diff --git a/light9/collector/output.py b/light9/collector/output.py
--- a/light9/collector/output.py
+++ b/light9/collector/output.py
@@ -223,7 +223,7 @@ class Udmx(BackgroundLoopOutput):
                 if logAllDmx.isEnabledFor(logging.DEBUG):
                     # for testing fps, smooth fades, etc
                     logAllDmx.debug('%s: %s...' % (self.shortId(), ' '.join(map(str, buf[:32]))))
-
+                t1 = time.time()
                 sent = self.dev.send_multi_value(1, bytearray(buf))
                 if sent != len(buf):
                     raise ValueError("incomplete send")
@@ -255,6 +255,9 @@ class Udmx(BackgroundLoopOutput):
                     return
 
                 raise
+            dt = time.time() - t1
+            if dt > 1/self.rate*1.5:
+                log.warning(f'usb stall- took {(dt*1000):.2f}ms')
 
 
 '''