Hi forum ,
coming from sinclair and commodore the cpc464 is a small step aside ;-)
Now , knowing there is no voltage regulator on board the input voltage must be rather precise .
So a little more than 5 volt goes in, BUT ..................
I do measure 3,5 volt on chips the board ,
Do i wait for smoke ? or is there a known culprit which might be the number-one to look for ?
Quote from: cuberdon on 15:54, 29 October 24Hi forum ,
coming from sinclair and commodore the cpc464 is a small step aside ;-)
Now , knowing there is no voltage regulator on board the input voltage must be rather precise .
So a little more than 5 volt goes in, BUT ..................
I do measure 3,5 volt on chips the board ,
Do i wait for smoke ? or is there a known culprit which might be the number-one to look for ?
Hi, if the rail is dropping to 3.5V then something is getting hot. Find the component that's hot and you'll have found the problem.
Bryce.
i will need to verify my powersupply :doh:
The 5V Powersupply needs to provide >1Amps better 2Amps. If it cannot provide 1Amp it will probably drop the voltage to much for the CPC to work, or shutdown completely.
However as Bryce pointed out, one or more chips might be shorted and that drawin all the power the PS can deliver and then dropping the Voltage (the PS cannot keep it up).
current powersupply can do up to 5 amp , but its output is under 5 volt ( i noticed at no-load ) .
so i need to verify if i can source a better one
Be careful cranking up the powersupply until you've identified what is pulling down the 5v rail.
Although there is a oldschool technique for finding shorts where you turn up the power until the offending component explodes.
I wouldn't recommend it :laugh:
Quote from: cuberdon on 20:22, 31 October 24current powersupply can do up to 5 amp , but its output is under 5 volt ( i noticed at no-load ) .
so i need to verify if i can source a better one
Depending what you want to do after this, further repairs or small projects, I would buy a small bench power supply with current limiting capability. Think mine cost around £50. Of course you would also need to make up a power lead.
This video may help Noel's Retro Amstrad CPC 6128 Black Screen Repair (https://youtu.be/EyT7gYs--vo?si=ALjdedUNXqaXknMx)
as soon as all video components have arrived i will be able to do some testing .
in the mean time all info is helpful.
scart to hdmi converter has arrived , scart cable has been made , now to wait for the new powersupply and testing can begin .
So i switched on the 464 and nothing heats up , it is the GA which becomes warm-ish .
So time for the logic-probe , and maybe more .
All help highly appreciated .
Try removing all socketed chips and see if the rail goes back up to 5V.
Bryce.
a small delay , need to partly re arrange my workspace ;
my workdesk is gone ..................
report back when i can do some testing .
slowly getting there ;
(https://i.ibb.co/rcgTPmW/IMG-6906.jpg) (https://ibb.co/rcgTPmW) (https://i.ibb.co/vsnrtyN/IMG-6907.jpg) (https://ibb.co/vsnrtyN)
still need some time to finish the desk .
powersupply has arrived too .
Your desk is badly damaged, there is no any Amstrad CPC on it. :o :-\ :-X :'( ;D
wait .......................
like this ?? ;
(https://i.ibb.co/NL8kfgG/m-IMG-6954.jpg)
poor 464 in tha background just after another zeddy
we need a narrower spectrum to investigate this :P
mmm , if you look very closely you could see 5 !!
those speccy's are the last in for surgery , after that the spectrum activities wil close .
Needles to say there is a cpc waiting to be repaired ( with this forums help )
And a commodore 128 , and a rather sad amiga 500 .
Quote from: cuberdon on 17:34, 23 November 24mmm , if you look very closely you could see 5 !!
those speccy's are the last in for surgery , after that the spectrum activities wil close .
Needles to say there is a cpc waiting to be repaired ( with this forums help )
And a commodore 128 , and a rather sad amiga 500 .
Well at least you can use some of the speccy parts to fix further Amstrads! And the rubber keyboards are useful as a mat to stop the CPC from slipping off the table.
Bryce.
Bryce ,
speccy's are multi purpose !!
Nowto find time to re-connect everything , and start testing the cpc.
::)
Many doors are waiting for Sinclair ZX
as the zx81 is only made with 4 chips , one of them being an ULA ( expensive !! and hard to get ) every enthusiast has a doorstopper laying around
(https://revspace.nl/images/c/c8/PCB_Preview_ZX81%2B38_rev_1%2C9_top.png)
There is a replica without the ULA. This one is called ZX81Plus38. The Plus38 stands for 1981+38=2019, the year when the original author started the project. However it did not come to live in 2019 ...
As always the ULA is just the one chip that made the ZX81 commercially viable (cheap). However it does work completely without it.
Very interesting read on the development of the whole replica here:
https://revspace.nl/ZX81plus38_simple_to_build_ZX-81_clone
The first schematics were done in 2019 - even Rev1.3 however the first actual hardware has been done in 2020 with Rev1.4 was still problematic and required bug fixing and other changes, so that we are now at Rev1.10 at github repo.
