Hi all.
First poster here.
I have this CPC 464 I got in a mixed lot. I cleaned it up and it did work for some time. But now it just gives blue screen, but still manage to make sound and some image related things with Dandanator Mini.
I made a youtube video where I try some different things. But besides that I don't know where to go from here.
I checked some random stuff with my multimeter, but I don't really know what to check. It seems all print lanes between rams are ok and I did not find any other faulty print lanes, but again I mostly just checked on random.
Hi, sounds like the CPC is working and looks like the monitor is ok. Have you checked the monitor socket on the back of CPC for dry joints. Try reflowing the connections.
Well, that is one thing I have not tried for some reason.
I will let you know if that works.
Connection to monitor seems to be good. Check the expansion port connector. Maybe needs cleaning?
I cleaned up the monitor socket, checked the soldering joints too.
I also took out all socketed chips and cleaned the legs and connections.
20230202_235004.jpg
This is how it looks when I boot without the Dandanator.
20230202_234939.jpg
This is the screen it gives when I boot with the Dandanator.
The picture is actually better and connection seems less glitchy, but there is still no actual text on start up or anything.
It did work at one point (before I had the Dandanator) and I have managed to play several different games on cassette.
Does it beep when you press Delete?
I would think that one of the multiplexers is causing problems and the CRTC/GA cannot access the memory.
If the CPC responds to keystrokes, blindly type poke &4000,255 and see what happens.
It does beep when I press Delete and when pressing the arrows. It also has sound when I am using the Dandanator and responding to keystrokes when I use the Dandanator.
I tried that poke just now, but I could not get it to do anything as a result.
Could be a ROM problem. Somewhere in this forum there is a test ROM, maybe this can be put into Dandanator. Does somebody know?
Quote from: CPC78 on 00:34, 03 February 23It does beep when I press Delete and when pressing the arrows. It also has sound when I am using the Dandanator and responding to keystrokes when I use the Dandanator.
I tried that poke just now, but I could not get it to do anything as a result.
Confusing. I guess because the CPC is beeping when you press delete that this implies that the AY and PIO are scanning the keyboard, which implies the Z80 is running the lower ROM and I guess implies that RAM is good (maybe). This then points to a display issue but the display with the Dandanator contradicts this and looks like it is hanging.
My go to diagnostics tool is the Diagnostics ROM and I use a ROM board with the Diagnostics ROM acting as the lower ROM. I guess you can get the Dandanator to do the same.
I have had problems with edge connectors and even after countless cleaning attempts, sometimes I still have to reinsert connectors to get a clean contact. I clean the edge connectors with an old ink eraser and I never connect anything while the CPC is on.
Did the Dandanator ever work? Sounds like no. So maybe two separate issues.
I would clean and clean again the edge connector and get the Dandanator to boot with the Diagnostics ROM and go from there.
Hope this helps.
Trying to make sense of this:
- there is no proper display - but at least with the Dandanator we see some lines
- Dandanator works - games will play as we hear the sound
- CPC also boots without Dandanator as the "DEL-beep"-trick works
To my knowledge, we can rule out RAM and ROM:
- ROM fault is very unlikely. It is no short as then the CPC would not boot at all. A bit flip could happen, but then it would work with the Dandanator, as the Dandanator takes over full control (afaik) anyway
- RAM fault is also very unlikely as Dandanator copies over a snapshot to RAM and then only having a display problem but the rest of the game/system works wouldn't make sense
Since there is a somehow proper display then the Dandanator is connected, my next best guess would be, that something is wrong with the CRTC or GateArray.
My bet is that one of the 74LS153's has failed.
Bryce.
Quote from: Bryce on 09:42, 03 February 23My bet is that one of the 74LS153's has failed.
Bryce.
OK.
I will see if I get time today or during the weekend and I will test to see if there is any print lines to/from the 74LS153's that are broken.
Is there any way I can test the actual 74LS153's? Or will I have to find some other ones to swap with?
I don't know where I can find new ones or if there is alternative chips I can use.
Thanks for all the help so far. I am very new to working with Amstrad CPC and even new to working with the electronic side of old tech in general.
I defer to @Bryce and @eto as they have way more knowledge and experience than me but agree it looks like the CPC is working but the display is suspect. But cannot understand why the Dandanator has a display (of sorts). I did have what appeared to be a 74LS153 failure, showed as a total RAM failure (grey screen), so different. But this worked then failed. In the end the power was not stable and I had a bad joint on the internal power connector. Reflowed the joints and this fixed it. Just a thought.
