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 :)
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...
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 (http://www.cpcwiki.eu/forum/index.php?action=profile;u=135): It's only pulling 500mA, I doubt anything is getting hot!
Quote from: Bryce on 10:38, 29 July 15
@Joseman (http://www.cpcwiki.eu/forum/index.php?action=profile;u=135): 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...
A 13 year old with more technical skill and knowledge than I have. I feel so inadequate...
But you are very good with graphics :D
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)
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?
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 :)
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
Maybe a RAM chip has gone bad? At least with arcade games from the 80s that seems to be a common issue.
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 ;)
This page (http://forums.arcade-museum.com/showthread.php?t=177192 (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 (https://www.youtube.com/channel/UC0zwTpEMt8IsETC7mv9Tt3g/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).
Quote from: Alexandre Rouma on 19:19, 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 ;)
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 ?
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
What is not normal, it's that it should take 2 amp from the power supply
10Wh / 5V = 2Amps
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.
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
Quote from: Alexandre Rouma on 21:24, 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
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.
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
Quote from: Alexandre Rouma on 21:40, 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.
Oh yes sorry, It was a typing error :D
I meant that I wasn't getting anything from the 8th pin of IC125
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.
Quote from: Alexandre Rouma on 21:48, 29 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 (http://www.cpcwiki.eu/index.php/Service_Manuals)
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... ;)
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
So in other words the crystal is bad?
As stated above, if the crystal was bad or the signal wasn't correct at pin 8 of IC125, he would not get the correct measurement at the 4Mhz signal path, which he has already measured as correct.
I suspect that he is either measuring it wrong or his scope isn't set up correctly. Eitherway, it's highly unlikely that the crystal is the problem. We should concentrate on where the real problem is.
My next suggestion would be to check each data / address line coming from the CPU. Are they toggling at all?
Also as mentioned earlier, a picture of the screen would be helpful.
Bryce.
Edit: Alexandre, I've been trying to find more information about your scope online, but I can't find a thing. Is it really just called PM3008? Do you have a picture of it?
so, while I take picture
My address lines are toggling
My data lines are also toggling
Ok, well that's a start and it confirms that both the 16Mhz and 4Mhz clock ar eworking fine.
Bryce.
Quote from: Alexandre Rouma on 11:02, 30 July 15
so, while I take picture
Take pictures of your scope and the PCB too while you're at it.
here are already picture of the PCB:
http://redalex18.olympe.in/img/DSCN1261.JPG (http://redalex18.olympe.in/img/DSCN1261.JPG)
http://redalex18.olympe.in/img/DSCN1262.JPG (http://redalex18.olympe.in/img/DSCN1262.JPG)
http://redalex18.olympe.in/img/DSCN1263.JPG (http://redalex18.olympe.in/img/DSCN1263.JPG)
http://redalex18.olympe.in/img/DSCN1264.JPG (http://redalex18.olympe.in/img/DSCN1264.JPG)
http://redalex18.olympe.in/img/DSCN1265.JPG (http://redalex18.olympe.in/img/DSCN1265.JPG)
http://redalex18.olympe.in/img/DSCN1266.JPG (http://redalex18.olympe.in/img/DSCN1266.JPG)
Wow, that CPC is dusty and dirty inside. ;D
Here are some picture of my oscilloscope and video cable:
http://redalex18.olympe.in/img/DSCN1267.JPG (http://redalex18.olympe.in/img/DSCN1267.JPG)
http://redalex18.olympe.in/img/DSCN1270.JPG (http://redalex18.olympe.in/img/DSCN1270.JPG)
http://redalex18.olympe.in/img/DSCN1271.JPG (http://redalex18.olympe.in/img/DSCN1271.JPG)
Alright, here's the manual for the scope, Bryce: http://bee.mif.pg.gda.pl/ciasteczkowypotwor/Philips/pm3208.pdf (http://bee.mif.pg.gda.pl/ciasteczkowypotwor/Philips/pm3208.pdf)
But seriously, you should really use some wipes, compressed air, etc. to get rid of all that dust. How are you supposed to measure anything on the board when it looks like it was stored in a sawmill?