Just if you want to build one. I do have a kit lying around here as well as a spectrum+ replica kit. I just need to find the time to solder everything in place. As now the dark nights are coming ... I will probably find some time.
Got 2 of those and both refuse to load data .
altough all options have been tested they simply crash .
the zx81+38 is an ongoing project wich is still changing a bit .
It uses the original rom .
i also have 2 zx80 clones which are housed in a 3d printed replica case and look the thing .
I've one of these (ZX80Core) lying around somewhere here, but I think I've only ever used it twice.
https://www.8bity.cz/wp-content/uploads/2014/08/ZX80Core_Martin_AcrylicCase_front.jpg
Bryce.
unfortunately inserting an image is almost impossible ,
https://i.ibb.co/bL62L9G/clock-circuit.jpg
i verified the pcb with this schematic and it does not match .
i have a pulse at pin 8 of ic 125 , but nothing at pin 8 of ic 116 ????
pcb Z70200 MC0002D
am i overlooking something here ??
Hmmm, you just need to click on the 'insert picture' icon to the right of the YouTube one, write the url you just linked, click 'Insert' and that's it:
(https://i.ibb.co/bL62L9G/clock-circuit.jpg)
In total, there were quite a few CPC versions
This schem is one of the first.
Find Your main board here... https://www.cpcwiki.eu/index.php/Mainboard_Versions
ps. first click PREVIEW... after this You can add image
Quote from: McArti0 on 21:57, 08 December 24In total, there were quite a few CPC versions
This schem is one of the first.
Find Your main board here... https://www.cpcwiki.eu/index.php/Mainboard_Versions
ps. first click PREVIEW... after this You can add image
That works if you'd like to upload an image from your computer.
To link an image from internet, you need to click on the "Insert an image" icon to the right of the YouTube one, that will open a small dialog, enter the url of the image and then click on the "Insert" button on the dialog.
https://www.cpcwiki.eu/manuals/Amendment%20Service%20Manual.zip
and look this manual
Thanks for this info ,
i go and search with the other schematics to see if that matches my pcb
Your clock circuit is in the amendet service manual linked by McArti0
clock_circuit.jpg
The improved it and made it much simpler (less parts), now with NOT gates instead of NAND gates.
So , after some testing with the new schematic ,
the clock signal is available on ;
ic 125 -4
ic 126 -8
ic 125 -6
ic 111 -6
i verified the data and address lines with a logic probe , but no activity there .
what am i missing ??
any advice highly appreciated
Quote from: cuberdon on 18:48, 22 December 24So , after some testing with the new schematic ,
the clock signal is available on ;
ic 125 -4
ic 126 -8
ic 125 -6
ic 111 -6
i verified the data and address lines with a logic probe , but no activity there .
what am i missing ??
any advice highly appreciated
Ok, the thread got slightly diverted, so lets recap... Do you have 5V on the PCB (power pins of any chip)? Is the screen completely black or is it a black square in the middle?
Bryce.
Have You 40007 with radiator?
@Bryce ,
no screen image at all ,
but maybe my converter is not correct too ( scart cable to converter )
i will try to get composite connected
@ McArti0 (https://www.cpcwiki.eu/forum/profile/?u=4820) ,
the aluminium radiator is present en get's warm too
Try IC111 Z80 signal M1 Pin27 (if working Z80)
Try IC126 40007 GA signal READY Pin2 (If working GA)
@ McArti0 (https://www.cpcwiki.eu/forum/profile/?u=4820) ,
Both pins pulse on my logic probe
Quote from: cuberdon on 08:06, 23 December 24@Bryce ,
no screen image at all ,
but maybe my converter is not correct too ( scart cable to converter )
i will try to get composite connected
Until you've confirmed that your video setup works, there's not really any point in trying to diagnose anything further.
Bryce.
Bryce ,
How to get composite working ?
pin 6 and pin 5 do not generate any image
(and the input on my monitor is working )
my monitor does not have scart
middle pin is composite.
look on oscilloscope.
middle pin and ground do not give me image on a working composite monitor
-verified with a sinclair spectrum :-)
GA pin1 nCpu 1MHz
GA pin40 cclk 2MHz
GA pin15 vsync 50Hz (or ~4Hz)
GA pin14 hsync 15,6kHz (or ~7kHz)
GA pin11 vsync+hsync
Quote from: cuberdon on 15:11, 23 December 24middle pin and ground do not give me image on a working composite monitor
-verified with a sinclair spectrum :-)
In that case, and if holding the DEL key also doesn't give you a beep, I'd suspect the Z80 as the most likely failure.
Bryce.
Bryce ,
luckily i have some z80's available .
I will try setting up my oscilloscope to get some waveforms measured
Quote from: cuberdon on 17:04, 23 December 24Bryce ,
luckily i have some z80's available .
I will try setting up my oscilloscope to get some waveforms measured
Why? Just swap it out and see if it works. It's in a socket. No need to do any further tests beforehand.
Bryce.
Unfortunately changing the z80 for a known good one , does not change the problem .
i will set up my oscilloscope to get a better view on things