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
check RESET circuit. IC110 pin3 (Lo), pin6 (Hi)
Quote from: McArti0 on 17:37, 26 March 25check 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
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
Quote from: McArti0 on 17:37, 26 March 25check 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.
Quote from: McArti0 on 01:53, 27 March 25https://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
Does a working CPC get a black screen itself after some time?
Quote from: McArti0 on 16:42, 27 March 25Does 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
Mayby C135 (or name C126) have not capacitance.
Quote from: willow3411 on 16:49, 27 March 25It'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.
Quote from: eto on 18:11, 27 March 25Quote from: willow3411 on 16:49, 27 March 25It'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
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.
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.
Quote from: eto on 19:15, 27 March 25IC117 is also part of it.
I have the gut feeling that IC117 could be
in CPC664 is IC125, not IC117
Quote from: McArti0 on 21:11, 27 March 25in CPC664 is IC125, not IC117
oops... :doh:
right, wrong schematics.
and old error
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
The 664 has a sensitive, tender soul inside a muscular body. Always fragile.. ;)
@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