Hi Guys,
I picked a CPC 664 untested for a few bucks some days ago and first time I powered it up the led was off and black screen. I firstly suspected the infamous power switch but a test with the multimeter confirmed it was ok. The PCB was covered with a thick layer of dirt and dust so I decided to give it a good cleaning before continuing the troubleshooting. I removed all socketed IC's, cleaned with water and soap and let it dry under the sun. I sprayed some contact cleaner on sockets, power connector and video connector.
Second power up made things moving as the power led came to life but still a black screen, then I power cycle again and after a few seconds the prompt screen pop up like magic and looked fine. Then after another power cycle I got a black screen again and again. I though the problem may be bad caps so I replaced all of them. On first cold power up the prompt blue screen was there again then another power cycle and black screen again ::) ::) ::) . I am trying to guess where the problem is coming from. I think that the machine is powering up correctly but something is preventing the video to be displayed once one or more components are energized (as I said on a cold power up it will turn on then if the CPC is switched off and on again it will just give a black screen). I have tried to wiggle the video connector and applied fresh solder but no change.
Any suggestion on where to look at? I have also a CPC 464 in case some IC's need to be swapped for testing.
Thanks,
Rick
PS : I have good skills in soldering and desoldering station for easy IC removal in case.
If it boot, you can check it pressing del, then it should made a piriiiiiiii from the speaker. Or run"disc, if its booting it try read the fdd. If it sound, that mean he have read the rom and boot, so you can discard the rom the z80 the ppi and the ay at least.
Also you can check first if all ics are reciving the 5v when it show black screen.
It sounds like a problem with the reset circuitry, which is unusual, that happens extremely rarely. But it may just be a dry joint somewhere in the system, check all the solder joints.
Bryce.
Quote from: Bryce on 07:48, 17 July 19
It sounds like a problem with the reset circuitry, which is unusual, that happens extremely rarely. But it may just be a dry joint somewhere in the system, check all the solder joints.
Bryce.
Any particular area where to look at and apply fresh solder?
All caps where replaced except for one Non Polarized caps of 1uF (I don't have this NP in my stock and it is one of the caps sitting top left area close to the DIN9 connector) but I really doubt this can cause the issue. I will try to make it boot again and check with the keyboard connected as suggested by Dragon then look for areas where to apply some fresh solder.
I've marked the chips here that look after the reset. Look closely at the clock circuitry (directly above the right red circle) too as an unstable clock could also be an issue. Also check that the voltage isn't too close or just 4.75V as this can also cause something like this. It may be a problem with resistance in the 5V socket or power switch.
Bryce.
Quote from: Bryce on 10:30, 17 July 19
I've marked the chips here that look after the reset. Look closely at the clock circuitry (directly above the right red circle) too as an unstable clock could also be an issue. Also check that the voltage isn't too close or just 4.75V as this can also cause something like this. It may be a problem with resistance in the 5V socket or power switch.
Bryce.
So cold start now will give just a black screen :picard: . I have measured at the power connector a steady 5.08V. Is that too much? The power switch seems not to be the problem as when I take it out and shorten the two power pins on the pcb with a screwdriver I have the same black screen of death. Need deeper investigations ::)
I checked the resistors line and the diode close to the crystal and they look fine. I am close to the resistance values for each but for a proper test I should normally desolder them and test out of circuit. The diode is ok, resistance on one side and infinite the other way around.
Could be the 74LS 132 or any chance the Z80 will not reset properly?
Try shorting pin 26 of the Z80 to GND just for a second. This will give a soft reset. If the computer boots you have a problem with the reset circuitry, if it still has a black screen, then you most likely have a RAM or ROM issue.
5.08V is perfect. Less than 4.75V or more than 5.25V is a problem.
Bryce.
Quote from: Bryce on 14:01, 17 July 19
Try shorting pin 26 of the Z80 to GND just for a second. This will give a soft reset. If the computer boots you have a problem with the reset circuitry, if it still has a black screen, then you most likely have a RAM or ROM issue.
5.08V is perfect. Less than 4.75V or more than 5.25V is a problem.
Bryce.
Thanks Brice, I'll do that and report back. 8)
I made a short with a wire between pins 26 and 29 on the Z80 but still silent. The ROM is the one socketed marked 40015 right? Can I program an Eprom 27C256 and test it? Where can I find the bin file to load? Alternatively can I use a 32k bib with both Basic and OS of the 6128? Just need to find a 32k compiled binary ready to be programmed.
