Sinclair ZX80 / ZX81 / Z88 Forums

I've been enjoying my new Logic Probe!! Spectrum Chips copy.jpg Checked out the four chips on the bottom of the board. No idea if this is helpful! H=HIGH L=LOW B= BOTH (pulsing?) One other thing that I have noticed now that I turn the machine on after it is connected it that you get a black rectangl...

Hi Mark, Many thanks as always for your time. Most of the tests were correct, apart from the two highlighted. Just to check though. I assume that when it should be pulsing you should get both lights on? On the 16 pin it was red (high) on and on the 19 pin it was green (low) on. Fascinated to hear yo...

Mark, I am now the proud owner of a logic probe! Are there any simple checks that I can do on the Z80A, ROM and RAM? Many thanks for your time.

Neil.

Hi Mark. I will have the use of a logic probe by Thursday hopefully. I have connected up an amp. I checked by playing a tape which was very loud. There are no clicks when I press on the cursor up or down or indeed any of the keys. So I guess that means either one or all of the Z80A, ROM and RAM aren...

Hi Mark, My apologies. I checked that pin 11 again and it was a solid 5.02V. I was not pressing hard enough on my ground. I have lots of 3.5mm leads. Male to male or male to female. I have basic soldering skills and I do have a soldering iron. I don't have a logic probe unfortunately. I might be abl...

Definitely Issue 1 Mark.
Here are some closeups:

Hi Mark,

It is 11.89V on the colour encoder chip so this seems good.

Pin 11 on the CPU flickered around a bit, but stayed within the correct ranges as well, around 5V.

Are there any other tests that I could do?

Thanks,

Neil.

Brilliant Mark.
The power supply appears to be almost perfect with its voltages.
I will see if I can carry out some of those other tests that you suggest later.
Cheers Neil.

Thank you Mark.
I will not plug the DIN in when it is on again!

I do have a multimeter.

I've actually got a Physics degree but my electronics knowledge is rubbish !!!!

Many thanks for replying Mark. The case is definitely dark grey or black. The PSU is the big one with the DIN plug on the back. When it is plugged in the screen is just completely dark grey. No border at all. When I press the RESET the screen goes slightly blacker and then goes back to dark grey. Th...