So I made a little video so you can realy see what's happening. I'm uploading it on youtube so while it's uploading, I wanted to show you the schematic of my cable so you can tell me if it is correct:
(http://www.cpcwiki.eu/imgs/thumb/2/2b/CPC2SCART_-_RGB.jpg/600px-CPC2SCART_-_RGB.jpg)
Yes, it's a PM3208. Alexandre's been saying PM3008 up to now. Eitherway, it's more than enough to fix a CPC, a lot more than I had when I fixed my first CPCs!
Definitely dirt will be a problem. If that what the PCB looks like, then I can imagine what the terminals in the monitor port must look like. Alexandre, clean the PCB with a dry paint brush. Clean the monitor port socket with some form of contact cleaner.
Bryce.
Oops, wait! You've got that cable connected to a TV? That possibly gives a blue screen when nothing recognisable is connected?? So it's not a CPC Blue screen, it's a TV "no input signal" blue screen?
Bryce.
no, The blue screen is from the CPC you will see on the video that the no signal screen of my TV is black with No signal written on it
Also, should I clean the contacts with some alcohol
So it looks like the system is at least trying to display Mode 1 characters as it should when it boots up. Each vertical stripe appears to be four Mode 1 characters wide. The characters itself look garbled though.
We need more Bryce advice here. :)
Also, in the video the text colour looks like pen 2 (light blue-green) when it should be pen 1 (yellow).
no, It's my camera, It's blue with white lines
Ah ok. that's not a blue screen as I had imagined it, that's why a picture is always good. One of your RAM ICs is most likely dead.
Bryce.
How could I know which one ?
You might be able to check by monitoring their Dout pin. As the CPC is only pulling 500mA the chip won't be shorted, so it won't be getting hot.
Bryce.
Is it possible to replace it by making a circuit with a 24LC64 ?
?? A 24LC64 is an EEPROM, you need RAM.
Bryce.
Quote from: Bryce on 13:00, 30 July 15
One of your RAM ICs is most likely dead.
So I was correct with my initial wild guess. Yay, remote diagnosis! I demand the golden CPC award for repair excellence for that. :D
Quote from: Morn on 15:41, 30 July 15
So I was correct with my initial wild guess. Yay, remote diagnosis! I demand the golden CPC award for repair excellence for that. :D
Consider yourself awarded. Please come to the front of the class to get a star on your copy book.
Bryce.
Quote from: Bryce on 15:44, 30 July 15
Consider yourself awarded. Please come to the front of the class to get a star on your copy book.
Could you put the star on my framed Sir Alan Sugar autograph pretty please? It could go next to my "This user always buys systems that fail commercially within two years" trophy cup I got awarded for my Amiga 2000 from Microsoft and Intel back in the day. ;D
Quote from: Joseman on 10:35, 29 July 15
Also check if any chip memory is more hot than the others...
Calm down guys calm down guys..., this was the FIRST answer to the problem, and i mentioned the memory in it!!
Sorry @Morn (http://www.cpcwiki.eu/forum/index.php?action=profile;u=316), but this award will come to me this time :P
Where can i collect the 10000 euro award for this?
Quote from: Joseman on 16:25, 30 July 15
Calm down guys calm down guys..., this was the FIRST answer to the problem, and i mentioned the memory in it!!
Sorry @Morn (http://www.cpcwiki.eu/forum/index.php?action=profile;u=316), but this award will come to me this time :P
Where can i collect the 10000 euro award for this?
Too late, Sir Alan Sugar's bank on the Bahamas has already authorized the transaction from their super secretive Save the CPC fund. At least they wrote "the check is in the mail" and I believe them. The postman should arrive aaany minute now. They would never lie to me, would they? :D
Also, your post was about "chip memory", so you get disqualified for using Amiga terminology when debugging a CPC issue. I on the other hand mumbled something about "check your pins", so I get bonus points for using vague technical jargon that could mean anything. :P
So, I checked all of my ram chips and they are all outputting data
Is is a problem of the GateArray maybe?
which chip is the gate arrray and how could I test it
From what I see i dont think the gate array is the problem:
1) I get a clock signal
2) It's outputing a video singal
Quote from: Alexandre Rouma on 16:48, 30 July 15
So, I checked all of my ram chips and they are all outputting data
Gate Array is IC116.
