Author Topic: CPC 464 blue sceen problem  (Read 8000 times)

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Offline Alexandre Rouma

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CPC 464 blue sceen problem
« on: 12:24, 29 July 15 »
Hi, I'm new on this forum and I have a problem. I'm 13 years old and my dad gave me his old Scheider (Amstrad) CPC 464. Since I'm good in electronics,
I made a new video cable for it. I powered it up at 5V DC with my regulated power supply. When I flipped the ON switch, The image was blue and It was drawing 500ma from my PSU. Sometimes, Some vertical and horisontal lines apear. But when I reset the computer the white lines disapear.

I verified all solder connections, And verified all ICs where inserted correctly.

At first, I thought the problem came from the video chip, so I put a tape in the tape reader and I typed:

run"

then I pressed play and I pressed ENTER

but nothing happend

I hope somebody can help me  :)
« Last Edit: 12:28, 29 July 15 by Alexandre Rouma »
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Offline Joseman

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Re: CPC 464 blue sceen problem
« Reply #1 on: 12:35, 29 July 15 »
Hi alexandre

First, there is run" then ENTER and THEN another key!!

I highly doubt that if the cpc is not booting correctly the tape mechanism will react... the firmware tells it to start, and the firmware is not loading on this cpc almost sure

Check all the socketed chips, remove the chips and clean all the sockets with isopropyl alcohol and a toothbrush, then relocate the chips firmly.

Also check if any chip memory is more hot than the others...
« Last Edit: 12:39, 29 July 15 by Joseman »

Offline Bryce

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Re: CPC 464 blue sceen problem
« Reply #2 on: 12:38, 29 July 15 »
Hi Alexandre,
          Welcome to the Forum, I think you are officially our youngest member! First I would try removing and re-inserting the chips that are in sockets. Next I would check the power switch contacts. You can do this by shorting the contacts on the back of the switch to see if the computer then runs properly. If it does then you will need to repair the switch by opening it and cleaning the contact surfaces (be careful, there are a few very small parts inside).
If neither of those help, then there is a chance that some IC is broken. You say you are good at electronics (you even own a regulated PSU!), what test equipment do you own and how many amps can your PSU actually supply?

Bryce.

@Joseman: It's only pulling 500mA, I doubt anything is getting hot!

Offline Joseman

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Re: CPC 464 blue sceen problem
« Reply #3 on: 12:44, 29 July 15 »
@Joseman: It's only pulling 500mA, I doubt anything is getting hot!

You're right as always Bryce  :)

Maybe an oscilloscope or a frequencymeter will be handy to know if the clocked chips are working...

Offline Carnivius

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Re: CPC 464 blue sceen problem
« Reply #4 on: 14:29, 29 July 15 »
A 13 year old with more technical skill and knowledge than I have.  I feel so inadequate...
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Offline ||C|-|E||

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Re: CPC 464 blue sceen problem
« Reply #5 on: 17:03, 29 July 15 »
But you are very good with graphics  :D

Offline Alexandre Rouma

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Re: CPC 464 blue sceen problem
« Reply #6 on: 19:14, 29 July 15 »
Thank for all you replies  :D
So, I tried removing all ICs and I even clean the pin but it doesn't change anything.
I'm going to try to clean the switch

Is it possible that it would be the main ROM (That contains the firmware of the Z80) that has been erased. You know, a simple JMP command erased so
it's not jumping to the main program
It has not been turned on for 30 years!

Here is my test equipment:
3A 30V DC regulated power supply
Analog oscilloscope (Maybe my parents will buy me a Rigol DS1054Z, but not sure)
Frequency generator (0.1 - 200Khz)
Multimeter (0 - 1000V AC/DC)
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Offline TFM

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Re: CPC 464 blue sceen problem
« Reply #7 on: 19:20, 29 July 15 »
Can you enter the command:


sound 1,100


then press return


Do you hear it making a sound?


O do the following: Press Space a couple of times, then press the cursor up key. Do you hear a sound?

TFM of FutureSoft
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Offline Alexandre Rouma

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Re: CPC 464 blue sceen problem
« Reply #8 on: 19:38, 29 July 15 »
No, it doesn't make any sound (I tried the command methode, the space and key and I also tried to keep pushing on a key for 10 second)
I opened it and touch the rams and other ICs, they are all the same temperature. The Z80 heats up a little (40 °C in the center) and other ICs like the rom
and other things.

I will make picture of the screen tomorow  :)
« Last Edit: 19:42, 29 July 15 by Alexandre Rouma »
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Offline Alexandre Rouma

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Re: CPC 464 blue sceen problem
« Reply #9 on: 20:59, 29 July 15 »
A little update:

I'm getting a 2V signal from the crystal oscillator (Can't tell you the frequency because my old analog scope cant keep up)
The Z80 is outputting data on the address and data port. The z80 seem to be working properly
I will try to connect the ROM chip to a programmer to read its content

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Offline Morn

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Re: CPC 464 blue sceen problem
« Reply #10 on: 21:12, 29 July 15 »
Maybe a RAM chip has gone bad? At least with arcade games from the 80s that seems to be a common issue.
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Offline Alexandre Rouma

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Re: CPC 464 blue sceen problem
« Reply #11 on: 21:19, 29 July 15 »
How could I know if a ram chip went bad ? Can I test them with my arduino (I'm good at programming an arduino) ?
The rams are not getting hot and I cant see anything rong

Thanks the the help  ;)
« Last Edit: 21:21, 29 July 15 by Alexandre Rouma »
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Offline Morn

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Re: CPC 464 blue sceen problem
« Reply #12 on: 21:33, 29 July 15 »
This page (http://forums.arcade-museum.com/showthread.php?t=177192) about repairing arcade boards tells us to check the chip enable, WR and OE lines. Maybe if you google the CPC's RAM chips you can find out which pins to check.

