CPC 464 black screen - LED on - no beep

[Bryce]

Never buy retro chips from Aliexpress. China wasn't involved in either chip production or product assembly back then. With modern chips there's a chance that Aliexpress has genuine left over stock, but with retro chips... Why would those chips ever have been there?

There are several EU sellers on ebay where you can get CRTC's that are either old stock or have been removed from old equipment.

Bryce.

[McArti0]

[willow3411]

@Bryce 
@McArti0 

Hi,
me again: the pain 
Come on, let me move forward a little...
I replaced the CRTC (taken from a donor CPC 6128 motherboard).
I did the oscillophone test.
Test OK
I have a signal on pin 39
on the other hand no signal on Pin40 
1Mhz on pin21

thanks
willow

[McArti0]

If you listen carefully, there should be ticks on pin40 approximately every 0,5 seconds.

[willow3411]

If you listen carefully, there should be ticks on pin40 approximately every 0,5 seconds.

I don't have ticks on pin 40 nor on pin 39 (like in your video)

[McArti0]

Now check pin32 GA. Should be freq of pin39 crtc divide by 52. ~150 Hz. Somethink like brum.

[willow3411]

Now check pin32 GA. Should be freq of pin39 crtc divide by 52. ~150 Hz. Somethink like brum.

random frequency on pin 32 of the GA.
one shot 7Mhz
one shot 17Mhz
suddenly 10Mhz...

[McArti0]

With an oscilloscope you have to work the horizontal knob.
Check if you can see the signal from pin 39 of the crtc, because you heard it is there.

And  pin 32 GA first check with an oscillophone.

[willow3411]

With an oscilloscope you have to work the horizontal knob.
Check if you can see the signal from pin 39 of the crtc, because you heard it is there.

And  pin 32 GA first check with an oscillophone.

So on pin 32 of the GA --> no sound 
and no signal

I adjusted the horizontal each time.
I configured the oscillator at 2v and the trigger at 3.6v
I have no signal on pin 39 of the CRTC (which does not beep on the oscillophone)

on pin 40 of crtc random signal 
I'm going crazy!!!

I'm going to reread the entire post and start from scratch because I'm getting lost with all these measurements..
thank you once again

willow

[McArti0]

Forget about pin32 GA. No IC is configured by software.

The fact that you can't catch a signal on an oscilloscope from pin39 of the crtc shows that it's too early for you to use an oscilloscope on a broken CPC. You can test difficult signals on a working CPC. An oscillophone is better, simpler and cheaper. Besides, an oscillophone is retro

Now check if the Z80 works. On the oscilloscope, check the M1 pin27, MREQ pin19 and RD pin21 signal and A0 pin30. These won't be constant frequencies, but there will be life on them at about 1MHz.

[McArti0]

I have a signal on pin 39

nor on pin 39 (like in your video)

What have You and what haven't you?

[willow3411]

Forget about pin32 GA. No IC is configured by software.

The fact that you can't catch a signal on an oscilloscope from pin39 of the crtc shows that it's too early for you to use an oscilloscope on a broken CPC. You can test difficult signals on a working CPC. An oscillophone is better, simpler and cheaper. Besides, an oscillophone is retro

Now check if the Z80 works. On the oscilloscope, check the M1 pin27, MREQ pin19 and RD pin21 signal and A0 pin30. These won't be constant frequencies, but there will be life on them at about 1MHz.

Pin27 ---> 35Mhz
Pin19  ---> 32 Mhz
Pin21   ---> 32 Mhz
Pin30  ----> No signal

Z80 it's hot but works on the other motherboard

I have a signal on pin 39

nor on pin 39 (like in your video)

What have You and what haven't you?

Not the ticks on pin39

[McArti0]

I did the oscillophone test.
Test OK

Test not OK?

[McArti0]

First you need to know how to control an oscilloscope without an automaton. Find out how to set V/div vertically and ms/div or us/div. horizontally.

[willow3411]

I did the oscillophone test.
Test OK

Test not OK?

Yes pin 40 , 38,37,36,35.... without pin39 no Sound

[McArti0]

Has pin39 sound?

[willow3411]

Has pin39 sound?

Sorry,
No sound pin39
Sound Pin 38,37,36,35....
clic on pin40

[willow3411]

First you need to know how to control an oscilloscope without an automaton. Find out how to set V/div vertically and ms/div or us/div. horizontally.

but I can't find a good tutorial.
So I watch the Noel's Retro Labs video.
I look at how he configured his oscilloscope
 V/div vertically: 2v
ms/div: 800ns
us/div. horizontally: 2.88v
Is it good?
I have a lot of trouble understanding how this oscilloscope works.