I think it would be best to shotgun this and replace all RAM chips with new ones and hope for the best. If the Gate Array really has an issue you should probably ditch this CPC and buy a working one on eBay.
Quote from: Morn on 17:08, 30 July 15
Gate Array is IC116.
I think it would be best to shotgun this and replace all RAM chips with new ones and hope for the best. If the Gate Array really has an issue you should probably ditch this CPC and buy a working one on eBay.
I think that gate arrays can be bought nowadays...
is there a way I can test the gate array
Quote from: Joseman on 17:24, 30 July 15
I think that gate arrays can be bought nowadays...
Yes, but if it turns out the price for a working CPC GA is more less the same as for a complete CPC (and that might be the case), I'd say go for a new CPC.
And besides, his CPC is in pretty bad shape generally with its dirt issue (probably due to bad storage), so the question is how much time and money it is worth to repair it. E.g. the sound problem could be a whole separate issue that requires even more repairs.
Quote from: Alexandre Rouma on 17:32, 30 July 15
is there a way I can test the gate array
Maybe this would help: documentations:devices:gatearray [Grimware] (http://www.grimware.org/doku.php/documentations/devices/gatearray)
You could PM Grim (http://www.cpcwiki.eu/forum/profile/?u=123 (http://www.cpcwiki.eu/forum/profile/?u=123)), although he hasn't been active for a while.
Quote from: Morn on 17:39, 30 July 15
Yes, but if it turns out the price for a working CPC GA is more less the same as for a complete CPC (and that might be the case), I'd say go for a new CPC.
And besides, his CPC is in pretty bad shape generally with its dirt issue (probably due to bad storage), so the question is how much time and money it is worth to repair it. E.g. the sound problem could be a whole separate issue that requires even more repairs.
Maybe this would help: documentations:devices:gatearray [Grimware] (http://www.grimware.org/doku.php/documentations/devices/gatearray)
You could PM Grim (http://www.cpcwiki.eu/forum/profile/?u=123 (http://www.cpcwiki.eu/forum/profile/?u=123)), although he hasn't been active for a while.
yes, but is his father's CPC, it must be repaired!!
Quote from: Joseman on 17:41, 30 July 15
yes, but is his father's CPC, it must be repaired!!
If his father had properly cared for it (e.g. stored it in a sealed plastic bag) and cleaned its insides occasionally, this CPC would probably still work. Obviously he did not value it too much, so no point in getting sentimental now. ;)
Quote from: Morn on 17:53, 30 July 15
If his father had properly cared for it (e.g. stored it in a sealed plastic bag) and cleaned its insides occasionally, this CPC would probably still work. Obviously he did not value it too much, so no point in getting sentimental now. ;)
Sometimes we do mistakes, he knows how to repair his father's cpc and i encorage him to do it.
next he can upgrade it with xmem & xmass and find how his father world was on 1986!
If it's in such a bad shape, It's because my dad had much better computer like a ZX81 Commodore 64 and other that I don't remember. So it's stayed at the same place for 30 years
Quote from: Alexandre Rouma on 18:01, 30 July 15
If it's in such a bad shape, It's because my dad had much better computer like a ZX81 Commodore 64 and other that I don't remember. So it's stayed at the same place for 30 years
trust me, as a COMPUTER, nor the ZX (any) nor the C64 are better than the CPC ;)
Quote from: Alexandre Rouma on 18:01, 30 July 15
If it's in such a bad shape, It's because my dad had much better computer like a ZX81 Commodore 64 and other that I don't remember. So it's stayed at the same place for 30 years
Well, dust and electronics don't mix and can cause shorting/overheating problems. So if he didn't use the CPC anyway he should have stored it away properly.
