Roland Practica PRZ 00 2+0 (Series 180) – 2nd unit pressure engagement and speed issues.

[Ivaylo Minchev]

Hi everyone,
I’m having a recurring issue with a Roland Practica PRZ 00 Series 180 (2+0) and I’m hoping someone here might have encountered something similar.
The Problem:
The 2nd unit fails to engage impression (pressure) and the machine won't ramp up the speed (RPM). The issue is intermittent – sometimes it works fine for several cycles, but after stopping and restarting the feed, only the 1st unit engages and the speed stays low.
What I’ve checked so far:

1. Mechanicals: Everything on the 2nd unit is mechanically sound. I can manually engage/disengage the pressure via the toggle switch without issues.
2. Sensors: The photocell (sheet detector) between the two units is working perfectly.
3. Single Unit Mode: If I switch off the 2nd unit to run only the 1st, the 1st unit engages pressure correctly, but the machine still won't speed up, and the speed "+" button becomes unresponsive.
4. Electrical / Boards: I’ve identified the boards involved in this circuit. In the electrical cabinet at U3, I inspected the relays on board U3/64. Some looked burnt or worn. An electrician tested them and confirmed poor contact on several. I replaced the board with another U3 unit that had good relays, but the problem persists.

Since replacing the board didn't fix it, I suspect the root cause might be elsewhere in the logic circuit or a communication error between the units.
Has anyone dealt with this specific logic failure on a Practica? Any suggestions on where to look next would be greatly appreciated.
Thanks in advance!

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