I only have a little experience repairing CPCs (my 6128 only ever had minor issues), but I watch a lot of retro arcade repair videos on YouTube. So I'm approaching this like a non-functional Pac-Man, the hardware of which is a bit similar to a CPC (RAM/ROM/Z80/a sound chip).
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Offline gerald

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Re: CPC 464 blue sceen problem
« Reply #13 on: 21:42, 29 July 15 »
How could I know if a ram chip went bad ? Can I test them with my arduino (I'm good at programming an arduino) ?
The rams are not getting hot and I cant see anything rong

Thanks the the help  ;)
The common symptom for failing RAM is a grey screen with black border.
Also did you check that the 5V on board is really 5V ?

Offline Alexandre Rouma

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Re: CPC 464 blue sceen problem
« Reply #14 on: 22:00, 29 July 15 »
So it mean that my rams are good because a get a totaly blue screen.

Yes, I check the voltage, It's correct everywhere !
But does anybody know what's happening with the white line that apear randomly on the screen ?

also, I noticed that I got a 1mhz square wave out of the 44th pin of the printer port
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Offline Alexandre Rouma

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Re: CPC 464 blue sceen problem
« Reply #15 on: 22:02, 29 July 15 »
What is not normal, it's that it should take 2 amp from the power supply

10Wh / 5V = 2Amps
« Last Edit: 22:06, 29 July 15 by Alexandre Rouma »
The fitnessgram pacer test is a multi-stage arobic capacity test

Offline Bryce

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Re: CPC 464 blue sceen problem
« Reply #16 on: 22:46, 29 July 15 »
What scope do you have? Surely it manages at least 20Mhz?? Even with an analogue scope you should be able to read a relatively clean 16Mhz clock signal on pin 8 of IC125 (7400). This is the main clock. On pin 6 of the Z80 you should be able to read the 4Mhz clock signal produced by the Gate Array.

It's extremely rare for a ROM IC to go bad on a CPC, so I doubt that's the problem. You won't be able to remove it anyway, because they aren't socketed.

Maybe if you can take a picture of the screen (with white line) it may tell us more. Although I suspect that the CPU is most likely bad. Do you have a spare CPU to test this? If not, where are you located?

Bryce.



Offline Alexandre Rouma

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Re: CPC 464 blue sceen problem
« Reply #17 on: 23:24, 29 July 15 »
Oups, think you found the problem: I get nothing on pin 8 of the IC175 but, I get a 4Mhz signal on the 6th pin

My scope is a PM3008
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Offline Bryce

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Re: CPC 464 blue sceen problem
« Reply #18 on: 23:30, 29 July 15 »
Oups, think you found the problem: I get nothing on pin 8 of the IC175 but, I get a 4Mhz signal on the 6th pin

My scope is a PM3008

IC175?? What chip is it?

I don't know the PM3008. The name would suggest it's a Phillips / Fluke mid-range scope, CRT, possibly 2 channel 80Mhz?

Bryce.

Offline Alexandre Rouma

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Re: CPC 464 blue sceen problem
« Reply #19 on: 23:40, 29 July 15 »
My scope is a Phillips 2 Channel 20Mhz with a CRT screen (green)

When I check pin 6 of the Z80, I get a 4Mhz signal


IC175 is a 7400
You told me I should normally get a 16Mhz signal on pin 8 of this chip but I have 0V

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Offline Morn

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Re: CPC 464 blue sceen problem
« Reply #20 on: 23:45, 29 July 15 »
IC175 is a 7400
You told me I should normally get a 16Mhz signal on pin 8 of this chip but I have 0V
He wrote IC125.
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Offline Alexandre Rouma

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Re: CPC 464 blue sceen problem
« Reply #21 on: 23:48, 29 July 15 »
Oh yes sorry, It was a typing error  :D

I meant that I wasn't getting anything from the 8th pin of IC125
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Offline Bryce

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Re: CPC 464 blue sceen problem
« Reply #22 on: 00:46, 30 July 15 »
You must be measuring it wrong. If there was nothing there, the 4Mhz wouldn't be there either.

Your scope may not be cutting edge, but it's a good scope and more than enough to diagnose and repair a CPC.

Bryce.

Offline Morn

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Re: CPC 464 blue sceen problem
« Reply #23 on: 02:42, 30 July 15 »
Oh yes sorry, It was a typing error  :D
By the way, have you seen the CPC service manuals on the Wiki? Service Manuals - CPCWiki

I've noticed sometimes people go to this forum directly from Google and completely miss the CPC-Wiki, so I'll play Captain Obvious here just in case…  ;)
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Offline Alexandre Rouma

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Re: CPC 464 blue sceen problem
« Reply #24 on: 10:38, 30 July 15 »
Yes, I've read it.

But  I noticed something strange: The signal from the 8th pin of the IC125 changes randomly from 0.7V to 4.7V. It's changing about 2 times per minute
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