cpc464 repair black screen newbie question

[cuberdon]

Got 2 of those and both refuse to load data .

altough all options have been tested they simply crash .

the zx81+38 is an ongoing project wich is still changing a bit .

It uses the original rom .

i also have 2 zx80 clones which are housed in a 3d printed replica case and look the thing .

[Bryce]

I've one of these (ZX80Core) lying around somewhere here, but I think I've only ever used it twice.

https://www.8bity.cz/wp-content/uploads/2014/08/ZX80Core_Martin_AcrylicCase_front.jpg

Bryce.

[cuberdon]

unfortunately inserting an image is almost impossible ,

https://i.ibb.co/bL62L9G/clock-circuit.jpg

i verified the pcb with this schematic and it does not match .

i have a pulse at pin 8 of ic 125 , but nothing at pin 8 of ic 116 ?

pcb Z70200  MC0002D

am i overlooking something here ??

[robcfg]

Hmmm, you just need to click on the 'insert picture' icon to the right of the YouTube one, write the url you just linked, click 'Insert' and that's it:

[McArti0]

In total, there were quite a few CPC versions

This schem is one of the first.

Find Your main board here... https://www.cpcwiki.eu/index.php/Mainboard_Versions

ps. first click PREVIEW... after this You can add image

[robcfg]

In total, there were quite a few CPC versions

This schem is one of the first.

Find Your main board here... https://www.cpcwiki.eu/index.php/Mainboard_Versions

ps. first click PREVIEW... after this You can add image

That works if you'd like to upload an image from your computer. 

To link an image from internet, you need to click on the "Insert an image" icon to the right of the YouTube one, that will open a small dialog, enter the url of the image and then click on the "Insert" button on the dialog.

[McArti0]

https://www.cpcwiki.eu/manuals/Amendment%20Service%20Manual.zip

and look this manual

[cuberdon]

Thanks for this info , 

i go and search with the other schematics to see if that matches my pcb

[SerErris]

Your clock circuit is in the amendet service manual linked by McArti0
You cannot view this attachment.
The improved it and made it much simpler (less parts), now with NOT gates instead of NAND gates.

[cuberdon]

So , after some testing with the new schematic , 

the clock signal is available on ;

ic 125 -4
ic 126 -8

ic 125 -6
ic 111 -6

i verified the data and address lines with a logic probe , but no activity there .

what am i missing ??

any advice highly appreciated 

[Bryce]

So , after some testing with the new schematic ,

the clock signal is available on ;

ic 125 -4
ic 126 -8

ic 125 -6
ic 111 -6

i verified the data and address lines with a logic probe , but no activity there .

what am i missing ??

any advice highly appreciated

Ok, the thread got slightly diverted, so lets recap... Do you have 5V on the PCB (power pins of any chip)? Is the screen completely black or is it a black square in the middle?

Bryce.

[McArti0]

Have You 40007 with radiator?

[cuberdon]

@Bryce , 

no screen image at all ,

but maybe my converter is not correct too ( scart cable to converter ) 

i will try to get composite connected 

[cuberdon]

@ McArti0 ,

the aluminium radiator is present en get's warm too

[McArti0]

Try IC111 Z80 signal M1 Pin27 (if working Z80)

Try IC126 40007 GA  signal READY Pin2 (If working GA)

[cuberdon]

@ McArti0 ,


Both pins pulse on my logic probe

[Bryce]

@Bryce ,

no screen image at all ,

but maybe my converter is not correct too ( scart cable to converter )

i will try to get composite connected

Until you've confirmed that your video setup works, there's not really any point in trying to diagnose anything further.

Bryce.

[cuberdon]

Bryce ,


How to get composite working ?

pin 6 and pin 5 do not generate any image

(and the input on my monitor is working )

my monitor does not have scart

[McArti0]

middle pin is composite.

look on oscilloscope.

[cuberdon]

middle pin and ground do not give me image on a working composite monitor


-verified with a sinclair spectrum :-)

[McArti0]

GA pin1 nCpu 1MHz
GA pin40 cclk 2MHz

GA pin15 vsync 50Hz (or ~4Hz)
GA pin14 hsync 15,6kHz (or ~7kHz)

GA pin11 vsync+hsync

[Bryce]

middle pin and ground do not give me image on a working composite monitor


-verified with a sinclair spectrum :-)

In that case, and if holding the DEL key also doesn't give you a beep, I'd suspect the Z80 as the most likely failure.

Bryce.

[cuberdon]

Bryce , 

luckily i have some z80's available .

I will try setting up my oscilloscope to get some waveforms measured 

[Bryce]

Bryce ,

luckily i have some z80's available .

I will try setting up my oscilloscope to get some waveforms measured

Why? Just swap it out and see if it works. It's in a socket. No need to do any further tests beforehand.

Bryce.

[cuberdon]

Unfortunately changing the z80 for a known good one , does not change the problem .

i will set up my oscilloscope to get a better view on things