ATS Alarm showed CBTC Applied EB due toobstructed motion detected at tk cct N632. TC reset EB and t ried proceeding in AM and ATPM mode but fault persisted. EB applied due to rollback tolerance exceeded. TC feedback ther ~~~~~ 603/604 Train EB due to obstructed motion (L3)
Obstructed Motion - BSD Siding:
Train encountered obstructed motion when withdrawing back to BSD-TB3. TC reported train unable to power up. Tripped DIRBS and reset EB but to no avail. 

1. Fault confirmed/ Fault cannot be duplicated
Fault cannot be duplicated in depot. 

2. What was found from ER/ Fault Trace
From TIMS, no propulsion FC at all cars at time of fault.

Timeline based on ER, ATS playback and LDC logs
10:51:00H Train depart BSH towards BSD TB3 (upslope) with TSR of 15kph

10:52:42H Train at 7-10kph when line voltage dropped progressively across cars 1603, 2603 and then 2604. 

10:52:57H Train attempted to propel upslope with one fully powered motor car (1604) but was unsuccessful. CBTC triggered EB after 9 seconds of unsuccessful propulsion (normal behaviour). This occurred two more times.

10:55:20H TC attempted to propel in ATPM mode to no avail; train EB due to rollback. Propulsion was still unsuccessful after DIRBS was tripped in ATPM in the second attempt.

10:58:24H TC changed end and managed to return to BSH (downslope) without EB. 

All 6-car line voltage recovered and train was able to propel normally with no further abnormalities. Train returned to BSD via AMKMT.

3. Troubleshooting details
Probable Causal Factors
These are 3 identified causal factors based on FTA:

A. Lost of power source (third rail 750VDC)
Likely
From the ER, three cars progressively drop in line voltage. 

When train complete stop, 1603 line voltage 0VDC (APS and propulsion controller shutdown when line voltage < 400VDC), 2603 & 2604 line voltage 400VDC. Only 3603, 1604, 3604 above 700VDC.

ER of rear train EMU659/660 showed similar drop in line voltage
 
Contributory factor: TSR with upslope gradient
Train was commanded to brake before commanded to propel when train speed was less than 10kph. Only 1604 had full propulsion.

B. Faulty Relays in Train Propulsion Control Circuit
Unlikely
Checked train powering control circuit satis
- AMR-2 (1028/7025) 0.5ohm
- SR (7005/7006) 1ohm 
- SR (7029/7030) 0.3ohm
- SNR (7006/3) 0.2ohm
- TNR (7007/5) 0.4ohm
- CH4R (7006/3) 0.2ohm
- Coil resistance satis

DIR remained energised throughout the incident. DIRBS did not resolve the propulsion issue.

C. Propulsion/APS Equipment Faulty
Unlikely
a. Checked all CCD shoe fuse and height satis except 1604 
- #1604 B4 CCD shoe flashover (Side finding)
- #1604 A1 CCD fuse blown (Side finding)

b. TM, VVVF Controller, LB/K/L, CHR – satis

c. Performed power satis cx – satis

d. Performed limited movement by powering train using individual M-car - satis. Depot shunting satis.

4. Rectification details
-#1604 B4 CCD shoe flashover, replaced
-#1604 A1 CCD fuse blown, replaced

Performed limited movement by powering train using individual M-cars – satis

Depot shunting in RM ok.

We propose a mainline test to verify that the train will be able to enter BSD through TB3.