Refurbishing a 48K Rubber Keyed Sinclair ZX Spectrum – Pt.2 Replacing the Regulator

The poor 7805 in any Sinclair Spectrum always works really hard. It was probably the best solution when the machine was designed but things have moved on. Switch-mode technology has improved and reduced in size. Therefore, when refurbishing any Sinclair Spectrum, it’s good to replace the 7805 regulator with a more modern solution.

As I said in the preparation post, there are a few good alternatives now. One is the Murata Switch Mode 5V 1.5A Regulator (They are available HERE), the TRACO TSR 1-2450 1A 5V Regulator or, I have since found out, the TRACO TSR 2-2450 2A 5V Regulator. I have a few of the 1A TRACO units in stock and the Spectrum I’ve refurbished will seldom be used and in my own collection so I decided to fit one of those.

The board was still bare from re-capping but obviously, from scratch, you would extract the board from the Spectrum’s case. Again, pay attention to those membrane ribbons!

Spectrum Heatsink Removed

Spectrum Heatsink Removed

This series documents refurbishing an issue 3b board but re-capping and replacing the regulator will be the same for all of the 16/48K models. In the above image, you can see I removed the heatsink, held on to the 7805 and board by a screw and nut. All thats required is to loosen them and the rest of the removal can be done by hand.

Using a de-older pump, I removed as much solder from the underside of the 7805 connections as possible. It proved to be a little difficult to remove completely and I had to resort to gripping the componet’s tab (the part with the hole!) with a pair of long-nosed pliers and heating the connections in turn to free it completely from the board. The trick is to take your time and not to heat any of the connections for too long. If the pads on the board get too hot, they can separate and lift.

Eventually, I successfully removed the 7805 and checked the pads for damage. All was OK. The TRACO TSR 1-2450 is a ‘drop-in’ replacement but does not require a heatsink. In fact, in use, I haven’t felt it even warm up. I used an old trick to help solder in the new component. A small piece of Blu Tack can be pressed in to service to prevent the component from falling out of the board before it is soldered.

7805 Replaced

7805 Replaced

As you can see, not having a heatsink on the board makes a big impact on the board’s weight and accessability.

TRACO TSR 1-2450 Installed

TRACO TSR 1-2450 Installed

As when I re-capped the board, it would be usual to test the board at this point but since I had already accertained that the upper RAM was faulty and I was going to replace it with a Retroleum Upper RAM module (available from HERE), I decided to leave the testing until after the next stage.

 

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