Just a pink screen 464 Plus

[Overkill]

Hi all,


I'm trying to fix a 464 Plus that just has a pink screen, you know normaly you get a yellow/bright-green or light-blue screen with some black lines down the left side, when the cartridge is not inserted?  Well I get a pink screen with those black lines even with a cartridge installed.


> I know the CPU is good.
> I know the RAM is good.
> I know IC16 (NOR?) is good.
I can't see any damage to the tracks.


Before I send a life time tracing every connection, does anyone know if a pink screen means something?

[Bryce]

Any plus (and it was several) that I've encountered with a fully pink (sometimes other bright colour) screen had a dead ASIC.

Bryce.

[gerald]

Hi all,


I'm trying to fix a 464 Plus that just has a pink screen, you know normaly you get a yellow/bright-green or light-blue screen with some black lines down the left side, when the cartridge is not inserted?  Well I get a pink screen with those black lines even with a cartridge installed.


> I know the CPU is good.
> I know the RAM is good.
> I know IC16 (NOR?) is good.
I can't see any damage to the tracks.


Before I send a life time tracing every connection, does anyone know if a pink screen means something?

Pink does not mean anything. It's just the result of non initialized color registers.
Is there any visible border or is it just a full pink screen ?

[Overkill]

Yes I think you are right, I've since plugged a few Plus's in and they all seem to have different colour screens.


There is no border, so maybe I should check all the connections to the cartridge?

[gerald]

Yes I think you are right, I've since plugged a few Plus's in and they all seem to have different colour screens.


There is no border, so maybe I should check all the connections to the cartridge?

You can check the cartridge connection, but the are good chance that you have dead asic.If you have a scope, start by checking if the Z80 has a clock.

[Overkill]

I've got what I think is a good looking scope signal on the M1 pin of the Z80.


I'm checking the cartridge connections, but I'm stuck on B8, checking the circuit diagram it says "NCE" at the cartridge port and it looks line "NROM" on the mainboard connection, what is NCE or NROM?

[gerald]

I've got what I think is a good looking scope signal on the M1 pin of the Z80.


I'm checking the cartridge connections, but I'm stuck on B8, checking the circuit diagram it says "NCE" at the cartridge port and it looks line "NROM" on the mainboard connection, what is NCE or NROM?

NCE : it's the (EP)ROM chip enable, negative polarity.

[Overkill]

I don't know where that NCE should connect, I carried on test all the others and found them all fine apart from B17 says CLK4, which looks like it should connect to the ASIC's pin 125, but I have no circuit.

[Overkill]

ignore that, it goes through a resistor.

[Overkill]

Does getting a picture with those black lines on the left mean that IC15 is working?

[gerald]

I don't know where that NCE should connect, I carried on test all the others and found them all fine apart from B17 says CLK4, which looks like it should connect to the ASIC's pin 125, but I have no circuit.

CLK4 connect to asic pin 125 (and goes to Z80 clock input via a 22Ohm resistor). On the cartridge it goes to pin 3 of the ACID chip
NROM is on ASIC pin 29 and on pin 6 of the ACID chip in the cartridge.

[Overkill]

Thanks for that.  Do you think my IC15 must be OK, because I get a picture?

[gerald]

Thanks for that.  Do you think my IC15 must be OK, because I get a picture?

IC15 is only responsible for the RGB signal. To have a picture you also need sync which are generated by the ASIC.
If IC15 would be on only failing IC, you would be able to get sound out of the Plus, either by using a game cartridge or just the traditional del key
Do you have an idea of the Plus consumption, is the 5V ok ?