PS : The Basic+Rom should be the 40022 as the 40015 is the AMSDOS rom as far as I understood.
They are in the wiki, but splitter.
http://www.cpcwiki.eu/index.php/ROM_List
Quote from: dragon on 16:50, 17 July 19
They are in the wiki, but splitter.
http://www.cpcwiki.eu/index.php/ROM_List (http://www.cpcwiki.eu/index.php/ROM_List)
Found a 32k bin for the CPC664 coming from the MESS romset thanks. ;)
Quote from: dragon on 16:50, 17 July 19
They are in the wiki, but splitter.
http://www.cpcwiki.eu/index.php/ROM_List (http://www.cpcwiki.eu/index.php/ROM_List)
Just to know for future manipulations. When merging the two 16k BIOS and BASIC into one single 32k what do you put first?
Quote from: Bryce on 14:01, 17 July 19
Try shorting pin 26 of the Z80 to GND just for a second. This will give a soft reset. If the computer boots you have a problem with the reset circuitry, if it still has a black screen, then you most likely have a RAM or ROM issue.
5.08V is perfect. Less than 4.75V or more than 5.25V is a problem.
Bryce.
I have swapped the Z80 with another one and same issue. I have programmed a 27c256 with a 32k BIOS+Basic for the CPC664 and will swap the ROM. If that does not fix then I will start with RAM. Is there any ram diagnostic I can use with an Eprom?
Quote from: repetto74 on 17:09, 17 July 19
Just to know for future manipulations. When merging the two 16k BIOS and BASIC into one single 32k what do you put first?
Lower rom+basic.
Quote from: repetto74 on 17:39, 17 July 19
I have swapped the Z80 with another one and same issue. I have programmed a 27c256 with a 32k BIOS+Basic for the CPC664 and will swap the ROM. If that does not fix then I will start with RAM. Is there any ram diagnostic I can use with an Eprom?
Ram test : http://www.cpcwiki.eu/forum/amstrad-cpc-hardware/quick-and-dirty-ram-test-for-cpc
Back with some more testing reports.
Replacing the ROM with a programmed Eprom does not fix this :-[ . Next step will be ram I suppose? Chances that the video chip is gone?
It's unlikely, but they do on rare occassions fail. The quickest way to test it is to stick a scope on pin 39 and/or pin 40. These are the outputs for VSync and HSync and they usually stop outputting anything when the CRTC fails.
Bryce.
Quote from: Bryce on 13:22, 18 July 19
It's unlikely, but they do on rare occassions fail. The quickest way to test it is to stick a scope on pin 39 and/or pin 40. These are the outputs for VSync and HSync and they usually stop outputting anything when the CRTC fails.
Bryce.
Does not have a scope unfortunately. I do have a replacement for this chip I will keep this option later. Changing ram IC's is the easiest now. Suspecting also the crystal to not working properly at this stage.
Quote from: gerald on 20:21, 17 July 19
Ram test : http://www.cpcwiki.eu/forum/amstrad-cpc-hardware/quick-and-dirty-ram-test-for-cpc (http://www.cpcwiki.eu/forum/amstrad-cpc-hardware/quick-and-dirty-ram-test-for-cpc)
How does this work exactly. There is a bin file of 485 bytes. Can I program this into an eprom and swap the original rom?
Quote from: repetto74 on 16:51, 18 July 19
How does this work exactly. There is a bin file of 485 bytes. Can I program this into an eprom and swap the original rom?
Yes, no more, no less !
Just program the .bin file at the beginning of a 32k eprom and put it in place of the system ROM.
It will test part of the RAM at boot and report result on screen. Anything red is not good.
And a black screen mean that there is something that prevent the test to be run.
Quote from: gerald on 18:16, 18 July 19
Yes, no more, no less !
Just program the .bin file at the beginning of a 32k eprom and put it in place of the system ROM.
It will test part of the RAM at boot and report result on screen. Anything red is not good.
And a black screen mean that there is something that prevent the test to be run.
Ok thanks I will try that also :-)
Unfortunately today I removed all rams, put sockets and replaced with a fresh new set of TMS4164 but still silent :-X
Actually this CPC has booted a couple of time randomly and then definitely died.
What has been done :
All caps replaced except the Non Polarized one of 1uF which I do not have
Z80 swap and soft reset
ROM swap with a 27C256
All rams removed and replaced
still no signs of life.
