[11] The conversion process was carried out by a partnership between the rolling stock leasing company Porterbrook and train manufacturer Brush Traction.

The conversion principally involved the addition of a pair of MAN diesel engines (one under each driving trailer vehicle), the output of which is fed into ABB-provided alternators to power the existing electric traction systems.

Twenty Class 319s were cascaded to Northern Rail and allocated to Allerton for use on the newly electrified lines between Liverpool Lime Street, Manchester Airport and Preston.

Engineers at Porterbrook, having been tasked with finding a new use for recently-surplus vehicles of the class, decided that there was an emerging market for a bi-mode suburban/regional train that could readily move between electrified mainlines and non-electrified adjoining routes.

[5] During a detailed evaluation to determine a suitable independent power source for the type, Porterbrook decided that the desired performance and range of the vehicle would be at least equal to a Class 150 Sprinter diesel multiple unit (DMU).

[5] Furthermore, it was also determined that these trains would be capable of interchanging between electrified and non-electrified lines via a straightforward switchover process, including potentially while in motion.

[5] The use of various energy storage mediums, including batteries, flywheels, supercapacitors and hydrogen fuel cells were examined, but most were discarded due to the insufficient range provided.

According to Porterbrook, the selected engine should produce lower emissions and reduced maintenance costs, as well as a higher tractive effort at low speeds, than a Class 150 train due to its use of modern technology.

[5] The cab controls and circuit breakers have been changed to allow the driver to choose between diesel, overhead AC, or third-rail DC (where applicable) power sources.

Furthermore, new and modified electronic control units are also installed to regulate the Diesel engine's power output and to help it emulate the DC conductor rail.

[5] Overall, the modifications add approximately 7.5 tonnes to each driving trailer; the additional weight is evenly distributed across the underframe, which imposed several constraints and necessitated the relocation of the original heating equipment to make room.

[5] On the initial eight trains converted, work such as reliability improvement, re-branding and other modifications were undertaken by Knorr-Bremse Rail Services (KBRS).

[5] Arriva Rail North (trading as Northern) were to be the first operator of the Class 769, with eight units (although Transport for Wales introduced a set into traffic first).