Dead CPC6128

[willow3411]

Hi all !
Hi Brice,
ok here is the progress.
I no longer have a short circuit on the motherboard.
I changed the RAM, but still black screen and no beep.
I have 4.45v on the Rams, on GA. I tested the Z80 and the 40010, they are OK.
on the other hand I noticed that the Chip which manages the Floppy (the IC 201) heats enormously.
I don't remember how to test the CRTC?.
I don't have an oscilloscope.
thank you in advance if you have any idea?

[Bryce]

4.45 Volts is way too low. Either there is still a short somewhere or there is resistance (dirt) in the power socket or switch. Remove all socketed IC's and see if the voltage ever gets to 5V. Clean the power socket (if you haven't already) and remove the power switch from the equation by shorting the power switch pins on the PCB.

Bryce.

[willow3411]

Hello Brice,
so I removed all the ICs (Z80, 40010, and 40031). I put a jumper to remove the switch.
on my lab power supply I have 5.02V and 1.3A
when I take the measurements on the RAM I have 4.54V and on GA pin 3 and 6 the same.
on the other hand I have the ROM (40051) which heats up as well as always the CI of the floppy: UPD765AC (IC201).
I have the same voltage on the CRTC (4.54V).
I go crazy...

[Bryce]

Ok. It's very likely that a ROM i/o pin (data or address pin) has a partial short to the 5V rail or ground. 1.3A is way too high. Check the resistance between each ROM data and address pin to GND and to VCC (with no power connected!). One of them is probably wrong (compared to the others). The floppy controller IC does tend to get a little hot, but the ROM should never get hot at all.

A further question: What lab PSU are you using? Does it still show 5.02V when the CPC is on? Is 1.3A the current limit you set or the reading that the PSU says is being pulled?

Bryce.

Btw: You get extra points and more support if you manage to spell my user name properly with a "Y" instead of an "i".
Je ne suis pas "Brice de Nice"

[willow3411]

Houla, Sorry Bryce (am I right there?). great i got a good point 
Well I will try to check the points of the ROM (with a multimeter?).
the power supply is me who put it at 5.02v and 1.3A is the limit (if that is what I understood in the documentation of the power supply).
the CPC consumes 5v 1.7 Amp right?
tomorrow I'll take pictures of it all.
thank you Bryce de pas de Nice ( in french )        
Willow de Montpellier   

[willow3411]

Hi Brice,
I just tested the 5v line using this:
https://pelrun.github.io/cpc-schematics/index.html
well everything seems ok except the D301 which beeps in both directions (but I have not unsoldered it).
what do you advise me?
I change it, I desolder it to test just one leg?...

now (still using the schematic) I will test the continuity of ROM 40051.
so far I'm okay?

Thanks

[willow3411]

Arfff ! Sorry Bryce !!! the translator

[willow3411]

@Bryce
Well I tested everything I did not see anything abnormal with the continuity tester.
I don't have an oscilloscope to test the ROM and CRTC output signals.
So I changed the ROM (4051): result still black screen but more heating of the ROM.
I changed the CRTC and now I have display but corrupted.
see the pictures.
At the third start I have the gray screen with black border (RAM).
What do you think ?

Thanks

[willow3411]

Bryce,
here is what it does to me now. At each start, to know that it works after 15 starts.

[willow3411]

autre photos

[willow3411]

@Bryce

It's ok !!!! Resolved . IC201 HS

I said from the start that the chipset was boiling
it was a Greek who gave me the confirmation (Vagelis you never know he must be on the WIKI).
So everything is OK I changed the RAM for nothing and CRTC and the 40051 too. but at least now I know! and I note it.
Thank you all for your advice and see you very soon for a new breakdown.

[Audronic]

@willow3411 

Orion
Saisho
Amstrad

As the opening Screen
It should be only one of the makers names not variable ?

Perhaps the IC107 M5L8255ap-5 has a Problem

Well done so far

Keep Safe

Ray

[willow3411]

tout est ok !!
Thanks