I will try to run the ram test tomorrow. I am just hoping that cleaning this pcb with water and soap has not killed it but the only signs of life I had was after this good cleaning.
I am start to think that if the video popped up suddenly this may be that the machine boots up normally but I cannot see it cause one or more component of the video circuitry are dead. There are a couple of transistor close to the video din socket and I may have to test those.
Other issue may just be the CRTC dead or the crystal not working. Any suggestion would be appreciated at this stage.
What is the purpose of this black box?
Its the cassette relay. The thing that molested me, as in the begging of all you don't have power led. Thats because i tell you check the voltage in all ics, even when you have led later.
You don,t have another cpc 464 or 6128 with a 40010?. You can try your gate array in another cpc to discard is socketed in all cpcs.
Quote from: dragon on 00:34, 19 July 19
Its the cassette relay. The thing that molested me, as in the begging of all you don't have power led. Thats because i tell you check the voltage in all ics, even when you have led later.
You don,t have another cpc 464 or 6128 with a 40010?. You can try your gate array in another cpc to discard is socketed in all cpcs.
I dragon,
Ok so this relay cannot prevent the machine from booting. Yes I do have a CPC 464. Good idea I can swap at least ROM, Z80 and the Gate Array 40010 to confirm they are working on the 464 :-). By the way the 664 has also an AMSDOS Rom 40015. Could it be that a bad 40015 can cause a black screen? And what about the I/O 8255? Can this also prevent from booting?
PS : the disk drive is disconnected (but I had a couple of succesfull boot before this eternal BSOD)
Well, probably it cause more a bluescreen that black screen. Because the fdd is initalise later that the screen in the rom i think remember.
The ppi control the tape part, keyboard, and the sound and is atached to the crtc vsync.
Probably your next option when the gatearray was tested. should be if the clock works and crtc works.
You have ear a cpc sometime?. The cpc make a little noise when is working a trutruturrutrutuu. That can indicate if the clock work. Totaly crazy test. Try if you ear it in the 464 when boot and compare with the 664.
But if you can check the clock with normal equipament better :D.
If the AMSDOS ROM is just not answering, then the CPC will freeze with half of the welcome screen displayed just before the Ready prompt appears. If the ROM has a data bit stuck high or low this could cause a black screen. Almost the same can be said for the 8255 - general failure would allow the CPC to boot, but you would see problems with things like sound, keyboard and cassette functions, but it's also connected to the databus, so a stuck bit could theoretically cause a black screen. However, the 8255 is an extremely robust chip and other than serious over-voltage or reverse polarity cases, I don't think I've ever seen an 8255 fail at all.
Bryce.
Quote from: Bryce on 10:06, 19 July 19
If the AMSDOS ROM is just not answering, then the CPC will freeze with half of the welcome screen displayed just before the Ready prompt appears. If the ROM has a data bit stuck high or low this could cause a black screen. Almost the same can be said for the 8255 - general failure would allow the CPC to boot, but you would see problems with things like sound, keyboard and cassette functions, but it's also connected to the databus, so a stuck bit could theoretically cause a black screen. However, the 8255 is an extremely robust chip and other than serious over-voltage or reverse polarity cases, I don't think I've ever seen an 8255 fail at all.
Bryce.
Hi Brice. Today I have tested again the Z80 and the Gate Array 40010 into a CPC 464 and they do work properly. The ROM was also replaced and did not fix so I assume that Z80, 40010 and ROM are fine. The 40015 cannot prevent from displaying something on screen so probably this is fine also.
Now as suggested by Dragon I powered on and put my ear close to the PCB in a silent environment, well there is absolute silent, no buzzing coming from the crystal or whatsoever. I measured voltage at the two crystal pins and read 0V (do not know if this is correct). I have an old scope here at my parent's place I can try to use but maybe if someone can let me know how to set it up? The probe on X or Y? Which pin on the Z80 to measure the clock signal?
Ok so putting the probe on X now gives some activity
First pix is what I have on one of the crystal pin (for ground I am using the ground wire of the floppy drive).
Pix 2 is at pin 39 of the CRTC and Pix 3 at pin 40 (no activity).
Hi, you can't measure a crystal by connecting a meter to it, you will just cause the signal to collapse and it will always look like it's not working.
Now to the scope (nice retro scope by the way): There are several points you can measure. The base clock (16MHz), the CPU clock (4MHz) and the sound clock (1MHz). They can all be measured at the 40010: 16MHz = Pin 24, 4MHz = Pin 19, 1MHz = Pin 14. The ground pin of the scope probe needs to be connected to the CPC GND (that wire with eyelet that goes to the disk drive).
