diff --git a/artiq/gateware/targets/kc705.py b/artiq/gateware/targets/kc705.py
index 56d9e97fe..520a0d5f4 100755
--- a/artiq/gateware/targets/kc705.py
+++ b/artiq/gateware/targets/kc705.py
@@ -544,13 +544,14 @@ class Phaser(_NIST_Ions):
             # while at 5 GBps, take every second sample... FIXME
             self.comb += conv.eq(Cat(ch.o[::2]))
 
-        # short transport layer test pattern
-        self.comb += [
-            self.ad9154.jesd_core.transport.sink.converter0.eq(0x01230123),
-            self.ad9154.jesd_core.transport.sink.converter1.eq(0x45674567),
-            self.ad9154.jesd_core.transport.sink.converter2.eq(0x89ab89ab),
-            self.ad9154.jesd_core.transport.sink.converter3.eq(0xcdefcdef)
-        ]
+        if False:
+            # short transport layer test pattern
+            self.comb += [
+                self.ad9154.jesd_core.transport.sink.converter0.eq(0x01230123),
+                self.ad9154.jesd_core.transport.sink.converter1.eq(0x45674567),
+                self.ad9154.jesd_core.transport.sink.converter2.eq(0x89ab89ab),
+                self.ad9154.jesd_core.transport.sink.converter3.eq(0xcdefcdef)
+            ]
 
         self.comb += jesd_sync.eq(self.ad9154.jesd_sync)