Black screen CPC464 seems to be failing more as i diagnose it

[ClintonGoodfellow]

Hi,

I'm getting a stable 16mhz on pin2 of ic125, i can see this on pin 8 of the unpopulated socket for the 40007, but im reading nothing from pin 40? is my gate array faulty?

I will note that the pio is very hot to touch if the machine is powered for a while, the vdu not as hot but still toasty, the cpu is warm and the GA is stone cold.

[ClintonGoodfellow]

Hi, 

Not sure why I'm not getting any further replies? If it's because I let it languish for a while due to personal circumstances, should I maybe start a new thread?

I'm struggling to find a replacement gate array chip for this poor cpc. I am finding modern recreations, but are kind of expensive just to rule out issues with this board.

I'm wondering if I should just write this machine off and search for a new one? Seems a bit of a shame. 

[arnoldemu]

Hi,

Not sure why I'm not getting any further replies? If it's because I let it languish for a while due to personal circumstances, should I maybe start a new thread?

I'm struggling to find a replacement gate array chip for this poor cpc. I am finding modern recreations, but are kind of expensive just to rule out issues with this board.

I'm wondering if I should just write this machine off and search for a new one? Seems a bit of a shame.

@Bryce please would you offer some assistance?

[arnoldemu]

Hi,

I'm getting a stable 16mhz on pin2 of ic125, i can see this on pin 8 of the unpopulated socket for the 40007, but im reading nothing from pin 40? is my gate array faulty?

I will note that the pio is very hot to touch if the machine is powered for a while, the vdu not as hot but still toasty, the cpu is warm and the GA is stone cold.

Is it possible to record a video or post some screensshots of what is happening or what you see on the screen when it is switched on?

I am hopeful it is not the gate-array but perhaps a rom or ram fault but I don't know enough about diagnostics to help.

[ClintonGoodfellow]

Hello,

Unfortunately I'm getting nothing on the screen whatsoever, just a black screen. There's no change on the screen when turned on, no evidence of sync at all on the tv.

It's connected to the tv using one of the 'retro computer shack' cables which I have no reason to doubt works as they're generally fantastic.

[arnoldemu]

Hello,

Unfortunately I'm getting nothing on the screen whatsoever, just a black screen. There's no change on the screen when turned on, no evidence of sync at all on the tv.

It's connected to the tv using one of the 'retro computer shack' cables which I have no reason to doubt works as they're generally fantastic.

OK. Is the power led lit up? If not take the switch apart and clean it.

If you turn up volume and press del do you hear any beep?

If you have a multimeter check the ics on the pcb have power.

If possible check the z80 is not being held in reset and it has a good input clock.

I guess if you have a digital scope check the syncs at the 6845 are doing something.

I believe its quite unusual for gate array to break and more likely to be something else like rom.

Edit: I had a thought. If the z80 is running but never gets to program the 6845 then you may not get any sync  from the 6845. I haven't checked but this may be true of mc6845 so this is why I suggest checking z80 is executing rom correctly.