Now, setting up the scope: Using channel X. Turn up H and adjust F until you have a horizontal line across the centre of the screen. Now re-adjust H until the line is as sharp as possible. Set G to the middle choice (where it is in the picture). Turn off C1 to 5 and D1 to 5 (ie: all buttons out). Turn A all the way to the left. Turn B to the smallest µs possible. You may have to re-centre the trace with I after doing this. Set E to 2V and you should be ready to go.Stick the probe on any of the pins mentioned above. The ITT 710 is only a 15Mhz scope, so don't expect a crisp squarewave to appear. 1MHz will be a rounded off square wave, but 4MHz will look something like a sinewave drawn after drinking 15 beers and 16MHz will just be a blurred area across the middle of the screen.
Bryce.
Hi Brice,
Thanks a lot for your tutorial and your precious time! :D I think I have set this as you asked (just confirm to me that for C1 and D1 you are asking each of the most right button to be pressed?). This is the best I can have in return from the measures.
pix 1 : 16mhz
pix 2 : 4mhz
pix 3 : 1mhz
1 mhz measure is silent while for the two other I can barely see a wave but there is one. Maybe some more tweakings to do?
No, all of those 10 buttons should be un-pressed. Or whatever you had chosen for your tests above, which should be fine too.
Bryce.
Ok Brice sorry and G was not set to the middle position. ::)
Now we have something better 16 - 4 and 1 respectively
Is E set to 2V? If so, the clock really doeas have a problem, it looks like they are peaking at 1V?? A proper clock signal at those points should be showing a wave that covers at least 2 boxes in height.
Bryce.
Hi Brice
Yes E knob is set to the 2V scale. Consider also the 40015 as tested and working on another CPC. So you think the crystal is dead or something after it? There is a TTL marked TC74HCU04P which gets the clock generation from the crystal I think.
Yes, I suspect the 74HCU04 might be the issue. Try replacing it. It needs to be the HCU version, a 74LS04 will not work.
Bryce.
Great work guys, i upload a capture of the probably part broken in the schematic.
Better pix of waves by tweaking the knob right side of A
PS : half an hour I am trying to upload three pix but keeping saying that there is already an attachment with same name :'(
Hi Bryce
here are link to pictures as I cannot post pictures anymore
https://ibb.co/qdxKWTx (https://ibb.co/qdxKWTx)
https://ibb.co/9yfdHXP (https://ibb.co/9yfdHXP)
https://ibb.co/swpKcZk (https://ibb.co/swpKcZk)
16, 4 and 1 mhz waves
To me sound defective, the 16mhz wave is distorted. But bryce tell better.
Quote from: dragon on 15:49, 19 July 19
To me sound defective, the 16mhz wave is distorted. But bryce tell better.
Ok let's wait for Bryce's conclusions on this :D
Today I replaced the 74HCU04 with a 74HCU04N and.....back to square one unfortunately :picard: . Still a black screen.
Do not know where to look at except the crystal and the CRTC (I forgot to measure with the scope the signal on pin 39 and 40, have to go back to where the scope is).
In case the CRTC is bad does it prevent the machine from booting or can I hear the speaker beep when pressing the DEL key?
Repeat the test with the osciloscope first with the new 74hc.
And try power on the cpc change it to other positions, vertical, it maybe can help if its a bad solder.
Maybe some track can be cut. Or loss the solder connection.
You don't know the status of the speaker. So if you test del, make a doble chek with headphones and the speaker.
Quote from: dragon on 14:45, 20 July 19
Repeat the test with the osciloscope first with the new 74hc.
Yes I'll do that later and report then.
Quote from: repetto74 on 14:33, 20 July 19
In case the CRTC is bad does it prevent the machine from booting or can I hear the speaker beep when pressing the DEL key?
Dead CRTC = no sound !
The CRTC is configured for proper display, then the GA uses the signal generated from the CRTC to generate the video signal and 300Hz interrupt.
That interrupt is used for keyboard scan and sound queue processing.
So if you do not have any HSYNC/VSYNC, there is no chance of having any sound, at least from original FW.
BTW, can you check the vsync (pin 40) / hsync (pin39) on CRTC :
hsync should look like a serie of pluse at 15.625KHz (64us period)
vsync should look like a serie of pulse at 50Hz (20ms period)
as well as IRQ on the Z80 (pin 16). Here you should have low pulse at 300Hz.
