Sinclair Research ZX Spectrum - ZX Spectrum Setup and System Test; General Alignment and Voltage Checks

SECTION 3
SETTING UP AND SYSTEM TEST
Sub-Section LIST OF CONTENTS Page No.
1 General Alignment 3.1
Introduction 3.1
Voltage Check 3.1
Colour Adjustment 3.1
Sub-Carrier Oscillator 3.2
14MHz Oscillator 3.2
2 System Test 3.3
1. GENERAL ALIGNMENT
1.1 Introduction. The Issue 3 Spectrum modification removes the need for
adjustment of the colour tuning using potentiometers and trimmers.
Therefore, the setting-up procedure for this board is confined to
checking that the internally generated power supply voltages and two
oscillator frequencies are correct. Adjustment instructions apply
strictly to the Issue 2 Spectrum boards only but are generally
relevant to the Issue 1 Spectrum as well.
To carry out the setting up procedure it is first necessary to remove
the ZX SPECTRUM from the case (Section 2, Assembly/Disassembly). For
convenience the keyboard may also be disconnected.
1.2 Voltage Check. Check that the internally generated power voltages are
as follows:
Circuit Reference Nominal Value Tolerance
IC6 pin 9 + 5V ± 0.25V
IC6 pin 1 - 5V - 5.5V to -4V
IC6 pin 8 +12V ± 1.2V
LT side of C52 +12VA ± 1.2V
1.3 Colour Adjustment. Potentiometers VR1 and VR2 are used to effectively
null the voltages between pins 4 and 2 (for VR1) and pins 2 and 3 (for
VR2) on IC14 (LM1889). To allow for thermal drift, the potentiometers
are set for non-zero voltages; furthermore these voltage off-sets are
set to satisfactory but non-optimum levels in production, and optimum
values may be used to advantage in servicing. The relevant figures
are given in the following table - voltages are given relative to pin
3 of LM1889.
3.1