TS1000 with no image :_(

[bola_dor]

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 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..
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"..

[bola_dor]

Please confirm that the Z80 has power. Test between any 0V/GND point and pin 11 on the Z80.
Test from any +5V point and pin 29 on the Z80.
On the Z80, test the actual pins of the chip.

Done

If you still have access to a ‘scope, and it is a dual channel type, use one channel to monitor pin 26 on the Z80. Use a second channel to monitor pin 28.

not this week at least..

Now briefly (for about one second) short out the two leads of capacitor C5 (1uF electrolytic). Pin 26 should go low, then as C5 charges, it should ramp up until it gets to nearly +5V. At which stage the Z80 should have just been reset and should now be executing code (or trying to).

I did this but with the plain multimeter, pin 26 goes low and then raises as you said..
But on 28 remins dead at 0v

If it still is not working, test pins 23 and 25 again. Are they both high?

yes .. 23 is 3.9v and 25 is plain 5v

Mark

ULA was tested OK in the working board too


Thanks.. if you think about something .. let me know please..

[stroebeljc]

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 wonder if it actually could be the resonator, somehow causing resonance at a much higher frequency than it is supposed to.