CPC 464 black screen - LED on - no beep

[willow3411]

Hello everyone!
Here I am again with a CPC 464.
The symptoms are simple:
Black screen with LED on and no beep with LED.
I changed the GA 40010, the Z80, the ROM 40009 (also put a DIAGROM), the RAMS, IC105, IC114, IC115, as well as the CRTC.
Still the same problem.
I checked the tracks as best I could (to see if there were any cuts), I redid the soldering just in case.
I still have black screen
My dandanator doesn't show me anything at all (unlike the other failure I had: see other post).
If you can tell me the step-by-step procedure to check the components I would be delighted.
I am equipped: voltmeter, oscilloscope (I'm a beginner) and soldering station.
I also have the CPC 464 diagram which I can half understand .
I also followed the Noellabs videos at the excellent LLOPIS, but I got a little lost.
A question to start with: at the CRTC level: Can you replace a UM6845R with an HD6845SP?
here are the photos of the motherboard

 thank you for reading me,
and thank you in advance
willow

[willow3411]

other photos

[d_kef]

The CRTCs are interchangeable. They have differences but only noticeable to some demos and maybe some games. 

For start use your oscilloscope to check the 16Mhz clock input at the GA as well as the 4Mhz input at the Z80 and 1Mhz input at the CRTC.

d_kef

[willow3411]

The CRTCs are interchangeable. They have differences but only noticeable to some demos and maybe some games.

For start use your oscilloscope to check the 16Mhz clock input at the GA as well as the 4Mhz input at the Z80 and 1Mhz input at the CRTC.

d_kef

Hi, Thanks for the response on the CRTC
Can you tell me which ports are used for testing with the oscilloscope?
thanks in advance
willow

[d_kef]

Ports?
If you are not familiar with working with an oscilloscope I'd suggest to follow one of the many tutorials on YouTube. 
Also I forgeot to tell you to ckeck the supply voltages on the motherboard. In fact you should start with it. The supply voltages on the ICs should be near 5V.

d_kef

[McArti0]

@willow3411
A question for you. What is the frequency of the INT signal and what circuit generates it?

What should be the CPU signal frequency?

[Rabs]

Normally, I would start by checking power across the board to ensure I have 5V or as near to. But I also would use a bench power supply to check the current draw and limit it in the case of a short.

[willow3411]

Hello Rabs
SO ,
I took the 5v line, I have 4.6v everywhere.
Here is the photo of my lab power supply.
I can't configure my DOS1102 oscilloscope to read the frequencies
thanks in advance
willow

[Bryce]

That's too low. Try cleaning the power switch contacts or bypass the switch to check if that's the problem.

Bryce.

[McArti0]

I think GA doesn't get voltage on the power pin through the socket.

[willow3411]

That's too low. Try cleaning the power switch contacts or bypass the switch to check if that's the problem.

Bryce.

Hi Bryce,
Thank you for your help,
I bypassed the switch (see photo).
I also cleaned the power socket and redid the soldering on it.
thanks
willow

I think GA doesn't get voltage on the power pin through the socket.

hi McArti0,
I will check this again with the diagrams
thanks
willow

[Rabs]

The current draw is too low and indicates to me that nothing is really running.

I have put an equivalent working board on my test rig.


You cannot view this attachment.

[willow3411]

The current draw is too low and indicates to me that nothing is really running.

I have put an equivalent working board on my test rig.


You cannot view this attachment.

hi,

I understood that.
but I don't know where it could come from...
I follow the tutorials and review my notes taken on other breakdowns encountered... I can't find anything there. 

thanks
willow

[McArti0]

If you have extracted a lot of ICs from their sockets. The probability that all pins have the correct contact after reinsertion is small.

So.... https://www.cpcwiki.eu/forum/index.php?msg=241960

Schematic your 464 is near page 7-8 i this PDF https://www.cpcwiki.eu/manuals/Amendment%20Service%20Manual.zip

[Rabs]

Normally once I am absolutely sure that power is correct and being provided to all ICs. I would check clock sources.

Z80 pin 6 should be about 4 Mhz maybe a little less
GA PIN 39 as above
GA PIN 8 16Mhz from the crystal logic circuit

[McArti0]

GA PIN 39 as above
GA PIN 8 16Mhz from the crystal logic circuit

Wrong, Wrong GA 40010, not 40007

[Rabs]

GA PIN 39 as above
GA PIN 8 16Mhz from the crystal logic circuit

Wrong, Wrong GA 40010, not 40007

Are sorry well spotted, did not notice that. What are the pins on the 40010?

[McArti0]

24 - 16MHz yellow on Screen
19 - 4MHz yellow on Screen
14 - 1MHz (nCPU)

[Bryce]

Your Power supply is showing 5V but the board is showing lower without an increased current. So no short, rather a series resistance. I'd check whether the power socket is clean and also look at the solder joints and traces around the power socket. Those volts must be going somewhere.

Bryce.

[willow3411]

Your Power supply is showing 5V but the board is showing lower without an increased current. So no short, rather a series resistance. I'd check whether the power socket is clean and also look at the solder joints and traces around the power socket. Those volts must be going somewhere.
Bryce.

Hello everyone!
Thanks for trying to help me because I'm going crazy with this card.
SO :
@bryce: I cleaned the power socket, redid the soldering above and below.I have 4.8v everywhere on the ICs.

24 - 16MHz yellow on Screen
19 - 4MHz yellow on Screen
14 - 1MHz (nCPU)

@McArti0
I have no signals on ports 24, 19 and 14 of the 40010...
I have another identical motherboard that works well just in case?
other ideas?
thanks in advance
willow

[McArti0]

IC125 Pin3,Pin4 should been voltage ~2.5V on multimeter and freq 16MHz on oscilloscope.

[willow3411]

IC125 Pin3,Pin4 should been voltage ~2.5V on multimeter and freq 16MHz on oscilloscope.

houla !!
it's no good for me !!
look the photos
Please note, I am not an oscilloscope pro (I am learning) 
thanks
willow

[willow3411]

@Bryce 

[McArti0]

remove GA40010 and check again.
write clearly which photo is from pin4

[McArti0]

did you press AutoSet?