The Spectrum +3 model repurposes the mono ‘Sound’ output connection to allow the use of an external cassette recorder with a suitable stereo to dual mono cable.
Despite the use of the same stereo socket on the Spectrum +2A and +2B models (Z70833 PCB), the left and right channels of the socket are joined together on the PCB so the same cable can’t be used.
A small modification can be made to reinstate full +3 tape/sound functionality however, this can be handy if you want to use an external audio source to load games into your Spectrum.
Please note that this modification only applies to black +2A and +2B Spectrums with the Z70833 PCB.
Tools required:
- Soldering iron
- Solder wick / desoldering pump
- A long piece of insulated wire
- Multimeter (ideally)
Step 1: Desolder the sound socket
You’ll need to open the Spectrum, and remove the main PCB from the bottom half of the case. To do this, disconnect the keyboard and tape connections, and remove the screws holding the PCB to the case. The PCB should then lift out.
Locate the sound socket at the top left hand corner of the case, and remove it by using solder wick or a desoldering pump. Be careful as we want to reuse this socket, and also bear in mind that these PCB’s are notoriously delicate and it is easy to lift a pad if too much heat is applied.
Step 2: Cut the trace joining the channels
On the top side of the PCB, where the sound socket was positioned you’ll see a trace running horizontally between the left and right pins of the through holes. Cut this track using a sharp knife, and verify that the two points are no longer connected using a multimeter in resistance mode.
Step 3: Reinstate the socket
Replace the socket back into position and resolder it in place. Do one pin at a time and ensure that the socket is mounted flush to the PCB.
Step 4: Connect the socket to the ASIC tape input
Now that you have your newly separated socket in place, we need to connect the now disconnected pin to a point on the PCB where the tape signal can reach the EAR input of the ASIC.
With the PCB upside down and connectors facing north, solder one end of your piece of insulated wire to the left hand solder point of the socket. Turning the board right side up again, locate radial capacitor C200 – this is immediately right of the rightmost RAM chip, on the bottom right of the board. Locate the solder point of this capacitor’s negative lead, and solder the other end of your wire to the same solder point on the underside of the PCB.
Step 5: Reassemble and test
In true Haynes fashion, reassembly is the reverse of removal. Make sure the board is clean in areas you’ve soldered, and you can then test your work with a suitable +3 tape lead. Details of this lead are contained in the diagram below (sourced from Chapter 10 of the +3 manual), or a lead can be purchased easily enough from eBay if you don’t fancy making your own.
