A ZX Spectrum that wouldn't load software until it had warmed up - Let's fix it!

This ZX Spectrum was one I had worked on previously and thought it was fine. However, I recently discovered it has an unusual fault... It doesn't like to be cold! Let's fix it!!
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[@RudysRetroIntel]

Thanks for sharing this

[@RetroComputingReboot]

I'm glad you liked it

[@JohnLeePettimoreIII]

15:00 (ish) when testing, perhaps a leaky cap could appear as a resistor. not sure, just throwing it out there.

[@RetroComputingReboot]

Yes I think it has to be. It's the only explanation I can think of

[@miked4377]

very good simon!!

[@RetroComputingReboot]

Thanks Mike 😊

[@Auberge79]

I'm pretty sure the problem appeared someday because of electrostatic discharge while connecting to tape player :-) This caused both capacitor failure and ULA tape port damage.

[@RetroComputingReboot]

Hi Auberge79. Thanks for the comment. I hadn't thought of that but it seems a pretty good reason. I've just never seen it before. To be fair, I suppose over the last 40 years it could have had pretty much anything jammed in there to cause the fault

[@NotMarkKnopfler]

Think about it... If the capacitor is measuring as a resistor then it _must_ be letting DC through it - therefore it's defective. Capacitors are supposed to block DC. In circuit it's functioning as a resistor and leaking the tape signal away to ground.

[@RetroComputingReboot]

Thanks for the comment. Yes, I have to agree with what you say. It puzzled me though with it intermittently testing as a resistor, then capacitor. I really didn't expect it to be faulty. I've never experienced one of these fail before either, which then made me start to doubt myself 😁

[@johnwiesen4440]

I sometimes load games from my phone using ear socket. I do this to test them.

[@RetroComputingReboot]

Hi John. Thanks for commenting. I've tried that in the past but with the absence now of audio jacks on phones, I struggle doing that these days

[@damianbutterworth2434]

I had to use the EAR socket on some Spectrums to get it to load with the TZX Duino. Much louder signal for some reason unless that`s the way it was meant to be and now we are used to EAR to MIC.

[@RetroComputingReboot]

Hi Damian. Thanks for the comment. It really puzzled me this one as I'd put the Bluetooth mod on a couple of other Spectrums and works perfectly. I'd heard rumours on the net though that the ULA could cause deafness, but had never experienced that before, and I've never had issues with these capacitors before

[@damianbutterworth2434]

@@RetroComputingReboot I did a R60 DV to DV mod and used a 1/4 watt resistor and it caused the 12 volt line to go up to 13.5 volts. By the time I tested it a couple of lower ram chips blew. I took them all out and the voltage went up to 23 volts. I used a 1/2 watt resistor and got it back down to 12 volts but the colour was off. I changed the ULA and it worked. Must of damaged the digital output pin for one of the colours. Now the Upper Ram has shown a 34 bit error. I changed the whole lot and now memory 4 bit it faulty. Nightmare lol.

[@RetroComputingReboot]

@@damianbutterworth2434 Thats one thing I love and hate about the Spectrums. Apart from breaking just by looking at them, they just have some of the weirdest faults 😂

[@jasejj]

​@@RetroComputingReboot You want to try fixing a Ted-based Commodore. I just had one literally blow the CPU *and* a logic IC between a test with the top off, and buttoned back together. Absolutely no idea why either.

[@RetroComputingReboot]

@jasonj4337 😂

[@ronnyverminck2741]

Is this a good idea to take power from over the capacitor? Why not directly from the power regulator?

[@RetroComputingReboot]

There's no reason you couldn't take it from the regulator, I just prefer to connect here 😊