SM 72 SP+L Stopping during production.

After replacing the Sheet Alignment Photocell, the SUM2 Signal Conversion Module and retiming the feeder the press is running quite well... or so I thought. The press will now just stop production as if it were an early sheet "bypassing" the head stops. However, there is no display of such action. When I put the safe on to check the alignment everything checks out. Nothing is showing up on the CPC. I checked Circle T and nothing. I don't have to do anything special to get the press running again, just press run to clear the sheets already in the press. Once that's done just hit production again and I'm off to the races. It's just random. 150 sheets / Stop 450 sheets / stop 1900 sheets / stop 4500 sheets / stop. Crazy, isn't it? Any suggestions?

 

Sounds all to familiar...not saying this is surely the problem, but the microswitches on the red nip bars can cause a lot of grief due to wear in the linkage pieces and worn contacts. I'd focus on them if you see nothing showing up at infeed sheet monitoring and diagnostics.

 

Thank you, Junker, for the reply. I spent most of this morning going through all of the micro-switches. (tedious on a 6color + coat but it's done). Everything seems fairly snug, meaning it takes an effort to trip the switches with the bars. However, I did find one suspicious linkage under the cover of the IR Dryer / Transport. It was caked with powder. I cleaned it out and I also checked and cleaned the sheet detecting sensor under the perfecting cylinder. I'm about to start production for the day. I'll post later this afternoon if the issue remains. Thanks again

 

Ok, it's only happening when the press goes on impression. Finally it gave a code long enough to determine where it is. 03. Unit 3. The perfecting eye is under there.. could it give me the same error? It's the type of sensor that has an air blown flap.

 

Problem is solved. Ended up being a timing issue. While mechanically the press would feed and not miss a beat, electronically it was out. Sheets were arriving a touch too slow; arriving at the ANK at 277 - 279 degrees. Its supposed to be between 262 and 272. The photo cell at the perfecting unit saw the sheet and it was on par with the mechanical timing, however the math didn't add up for the subroutine on whatever board is doing said math. So the press thought it was dropping a sheet and would give the code but the sensor/eye detected the sheet and cleared the code within nano seconds. Therefore, electronic math in conflict with mechanical photo-cell detection equals stop the press. I set the timing of the feeder to arrive at the ANK at 264 degrees and the press didn't stop once during production. Thank you to everyone contributing on these forums. I've read about 50 - 60 threads here on 102s, 74's and 72's having something relatively close to the problem I had and the input helped me arrive at my conclusion.