If the pin stays low, this mean the Z80 is not accepting IRQ and something is wrong (ROM/RAM ....)
If the pin stays high, this mean no hsync is being seen by the gate array.
The strange shape of the clock isn't that important. The fact that it is less than 2V Peak to peak is a problem, maybe the crystal really is dead?
@Gerald: He tested the Syncs here and they seem to be giving relatively normal looking signals (considering the scope he has available): http://www.cpcwiki.eu/forum/hardware-related/cpc-664-repair-***work-in-progress***/msg176337/#msg176337
Bryce.
Anyway if clock continue bad chek all around the 74hc resistance etc etc.
Quote from: dragon on 14:45, 20 July 19
Repeat the test with the osciloscope first with the new 74hc.
And try power on the cpc change it to other positions, vertical, it maybe can help if its a bad solder.
Maybe some track can be cut. Or loss the solder connection.
You don't know the status of the speaker. So if you test del, make a doble chek with headphones and the speaker.
I think speakers are ok , when they are connected and I power cycle the machine I can hear a clicking sound coming out from it.
I tested again with speakers and keyboard connected but no beep from the speakers with the Del depressed. A clicking is heard when powering off.
Quote from: Bryce on 14:59, 20 July 19
The strange shape of the clock isn't that important. The fact that it is less than 2V Peak to peak is a problem, maybe the crystal really is dead?
@Gerald: He tested the Syncs here and they seem to be giving relatively normal looking signals (considering the scope he has available): http://www.cpcwiki.eu/forum/hardware-related/cpc-664-repair- (http://www.cpcwiki.eu/forum/hardware-related/cpc-664-repair-)***work-in-progress***/msg176337/#msg176337
Bryce.
Hi Bryce,
Going back to the place where the scope is and will take again the measures of 16/4 and 1mhz signals with the new 74HUC04 to check if any difference. In case I have a 16mhz crystal brand new with me.
Quote from: gerald on 14:59, 20 July 19
Dead CRTC = no sound !
The CRTC is configured for proper display, then the GA uses the signal generated from the CRTC to generate the video signal and 300Hz interrupt.
That interrupt is used for keyboard scan and sound queue processing.
So if you do not have any HSYNC/VSYNC, there is no chance of having any sound, at least from original FW.
BTW, can you check the vsync (pin 40) / hsync (pin39) on CRTC :
hsync should look like a serie of pluse at 15.625KHz (64us period)
vsync should look like a serie of pulse at 50Hz (20ms period)
as well as IRQ on the Z80 (pin 16). Here you should have low pulse at 300Hz.
If the pin stays low, this mean the Z80 is not accepting IRQ and something is wrong (ROM/RAM ....)
If the pin stays high, this mean no hsync is being seen by the gate array.
Hi Gerald,
Will check again pin 39 and 40 of the CRTC and the Z80 IRQ with the scope and report back.
One question, if he use the 464 has clock?.
I mean take of the gate array in 464, put a wire in the clock socket pin.
Then in 664 take of the 74hc, and connect the wire to the pin socket in the 74hc that go to the gate array.
Then he can test 100% if with all changed it boot.
Is tecnically possible?.
Quote from: Bryce on 14:59, 20 July 19
The strange shape of the clock isn't that important. The fact that it is less than 2V Peak to peak is a problem, maybe the crystal really is dead?
@Gerald: He tested the Syncs here and they seem to be giving relatively normal looking signals (considering the scope he has available): http://www.cpcwiki.eu/forum/hardware-related/cpc-664-repair- (http://www.cpcwiki.eu/forum/hardware-related/cpc-664-repair-)***work-in-progress***/msg176337/#msg176337
Bryce.
Bryce the hsync and vsynch were measured with the scope not set up properly so better if I redo this.
Quote from: dragon on 15:37, 20 July 19
One question, if he use the 464 has clock?.
I mean take of the gate array in 464, put a wire in the clock socket pin.
Then in 664 take of the 74hc, and connect the wire to the pin socket in the 74hc that go to the gate array.
Then he can test 100% if with all changed it boot.
Is tecnically possible?.
Technically yes, but you would have to also connect the ground of both computers together and keep the wires as short as possible, you may have to even use shielded wires.
Bryce.
Here are the result with measures taken again with the replaced 74HCU04. I had to tweak a lot to try to lock the waving signals it is very sensitive.
