CPC464 Lost one colour

[simwalsh]

Hi, 
I took my CPC464 out of the attic and started her up mainly for the kids. It's looks like it has lost red in the rgb output. Bright red {colour 6} shows as black on the monitor. Got a scart lead to check it wasn't the monitor and still shows as black. I checked the resistors after the 40007 chip. Is there something else I should consider or is it the 40007 chip faulty?

Many thanks for your help! 

[Rabs]

Hi,
I took my CPC464 out of the attic and started her up mainly for the kids. It's looks like it has lost red in the rgb output. Bright red {colour 6} shows as black on the monitor. Got a scart lead to check it wasn't the monitor and still shows as black. I checked the resistors after the 40007 chip. Is there something else I should consider or is it the 40007 chip faulty?

Many thanks for your help!

Over time and with the stress of the RGB connector being inserted,  dry joints can occur on the PCB and this sometimes results in the loss of one of the colour signals. Try reflowing the solder on the RGB connector.

[simwalsh]

Over time and with the stress of the RGB connector being inserted,  dry joints can occur on the PCB and this sometimes results in the loss of one of the colour signals. Try reflowing the solder on the RGB connector

Tried reflowing the solder on the RGB connector and some others. 

Colour 3 (dark) red actually looks good but colour bright red comes out as black. colour 26 bright white shows as colour 23 pastel cyan. it is like R of RGB can't go any higher than 128 value

[Rabs]

Over time and with the stress of the RGB connector being inserted,  dry joints can occur on the PCB and this sometimes results in the loss of one of the colour signals. Try reflowing the solder on the RGB connector

Tried reflowing the solder on the RGB connector and some others.

Colour 3 (dark) red actually looks good but colour bright red comes out as black. colour 26 bright white shows as colour 23 pastel cyan. it is like R of RGB can't go any higher than 128 value

Ah, I see what you mean.

Are you able to measure the output levels?

This link may be of interest RGB Outputs.

[Brocky]

maybe check the resistors between the gate array and connector

[Rabs]

Is there anything in this thread that helps Cpc 464 not displaying red?

Similar but maybe not the same root cause. Contains some tips on checking the RGB connector and resistance.

[SerErris]

Can you bend up the red color from the gatearray and measure the three voltage levels for Red of, red half and red full?

This can rule out the GA for beeing faulty (or confirm fault there).

If there is a fault in the output of the GA, then there is no other fix than replacing the GA.

[simwalsh]

Can you bend up the red color from the gatearray and measure the three voltage levels for Red of, red half and red full?

This can rule out the GA for beeing faulty (or confirm fault there).

If there is a fault in the output of the GA, then there is no other fix than replacing the GA.

Thanks for all the help from everyone. I flipped out the red leg of the GA and measured got the following when selecting one colour for the entire screen:

0% Red 0.097 V
50% Red 0.119 V
100% red 0.097 V

Compared it to green

0% Green 0.485 V
50% Green 0.623 V
100% Green 2.85 V

Based on these results looks clear to me that the GA is the problem. found one on ebay so hopefully that solves it

[SerErris]

There is now also an gatearray replacement available if you cannot get your hands on the real thing.

Yes looks like red is actually not doing a lot at all. Regardless of the output it is more or less the same. Sure the pulldowns are missing without the pin attached, but there is nothing driving it high.

[Audronic]

@SerErris 

Do you have a link to the Replacement Gate Array Please

Keep Safe

Ray

[SerErris]

https://www.vretrodesign.com/collections/for-amstrad-cpc-computers

40007 is in the process of validation.

[simwalsh]

Update: fitted the new gate array and it works very well, i'd even say the colours are more vibrant than they used to be.

Thanks for all the help. now to annoy my kids with my childhood experiences