A particular customer with Honda accord 2007 model with faulty gear box. we have changed the gear box thrice with still the same problem.?

Not the gear box problem,,check all linkage.same like pit man arm,druglink,check also the the idler arm support nd bushing inside and nuts maybe loss

If changed gear box new one but defect not rectified.then park car near garbage area.

1. Check the OBD Codes
2. Check the Fluid Level
3. Test Transmission Pressure
4. Drop the Transmission Pan
5. Repair, Replace or Rebuild
6.  If problem persist, check the engine gearbox alignment.
7. Contact the manufacturer for faulty design if there could be a recall.

what is the problem ??

chechk  if there is afault code by diagnostic tool or not , first . 

Need to review the customer complain, to get a maximum of info. Followed by reviewing the trooble shooting process applied by a qualified technician and guaranty that the spare parts installed are original.

Since its the same results occurring after changing the gear box thrice.The best thing is to change the engine and gear box completely.

base on my experience i have the same problem with faulty gearbox twice and the first one i trouble shoot and i see the problem is from the converter torque and the last one experience is electrical problem.. but some of that faulty gear box is coming from the sensors. this idea is for automatic transmission only

First scan the vehicle go to the current data test to know its performance, Notice the manufactural recommended T/fluid,  Notice the Engine rpm trough the torque converter then compare to the transmission speed because a faulty torque converter can e.g :Old/worn out torque converter, wrong torque converter installed, vehicle used for heavy towing and/or harsh driving conditions: Open circuit in electrical system, failed PCM/TCM, faulty or stuck shift solenoid, failed speed sensor: Blown fuse, faulty brake light switch, faulty shift interlock solenoid, faulty ignition switch, lodged parking pawl, open circuit in electrical system.

Some problem that involve with the gear box is alignment, broken bearings, loss bolts(nut) that result to vibration. And last improper installation and assembly of the gear box.

Can you describe the actual problem? 

you are not telling us what the problem is