Please note that I have used the 2V scale but for the IRQ Z80 pin 16 and the Vsinc on the CRTC I had to go down to 50mV scale to properly display a wave.
The first measures on cold start where exactly the same as the one posted before in this topic but strangely after letting the CPC run for a while I started having the signals here below. ::)
PS : I forgot to align the two beams on the scope to the centre but I think that does not alter the results.
Three first pix are for the 16/4 and 1 mhz signals
pix 4 and 5 for the Hsync and Vsync(50 mV scale)
Pix 6 the IRQ signal (50 mV scale also)
A clock is a clock it not should change over time c130, c131, c132?
Quote from: dragon on 17:43, 20 July 19
A clock is a clock it not should change over time c130, c131, c132?
Of course I still have a black screen. I am just keeping it turned on for a while to see if any changes. How to test the three ceramics? Can they fail? Is the Vsync signal on the CRTC correct and not weak then?
I have this 16mhz crystal in case...
Clock look fine for me, but are you sure you are on the 2V scale for the 3 first picture. I would consider the gate array to be OK.
The 16MHz is lower than the other, but that's expected. The OX710 only have a 15MHz bandwidth, that mean a 15MHz sine would be attenuated by 3dB ie divided by 2.
Other picture taken on 50mV range just mean you are capturing noise, not signals.
BTW, if you are only using one channel, disable the second one (ie only YA key pressed)
So if the Z80 and ROM are proven good, the CRTC is probably dead.
But the clock is diferent when it power up gerald thats normal in a clock?.(crtc apart)..
Quote from: repetto74 on 17:53, 20 July 19
Of course I still have a black screen. I
If you force a reset signal when the clock is estable?.
Quote from: gerald on 17:55, 20 July 19
Clock look fine for me, but are you sure you are on the 2V scale for the 3 first picture. I would consider the gate array to be OK.
The 16MHz is lower than the other, but that's expected. The OX710 only have a 15MHz bandwidth, that mean a 15MHz sine would be attenuated by 3dB ie divided by 2.
Other picture taken on 50mV range just mean you are capturing noise, not signals.
BTW, if you are only using one channel, disable the second one (ie only YA key pressed)
So if the Z80 and ROM are proven good, the CRTC is probably dead.
Yes I was on the 2V scale as suggested by Bryce for the scope set up. The 40010 has been tested good on the CPC464. The Z80 has been also tested good on the 464 and the ROM was replaced with a programmed 27C256 but that did not fix so I assume the ROM is ok also. All 8 ram chips are replaced with fresh new TMS4164 also.
The Vsync signal on the CRTC is completely flat on the 2V scale.
Quote from: dragon on 17:59, 20 July 19
But the clock is diferent when it power up gerald thats normal in a clock?.(crtc apart)..
If you force a reset signal when the clock is estable?.
you mean a soft reset by shorting pins 26 and 29 of the Z80? tried already but no luck.
Quote from: dragon on 17:59, 20 July 19
But the clock is diferent when it power up gerald thats normal in a clock?.(crtc apart)..
If you force a reset signal when the clock is estable?.
Well, the clock should start "instantly".
If the issue is only a clock startup issue, yes, a reset could do something.
But better hardware reset: http://www.cpcwiki.eu/index.php/Reset_Button
Quote from: dragon on 18:14, 20 July 19
But better hardware reset: http://www.cpcwiki.eu/index.php/Reset_Button (http://www.cpcwiki.eu/index.php/Reset_Button)
The CPC664 pcb is different but it may not be a good idea to add a circuit and more uncertainty. If the clock signal appear to be ok and the gate array is fine then the CRTC may be the problem. It may have worked a couple of time when I had a correct boot then failed permanently. Or could be also one of the TTL logic on the pcb.
I refer more to made the same that with soft reset made a shortcut in the expansion connector.
But if you prefer try the crtc perfect.
Quote from: dragon on 18:36, 20 July 19
I refer more to made the same that with soft reset made a shortcut in the expansion connector.
But if you prefer try the crtc perfect.
I can try shorting Pin 40 of the expansion port to gnd. Is is the long connector at the back?
Quote from: dragon on 18:14, 20 July 19
But better hardware reset: http://www.cpcwiki.eu/index.php/Reset_Button (http://www.cpcwiki.eu/index.php/Reset_Button)
No reset after shorting pin40 of expansion port to GND.
