Single DIODE not imaging

Hi Everyone,
We have recently installed a QMDI PLUS. After 6 imaging cycles we experienced a problem on Unit 4 where DIODE 5 stopped imaging. After removing and replacing the same DIODE, the zone then imaged about 80% width. I then replaced the problem DIODE with a replacement DIODE but the problem returned after one good imaging cycle.

I swopped the boards inside the LDM (black box) but still same result. We then swopped the power and logic boards from Unit 1 to Unit 4 trying to eliminate any problems there - same result though. There is however a RED LED that stays ON permanently on the board for Unit 4 - see picture attached.

Can anyone suggest anything else to test / check please? What does the RED LED indicate?

There is definitely no dirt on the glass as we did clean it thoroughly. Also, we did have one successful imaging cycle after we replaced the laser DIODE, then the problem returned.

Could it be a loose connection on the carriage where the DIODE connects? Could it be a faulty cable that runs from the box to the carriage? Are the cables from a PLUS the same as a CLASSIC? (We have spare cables from a Classic).

Please could anyone reply with some suggestions. Your assistance would be greatly appreciated.

Regards
Shawn

 

Hi sir:
Happy New Year.
I saw the indication problem.
1) It does Not matter the you swopped the power and logic boards from Unit 1 to Unit 4 trying to eliminate the failure
2) There 4 for Logic cards in the machine;
One after the other, the logic boards
receive the imaging data for the printing units assigned
to them from processor board . Incoming data
are edited and buffered in a large memory.
Data exchange between the logic board and
processor board is signalled by the red LED.
When imaging is in progress, the green LED is
dimmed. During the imaging break in the plate cylinder
gap, the LED goes out for a short period.
3) I recommend that you test Meaure the +12Vdc+ -12Vdc in firts Steps in the connector JXC3:+12Vdc -12Vdc

 

Hi again everyone,

Our problem with diodes on unit 4 of our QMDI PLUS continues. Yesterday we had Zone 13 giving us a problem. However, unlike Zone 5 which was not imaging at all, Zone 13 is imaging intermittently. The diode starts imaging, then misses a few millimetres, images again and then misses a few mm again.

What could be the cause of a diode firing intermittently like this. By the way, much to our surprise, later in the day yesterday after changing diodes again and trying new cables from the LDM to the carriage, I got Zone 5 to work. So now I have switched off Zone 13 (dead diode function) and we are imaging with zone 13 switched off. However, this is only a short term solution. What can I check regarding this diode?

Any help would be appreciated.

 

Dear Sir:
I can understand that you did NOT test Meaure the +12Vdc+ -12Vdc in firts Steps in the connector JXC3
This is the secret for the your problem

 

Dear Sir,

If there is a problem with the voltage from connector JXC3 as you mentioned, how are the other diodes still working? I do not think that this is the problem. I think there may be a bad connection either in the cable from the LDM to the carriage or on the plug where the diode connects to the carriage. Thank you for your feedback.

Kind Regards

Shawn

 

Good day Mr Shawn:
You must understand , as Tripple Engineer P.E that I am (Electrical/Electronic/IT-Software), and as Retired by my age, and over 46 years of experienced in Many Trades,Industrial, Design, Maintenance, Fitness ,Trained by a Lot of Companies: Like Heidelberg, Polar, etc.
The power supply in ANY equipment of world: is The Blood = like the Blood is in the Human Being.
By that reason, i am insisting you, and you are agree that you have problem with the voltage from connector JXC3; Never you will fix it Unless First repair that. Secondly you will fix it the problem sir.
My only Concern is to help you.

 

Hi Everyone,

Just an update to our problem.

This morning I did a 60% image on all 4 units of our QMDI Plus and I switched OFF the dead diode feature. By some stroke of luck, all zones on unit 4 imaged perfectly. I assumed that the problem had somehow disappeared.
Unfortunately, when I attempted to image a job on the press about half an hour later, the problem with Zone 13 on Unit #4 returned.

Does anyone out there have any thoughts or ideas on what might be going on or how we can identify the fault?

There is obviously nothing wrong with the lens as the 60% image earlier today would not have been OK if there was. Also, the diode seemed fine when we did the 60% image.
Could it be a bad connection on the laser carriage or a bad connection withing the cable leading from the LDM to the carriage? How can we troubleshoot this problem.

Any feedback would be greatly appreciated.

Many Thanks

Shawn