Can a locked phone's data be accessed when being repaired? I had an HTC One S device which suddenly turned off and refused to start. On giving to the service centre, it turns out the device needs replacement of an item 'PCBA-MAIN BOARD WITH SKU ID MS' which alone is costing me Rs 10000. I chose not to repair it with them. So i plan to visit a local phone repair shop and give it to them to repair it.

My query is, that the phone had some important private stuff (phone was locked though) before it went kaput. Now this local repair shop, can it in any way access this data while/after repairing the phone in anyway?
HTC service centre would not do that because they are bound by legal terms. 
Please advise.
Anyone with physical access to the device can potentially do that. If the device was completely encrypted, that would be pretty tough to do (and hence really unlikely) – but all unencrypted stuff can be accessed. After all, you expect them to dis- and re-assemble the device – so put in easy terms, they could also "plug" the storage into "some of their readers" and copy all the content – no screen-lock or whatever prevents that. And a little more hardcore: those tech-guys should be expected to be able handling a JTAG device.

So the question is less whether it's possible (it perfectly is), but how easy and how likely it is. If you feel your data being more sensitive than your trust is high, that poses a problem.