Hornby HM2000+ slave unit alternate power supply

[GWR-fan]

I recently purchased a Hornby "Signature" train pack pre-owned from Hattons that is supplied with a Hornby HM2000 twin track power unit.   While awaiting it to arrive I spotted a left hand slave unit (HM2000+) for sale on the site and purchased it.  Unbeknown to me the later power units do not have the serial ports to accommodate slave units so the purchased slave unit was basically useless to me.

 

Having nothing to lose,  I decided to investigate a standalone power supply for the slave and removed the two security screws in the case and removed the circuit board.  There are five connections utilised on the serial port connection.  Two direct power through the unit to power another slave and are not connected to the slave control board.  One connection is not utilised.  Two connections are used to power the rotary controller and associated circuitry.  I know just enough about electrics to get me into trouble but noted the four "ganged" diodes (bridge rectifier) so assumed that the board most likely was powered by 16 - 17VAC and not DC power.   I soldered two wires to the left hand serial port connections that are utilised by the circuit board and fed them out through a hole drilled in the case adjacent the track connections on the case.  The case was then reassembled.

 

Fingers crossed,  I connected the wires to a 17V AC power supply and switched on the mains.  No smoke was emitted so I hooked up a multimeter and rotated the dial on the case.   Magically it seems all worked and I had a controllable DC output up to around 13 volts.  I then hooked it up to the track and noted very smooth control of a basic Hornby Jinty type chassis.

 

This may be some help to others who perhaps require a reasonable quality controller.   The slave unit cost me GBP16.00.   

 

Edit:  as an after thought I feel that possibly additional slave units could be connected and the individual slave unit rotary controllers would work independently of each other thus giving multi track operation..

Edited September 10, 2022 by GWR-fan
Additional information

[RAF96]

One of the limitations of the add on modules according to the instructions was they shared power from the main unit, so although you could endlessly daisy chain these modules it watered down the available track power.

 

[GWR-fan]

In my situation I am not using the HM2000 twin track controller power so the slave output would rely on the independent power supply capacity hardwired to the slave internals (with consideration to any internal limits on what the slave unit could supply).  It is such an easy conversion and seems to be a more than reasonable controller.

 

I read your excellent breakdown on the pre-2013  HM2000 twin unit as I was going to purchase a twin unit with serial port connections to use the slave but considering the possible reliability issues with the early HM2000 units I decided to set about independently powering the slave that I had purchased. 

[RAF96]

As you say not all of the D-connector pins are used. Essentially two AC feeds from upstream of the main unit bridge rectifier and two AC direct feed throughs from unit to unit. Hence each sub unit could easily be modified by your method with an independent plug in power cable to provide a capable stand alone controller.

I had wanted to get hold of a ‘Mk2’ unit to pull to bits to update the teardown but so far nothing in hand.