diff --git a/src/main.cpp b/src/main.cpp
index ee927fd..129e9b0 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -32,14 +32,22 @@ void midi_task(void* parameter) {
         midi_transport.update();
         exp_pedal.update(midi_transport);
 
-        uint32_t beat = midi_tick_count / 24;
-        if (beat != last_beat) {
-            last_beat = beat;
-            flash_start = millis();
+        uint32_t tick = midi_tick_count;
+        uint32_t now = millis();
+
+        if (tick / 24 != last_beat) {
+            last_beat = tick / 24;
+            flash_start = now;
             mux.set_led_color(6, 255, 255, 255);
             mux.show();
         }
 
+        static uint32_t last_diag = 0;
+        if (now - last_diag > 2000) {
+            last_diag = now;
+            Serial.printf("[CLK] ticks=%lu beat=%lu\n", (unsigned long)tick, (unsigned long)last_beat);
+        }
+
         if (flash_start > 0) {
             uint32_t elapsed = millis() - flash_start;
             if (elapsed >= 80) {
diff --git a/src/midi_transport.cpp b/src/midi_transport.cpp
index 2c12f66..5501bed 100644
--- a/src/midi_transport.cpp
+++ b/src/midi_transport.cpp
@@ -50,12 +50,20 @@ void UsbMidiTransport::update() {
                       TinyUSBDevice.mounted() ? "YES" : "NO");
     }
 
+    static uint8_t clock_diag_count = 0;
     while (usb_midi.available()) {
         uint8_t packet[4];
         if (usb_midi.readPacket(packet)) {
             uint8_t cin = packet[0] & 0x0F;
             if (cin == 0x0F) {
-                if (packet[1] == 0xF8) midi_tick_count++;
+                if (packet[1] == 0xF8) {
+                    midi_tick_count++;
+                    if (clock_diag_count < 5) {
+                        Serial.printf("[CLK] pkt=%02X %02X %02X %02X cin=%X\n",
+                                      packet[0], packet[1], packet[2], packet[3], cin);
+                        clock_diag_count++;
+                    }
+                }
                 continue;
             }