spectrum 128 with only 12 volt

[jojo]

Mark ,

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


Scope is on my right .

[1024MAK]

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

[jojo]

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 ??

[1024MAK]

Okay, now I understand.

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

[jojo]

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 !!

[1024MAK]

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

[jojo]

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 ..................

[jojo]

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

[1024MAK]

Mark