Quote from: Rabs on 13:59, 03 February 23I defer to @Bryce and @eto as they have way more knowledge and experience than me but agree it looks like the CPC is working but the display is suspect. But cannot understand why the Dandanator has a display (of sorts). I did have what appeared to be a 74LS153 failure, showed as a total RAM failure (grey screen), so different. But this worked then failed. In the end the power was not stable and I had a bad joint on the internal power connector. Reflowed the joints and this fixed it. Just a thought.
Actually I previously completely replaced the power connector in the CPC as I thought it might be a problem, but that did not change anything. So I don't think that is the problem, but my solder skills are not the best, so I might check out again if I made a mistake there.
To my knowledge a lot of old machines often has problems in the power connectors since for many years people have pulled them out and plugged in over and over. This has been the case on a couple of Commodore machines I worked on in the past.
Quote from: CPC78 on 14:05, 03 February 23Quote from: Rabs on 13:59, 03 February 23I defer to @Bryce and @eto as they have way more knowledge and experience than me but agree it looks like the CPC is working but the display is suspect. But cannot understand why the Dandanator has a display (of sorts). I did have what appeared to be a 74LS153 failure, showed as a total RAM failure (grey screen), so different. But this worked then failed. In the end the power was not stable and I had a bad joint on the internal power connector. Reflowed the joints and this fixed it. Just a thought.
Actually I previously completely replaced the power connector in the CPC as I thought it might be a problem, but that did not change anything. So I don't think that is the problem, but my solder skills are not the best, so I might check out again if I made a mistake there.
To my knowledge a lot of old machines often has problems in the power connectors since for many years people have pulled them out and plugged in over and over. This has been the case on a couple of Commodore machines I worked on in the past.
Oh well just a thought, My problem was on the internal jumper pins.
Quote from: Rabs on 13:59, 03 February 23But cannot understand why the Dandanator has a display (of sorts).
Because that are Rasterbars that don't change anything in Memory. They are only perfectly timed ink-changes.
On another note. I don't know if it is of any importance.
My board is the "COPYRIGH 1983" "MC0001A" with the slashed zeros and "PT NO 270100" version.
It also seems like all the 74LS153 chips are "Toshiba Japan TC74HC153P 8134H" chips
Quote from: CPC78 on 15:00, 03 February 23On another note. I don't know if it is of any importance.
My board is the "COPYRIGH 1983" "MC0001A" with the slashed zeros and "PT NO 270100" version.
It also seems like all the 74LS153 chips are "Toshiba Japan TC74HC153P 8134H" chips
The 153's should be easy to find. Only the 74HC153 bit of the name is important, it can be from other manufacturers than Toshiba and the 8134H is not part of the name, it's the manufacturing date and packaging type. The reason why I suspect the 153's are the issue is because I think the CPC's ROM isn't able to set up the CRTC properly. Possibly just a single bit not arriving. The Dandator possibly uses different values where the bit is missing. You could try starting with a different ROM such as Firmware 3.1 which also uses different values if you have a method to do this.
Bryce.
Quote from: Bryce on 15:24, 03 February 23The 153's should be easy to find. Only the 74HC153 bit of the name is important, it can be from other manufacturers than Toshiba and the 8134H is not part of the name, it's the manufacturing date and packaging type. The reason why I suspect the 153's are the issue is because I think the CPC's ROM isn't able to set up the CRTC properly. Possibly just a single bit not arriving. The Dandator possibly uses different values where the bit is missing. You could try starting with a different ROM such as Firmware 3.1 which also uses different values if you have a method to do this.
Bryce.
I just included all info on the chip, sometimes there is known issues on specific batches or such.
But yes. I think I will see if I can fin dif there is any fault on any of the print lanes to or from the 153's and if I find no issue with print lanes I will try and order some new ones. I guess I can desolder and install sockets while I await new ones.
I have no means to change firmware at the moment. This is my only Amstrad computer and I have no Eprom Programmer or such yet.
Quote from: CPC78 on 15:39, 03 February 23Quote from: Bryce on 15:24, 03 February 23The 153's should be easy to find. Only the 74HC153 bit of the name is important, it can be from other manufacturers than Toshiba and the 8134H is not part of the name, it's the manufacturing date and packaging type. The reason why I suspect the 153's are the issue is because I think the CPC's ROM isn't able to set up the CRTC properly. Possibly just a single bit not arriving. The Dandator possibly uses different values where the bit is missing. You could try starting with a different ROM such as Firmware 3.1 which also uses different values if you have a method to do this.
