Another was ZX Spectrum+ 48K (s/n S01-135100). After turning it on could not see clear image (sorry did not take image of that picture). When I disassembled this device I found that it already had some changes, lower RAM chips were not original, it had some jumper wires soldered on PCB, transistor TR4 seemed like already replaced (at least someone did some soldering with it).
Expecting the worst I started to check voltages (using this guide) and noticed that 12V is missing on lower RAM chips. When checked transistors TR5 and TR4 found that TR4 is most probably faulty.
TR4 is ZTX650 and I started searching replacements for it. Somewhere in a forums I fount that:
- TR4 ZTX650 can be replaced with 2SD1207.
- TR5 ZTX 213 can be replaced with 2SA733 ( or BC212, BC257, BC307, BC557).
I could easily find 2SD1207 and replace it. Just one important thing – pins of ZTX650 and 2SD1207 are different:
But good thing is that it was already overlooked by ZX Spectrum PCB designers and it had holes for alternative pinout transistor near the original one ( see photo ).
Voltages immediately changed to correct ones. After powering it up it started nicely. Whoohoo, it was an easy fix.
*One interesting thing is that on the back of ZX Spectrum case there was a sticker with text: 31.7.86 RR 47293 C.DAVIES. Not sure what does it mean, maybe information about performed repair or previous owner.
Oh.. and noticed just now, there is a sticker about repair on RF module also: