I am not used to this equipment.. so I can't tell what exactly means that frequency.. I noticed ed that number too so I measured on cycle and gives 154ns (a bit more than three Mark's in the axis..1024MAK wrote: ↑Sat May 16, 2020 11:52 am Hang on a minute!
That photo of the ‘scope screen showing the clock on pin 6 is showing a 6.4MHz signal . The NMOS Z80 is only rated for a maximum of 4MHz and in a ZX81/TS1000 should be 3.25MHz.
Are you using a modern ULA module rather than an original Ferranti ULA?
The waveform on ULA pin 16 is also double the frequency I would expect. So there may be a problem with the ULA oscillator circuitry. But the simplest test, is to either try this ULA in another ZX81/TS1000 or try another ULA in this board.
Mark
I am using regular Ferranti 22C210E ULAS..
Pin 6 in the working board is exactly the same (I checked it as I expected it to be more square "ish"..