Bryce.
I just included all info on the chip, sometimes there is known issues on specific batches or such.
But yes. I think I will see if I can fin dif there is any fault on any of the print lanes to or from the 153's and if I find no issue with print lanes I will try and order some new ones. I guess I can desolder and install sockets while I await new ones.
I have no means to change firmware at the moment. This is my only Amstrad computer and I have no Eprom Programmer or such yet.
In a gin fuelled ebay session, I bought 40 74LS153s. I only wanted 4 and did not realise they came in packs of 10 and in the end mine were not faulty. :laugh:
You could have some for free but they will take forever to get from the UK.
The computer itself seems to be working, the gate array seems to be working, the CRTC seems to be generating the sync signals correctly and the monitor is displaying colour splits but no pixel data...
I assume the Dandanator is trying to display this screen:
(https://iili.io/H1vTHDQ.png)
Like Bryce says, all it would take is one bit not arriving to the CRTC correctly for this to happen. Or could one of the counters inside the CRTC have failed internally? Are CRTCs known to fail? I assume you've checked all the traces.
Or perhaps the CRTC is fine and it just can't access the screen RAM to display the pixels, so it's just reading &00s?
CRTC's do fail, but they usually fail completely and then you get no sync signals on pins 39 and/or 40.
Bryce.
Quote from: Bryce on 12:29, 04 February 23CRTC's do fail, but they usually fail completely and then you get no sync signals on pins 39 and/or 40.
Bryce.
@Bryce, as I have loads of 74LS153s ;) and some spare CRTCs, I am thinking of making a little electronics project mock-up to better understand their use. What is the best info on how they are used in the CPC?
If you get sound out of it, I assume the basic is running OK.
From the 2 screen you posted, one option is that the DISPEN output of the CRTC is not getting to the gate array such the gate array always display a border.
On simple thing to test is to change the border color with a
BORDER 0
Quote from: Rabs on 12:52, 04 February 23Quote from: Bryce on 12:29, 04 February 23CRTC's do fail, but they usually fail completely and then you get no sync signals on pins 39 and/or 40.
Bryce.
@Bryce, as I have loads of 74LS153s ;) and some spare CRTCs, I am thinking of making a little electronics project mock-up to better understand their use. What is the best info on how they are used in the CPC?
The 153 is a dual 4 into 2 multiplexer. Each multiplexer has a 4bit input and 2bit output. Using pins 2 and 14 (S0 and S1) you can decide which two of the inputs are getting passed on to the two outputs. The chip has two of these multiplexers, so it has 8 inputs in total and 4 outputs. On the CPC, the GA controls S0 and S1 to control whether the RAM is getting address info from the CPU or the CRTC. This is how the CRTC accesses/reads the screen content from the main RAM.
You can experiment with this chip without having a CRTC or RAM, just using an Arduino and some LED's to see what's being outputted.
Bryce.
Quote from: Rabs on 16:50, 03 February 23You could have some for free but they will take forever to get from the UK.
I ordered a pack of 20 from Poland. It should not take long to recieve and actually also cheaper than getting anything for free from UK. After Brexit I have to pay 25% VAT on anything I recieve from outside the European Union and on top of that there is also a flatrate fee of 28euro. :o
Quote from: gerald on 13:02, 04 February 23If you get sound out of it, I assume the basic is running OK.
From the 2 screen you posted, one option is that the DISPEN output of the CRTC is not getting to the gate array such the gate array always display a border.
On simple thing to test is to change the border color with a
BORDER 0
I will try that.
Quote from: CPC78 on 16:17, 05 February 23Quote from: Rabs on 16:50, 03 February 23You could have some for free but they will take forever to get from the UK.
I ordered a pack of 20 from Poland. It should not take long to recieve and actually also cheaper than getting anything for free from UK. After Brexit I have to pay 25% VAT on anything I recieve from outside the European Union and on top of that there is also a flatrate fee of 28euro. :o
No problem and good luck, interested to see how you get on.
I started to read THE AMSTRAD CPC CRTC COMPENDIUM and realised how little I know and how much there is to learn :)
Hi all.
