Modifying on of these old receivers gives a low cost entry into 23cm ATV receiving. Modifying this receiver comes in four parts:

1. Video level - amateur transmissions use a lower deviation than satellites.
2. Audio - the generally used sound sub carrier is 6.0MHz on amateur transmissions which isn't catered for in the Amstrad receiver.
3. AFC (automatic frequency control) - disabling the AFC and using it as a fine tune function.
4. Tuner - threshold extension, a circuit which effectively increases the receiver sensitivity.

Video and audio modifications are required, the AFC and tuner mods improve the usefulness of this receiver.

To increase the video output level to one acceptable for TVs and monitors a simple two components need changing; change R702 from 7.5K to 10K Ohms, change R704 from 910 to 1K2 Ohms. Whilst viewing an amateur transmission adjust VR701 for the correct video output level (often fully clockwise).

These components can be found just to the left of centre at the front of the receiver.

Amateur transmissions use 6.0MHz as the main sound sub-carrier. This modification is made by removing the oscillator and mixer parts from the circuit, replacing the ceramic filters with 6.0MHz types.

Firstly disable the sound oscillators; remove L304 feeds pin 14 of IC301 on early circuits or remove sub-board CP201 if fitted. remove ceramic filters CF301, CF303 and CF305. If fitted also remove capacitor at junction of CF301 / CF303 and ground. replace CF303 and CF305 with 6.0MHz types - SFE6.0 for CF303 and a two legged 6.0MHz resonator for CF305, as the later aren't common its possible to substitute this component (sound detector) with a three legged resonator type T6.0MHz or an L/C circuit resonant at 6MHz. Both should be fitted between pins 7 and 8 of IC302.

Connect a 330-Ohm resistor to the un-terminated pin of CF303 and the base lead of Q711, if an L/C circuit is fitted as the sound detector this will need adjusting for best sound whilst tuned to an amateur transmission.

Use audio setting number 3.

An AFC circuit is fitted to the Amstrad receiver, on low input signal levels this is ineffective but can easily be modified to a fine tune function.

Remove R112; marked as R113 on top side of some boards, connected between pins 3 and 6 of IC102, connect a wire between the junction of R110 / R111(use legend on underside of PCB). When touched to earth this will fine tune down in frequency. Connect a wire from the junction of R107 / R108, when connected to earth this will increase the tuned frequency.

By removing channel buttons 15 and 16 from circuit it is possible to use them for the fine tune function. Carefully cut the common switch connection from the rest of the switches and connect this to ground; a convenient ground can be found on C151 at top of switch board. Carefully cut the fine track from SW15 and SW16, connect SW15 to the junction of R110 / R111 and SW16 to the junction of R107 / R108.

VR1 in the tuner can may be adjusted whilst monitoring a weak signal, adjust this pre-set for minimum "sparlkies", don't touch any other pre-set resistors or capacitors! VR1 may not be fitted although pads exist on the PCB, a resistor is normally fitted in lieu of this component, try shorting it out - this normally improves the threshold for amateur transmissions.