Pilot reported technician failed to follow correct procedure when deactivating the WiFi. The procedure followed deactivated the hydraulic PTU; which was required for flight due to another MEL; resulting in an air turn back and precautionary landing.

Narrative

The aircraft we picked up was slightly behind schedule inbound from ZZZ. We met with the previous flight crew and during the exchange covered an existing MEL for the AUTO function of the Power Transfer Unit (PTU) and a new write-up for the In-flight Entertainment System. The existing MEL for the PTU has an Operational Procedure (O) for the flight crew to follow. We reviewed MEL 29-11-XX; which simply has the crew manually turn the PTU ON or OFF depending on the phase of flight. I'd like to point out that step (1) of this Operational Procedure has the crew turn ON the PTU and ensure a particular message is displayed on the EICAS.The previous crew had already contacted Operations for the new write-up of the Entertainment System. A technician arrived to diagnose the new write-up. He first asked us to completely power down the aircraft and restart everything to see if this would clear the issue. The complete restart failed to fix the problem. The technician decided to deactivate the system by following the procedure laid out in the Nonessential Equipment and Furnishings (NEF) Guide. While he was doing this; we continued with our normal duties to get the flight out on time. [The NEF Guide] has a Maintenance Procedure (M) that requires several electronic circuit breakers to be OUT and LOCKED and two thermal circuit breakers to be OUT and COLLARED.The LTV technician appeared to be unfamiliar with the aircraft and the location of certain circuit breakers that needed to be locked. He was also not equipped with his own iPad resulting in the crew being more involved in the deferral than normal. The CA contacted operations and asked if Tech Ops could come out to assist the technician twice during the deferral. The second time our tech ops came out and the Captain asked about an EICAS message and whether or not it was related to the PTU. The technician confirmed it was. We assisted the technician with the location of the electronic circuit breakers on the synoptic page; however; we were unable to assist with locating the thermal circuit breakers. The technician eventually found all the circuit breakers and locked them as part of the procedure. The write-up was logged; signed off and the aircraft was released for flight.[The NEF Guide] does NOT have an Operational Procedure for the flight crew like the MEL for the PTU. There is no requirement for the crew to verify that the listed breakers are LOCKED or to cross-reference the EICAS display with the NEF. However; since we were assisting the technician with the location of the electronic circuit breakers; we did verify what was listed in the NEF was shown as LOCKED on the CB synoptic page.After take-off during initial climb out at approximately 1;000 feet; a CAUTION warning HYD 2B INOP displayed on the EICAS. The displayed message was extinguished once the flaps were completely retracted. Passing 10;000 feet; we discussed the message and thought it may have had something to do with the PTU MEL. We decided to review the NON-NORMAL ECL for HYD 2B INOP. This ECL has the crew manually turn ON the HYD 2B pump and see if the caution message remains displayed. We did this and the caution message reappeared. The ECL then directs the crew to turn OFF HYD 2B.We then reviewed the Hydraulic synoptic page and noticed that the PTU is tied to that system. With the loss of redundancy for that system coupled with the MEL for the PTU; the CA opted to contact dispatch and maintenance. They conferred and Operations requested we do an air return to ZZZ.After landing in ZZZ; MX arrived at the aircraft and started diagnosing the problem. It was discovered that circuit breaker ACMP 2B was OUT and LOCKED and this was the reason for the CAUTION message we experienced during takeoff. Needless to say; we were dumbfounded as to how the wrong circuit breaker was locked.We did an aircraft swap and were on our way to our destination. En route we were reviewing the events as they transpired to try and figure out how this had happened. We reviewed [the NEF guide] and noticed a hyperlink called 'ECB (Electronic Circuit Breaker) Locking Procedures'. Following this hyperlink brings you to a new page within the NEF that outlines the procedure on how to LOCK an electronic circuit breaker. The second page of this procedure shows circuit breaker ACMP 2B being locked. It became apparent to us that the LTV technician followed this procedure exactly as shown believing that this was part of the procedure. Due to the large number of circuit breakers that were LOCKED; ACMP 2B was lost in the list.