[Irinikus]

The area to the right of the crystal oscillator on the mainboard looks kind of gruesome... 😲

That’s a form of black double-sided tape that they originally used to hold the crystal oscillator down, so it should be there. (It’s ugly, but original!)

[Irinikus]

Here's a video showing a similar type of fault to mine:

[Irinikus]

I've re-capped the ZX Spectrum and fitted a new Voltage Regulator





The Lower RAM issue still persists:



So now I have to wait for the new RAM chips to arrive from the UK, which may take a while, as they've been sent via the Postal Service! (I hate the Postal Service, as they're ridiculously slow!)

Here's the composite mod I did: (Bypassing the RF Modulator, allowing the Spectrum to output a composite signal rather than an RF signal.)

[vishnu]

Interesting they had to modify the circuit with what looks to be 30 gauge Kynar insulated wire wrap wire. We've had to do that many times while we were prototyping, but we never shipped any modified boards like that...

[Irinikus]

That’s what makes the Issue One special!

It was basically a shipped prototype!

[Irinikus]

My Interface 2 for the spectrum arrived, so it's now plugged into the Interface 1:



I'm, still awaiting the spares to get this little monster up and running! (They have arrived in the country though!)

[vishnu]

Fun to see all the old-school 10th of an inch center ICs! In my place of employ, we do all our prototyping using 10 of an inch center ICs, in a way it's kind of a miracle that they're still so widely available. There's nothing worse than having to diddle around with surface mount components when you're trying to make functional changes to the circuit.

[Irinikus]

I finally received the spares that I need to get this little machine up and running HOPEFULLY!



But I'm in Pentium Pro mode at the moment, so this will have to wait for a bit!

[Irinikus]

Today I installed the new lower memory into the system. (Allot of desoldering and soldering work!!!)

Only to find that the problem persists, SO IT CAN'T BE THE MEMORY CHIPS THEMSELVES!!!





The only other thing that I can think of at this point is that it may be the oscillator on the board which produces the 12V power supply for the RAM chips, which may be introducing too much ripple (It is making a rather loud low frequency bussing sound!)

WHAT A PAIN IN THE ASS!!!

---

This is what the system gives me when the lower RAM is removed, and it looks the way it's supposed to look!!!

[Irinikus]

I just bought these components for this little system. (At this point it looks like I may to have to replace all the silicon on the board, as there's now a wide range of possibilities as to what the problem could be!!!)



So I've ordered a new Z80 CPU and Socket, two new multiplexers and a new ROM chip, that's flashed with the standard ROM as well as a diagnostic ROM, which can be switched out with a mechanical switch on the module.

I really hope that I don't have to end up replacing the LRU, as it with it's modification gives the Issue One allot of character!