:(. Then try the crtc, the good news is if he broken in another time you have all in socket. :picard2:
Guys I have desoldered both 6845 from the two CPC, socketed and swapped. Believe it or not but the CPC464 will boot up normally so the CRTC is fine also :doh: . I do not know anymore where to look at.
There is the I/O chip 8255 but apparently this is not prompt to fail (does he stop the booting if it fails?).
It can be anything at this stage. I have no clue where to look at. Too bad this thing came to life for a brief period of time :'(
Can I test the CPC664 Rom with the CPC464? Rom version is 40022 where the CPC464 is 40009.
****EDIT**** I swapped the 40022 ROM in the CPC464 and normal boot. With this test I can declare at least that all main IC's are fine (missing sound chip and 8255).
Could be also the sound chip? Does it give a black screen when faulty?
If I let this machine run for a while the only two IC's getting warm are the Z80 and the CRTC, the Gate Array and Rams are cold.
As already suggested by Dragon the CPC emits a buzz from the crystal when powered on right? In my case there is a complete silence. Is it possible that the crystal is not oscillating correctly?
You can try what i suggested early, use the cpc 464 as clock, at least to not unsolder the crystal the three caps and the resistance for nothing. And discard it 100%
The next step for me was take the polimeter, take the service manual, and check continuity between ics resistance valors etc etc. But as bryce tell the 8255 can be a remote posibility.
Or take logic analyzer and take a look at the bus to view what is happen here between the ics.
Hi Dragon and Bryce
SUCCESS!!!!! :P :P :P :P :P :P :P :P :P :P :P
In a last desperate attempt I tried to put some fresh solder around the crystal circuit area on all transistors, caps and resistors. Believe it or not it is alive again!!! ;D ;D ;D
Another CPC664 saved from the trash!
Thanks a lot to all of you for your help and guidance. Job is done! ;D ;D
"IT'S A SMALL STEP FOR MAN BUT A GIANT LEAP FOR CPC!" 8) 8)
One question You have a buzz now?.
Quote from: dragon on 14:20, 21 July 19
One question You have a buzz now?.
No buzz. I am 45 I think my ears are ok but maybe the frequency range is out of my reach ;D
Jeje,well thats oscyloscope deformed signal nerver sound well to me. Maybe you can check the 16mhz now to view how it should be really for future reparations.
I have tested the keyboard, no sound from the speaker with the DEL key and some keys are not working such has "ENTER", "F7","F4" and a few others. The keyboard needs a good cleaning I hope to fix this. :)
Membrane. And in the 3,5mm socket? You have sound?
Quote from: dragon on 14:44, 21 July 19
Membrane. And in the 3,5mm socket? You have sound?
Not tested yet. I will fix the membrane before and then reassemble everything.
664 membrane are crapp, if you can't fix it. You can buy one new here:
https://www.ebay.es/itm/BRAND-NEW-Amstrad-CPC664-Keyboard-Membranes/133037095862?hash=item1ef9a0fbb6:g:c5cAAOxyg7xSZACq (https://www.ebay.es/itm/BRAND-NEW-Amstrad-CPC664-Keyboard-Membranes/133037095862?hash=item1ef9a0fbb6:g:c5cAAOxyg7xSZACq)
My 664 don't have sound when arrive, the speaker was dead.
Quote from: dragon on 14:52, 21 July 19
664 membrane are crapp, if you can't fix it. You can buy one new here:
https://www.ebay.es/itm/BRAND-NEW-Amstrad-CPC664-Keyboard-Membranes/133037095862?hash=item1ef9a0fbb6:g:c5cAAOxyg7xSZACq (https://www.ebay.es/itm/BRAND-NEW-Amstrad-CPC664-Keyboard-Membranes/133037095862?hash=item1ef9a0fbb6:g:c5cAAOxyg7xSZACq)
My 664 don't have sound when arrive, the speaker was dead.
Thanks Dragon :-). I am in the middle of the whole keyboard cleaning. The membrane was full of crap dust and hope a good cleaning will fix it.
By the way can I replace the 664 ROM with the one of the 6128?
You can try, i don't think it explode, or you can put parados.
Aren't they the same?
As far as I know both had the 1.1 rom.
