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Sinclair ZX Spectrum +2A and +2B

Introduction

The Spectrum +2A replaced the previous Spectrum +2 model in 1987 (actually coming to market just after the Spectrum +3).  The case was restored to the traditional Spectrum black making it easily distinguishable from the old grey model.

Although it kept the same name, it sported a completely redesigned motherboard based around the new Amstrad +3 4.1 ROM model with a much reduced chip count.

Essentially the +2A was a Spectrum +3 (as can be seen from the reference to +3 BASIC in the start up menu) with a cassette deck replacing the disk drive and so had two more 16K ROMs.  One held the second part of the reorganised 128 ROM and the other contained the +3's disk operating system which went unused of course on the the +2A and +2B.  The two new ROMs and the original two 16K ROMs were physically combined into two 32K chips.  The keypad scanning routines were also removed (not used since the days of the Spanish Spectrum+ 128).

 

Bank switching of memory was improved allowing the ROM to be paged out for another 16K of RAM at the bottom of the address space to permit the use of CP/M (on the Spectrum +3).

Several changes were also made on the bus and of course all this little lot caused many more incompatibilities with older software - even some written specifically for the 128K machines!

The Spectrum +2B did have some minor revisions over the +2A (the main board was at Issue 4 for the +2B), but the main thing of any significance was a move of manufacture to from Hong Kong to Taiwan.

Technical Details

  • CPU: Z80A
  • Speed: 3.5MHz
  • ROM: 64KB (32K for 128K mode, 16K for 48K mode, 16K for +3DOS)
  • RAM: 128KB (8 x 16K banks)
  • Full-stroke 58 key Keyboard (same layout as Spectrum+)
  • Colour Graphics
  • Sound - 3 Channels, 7 Octaves (Yamaha AY-3-8912)
  • RGB, RS232/Midi
  • Local price at launch: £200

Problems and Issues

The cassette mechanism on the +2A and +2B models was much superior to that used on the earlier grey +2 model and far more reliable, however, the drive belt does need changing as it suffers the same "kink" and stretching with age as its predecessor.

Similarly, the read and write heads will almost certainly need a good clean with alcohol and a chamois stick.

If the cassette drive does prove to be faulty, don't be fooled by the the misleading labelling of the "Tape / Sound" port at the back of the +2A.  This suggests that an external cassette player can be connected via this port in the same way as it can with a Spectrum +3.  It is not the case - the port on the +2A (and +2B) is wired only for sound out on the main board - it will not accept sound in.  There are ways around this with a hardware hack if you have decent soldering and de-soldering skills and I may cover this in a future article in the "Repairs" section.


If you do try and find that you have damaged the Sound socket, it is identical to the +3 socket and a replacement is available in the shop.

 


Don't expect to be able to connect an Amstrad external FD-1 or DDI-1
 to the back of the computer as the interface advertised by Amstrad before its launch was never implemented.  The external interface which was available for the Amstrad CPC464 is not compatible either, so there is no way to attach a 3" disk drive to this model.

All is not lost though if you're desperate for a disk drive - the Spectrum +3e ROMs from Garry Lancaster will work with the +2A which (with a suitable interface) will allow you to connect a standard density IDE 3.5" disk drive, or even a hard drive.

 

Built-in Test ROM
If you have random, or intermittent faults with your +2A, the built-in ROM test routines can help to diagnose the problem.


 

To start the test suite, hold down the [BREAK], keep it pressed, then press and release the reset button on the left side of the +2A.  This will bring up the colour and sound test screen which is detailed in the manual.

 


Whilst the screen is displaying the test card and is still beeping, press the following keys simultaneously:
 

[Q] [A] [Z] and [P] [L] [M]

This is fairly easy to do as the keys are down the left and right side of the keyboard.

A set of brief instructions will now be displayed, including a warning that disks will be corrupted.

If any of the tests fail, then special equipment will be needed for an accurate diagnosis and this of course is no longer available, but it will at least give an idea of what components are faulty.

When you get to the disk drive speed test, don't be alarmed that the test fails - there is no disk drive of course!  Proof again though that the +2A and the +3 shared the same ROMs.

 

 

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