CPC 664 Black Screen But with Dandanator OK

[willow3411]

Hello everyone,
So here's my problem:
CPC 664 with black screen .
Led on
No keyboard beep.

My tests:
with my dandanator the CPC starts well. I launch the romdiag and all tests are OK: RAMS, ROMS, KEYBOARD, Joystick.
with my dandanator under basic: Everything works too ( I have not tested diskettes ).
I did not notice any boiling components.
Do you have an idea?

thank you in advance
willow3411

[McArti0]

check RESET circuit. IC110 pin3 (Lo), pin6 (Hi)

[willow3411]

check RESET circuit. IC110 pin3 (Lo), pin6 (Hi)

hello McArti0
then,
I have about 0.15v on pin 3
and 5v on pin 6
on the other hand when I touch pin 6 and pin 5 at the same time the cpc displays the basic and prompt.
If I turn off the CPC and turn it back on, it works.
But if I wait 5 seconds: black screen

thanks
willow

[McArti0]

https://www.cpcwiki.eu/imgs/2/29/CPC664_Schematic.png   left side

check pinout IC125 is the same like in the schem.

always after 5 seconds black screen?

IC125 pin11 try join to 5v

[Bryce]

check RESET circuit. IC110 pin3 (Lo), pin6 (Hi)

Good call @McArti0 . I'd suspect IC110 as the most likely point of failure, especially if it's a HC132 they used. Pin2 goes straight to the expansion port with no protection, so it could easily get damaged from static discharge. If that's not the issue, I've also seen CPC's where D101 was the issue. I'd also check all the solder joints on the reset circuit components.

Bryce.

[willow3411]

https://www.cpcwiki.eu/imgs/2/29/CPC664_Schematic.png  left side

check pinout IC125 is the same like in the schem.

always after 5 seconds black screen?

IC125 pin11 try join to 5v

@Bryce 
I changed IC110

I will test the reset circuit


but  I suspect IC125
when I make quick on/off the cpc start.
if I wait 10 seconds and turn on the black screen.
if I redo on/off quick cpc start

willow

[McArti0]

Does a working CPC get a black screen itself after some time?

[willow3411]

Does a working CPC get a black screen itself after some time?

No. Once started, the CPC works fine!!
It's enchanted.
I'm going to test diode D101.

willow

[McArti0]

Mayby C135 (or name C126) have not capacitance.

[eto]

It's enchanted.

Not enchanted. Just an issue in the Reset circuit. I would expect when you start it and it's black and then you force a short reset, then it will become alive.

[willow3411]

It's enchanted.

Not enchanted. Just an issue in the Reset circuit. I would expect when you start it and it's black and then you force a short reset, then it will become alive.

Hello eto
Yes, that's exactly it, quick on/off and it wakes up and works fine.
So I need to find the reset circuit?
Is that right?
Thanks
willow

[eto]

You are already in the mid of the reset circuit. D101 and IC110 are part of it.

IC117 is also part of it. 

I have the gut feeling that IC117 could be the root cause of the problem. But that's just a wild guess based on what I have read about this kind of circuit and is not based on actual education ;-) 

What I don't understand though is, why it works, when you quickly turn off and on the CPC.

[willow3411]

Okay, I'll test IC117.
D101 was replaced on Bryce's advice.
For my part, when I do a reset (as shown in the photo), the CPC starts.

[McArti0]

IC117 is also part of it. 

I have the gut feeling that IC117 could be

in CPC664 is IC125, not IC117

[eto]

in CPC664 is IC125, not IC117

oops... 

right, wrong schematics.

[McArti0]

and old error

[willow3411]

Hi everyone,
Thank you all for your invaluable help.
So after replacing the diode, the result was the same.
I replaced IC125 and it works perfectly!!
A 664 saved.
Thanks again a thousand times.
Willow

[dodogildo]

The 664 has a sensitive, tender soul inside a muscular body. Always fragile.. 

[Audronic]

@willow3411 

Thanks for raising this problem.
Would you believe I have just had the SAME problem on a CPC6128
and replacing the same chip fixed my problem

Thanks

keep safe

Ray