Here is my latest update on my CPC adventures. I got some NOS multiplexers from Polandand I assume they work, but then again I have no ship tester, so I can't be 100% sure.
I haven't had time to work more on the Amstrad, but today I decided to set it up and trying to pickyback the new multiplexers onto the machine. But nothing changed.
I tried to pickyback several different of the new chips on all four of the ones in the machine, one at a time and also on all four at once, but it stayed the same.
I tried both with and without the Dandanator in, but it was still the same as previous.
After some time I just left it running with the Dandanator in, listening to the music of some of the games and then something strange happened. After some time just playing the music and have blue screen it sounded like a walkman loosing battery power and the screen went dark. I turned off the CPC and after a bit I turned it back on and it was again working (or not working) as it used to.
I don't know what to try next.
The 40007 chip was very hot, even with the heatsink on.
Quote from: CPC78 on 17:07, 03 March 23Hi all.
Here is my latest update on my CPC adventures. I got some NOS multiplexers from Polandand I assume they work, but then again I have no ship tester, so I can't be 100% sure.
I haven't had time to work more on the Amstrad, but today I decided to set it up and trying to pickyback the new multiplexers onto the machine. But nothing changed.
I tried to pickyback several different of the new chips on all four of the ones in the machine, one at a time and also on all four at once, but it stayed the same.
I tried both with and without the Dandanator in, but it was still the same as previous.
After some time I just left it running with the Dandanator in, listening to the music of some of the games and then something strange happened. After some time just playing the music and have blue screen it sounded like a walkman loosing battery power and the screen went dark. I turned off the CPC and after a bit I turned it back on and it was again working (or not working) as it used to.
I don't know what to try next.
The 40007 chip was very hot, even with the heatsink on.
i wouldnt try piggybacking the mux chips, it wont help, you'll need to remove the chips and put the new ones in (maybe use sockets)..
the 40007 does run very hot..thats normal..
Quote from: CPC78 on 17:07, 03 March 23After some time just playing the music and have blue screen it sounded like a walkman loosing battery power...
Wow, would like to hear this. How can that happen? I know the AY uses the same 1Mhz clock as the multiplexers
Quote from: WacKEDmaN on 02:59, 05 March 23i wouldnt try piggybacking the mux chips, it wont help, you'll need to remove the chips and put the new ones in (maybe use sockets)..
the 40007 does run very hot..thats normal..
OK, thanks, I have socket available, so I will try that. I just did not have space enough for soldering right now, I unfortunately don't have a static set up for soldering. As soon as I can find the time I will try this and update again.
Quote from: Rabs on 08:57, 05 March 23Quote from: CPC78 on 17:07, 03 March 23After some time just playing the music and have blue screen it sounded like a walkman loosing battery power...
Wow, would like to hear this. How can that happen? I know the AY uses the same 1Mhz clock as the multiplexers
Maybe if I had image on the monitor I could have more clues, who knows ;D
I just don't understand. So sounds like the CPC is working, except for that "loosing battery power" episode, and what is that about? If I remove a multiplexer from my CPC, I get different symptoms (grey screen with colour noise pattern) but guess it is all down to the type of failure.
Just on the off chance, have you tried a different power source or monitor? Can't work out what is happening but worth a go before you take a soldering iron to it?
Hi all.
Just a quick update here. I really tried my best to revive the machine, but after many frustrating attempts I ended up giving up. I think I destroyed it more than I repaired it, which made me quite sad.
I did not give up on Amstrad though. I bought a working CPC 464 and have been plowing through my cassette games to test the machine and the games I still had to try out. Also Dandanator now works and I am looking forward to find out how to add new games to it.
For the broken machine I have made an arrangement to donate it to a friend who is more experienced in soldering and trouble finding and I hope he can make it work and it gets a new life with him.
Another thing I found was that I apparently bought a faulty new power supply. I bought a powered screen cable to connect the Amstrad to more modern monitors with SCART and a new power supply, but it won't work. If I power the CPC with the original monitor I can easily get a picture to a new monitor though, so the power scart monitor cable is working fine.
Oh well. Sorry about my ramblings. I am just a bit sad about the process that took me here, but I am happy with the help I got and I am happy that I now have a working CPC 464 and the broken one hopefully will get fixed and get a new life too.
- Jonas
Sorry to hear your CPC did not make it.
But happy to see you are up and running with another CPC.
Thanks for the update.