Sinclair ZX Spectrum Service Manual
Spectrum For Everyone https://spectrumforeveryone.com/
48
9.1 INTRODUCTION
In line with Sinclair`s policy of continual product improvement a number of changes to the Spectrum
Printed Circuit board have been implemented. Since the Service Manual was published the printed circuit
board has been upgraded through Issues 4A, 4B, 5 and is currently at Issue 6A. This supplement details
the modifications, board by board and also provides additional servicing information and spare parts lists.
A substantial change has been introduced in the area of the DC-DC converter and the method of
implementing this modification is detailed under its own heading. It is recommended that this
modification is embodied in units on which either TR4 or the 16k DRAM has blown. Some Issue 3B and 4A
units, and all later issues have these modifications embodied.
9.2 DC-DC CONVERTER MODIFICATION
The following new materials are required:
Diodes
• D17 - BR157
• D18 - IN4148
• D19 - 5V1 Zener
Capacitors
• C78 - 1uF 25V WKG Electrolytic
• C79 - 1uF 16V WKG Electrolytic
Resistors
• R60 - 220R 5%, 0.25W
• R79 - 2k2 5%, 0.25W
Remove the following components from the printed circuit board:
• D12- IN4148 Diode
• D16 - 5V1 Zener
• C47 - 22uF Electrolytic
• R54 - 100k
• R55 - 56R
• R60 - 270R
Embody the modification as follows:
• Break the connection between D15 and C49
• Connect C78 between C49 and D15 (positive end of C78 to C49)
• Connect D17 between ground (positive end of D17) and the new connection of C78 to D15
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