CPC 464 black screen - LED on - no beep

[willow3411]

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.

hi Bryce !

yes it's 40010 on both motherboards.
so here are the measurements.
first my power supply connected to the motherboard with black screen (Out of Service).
The first photos are the measurements on the GA 40010 pin 24.
the last two, the measurements on Pin4 of IC125
(for information my oscilloscope was configured in DC and not in AC!!).

thanks.
Willow

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

ps. what's meaning HS?

HS = black screen

[McArti0]

Ok (meaning not ok).
Now connect Pin1 IC125 to ground and multimeter to pin 3. Voltage should be ~5V.

connect Pin1 IC125 to ground and multimeter to pin 4. Voltage should be ~0V.

connect Pin1 IC125 to 5V and multimeter to pin 3. Voltage should be ~0V.

connect Pin1 IC125 to 5V and multimeter to pin 4. Voltage should be ~5V.

beter without GA40010

[willow3411]

Ok (meaning not ok).
Now connect Pin1 IC125 to ground and multimeter to pin 3. Voltage should be ~5V.

connect Pin1 IC125 to ground and multimeter to pin 4. Voltage should be ~0V.

connect Pin1 IC125 to 5V and multimeter to pin 3. Voltage should be ~0V.

connect Pin1 IC125 to 5V and multimeter to pin 4. Voltage should be ~5V.

hello,

I disconnect the motherboard from the 5v?

[McArti0]

No.
I told you ADD small connection. 5V You have on Pin 14. Ground You have on Pin7. for .ex.

ps, its test of 74HCU04

[willow3411]

No.
I told you ADD small connection. 5V You have on Pin 14. Ground You have on Pin7. for .ex.
ps, its test of 74HCU04

OK, I understand.
Sorry for my ignorance, but my English is a bit poor hihi.
I don't have the pliers required to take the right measurements without risk.
I'm going to order them (grip pliers).

thank you for your patience
willow

[McArti0]

Here isnt risk. currents are very small.

Check only Pin1 to ground. Pin4 should be 0V

[willow3411]

Here isnt risk. currents are very small.

Check only Pin1 to ground. Pin4 should be 0V

ok

So to summarize and if I understood correctly:
I supply the motherboard with 5v without the GA.
I supply IC125 with 5v on pin 14 and ground on pin 7.
then I take the measurement with the multimeter on pin 1 and 4?
is that right?

willow

[McArti0]

Yes but Pin14 always have 5v and pin7 ground.
You don't have to do anything with pin14 and pin7.

[Bryce]

Hi,
    please don't do any jumper tests. Just measure the frequency on CLK input of the GA. The pin numbers that McArti0 is referring to are from the 6128 and later 464's. Original 464's used this chip differently and pin 4 is NOT the output of the clock circuit. So I don't think you should be comparing the pins 1 to 1 on these two computers and bridging 5V to an unknown point could damage your computer.
If there is a good 16MHz signal on the CLK input of the GA, then the clock circuitry is fine. One test, no jumpers.

Bryce.

[McArti0]

@Bryce You confused IC125 for 464 with IC117 for 6128
I checked schem 464 with two GA socket and photo.

[willow3411]

Hi,
    please don't do any jumper tests. Just measure the frequency on CLK input of the GA. The pin numbers that McArti0 is referring to are from the 6128 and later 464's. Original 464's used this chip differently and pin 4 is NOT the output of the clock circuit. So I don't think you should be comparing the pins 1 to 1 on these two computers and bridging 5V to an unknown point could damage your computer.
If there is a good 16MHz signal on the CLK input of the GA, then the clock circuitry is fine. One test, no jumpers.

Bryce.

hi Bryce,
ok I understand !

so my measurements are good?

[willow3411]

@Bryce You confused IC125 for 464 with IC117 for 6128
I checked schem 464 with two GA socket and photo.

hi,

So here is my measurement with the multimeter.
this oscillates between 0.02V and 0.06v

and I'm 4.7V to pin 14 and pin 7

it's good ?

[McArti0]

Jump pin1 ic125 to ground and check pin4 by multimeter.

