FACSAria Question: no signal with Red laser (Trigon)

Dear Flowers,
This is Aria related question and any tips would be greatly helpful to us 
(till BD guys get back to us). 
Until recently, when we ran QC with rainbow particles, we could see signals 
in Blue laser related PMTs (octagon) as well as Red lazer related PMTs 
(trigon). But today when I ran QC, I do not detect any major signal on Red 
related PMTs with the same batch of rainbow beads.
We checked (and incrementally changed) laser delay from -30 to -50 and did 
not get any signal. Also, changed area scaling (from .5 to 2.0 incremental 
changes) without any effect. (also changed sheath pressure:low high med as 
well as checked instrument configuration to see whether red related PMTs are 
included or not, they are).
I phyisically checked red laser is working by using shutter override and can 
see both the colors (blue and red).
Curiously, we see some very sharp noise like signal at ~60 in APC-cy7 as 
well as APC area histogram that does not move at all with change in voltage 
of that PMT.
Do you have any tips as to how to regain signal acquisition for our problem 
or what can be wrong.
Thanks in advance for your insights.

-- 
Achal Pashine
Chiron Corporation