The problem with eBay is that prices for CPCs have been going up in the past years, so you'd probably have to keep an eye on offers, get an idea about pricing, etc. And while you do that there is still plenty of time to explore repair options, e.g. by getting Grim's opinion on this.
Quote from: Joseman on 18:06, 30 July 15
trust me, as a COMPUTER, nor the ZX (any) nor the C64 are better than the CPC ;)
Yes, saying the C64 was better might be true but will still get you insta-banned on these forums. Get the torches and pitchforks! Release the hounds! :D
(http://img3.wikia.nocookie.net/__cb20131219082110/simpsons/images/7/70/TheHoundsButton.jpg)
(http://vignette1.wikia.nocookie.net/simpsons/images/c/c8/Release-the-hounds-o.gif/revision/latest/scale-to-width-down/200?cb=20131219084057)
Maybe you are right, since the gate array send the interrupts to the Z80. If the gate array was still working, I should be able at type command and to produce sound.
It's also the gate array the is in charge of the video so it would explain this strange blue screen
Do you think it's possible to buy some on ebay
XD.
Jokes aside as a COMPUTER the c64 was crap, dog poop.
1mhz bus, what a joke!!
a disc drive as slow as our tapes, what a joke.
a joke keyboard
the cpc has 640x200 (overscan aside). very high resolution.
is a FACT that the cpc is better computer than the c64
I think you are right for the C64, That maybe why the CPC is the only one that he didn't sell on ebay :D
I'm going to test other components to be sure but if the gate array is dead , I will have to buy an other.
Does somebody know where I can buy a gate array cheaper then Ebay ?
perhaps @Piotr have one?
Quote from: Alexandre Rouma on 18:17, 30 July 15
Maybe you are right, since the gate array send the interrupts to the Z80. If the gate array was still working, I should be able at type command and to produce sound.
It's also the gate array the is in charge of the video so it would explain this strange blue screen
Do you think it's possible to buy some on ebay
Actually I think the blue background is a good sign for the GA because that's the correct CPC background colour. Also, Bryce said faulty RAM and he calls himself the hardware guy for a reason...
Quote from: Joseman on 18:19, 30 July 15
XD.
Jokes aside as a COMPUTER the c64 was crap, dog poop.
1mhz bus, what a joke!!
a disc drive as slow as our tapes, what a joke.
a joke keyboard
the cpc has 640x200 (overscan aside). very high resolution.
is a FACT that the cpc is better computer than the c64
Yes, but hardware sprites, hardware scrolling, and a more versatile audio chip made the C64 hard to beat for games, especially when many CPC games were Spectrum ports with bad scrolling. The strength of the CPC lay always more in "serious" work like programming, CP/M, and so on. And occasional proper games that used its full hardware potential.
But if the GA was working properly I would be able to type command or to see text on the screen
Am I right ?
Or maybe the GA and RAM are dead
Quote from: Morn on 18:43, 30 July 15
Yes, but hardware sprites, hardware scrolling, and a more versatile audio chip made the C64 hard to beat for games, especially when many CPC games were Spectrum ports with bad scrolling. The strength of the CPC lay always more in "serious" work like programming, CP/M, and so on. And occasional proper games that used its full hardware potential.
you're talking about games, not computing.
for this better have a NES than a crappy computer-console that it is in the middle of nothing. The c64 would be a console, on the last instant they decided to make a computer.
either way, bad computer, bad console...
Quote from: Alexandre Rouma on 18:01, 30 July 15
If it's in such a bad shape, It's because my dad had much better computer like a ZX81 Commodore 64 and other that I don't remember. So it's stayed at the same place for 30 years
Thanks! You just made my day! ZX and c64 better than a CPC!
:laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh: :laugh:
Quote from: Alexandre Rouma on 18:48, 30 July 15
But if the GA was working properly I would be able to type command or to see text on the screen
Am I right ?
Or maybe the GA and RAM are dead
Well, without working RAM you would not get to the BASIC prompt I think. So because everyone says RAM and replacing RAM is one of the cheaper repair options, personally I would focus on that first.
