Issue 2 48k Yellow Display

Hi guys.

As the title says, I have an issue 2 that's displaying the typical yellow/green colour screen at switch on. The picture is clear and stable, but yellow.

So far I have done the following...

Checked voltages as per Zorns initial startup test video. All memory voltages present and correct.
Component video mod.
Recapped. Checked cap values before replacing all good. Installed in the correct polarity.
TR4 TR5 removed, checked tested good, refitted.
Replaced LM1889N with new one, no difference.
Replaced voltage regulator.
Tried to adjust VR1/2 trim pots, no difference..
Replaced VR1/2 with ones from another board, no difference.

The speccy does appear to be working fine - I have not tested with a keyboard yet, but it's not buzzing or anything, it's just got a yellow display. Adjusting the trim pots will alter the picture from blue to horizontal stripes etc, but I cannot get a white display.

Here's a pic. http://www.dropshots.com/RSwipeCA/date/2016-09-28/19:23:25

I am out of ideas here.

I will have access to a scope as I picked one up on Kijiji, collecting it tomorrow. It's a Siglent SDS1052DL. I am looking forward to learning how to use it - at least the basics anyway.

Any advice would be appreciated.

Thanks.

Damian.

Comments

  • The service manual states for Issue 1 machines: "47k resistor between pin 13 of LM1889 and ground - required only if the difference between white and yellow colours is inadequate." Worth a shot here.

    Otherwise, could well be a ULA fault - try swapping one in from another working Spectrum, if available.

    B
    The Spectrum Resuscitation Thread - bringing dead Spectrums back to life
    zx-diagnostics - Fixing ZX Spectrums in the 21st Century (wiki)
    Sinclair FAQ Wiki
  • Is this the fault that makes the colours pink and dark green too. I had a speccy like this years as a kid and got used to the "alternative" colours :D
  • balford wrote: »
    The service manual states for Issue 1 machines: "47k resistor between pin 13 of LM1889 and ground - required only if the difference between white and yellow colours is inadequate." Worth a shot here.

    Otherwise, could well be a ULA fault - try swapping one in from another working Spectrum, if available.

    B

    Thanks for insight balford. I will give that a whirl and get back to you.
  • RSwipeCA wrote: »
    balford wrote: »
    The service manual states for Issue 1 machines: "47k resistor between pin 13 of LM1889 and ground - required only if the difference between white and yellow colours is inadequate." Worth a shot here.

    Otherwise, could well be a ULA fault - try swapping one in from another working Spectrum, if available.

    B

    Thanks for insight balford. I will give that a whirl and get back to you.


    Yep swapping the ULA did the trick! Thanks balford.







  • Yay! But boo for another ULA down. At least NebULAe are available these days.

    B
    The Spectrum Resuscitation Thread - bringing dead Spectrums back to life
    zx-diagnostics - Fixing ZX Spectrums in the 21st Century (wiki)
    Sinclair FAQ Wiki
  • edited September 2016
    balford wrote: »
    Yay! But boo for another ULA down. At least NebULAe are available these days.

    B

    Yes I agree its a shame. I did have one spare ULA from a motherboard that had been picked almost bare by the previous owner, all that was left was the ULA! So that has now gone to a good home.

    I have a couple of those NebULAe running in other systems. They are great! And I agree, lucky that they are available for sure.

    Thanks again for you advice.

    *** I now have another issue with a issue 2 not responding to the outermost columns of keys. Hmmmm, problems are like buses.... .

    Post edited by RSwipeCA on
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