Sinclair ZX80 / ZX81 / Z88 Forums

Mark ,

The display is the same as i used yesterday to get the ill speccy tested.


Scope is on my right .

Sorry, maybe I was not clear.

How are you connecting the video output of the 128K, are you using composite video and ground (pins 1 and 2 on the 128K’s DIN socket). Or are you using the three video channels (R, G, B), bright, and combined sync. (pins 2, 3, 4, 6, 7 and 8 on the 128K’s DIN socket)?

Or have you done something different?

And where does this go, directly to a “normal” TV or to an adapter or converter?

In the photo you posted, it looks like you are using a video capture device and displaying the result in a window on a PC.

I’m just trying to get an understanding of your current set up. Then I hope to be able to help you further.

Mark

Mark ,

composite video 2 wire to an usb converter , or composite video 2 wire to an hdmi converter .

my own 128 does work fine that way.

with the defective one i can only see "something" happening if i use the usb converter .
this "something" changes when i switch the 128 on or off.

the hdmi converter does not detect any video signal with the defective 128




btw , does both the cap or transistor video-mod not work on a 128 ??

Okay, now I understand.

jojo wrote: ↑Sun Jul 17, 2022 6:07 pm btw , does both the cap or transistor video-mod not work on a 128 ??

It isn’t needed, and because of the different internal circuitry, it’s not recommended.

With your ‘scope, can you test on the TEA2000 pin 6. This should be a composite video signal, but at different (higher) voltage levels compared to a standard composite video signal.

Try to use the trigger control on your ‘scope to lock to a positive to negative edge, so that it uses the line or field sync. Unless you use a more complex trigger control, the ‘scope image will keep changing. So if you have a “one shot” mode, use that.

If your ‘scope has two channels, you could trigger off of pin 16 of the same chip.

Mark

Mark ,


After a good look into the analogue and the use of the scope ( which could not find ANY signal !! ) i noticed this ;

an rgb modification , which renders the cvbs output fully useless.
replacing the correct resistor gives this ;
tomorrow i will fit the yellow-mod , and do some more testing with the test-card .


THANK YOU and all others !!

Ahh, you mean this RGB modification (really a SCART signalling modification).

Yeah, I’m not keen on that type of modification. And if owners do want to do that kind of thing, they really should attach a label on the bottom of the case saying what they have done.

Anyway, glad that you have found the “problem”

Mark

the problem is that these units are not even second hand , but maybe 10th hand , so no-one really knows what has been done to them .

This one came in with a distinct burning smell ( as did the ill speccy from yesterday ) ,

so start searching ...................


Thanks for your help and advise !!


jojo


- now step over to a speccy which burns the same memory chip every time i try ..................

so , last pieces of the puzzle completed ,

with un-rainer mod ;
And the yellow-mod fitted ;
and tried some games too ;
memory test ran for 4 hours without problems , so another saved 128 .



jojo

Mark