Sinclair ZX80 / ZX81 / Z88 Forums

Soldering is about a combination of good technique and practice.

So start again with a good iron and a cheap electronic kit from say eBay or another source.

There are plenty of tips on soldering both as text tips and help and as videos online.

Mark

Rabs wrote: ↑Sun May 12, 2024 3:12 pm In my excitement of passing the RAM tests, I forgot to put the ROM back in

Mark

The joystick chip is believed to be the same as the chip in the Sinclair Interface 2. Hence it's not believed to be essential. The other thing of note, is that the data bus outputs can only drive each data line low (like open collector/open drain).

Well done on making progress

Mark

Moved to the ZX Spectrum BASIC section, as this is a more appropriate section. I’ve left a shadow in the development section.

Mark

If the fault is or has been intermittent, poor IC socket contacts, dry jointed solder joints, and PCB track faults are still possibilities.

Mark

The length (time) of the back porch and the trigger level have to be in the right range, otherwise it affects both line (horizontal) and field (vertical) synchronisation of the picture. If you are using a NE555, I’ve found that cheap versions from trading sites are too slow. It’s impossible to set u...

Unlikely given that resistors are used to divide the data bus and the two groups of DRAM are controlled differently.

I’m wondering if the ULA is receiving all the control signals from the Z80.

Mark

Yes, this is a tricky fault. You said earlier that you had changed the Z80. Did you try the removed chip in another Spectrum?

Mark

Yeah, there are replacement modules, but these are not exactly cheap. Especially if it's more of a guess as to what's wrong...

Mark

So the Z80 is likely able to write to this RAM and the ULA can read from it okay. It could be that something is causing the signal to be marginal at the Z80, or it could be that there is a strange control fault. Strange RAM faults in models that use the custom multiplexer chip (IC10, PCF1306P / ZX84...