[Bryce]

Hi,
    please don't do any jumper tests. Just measure the frequency on CLK input of the GA. The pin numbers that McArti0 is referring to are from the 6128 and later 464's. Original 464's used this chip differently and pin 4 is NOT the output of the clock circuit. So I don't think you should be comparing the pins 1 to 1 on these two computers and bridging 5V to an unknown point could damage your computer.
If there is a good 16MHz signal on the CLK input of the GA, then the clock circuitry is fine. One test, no jumpers.

Bryce.

hi Bryce,
ok I understand !

so my measurements are good?

The frequency is good, but the voltages are wrong. Can you check the resistance of R143, 144 and 145?

Bryce.

[willow3411]

Hi,
    please don't do any jumper tests. Just measure the frequency on CLK input of the GA. The pin numbers that McArti0 is referring to are from the 6128 and later 464's. Original 464's used this chip differently and pin 4 is NOT the output of the clock circuit. So I don't think you should be comparing the pins 1 to 1 on these two computers and bridging 5V to an unknown point could damage your computer.
If there is a good 16MHz signal on the CLK input of the GA, then the clock circuitry is fine. One test, no jumpers.

Bryce.

hi Bryce,
ok I understand !

so my measurements are good?

The frequency is good, but the voltages are wrong. Can you check the resistance of R143, 144 and 145?

Bryce.

Hi Bryce,

so I soldered a leg to each resistor to take the measurements.
On 
R143: 9.47 Mohms
R144: 4.671 Kohms
R145: 9.97 Mohms

I think it's good if I understand the electronic diagram correctly
No ?
Thanks
willow

[McArti0]

Jump pin1 ic125 to ground and check pin4 by multimeter.

[willow3411]

Jump pin1 ic125 to ground and check pin4 by multimeter.

hi, McArti0

I put pin1 to ground and measured pin4, I have 1.8V
on pin3 4.7v

[McArti0]

Pin 4 should have about 0.1V. The inverter between pin 3 and pin 4 is damaged. IC125 (74HCU04) is damaged.

[willow3411]

Pin 4 should have about 0.1V. The inverter between pin 3 and pin 4 is damaged. IC125 (74HCU04) is damaged.

hi,

ok, 
I'm going to see if I have stock on this component to do a test...
This is not due to the fact that I only have 4.7v entering the CPC just after the power socket?
THANKS 
I will test and get back to you.

willow

[McArti0]

This is not due to the fact that I only have 4.7v entering the CPC just after the power socket?

No.
Look at manual this IC...
https://www.ti.com/lit/gpn/sn74hcu04

For  power supply vcc=4.5v,  ViH= 3,6v - is interpreted as Hi.

[willow3411]

Pin 4 should have about 0.1V. The inverter between pin 3 and pin 4 is damaged. IC125 (74HCU04) is damaged.

hi,
so I changed IC125 (put on support and taken from a CPC 6128 donor motherboard).
I took the measurements on pin4, I have 0.2V and on pin3 4.5v and pin 1 on the ground
frequency level:
pin6 Z80: 4Mhz
Pin 24 GA 40010: 16Mhz
Pin 19 GA 40010: 4Mhz
Pin 14 GA 40010: 1Mhz
Results : Black Screen 

@Bryce 

@McArti0

[McArti0]

Greate! GA work.

Now CRTC.
Pin 39 Hsync
Pin 40 Vsync
Pin 13 MA9

any Freq?

GA
Pin32 INT
Pin22 Ready/Wait
any freq?

[willow3411]

Greate! GA work.

Now CRTC.
Pin 39 Hsync
Pin 40 Vsync
Pin 13 MA9

any Freq?

GA
Pin32 INT
Pin22 Ready/Wait
any freq?

hi
@McArti0 

Now CRTC.
Pin 39 Hsync: Random frequency
Pin 40 Vsync: Random frequency
Pin 13 MA9: random frequency



GA
Pin32 INT: OK
Pin22 Ready/Wait: OK
 So to summarize:
when I take the measurements three times in a row, the oscilloscope shows me no signal detected but finds a frequency (I think it's noise, right?)
This does it to me on the CRTC.
Or maybe I didn't get the mass right.
FYI the CRTC is new and changed twice

Thanks

[McArti0]

can You use triger? in oscylo.

[willow3411]

can You use triger? in oscylo.

arff ; i not understand .... triger ??