Despite the fact that the Locomotive BASIC keeps displaying 1.1 on startup, several revisions exist if we refer to the ROM header:
CPC664 (v1.10) (https://web.archive.org/web/20160623222202/http://www.grimware.org/lib/exe/fetch.php/documentations/hardware/amstrad.cpc/roms/basic.v1.1.cpc.664.zip)
- CPC6128 (v1.20) (https://web.archive.org/web/20160623222202/http://www.grimware.org/lib/exe/fetch.php/documentations/hardware/amstrad.cpc/roms/basic.v1.2.0.cpc.6128.zip)
- CPC6128 (v1.21) (https://web.archive.org/web/20160623222202/http://www.grimware.org/lib/exe/fetch.php/documentations/hardware/amstrad.cpc/roms/basic.v1.2.1.cpc.6128.zip)
- CPC6128 (v1.23) (https://web.archive.org/web/20160623222202/http://www.grimware.org/lib/exe/fetch.php/documentations/hardware/amstrad.cpc/roms/basic.v1.2.3.cpc.6128.zip)
- Amstrad Plus (v1.40) (https://web.archive.org/web/20160623222202/http://www.grimware.org/lib/exe/fetch.php/documentations/hardware/amstrad.plus/roms/basic.v1.4.plus.zip)
- AFAIK the differences, if any, between the v1.10 and later versions are undocumented. You can check the version installed on your own CPC with [color=rgb(53, 173, 27) !important]a small BASIC listing (https://web.archive.org/web/20160623222202/http://www.grimware.org/doku.php/documentations/software/locomotive.basic/romversion)[/color]. (And if you discover a version not listed here, eg. v1.22, spread the infos and the ROM dump! Thanx!)" https://web.archive.org/web/20160623222202/http://www.grimware.org/doku.php/documentations/software/locomotive.basic/start
Quote from: repetto74 on 14:12, 21 July 19
In a last desperate attempt I tried to put some fresh solder around the crystal circuit area on all transistors, caps and resistors. Believe it or not it is alive again!!! ;D ;D ;D
"Rework all the solder joints in case there are invisible dry joints" seems to be better and better advice every time I see something like this. I'm seriously tempted to give my 6128 a quick once-over :D
Quote from: dragon on 18:56, 21 July 19
Despite the fact that the Locomotive BASIC keeps displaying 1.1 on startup, several revisions exist if we refer to the ROM header:
CPC664 (v1.10) (https://web.archive.org/web/20160623222202/http://www.grimware.org/lib/exe/fetch.php/documentations/hardware/amstrad.cpc/roms/basic.v1.1.cpc.664.zip)
- CPC6128 (v1.20) (https://web.archive.org/web/20160623222202/http://www.grimware.org/lib/exe/fetch.php/documentations/hardware/amstrad.cpc/roms/basic.v1.2.0.cpc.6128.zip)
- CPC6128 (v1.21) (https://web.archive.org/web/20160623222202/http://www.grimware.org/lib/exe/fetch.php/documentations/hardware/amstrad.cpc/roms/basic.v1.2.1.cpc.6128.zip)
- CPC6128 (v1.23) (https://web.archive.org/web/20160623222202/http://www.grimware.org/lib/exe/fetch.php/documentations/hardware/amstrad.cpc/roms/basic.v1.2.3.cpc.6128.zip)
- Amstrad Plus (v1.40) (https://web.archive.org/web/20160623222202/http://www.grimware.org/lib/exe/fetch.php/documentations/hardware/amstrad.plus/roms/basic.v1.4.plus.zip)
- AFAIK the differences, if any, between the v1.10 and later versions are undocumented. You can check the version installed on your own CPC with [color=rgb(53, 173, 27) !important]a small BASIC listing (https://web.archive.org/web/20160623222202/http://www.grimware.org/doku.php/documentations/software/locomotive.basic/romversion)[/color]. (And if you discover a version not listed here, eg. v1.22, spread the infos and the ROM dump! Thanx!)" https://web.archive.org/web/20160623222202/http://www.grimware.org/doku.php/documentations/software/locomotive.basic/start (https://web.archive.org/web/20160623222202/http://www.grimware.org/doku.php/documentations/software/locomotive.basic/start)
Tanks Dragon I'll try and let you know and yes the version on the 664 is 1.1
Quote from: repetto74 on 22:44, 21 July 19
Tanks Dragon I'll try and let you know and yes the version on the 664 is 1.1
Here is the result :-)
V 1.10
https://ibb.co/2h87BTc
https://ibb.co/QfTWK4P
This CPC664 needs either a conductive coating on the membrane contacts or a new membrane to fix the non working keys.
Yep, thats the problem my 664 membrane was killed to. If the 664 is rare a 664 with original membrane working is ultrarare.
I may try to put some graphite on contacts before and see if that solves.