No video out on Timex Sinclair 1000

[jason21]

Ok, yeah that seemed like the most likely cause, but was hoping something else since seemed to have some life. I don't have another to swap in, so I just ordered a vLA81

[1024MAK]

What signals do you get on the following pins of the Z80A CPU?
Be very careful, if you short the probe between adjacent pins you may damage one or more of the chips.

Pin Function
16 /INT (should be pulsing)
17 /NMI (should be pulsing)
18 /HALT (should be pulsing)
19 /MREQ (should be pulsing rapidly)
21 /RD (should be pulsing rapidly)
22 /WR (should be pulsing)
24 /WAIT (should be pulsing)
25 /BUSRQ (should be high)
26 /RESET (should be high, except for a very short time after power is applied)
27 /M1 (should be pulsing)
28 /RFSH (should be pulsing)

Then test address lines A14 and A15. These give an idea of which memory the Z80A is accessing and if it is trying to generate a TV display.
You can also test the remaining address lines A0 to A13 and the data lines D0 to D7. A lack of activity is suspicious.

Mark

[jason21]

All of the pins you note as pulsing I believe are - I see sine / square waves.

For pin 25/26 I'm not sure is correct based on scope, but not sure proper setup - but on multimeter they show 5v

busrq

reset

I see waveforms on all data and address lines, and example of each:

d1

a9

[1024MAK]

The trouble with using autoset, is that the ‘scope will ‘home in’ on any noise superimposed on a slower moving signal.

Set the vertical scale to a sensible setting. All these signals are around 5V, so use DC coupling and set the vertical scale to say 1V/div.

For the horizontal timebase, when looking at what should be a (more or less) flat line (steady voltage), it does not really matter. But set it to a slower figure (larger number).

Similarly, with the signals, stay on the 1V/div. setting and twiddle with the timebase and the trigger controls to see the signal. Most of the signal pins are non-repetitive (for the duration as far as the ‘scope is concerned), so for these, either use the ‘single’ ‘sweep’ mode (or similar) or just the stop button.

Mark

[jason21]

Ok, I think these should be better, still learning how to use the scope - now the high / low on 25 & 2 6 look like I'd expect, set to 2v div to fit

cpu pin 25

cpu pin 26

cpu pin 21

cpu d1

cpu a9

[bola_dor]

Now you can set the scope properly re test ULA pin 16.. you should see a video signal at 15khz no matter if Z80 is good or not. it only depends on the resonator signal to make a completely white screen.

[jason21]

This is ULA 16 with same settings, seems bad. I guess only the video part is bad - will see once I get the replacement, will take a bit coming overseas