Sinclair ZX80 / ZX81 / Z88 Forums

in that case there is a problem with the lm1889 or its circuitry....is the tv on the correct colour standard, almost always should be pal, there were ntsc speccies but are as rare as honest politicians...

need to check its 12v supply... but as it boots ok and gives correct result for 48k thats probab'y ok as lower ram uses the 12v line as well, unless its a bit low...migĥt be high enough for the rams but too low for the lm chip.?? if ok (11.5 to 12.5 i'd say..)need to check/replace the lm chip and its 4.433 crystal and if still no colour could be partly duff ula, i have one that has one colour difference output missing,otherwise ok, so possible there may be one with no colour difference outputs at all....BUT looking closely at that pic, looks like the colour signal is there as you can see the dot pattern...... which makes me think either tv is on the wrong colour system or its colour killer is operating for some other reason..does the tv work ok on other signals?

i assume you HAVE got the colour turned up on the tv...?????

how exactly has the composite mod been done ?? the white paper looks rather grey so maybe insufficient composite amplitude? that might cause problems with picky tvs...

Hi Gozzo

You are asking a good question
The TV I am using is a small LCD screen with different video input at the back such as HDMI , SCART, composite, dish antenna.
I am using this TV with my own pc through the hdmi connector and hooking my C64 through the scary connector and for both color is of course ok. The spectrum is connected then via the composite connector using the standard composite cable y/r/w. I have never hooked up anything other then the ZX on this port so could be that the connection is wrong or a failure on this connector.
I may have to check this one then. As you said colors looks to be generated but not displayed on screen.

For the composite mod I followed this tutorial
http://www.retrogamescollector.com/simp ... osite-mod/

Very simple mod.

That's the "standard" composite video modification for a 16k/48k Spectrum. It works fine for most (but not all) displays. If you get a reasonable monochrome picture, there is nothing much wrong with the connections or the mod. So I don't think this is the cause of the lack of colour.

I have a LCD TV that I use. For some computers, it can get confused when the colour system setting is left at it's default of "AUTO". I then get a monochrome picture with no colour. So on mine, I go via the on screen menu settings system to set the colour system to "PAL". Then I get a colour picture. So can you see if your TV/display has any settings for the colour system?

Mark

Hi 1024MAK

I will check for any settings on the LCD but I do not think there is such an option on this LCD. Best things to do is try on a different LCD screen with composite video in.
Ok so the board is the issue 4A year 1983. The LN1889 is socketed.

On the LM1889, test the DC voltage between pin 16 and 0V/GND (you can use the case of the modulator, or the heatsink of the 7805 voltage regulator for 0V/GND). It should be around +11V to +12V.

Mark

hmm, no dc isolating cap in that mod, try fitting one 100uf 6.3v or higher in series with it.. is there any way you can check if the tv is selecting pal or maybe selecting it manually? my 16 inch alba thing seems to select ntsc even if fed pal from a professional tv pattern generator and obviously displays in monochrome, it has no way of manually selecting...damn bitch!

ooh, if the lm is socketed it may have been replaced or tested in the past?? doubt if it was factory socketed...