplane is a problem. I would take the backplane board out and check the solders on the back of it for the ribbon cable connectors. I have seen these solders cracked before from frequent removal of the cables in the case of machines that have been moved from one shop to another multiple times. A few of the pins may have hairline cracks causing intermittent imaging issues.

One of the machines we used for trade shows when the QMDI first came out did this to me, it was the 2nd machine built and had been shown all over the country. In Atlanta I was to run the machine for a show and during set up I started getting wierd images all over the plate in the 1st unit. I replaced cables, LDM's, Logic boards and finally 6 hours before the show started I pulled the backplane board one more time (After having already done it 5 times.) and looked closely at the solders with a magnifying glass only to find them cracked. Once resoldered the press imaged fine.

Also make sure all the pins in the plug on the backplane board are straight. I have seen these folded over before, that will also cause an array of issues.

Good luck and let us know what you find.

Thanks Paul. Our press used to be a Heidelberg demo press here in California but has not been moved since we got it in 97. It seems like the backplane board is the only thing we have not looked at. I've never taken one out before, but I suppose it can't be too bad if you've had to remove it 6 times before a show. Nothing to crazy to watch our for when removing it?

Does it make sense that both halves of the plate would image sometimes completely but with strange a looking image? If it was the connection on the board to one of the cables then would't one half of the plate look correct all of the time when it finishes the imaging process?

There is more that can be going on. The Power Driver board is responsible for the axial movement of the laser carriage. It gets its signals from the Logic Board through the backplane board. If there is an issue between these two the carriage may not be moving properly causing your image to be distorted. My only reservation about this diagnoses is that typically when there is a failure in axial movement you will get stripes of non imaged areas on the plate.

It is strange that both halves of the plate are not imaging correctly, this would indicate that both ribbon cable connectors on the backplane board would have issues. It could also be there is an issue with the data that is coming from the RIP for the black plate.

One way to check and see if the issue is solely on the first unit or related to the black image only is to image the Cyan in the first unit and the Black in the 2nd unit. If the problem follows the Black there is a network issue. Also, what happens when you burn the 60% screen diode test job that is found on the press PC and does not come from the RIP?

Removing the backplane is not entirely difficult, just time consuming. Make sure everything is unplugged and the entire rack can be removed from the cabinet. You can actually look at the backplane board in the rack once it has been removed from the control cabinet.

We have not Imaged Cyan information on unit 1 yet. We have however imaged black plates on unit 2 a number of times without error and we have been using the 60% test file from the DI to test unit 1 and still get the errors.

Most of the time that it fails there are strips of non imaged plate. Sometimes it will not start imaging at all, other times the entire plate images but looks wrong and sometimes the entire plate images an is correct.

Sounds like I could try swapping the power driver board from unit 1 to unit 2 maybe before I take the whole backplane board out right?

thanks

If you are still getting the problems imaging the 60% screen then the problem is isolated to the press. If there are strips that are non imaged across the entire plate in all 16 zones it could be the stepper motor. Do you ever get "Cant find home" position errors at the beginning of the imaging process?

Swapping the Power Driver boards are something I would do before pulling the backplane board.

I would also look at the spring coupling that attaches the stepper motor to the imaging head. It is possible it is either broken or the grub screws which fasten it to the shafts are loose. When the stepper motor moves the shafts slip in the coupling causing the head not to move when it should.

I would be curious to see some photos of the imaging issues you are having.

I have not seen any errors at all. Is the "can't find home error" something that would should up in SF 62 or would that error be somewhere else? The spring and grub screws on the stepper motor appear to be in good.

I did swap the Power board with unit 2 without any change. Unit 2 still images and Unit 1 does not after the swap.

I'll try to send an image of what the bad plates look like but lately it has been simply not starting to image at all on unit 1.

I guess I'm back to looking at the backplane board.

Thanks

You want to swap out the the stepper motors see if it changes. I have had a similar problem and it turned out to be the stepper motor.
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Would the stepper motor work some of the time and not work other times? Its odd cause it works some of the time and when we mess with the cables on the backplane board it seems to improve.

The stepper motor uses an opticle encoder. It is possible it may have an issue. Sometimes due to the eyes that read the disk increments or sometimes the opticle disk itself. Your problem may be there as Anthony suggested.

Looks like it turned out to be the encoder. its up and working now after we replaced that.

Glad to see you are back up and running.