Of course if you can get a cheap GA somewhere, it couldn't hurt to try. By the way, according to Grimware you have a 40010 GA, a later revision of the chip which was also used in 6128's.
Quote from: Joseman on 18:55, 30 July 15
you're talking about games, not computing.
for this better have a NES than a crappy computer-console that it is in the middle of nothing. The c64 would be a console, on the last instant they decided to make a computer.
either way, bad computer, bad console...
In the 1980s, most people got their home computers for games primarily. There simply weren't many serious applications for a home computer in most households, but even the most basic computer ever can play games that are fun. So I think it's undeniable that the strength of the C64 for games was a major factor that influenced potential buyers.
Quote from: Morn on 18:13, 30 July 15
Yes, saying the C64 was better might be true
Bullcrap! The CPC CPU is four times faster (4 MHz compared to 0.9 MHz), the CPC has 27 instead of only 16 worn out colors, the CPC can play music in stereo not only mono, the CPC has 640 pixel in X while the c64 only has 16, the CPC has flexible software sprites instead of predefined hardware crap sprites, the CPCs hardware scrolling is way more quick than on CPC. SID sound suxx anyway and the CPC is just fecking way more cool! 8)
Of course everybody shall be burned beyond recognition who tells that any other 8 bit system is better than the CPC. ;D
True, TFM, but if you e.g. demo Out Run both on a CPC and C64, the C64 version looks and sounds reasonably fast and fun (even if the colours are ugly), while the CPC version looks like, well, we all know what it looks and plays like.
And then there was e.g. speech output in Ghostbusters which you could actually kind of understand on the C64. Quite a few things that wowed people in the 1980s.
From a modern perspective, the C64's text mode graphics, its 6502-like CPU with its zero page, the memory mapped registers, and that ancient Pet Basic are just weird of course. Speaking from 2015, I think we can safely say the wow factor of the 1980s has gone out of the C64. :D
Stop comparing the SID with the AY, please. You can't compare an analog synthesizer on a chip with a sound generator wich produces square waves :laugh:
I still think it's the RAM. All chips might be outputing data, but is it the correct data for all addresses? Without a logic analyser that's hard to test.
Bryce.
Edit: And stop talking about shite C64s and their SIDs, this thread is to fix Alexandres 464. Take that discussion to an appropriate thead (that I can ignore :)).
The BASIC prompt can be there even with failures in 6 of 8 RAM chips. The native CPC OS needs only the first page (for the RST's) and few RAM for the JUMP alley / system RAM (around &A800-&BFFF). Broken RAM will not always repeat the effect, or only show two effects.
I bet on the GA (/ CRTC) or maybe even the Z80. But the Z80 has a socket, one could replace it more easy and see what happens.
Quote from: TFM on 22:17, 30 July 15
I bet on the GA (/ CRTC) or maybe even the Z80. But the Z80 has a socket, one could replace it more easy and see what happens.
The problem is that the OP does not have any replacement parts like an Z80 available. He would have to order it e.g. on eBay, only to possibly find out the part he ordered does not fix the problem.
Quote from: TFM on 22:17, 30 July 15
The BASIC prompt can be there even with failures in 6 of 8 RAM chips. The native CPC OS needs only the first page (for the RST's) and few RAM for the JUMP alley / system RAM (around &A800-&BFFF). Broken RAM will not always repeat the effect, or only show two effects.
I bet on the GA (/ CRTC) or maybe even the Z80. But the Z80 has a socket, one could replace it more easy and see what happens.
They are 64Kbit x1 RAMs, so every chip stores 1 bit of every address. Basic couldn't possibly load if even 1 chip was dead.
Bryce.
Quote from: McKlain on 21:48, 30 July 15
Stop comparing the SID with the AY, please. You can't compare an analog synthesizer on a chip with a sound generator wich produces square waves [emoji23]
Personally I don't like the dull sounds of the sid, I prefer the AY over the sid without doubt.
