CPC 464 black screen - LED on - no beep

[willow3411]

did you press AutoSet?

yes !

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

exactly the same thing
on the name of the photo I put pin 3 and pin4 

[McArti0]

ok, I guess I didn't get enough sleep 

[willow3411]

ok, I guess I didn't get enough sleep 

hihi

[McArti0]

What setting are you using for the x1, x10, x100 probe?

Did you calibrate the probe on a square waveform?

Did you see the full shape of the clock waveform (pin4) on the screen?

Did you adjust the image scale with the knobs?

[willow3411]

What setting are you using for the x1, x10, x100 probe?

Did you calibrate the probe on a square waveform?

Did you see the full shape of the clock waveform (pin4) on the screen?

Did you adjust the image scale with the knobs?

What setting are you using for the x1, x10, x100 probe?
X10
Did you calibrate the probe on a square waveform?
yes
Did you see the full shape of the clock waveform (pin4) on the screen?
no
error message: DC voltage detected
Did you adjust the image scale with the knobs?
scale on oscillo button?

[McArti0]

Yes.
have you manual?

[willow3411]

Yes.
have you manual?

yes but is little manual for oscillo

[McArti0]

find How set AC input

[McArti0]

[willow3411]

find How set AC input

I switched to AC
here are the measurements
photos pin 3 and pin 4 without the 40010
thank you for your help

willow

[Bryce]

@Bryce

Did you do the reflow to the solder on the top side of R126 and R128? Whoever did it either used the wrong type of solder or the iron wasn't hot enough.

Also, you seem to have incorrect settings on the scope. All the values being stated in amps (A) should be stating them in Volts (V).

Bryce.

[McArti0]

I have another identical motherboard that works well just in case?

Check what your oscilloscope shows on that mainboard. But give a photo to check if it is really the same.

[willow3411]

@Bryce

Did you do the reflow to the solder on the top side of R126 and R128? Whoever did it either used the wrong type of solder or the iron wasn't hot enough.

Also, you seem to have incorrect settings on the scope. All the values being stated in amps (A) should be stating them in Volts (V).

Bryce.

hi Bryce,

I switched to Volts on the oscilloscope (at least I think) and re-soldered the resistors

always black screen

[willow3411]

I have another identical motherboard that works well just in case?

Check what your oscilloscope shows on that mainboard. But give a photo to check if it is really the same.

@McArti0 and @Bryce

Well I compared the signals on the two motherboards.
Here are the photos.
Pin 3 and Pin 4 of IC125 with the results.
I think I found the right oscilloscope configuration (thanks for the video).
FYI no signal comes out (unknown signal) on pin 39 and 38 of the CRTC. (while I have a signal on the motherboard OK)

[willow3411]

pin 4 on the two motherboard

[McArti0]

Pk-Pk 4.8v is good. 0.8v is wrong. Pin 4 is used by GA.

[willow3411]

Pk-Pk 4.8v is good. 0.8v is wrong. Pin 4 is used by GA.

I don't understand

sorry....

[Bryce]

Pk-Pk 4.8v is good. 0.8v is wrong. Pin 4 is used by GA.

I don't understand

sorry....

What he's saying is, that on the working CPC your measurements show a Peak to Peak Voltage of 4.8V, but on the non-working CPC the same signal is only showing a peak to peak voltage of 800mV. This would suggest that the possible failures are:  A bad solder joint in that area. A broken or "drifted" resistor (value no longer correct). Or a broken IC125.

However... As the frequencies are all present and close to what they should be, I'm not 100% sure about your measurements. It would be very difficult to get a crystal to start oscillating in those conditions. What measurement do you get on pin 8 of both computers? 

Bryce.

[willow3411]

What he's saying is, that on the working CPC your measurements show a Peak to Peak Voltage of 4.8V, but on the non-working CPC the same signal is only showing a peak to peak voltage of 800mV. This would suggest that the possible failures are:  A bad solder joint in that area. A broken or "drifted" resistor (value no longer correct). Or a broken IC125.

