Spectrum +2 dataset fix

Updated: Mar 25, 2022

Tape player schema, from the ZX Spectrum128 +2_Service Manual

Symptoms:

My Spectrum +2 did not load any games from tape, the screen did not change when loading the tape from BASIC, I tried from 48k and 128 mode. The lack of "stripes" hinted that the signal from the tape was not getting to the machine.

The stripes are visual representation of the actual data being loaded.

How does the tape player works?

The motion of the tape pulls a varying magnetic field on the head, which creates quite weak signal, that needs to be amplified to be useful. The first amplification happens over the C1815 NPN transistor. The second amplification happens on the LA6324 operational amplifier pin 5 and 6 are inputs and the pin 7 is the final signal that goes to the computer.

How to debug?

Having an oscilloscope definitely helps, the output signal could also be read with a logical probe.

Output on pin 7 on op amp before the fix. Basically 0V

Output on pin 7 after i swapped out the op amp. The output could also be measured with an logical probe.

Pinout and the location of the Single Supply Quad Operational Amplifier.

Fix

After I swapped out the Op Amp the machine started working. I've also recapped the tape deck and checked the capacitors with the tester, but all tested good, so that had no effect. I've also tested the transistor TR301 which also tested good. If you're having similar problems, it may be a good idea to check for cold solder joints before swapping out the op amp.