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Spectrum +2 hardware issue
Posted: Sun Jan 26, 2020 10:42 pm
by deano467
Hi I've acquired a dead spectrum +2. The uk1400 PSU reads around 14.8v which I've read can be normal under no load. When I power the spectrum up I'm getting 13.8V across most points in the spectrum PCB. I'm guessing either a short or a damaged voltage regulator. Is the spectrum worth repairing or has there already likely been damage to the chips and components?
Re: Spectrum +2 hardware issue
Posted: Mon Jan 27, 2020 1:00 am
by 1024MAK
The ZX Spectrum +2 (grey case and uses a 2.1mm / 5.5mm barrel power plug) uses a “Sinclair 128K Spectrum +2 Power Supply Unit” rated at 9V DC at 2.1 Amps. This is also in a grey case.
The PCB in the ZX Spectrum +2 has on board power supply circuitry. This produces a +5V DC rail, a +12V DC rail and a -12V DC rail.
All the logic chips run from the +5V rail. This should be between 4.75V and 5.25V. Above 5.5V the chips may suffer damage.
The RS232/serial ports and the aux port use the +12V and -12V rails. Some of the video circuitry also uses the +12V rail.
All the Sinclair 9V DC PSUs have a nominal voltage rating of 9V DC. But the output voltage will only be near this value at the units full load current. As they are the unregulated type. With no load (no computer connected), the output voltage can be between 12V and 16V. With a computer connected, the voltage should not be below 9V. The typical voltage is between 10.5V and 12V.
A UK1400 PSU is only rated at 1.4 Amps.
Please note that the later +2 in a black case (known as the +2A and the +2B) uses a DIN connector for power in, and it uses a completely different type of PSU.
Mark