[McArti0]

Oscilloscop show fast history of voltage. Left -Right you have time, up down you have voltage. How many time you see on screen you set by scale horizontal knob. Thats all.

[Bryce]

First you need to know how to control an oscilloscope without an automaton. Find out how to set V/div vertically and ms/div or us/div. horizontally.

but I can't find a good tutorial.
So I watch the Noel's Retro Labs video.
I look at how he configured his oscilloscope
 V/div vertically: 2v
ms/div: 800ns
us/div. horizontally: 2.88v
Is it good?
I have a lot of trouble understanding how this oscilloscope works.

You mentioned earlier, that your trigger is set to 3.6V. This is too high to catch weak signals. You should set it to 1V to make sure that you catch everything.

Bryce.

[willow3411]

First you need to know how to control an oscilloscope without an automaton. Find out how to set V/div vertically and ms/div or us/div. horizontally.

but I can't find a good tutorial.
So I watch the Noel's Retro Labs video.
I look at how he configured his oscilloscope
 V/div vertically: 2v
ms/div: 800ns
us/div. horizontally: 2.88v
Is it good?
I have a lot of trouble understanding how this oscilloscope works.

You mentioned earlier, that your trigger is set to 3.6V. This is too high to catch weak signals. You should set it to 1V to make sure that you catch everything.

Bryce.

hi,
ok it's good for me

Oscilloscop show fast history of voltage. Left -Right you have time, up down you have voltage. How many time you see on screen you set by scale horizontal knob. Thats all.

I'm starting to understand how the oscilloscope works.
I just watched 3 hours of video on oscilloscopes .
so I will take all the measures requested in the post.
with my motherboard working and then with the motherboard broken.

If I understood correctly, when I do not have a frequency displayed in my oscilloscope table. Should I move the scale button?

thank you very much to both of you.
I swear I will get there!!

willow

[McArti0]

There are signals that do not have one characteristic frequency. Think about it. Two short voltage pulses and one longer one and so on and so forth. This does not have one specific frequency.

Ps. Touch the probe with your finger. You will have a frequency of 50Hz and turn the horiz scale knob left and right.

[willow3411]

@Bryce 
@McArti0 
hello !

here are the different measurements taken on the motherboard which works very well.

Z80 Pin 6 : 1Mhz

GA 40010 Pin 24 : 4Khz
GA 40010 Pin 19 : 1Mhz
GA 40010 Pin 14 : 250Hz   ( ?)

CRTC Pin 39 : 15Khz
CRTC Pin 40 : ?(( no frequency )
CRTC Pin 13 : ?(( no frequency )
CRTC Pin 21 : 1Mhz

GA 40010 Pin 22 : 1Mhz

GA 40010 Pin 4 ( cclk ) : 1Mhz

Voltage CRTC Pin 20 : 4.725v

Z80 Pin 27 : 355Khz
Z80 Pin 19 : 1.333 Mhz
Z80 Pin 21 : 696Khz
Z80 Pin 30 : 357Khz

I repeat that it is the motherboard which works very well.
At the oscilloscope level:
2Volts probe in X10
Trigger 1v
then I modulate Scale Horizontal over time.

I don't use automatic measurement

Am I all right?

now I can take the same measurements on the broken motherboard...
I await your reply.
Thanks again for the advice.

[McArti0]

GA 40010 Pin 14 : 250Hz  ( ?)   300Hz

CRTC Pin 40 : ?(( no frequency ) 50Hz check by oscyllophone!
CRTC Pin 13 : ?(( no frequency )
CRTC Pin 21 : 1Mhz

Pin40 crtc - you should set horis. scale 2-5ms /div.

[willow3411]

GA 40010 Pin 14 : 250Hz  ( ?)  300Hz

CRTC Pin 40 : ?(( no frequency ) 50Hz check by oscyllophone!
CRTC Pin 13 : ?(( no frequency )
CRTC Pin 21 : 1Mhz

Pin40 crtc - you should set horis. scale 2-5ms /div.

I'm confirm
GA 40010 Pin 14 : 255Hz

And yes
CRTC Pin 40 : 50Hz ( it's good with scale 5ms /div and CH1 2Volts with TRIGGER 1v )

i'm repeat :it's the motherboard that works