What you need to do first is to change the ZTX651 and ZTX213 transistors (use 2N2369 or BC213 transistors as easy-to-find replacements). Also, Amstrad connected the audio signal to the sync signal, in their infinite wisdom. The RGB is a different problem – that’s because Amstrad soldered some of the transistors in back to front therefore the sync signal isn’t being amplified, and isn’t strong enough over the RGB signal for your television to pick up. Yes, that’s the usual problem with 128K Spectrums – the transistor(s) for the 12V line have gone, so the TV signal isn’t being created properly.
in a 48K those two govern the -5V and the +12V lines… There’s a ZTX213 and a ZTX650 coupled together. Aha! There’s no 12V line! Yet there is on the other end of the motherboard, because the coil is at the correct voltage!Ī quick look at the power circuit in the 128 looks very familiar. How about the multimeter – the TEA2000 requires a +12V supply. Removal of the diodes didn’t change anything, pin 6 was dead.Ĭheck the other lines, they seem a bit flat. out through a junction to two diodes, one for the Video Out, one for the modulator. Let’s see what happens to the composite signal then…. One quick swap-out later, and the TEA2000 is confirmed working. However, pin 6 (the composite video out) was dead. A quick look on pins 1, 3 and 5 showed that a signal was there just fine. The next thing to try – oscilloscoping the TEA2000 chip. Now we know the problem is to do with the video circuitry. It’s working! The machine is fine, it just can’t display anything. Wonder what is working… put some headphones into the MIC socket, attach a keyboard… press a key….
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