Bryce is right, let's talk about the CPC and not about a computer-toaster wannabe
Whatever :laugh:
To be fair, the SID is a much better sound chip, but it's also true that it usually sound like playing a violin with a saw. The Atari Pokey chip has a very special 'metallic' sound which I love.
When it comes to the machines, the C64 scene is super productive, and despite the specs, they create wonderful demos and games.
Now, off with the offtopic and more CPC coding! XD
I'm going to build a logic analyser with my arduino.
What is the protocol for the RAM chips ?
If it's possible I will make a tool with the arduino to automaticly test the CPC and I will post it on the forum :D
RAM chips don't have a protocol. It's a parallel TTL bus.
Personally I wouldn't go to the bother. Grab a full set of 4164s = 10 x KM4164B-10 Samsung 64K x 1Bit Dynamic RAM - DIP16 | eBay (http://www.ebay.de/itm/10-x-KM4164B-10-Samsung-64K-x-1Bit-Dynamic-RAM-DIP16-/131565523539?hash=item1ea1ea9253) and a few sockets and just swap them all.
Bryce.
but how can I read the data out, is it Serial data ?
To read it properly you'll need to do "state analysis". That means that your logic analyser is synchronised with the CPC clock. Your arduino will need to have an interrupt routine triggered by the CPU clock that reads the 8 data lines once per clock cycle. Each of the data lines will either have a 5V signal (1) or 0V signal (0) each cycle. By gathering this data at startup you can tell whether the Firmware (known data) is being sent to the CPU.
Bryce.
So:
int DATApin = 2;
int CLKpin = 3;
void setup() {
pinMode(2, INPUT);
pinMode(3, INPUT);
Serial.begin(9600);
}
void loop(){
int data[8];
int index = 0;
if (index < 8){
if (CLKpin == 1){
data[index] = digitalRead(DATApin);
index++;
}
}
else{
index = 0;
int dataOUT;
for (int i; i < 8; i++){
bitWrite(dataOUT, i, data[i]);
}
Serial.write(dataOUT);
}
}
I've never touched Arduino, so I can't confirm your code, but it looks to be going in the right direction. The Arduino will have to be running relatively fast, because it needs to do all that in the time of one Z80 cycle.
I've done a small diagram to explain a bit about how the CPC RAM works.
The CPU sets the address (on the address bus) it wants to read or write from RAM, the address bus is connected to each RAM chip. The /WR signal from the CPU decides which of the buffers is enabled (direction of data). The 8 data bits coming from CPU then each go to one of the 8 RAM chips and is then stored at the correct address. So each chip is just storing 1 bit of every address.
For reading, the exact same thing happens, just the other buffer is used. The reason for this is because the RAM ICs have a seperate Data In and Data Out pin, which you can't connect together, unlike the CPU where the same pin is used for input and output. The best place to start measuring the data is directly at the CPU (because data in both directions will be read), but later you might need to check input and output data seperately to check whether a buffer is possibly damaged. I've only shown one of the 8 Data Out lines so that the drawing isn't too cluttered.
For possible pedantic readers: Yes, I've left quite a few details out to keep it simple.
Bryce.
Ok, thanks, I'm going to try that :D
Also, do you think my arduino DUE will be fast enought (84Mhz, ARM core)
Quote from: Bryce on 15:14, 31 July 15
For possible pedantic readers: Yes, I've left quite a few details out to keep it simple.
:o
Quote from: Alexandre Rouma on 15:20, 31 July 15
Ok, thanks, I'm going to try that :D
Also, do you think my arduino DUE will be fast enought (84Mhz, ARM core)
With assembly code, maybe. With C/C++ and arduino library, it will be tough :( .
Read/Write cycles can be as short as 350ns, and can repeat every microsecond.
This is roughtly 30 instruction cycles for detection and capture, and 83-30=53 for processing that capture before being ready for next.
Or maybe though the parallel port of a computer ?
Quote from: Alexandre Rouma on 16:20, 31 July 15
Or maybe though the parallel port of a computer ?
Unlikely to be faster.
