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avatar_Kris

Need help to fix a 664

Started by Kris, 19:05, 19 May 16

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Kris

My 664 does not boot anymore:

- Power LED of the CPC is ON
- CTM is fully OK (tested with a 6128) but show a complete black screen when power ON the keyboard
- Gate array OK
- Z80 OK
- ROM 40015 OK

Any idea ?


gerald

are the Z80/GA/(ROM?) socket clean ?
Is the power switch OK ? If its resistance is high enough the voltage will drop enough for the CPC to fail, but the LED still on
Does the Z80 get a clock ?

Kris

#2
I have cleaned the 3 sockets and replaced each chips with good ones from a 6128: results is the same.
Power switch is OK (tested on a 6128 as well).

Not tested the clock on the Z80, I will have my oscillo with me tomorrow, it will be easier....

Thank you for your help.

Edit: here is the clock signal onto the Z80:



Audronic

Have a look at the Power Supply with the CRO, a lot of noise on the Photo between pulses ?


Ray
Procrastinators Unite,
If it Ain't Broke PLEASE Don't Fix it.
I keep telling you I am Not Pedantic.
As I Live " Down Under " I Take my Gravity Tablets and Wear my Magnetic Boots to Keep me from Falling off.

gerald

These is no clock. You expect a 5V square wave (50% duty cycle). Here only noise can be seen.
Did you check it at Z80 input pin or GA output pin ? There is a buffer and a resistor between the two.
And while you have  the scope out, check that the 16MHz is there  at GA iinput.

SOS

Quote from: gerald on 19:22, 19 May 16
Is the power switch OK ? If its resistance is high enough the voltage will drop enough for the CPC to fail, but the LED still on
IMHO Unusual tip - BUT Cool, i tried them, and now is an other CPC6128 back to life.  :D
Thanks Gerald!

Bryce

Quote from: SOS on 08:35, 20 January 17
IMHO Unusual tip - BUT Cool, i tried them, and now is an other CPC6128 back to life.  :D
Thanks Gerald!

It's not that unusual, it actually happens quite often.

Bryce.

robcfg

Indeed!


I got a 6128 from a friend this Christmas ans wasn't powering on.


So, I opened it, cleaned the power switch with contact cleaner and it's working like a charm!

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