ZX Spectrum 128k +2 - Fault

In May 2020 I bought a supposedly working 128k +2 Spectrum to sit in place of my existing 128k +3 model. The main reason was that the +3 model is incompatible with all of the PS2 keyboard modules out there.

On receiving the spectrum I powered it on to test, and everything seemed to be fine; the usual 128k menu shows:

… even my DivIDE+ interface seems to work.

But, since I didn't have it connected up to my keyboard interface, I didn't use it for any length of time… I should have.

The problem I seem to have, is that when left on for any length of time, or soon after loading a game, I start experiencing random screen corruption, reboots and other miscellaneous issues. These manifest as the following:

That's the screen shortly after a spontaneous reboot after loading a game from the DivIDE+ Fatware menu.

Those images are the contents of the screen after resetting the system, or powering it off and on again after it has been on for anywhere from 30 seconds to 5 minutes. After that point it won't return to loading the Spectrum menu until it has cooled down completely.

I ran the Spectrum without the keyboard so that I could monitor the temperature of the chips (just by feel), but nothing seems to get particularly hot.

I then took the board out and examined it - not obvious leaking capacitors, nothing that looked to be blown, no broken traces but on the rear of the PCB there were some poorly soldered pins on various chips (including the 16x DRAM chips), so I resoldered them and re-tested, but that didn't appear to make any appreciable difference.

I ordered a complete 128k +2 issue 1 replacement capacitor kit from Retroleum, and this will be my next fix attempt; the kit is mega cheap, and it's a pretty easy job since it is all through-hole and with relatively large components.

[Update 27th July 2020] - got around to removing the old capacitors… The Spectrum traces are really quite weak; a couple of them came away whilst heating up the legs of the old caps. I eventually settled in a method of snipping off the old caps and pushing through the tiny bit of let that was left.

Here's the new caps in place:

So any better? In a word, no. Next up has got to be DRAM chip replacement, and in the 128k there are 16x 4164 64kbit chips… That's a lot of pins to desolder…