Also, the arduino due has 3.3V IO and the CPC 5V may just kill them !
I would suggest you to first clean the main board.
Then remove the socketed IC (Z80 and 40010 GateArray) and check for oxydation on the socket.
I am not convinced that the RAM is dead.
what I mean by "though the parallel port" is with my Operating system
I made my own OS so I can directly Access the IO of the CPU (Now I'm just using it to conntrol a robotic arm, but with a few modifications, I could have the full 3.4Ghz of the CPU to read the data out of the RAM chips)
I will clean it tomorow and I will check for corrosion. Do you have any tip to remove corrosion if I find some ?
Quote from: gerald on 21:33, 31 July 15
Also, the arduino due has 3.3V IO and the CPC 5V may just kill them !
Make that *will* kill them. You'd need level conversion for every signal, and there's a *lot* of them. A series resistor on each line might be sufficient (if all you're doing is input), but you'd be relying on the ESD diodes in the ARM mcu to do clamping, and that's not the best idea. Better would be something like a few 74xx245 voltage translating buffers, or replacing the Due with a board that's 5v tolerant in the first place.
(I made a shield for my minispartan fpga board with a bunch of serial IO expanders to do it, but I need bidirectional IO...)
First, Sorry for not being here for a LLLLLOOOOONNNNNGGGGG Time. I've been on vacation then got back to school :)
I have some good news, I finaly got a new Oscilloscope ! It's a rigol ds1054z with all options enabled (CRACK 8) )
I check all the rams and I'm getting a changing paralelle signal on the data pins. Would it help if I post the data ?
The Pattern on the Screen is fascinating.
5 Blocks white, 5 Blocks blue.
If translated to Screenadresses and converted to binary results in a Pattern with the Problem Occuring at the third Bit of the Address. (D3/A3)
But, wouldnt it give an result as Bitpattern as if the bit were set or not set if the RAM is defective? Bits for D3 are stored in IC117...
Well, sorry for being disconnected for soooooooooooo long :) I had a LOT of school work so I couldn't play around with my CPC :'(
Now, I have a proper scope (a DS1054Z) so I can test every thing. I'll post screen shots of the scope, frequencies and data I find :)
Sorry again :'(
I also cleaned the board and remade all solder joints that looked bad.
Here is what I measure un the z80:
(http://i.imgur.com/Ep7Ynyc.png)
And, the gate array(IC116):
(http://i.imgur.com/tpaJudq.png)
I'm sure that's a good exercise to try out your new scope, but it doesn't really tell you much about what's wrong with your CPC. Try measuring pin 14 of each RAM IC and see what you get.
Bryce.
I get changing data, i'll upload a picture when I find my thumb drive ^_^
can't find my thumb drive :/
But, I get changing data on all ram chips I also measured there temperature and they are all under 30°C
Then the RAM is probably fine. The CRTC and the 74LS153 chips would be the next thing to test.
Bryce.
Ok, i'll test that right now :)
I haven't tested the crtc yet, but the 74LS153 are working. My dad needs the televison right now, so I can test the video now that I redid all the solder joints...
Apologizing for bumps (if that is sinful in this forum) but I just wanted to say that I find all the random "unnecessary" details Alexandre Rouma here posts pretty useful as i have a point of reference to compare all these signals to. I too have the a similar issue he has, recently got a CPC464 and it's original monitor both packed inside their original boxes with plastic bags and styrofoam!
Hi and welcome ReCat,
I would suggest that you start a new thread to discuss the issues you're having with your 464. To speed things up, you should post a picture of what the screen looks like on bootup in the first post.
Bryce.
Hey, Thanks. I had a local ametur radio friend over who is very familiar with these, so I think we have diagnosed what it's problem is already. I may open another thread to document my experience still, though. Good idea.
So... I'm very sorry for being absent this much time :( I had SO much work from school. I'll try to continue the repair this week or during july and august.
Also, I was wondering if someone now what type of screms are used to hold the case together ?
The screws were in the back cover of the CPC but my father knocked it of a shelf >:( ...
Anyway, have a nice day !