However... As the frequencies are all present and close to what they should be, I'm not 100% sure about your measurements. It would be very difficult to get a crystal to start oscillating in those conditions. What measurement do you get on pin 8 of both computers? 

Hi Bryce,
thanks a lot.
pin 8 on IC125 ?

[McArti0]

set your probe to x100.
where do you attach the probe ground?

[Bryce]

What he's saying is, that on the working CPC your measurements show a Peak to Peak Voltage of 4.8V, but on the non-working CPC the same signal is only showing a peak to peak voltage of 800mV. This would suggest that the possible failures are:  A bad solder joint in that area. A broken or "drifted" resistor (value no longer correct). Or a broken IC125.

However... As the frequencies are all present and close to what they should be, I'm not 100% sure about your measurements. It would be very difficult to get a crystal to start oscillating in those conditions. What measurement do you get on pin 8 of both computers? 

Hi Bryce,
thanks a lot.
pin 8 on IC125 ?

The CLK input pin of the GA.

@McArti0:   I doubt he has a x100 probe, I hope he is using 10x though and not 1x. But I also meant to ask the other question earlier: Where are you connecting to the CPC GND for these measurements?

Bryce.

[willow3411]

set your probe to x100.
where do you attach the probe ground?

What he's saying is, that on the working CPC your measurements show a Peak to Peak Voltage of 4.8V, but on the non-working CPC the same signal is only showing a peak to peak voltage of 800mV. This would suggest that the possible failures are:  A bad solder joint in that area. A broken or "drifted" resistor (value no longer correct). Or a broken IC125.

However... As the frequencies are all present and close to what they should be, I'm not 100% sure about your measurements. It would be very difficult to get a crystal to start oscillating in those conditions. What measurement do you get on pin 8 of both computers? 

Hi Bryce,
thanks a lot.
pin 8 on IC125 ?

The CLK input pin of the GA.

@McArti0:  I doubt he has a x100 probe, I hope he is using 10x though and not 1x. But I also meant to ask the other question earlier: Where are you connecting to the CPC GND for these measurements?

Bryce.

Thank you both for trying to help me.
I really appreciate it.
So I have an X10 probe with my HANMATEK DOS1102. The problem is that I still have big gaps in making it work and above all understanding how it works and its logic.
for the mass I take it from the CPC power socket or directly from my lab power supply.
Is this the right procedure?
I suspect that my oscilloscope is incorrectly adjusted...
I'm going to take the signal on pin 8 of the GA.
thanks again
willow

[willow3411]

What he's saying is, that on the working CPC your measurements show a Peak to Peak Voltage of 4.8V, but on the non-working CPC the same signal is only showing a peak to peak voltage of 800mV. This would suggest that the possible failures are:  A bad solder joint in that area. A broken or "drifted" resistor (value no longer correct). Or a broken IC125.

However... As the frequencies are all present and close to what they should be, I'm not 100% sure about your measurements. It would be very difficult to get a crystal to start oscillating in those conditions. What measurement do you get on pin 8 of both computers? 

Hi Bryce,
thanks a lot.
pin 8 on IC125 ?

The CLK input pin of the GA.

@McArti0:  I doubt he has a x100 probe, I hope he is using 10x though and not 1x. But I also meant to ask the other question earlier: Where are you connecting to the CPC GND for these measurements?

Bryce.

hi Bryce,

here is my connection and measurements pin 8 on GA 40010.
the first on an ok motherboard and the second on an HS motherboard.
At each measurement I press the "self-test" key on the oscilloscope.
thanks
willow

[Bryce]

Sorry, I didn't realise your 464 had a 40010. On a 40010 you should be measuring the signal on pin 24. It should have a clean 16MHz signal on it. If it does, all components (including IC125) in the clock generation circuit are good. Do both computers have a 40010 GA?

Your latest measurements were also partially useful too though. Pin 8 on a 40010 GA is the Blue output signal to the monitor. The good CPC shows exactly what would be expected. The broken computer is just showing noise.

My guess at the moment is that the CRTC has bad solder joints.

Bryce.

[McArti0]

First I want to see 16MHz Pk-Pk on pin4 IC125.

ps. what's meaning HS?