diff --git a/main.c b/main.c
index 2dfda61..a186170 100644
--- a/main.c
+++ b/main.c
@@ -51,7 +51,11 @@ void putc(char c)
 	// don't wait until the transmission is complete
 }
 
-void puts(const char* s)
+// enable/disable UART debug
+//#define puts(X) {}
+#define puts(X) puts_uart(X)
+
+void puts_uart(const char* s)
 {
 	if (NULL == s) {
 		return;
@@ -296,32 +300,41 @@ we will only be able to provide 1 extension block since we can only respond to o
 	} else {
 		IWDG_KR = IWDG_KR_KEY_REFRESH; // reset watchdog
 		puts("reading sink EDID: ");
-		softi2c_master_setup(100); // start the I²C master to talk to sink
-		bool i2c_success = false; // if the complete read succeeded
+		uint8_t i2c_rc = 1; // if the complete read succeeded
+		if (!softi2c_master_setup(1)) { // start the I²C master to talk to sink
+			i2c_rc = 2;
+			goto i2c_end;
+		}
 		if (!softi2c_master_start()) { // start transaction
+			i2c_rc = 3;
 			goto i2c_end;
 		}
 		if (!softi2c_master_select_slave(0x50, true)) { // select EDID
+			i2c_rc = 4;
 			goto i2c_end;
 		}
 		const uint8_t edid_addr = 0x00; // EDID address to read
 		if (!softi2c_master_write(&edid_addr, 1)) { // write address to read
+			i2c_rc = 5;
 			goto i2c_end;
 		}
 		if (!softi2c_master_start()) { // re-start transaction
+			i2c_rc = 6;
 			goto i2c_end;
 		}
 		if (!softi2c_master_select_slave(0x50, false)) { // re-select EDID
+			i2c_rc = 7;
 			goto i2c_end;
 		}
 		uint8_t edid_sink[256]; // buffer for sink EDID
 		if (!softi2c_master_read(edid_sink, ARRAY_LENGTH(edid_sink))) { // read EDID
+			i2c_rc = 8;
 			goto i2c_end;
 		}
-		i2c_success = true; // complete read succeeded
+		i2c_rc = 0; // complete read succeeded
 i2c_end:
 		softi2c_master_stop();
-		if (i2c_success) {
+		if (0 == i2c_rc) {
 			puts("success\r\n");
 			const uint16_t edid_len = edid_length(edid_sink); // get length
 			if (edid_len) { // EDID is valid
@@ -394,7 +407,10 @@ level pulse on the Hot Plug Detect pin. This pulse shall be at least 100 msec.
 				}
 			}
 		} else {
-			puts("fail\r\n");
+			LED_PORT->ODR.reg &= ~LED_PIN; // switch LED on to indicate I²C read fail
+			puts("fail (rc=");
+			putc('0' + i2c_rc);
+			puts(")\r\n");
 		}
 	}