Weird Video issue CPC464 "Solved"

[arnoldemu]

Yes, but it receives data from the databus.

Only when reading/writing to it's registers.

CRTC generates an address the gate-array reads the data from that address and outputs it as pixels.
CRTC address is also used for ram refresh, gate-array doing the read performs the refresh.

[imperious]

1st of all thanks for all the replies everyone. I Will pull the unit out of my cupboard and try what has been suggested.

Have you tried Tot0's site imperious? I have just had a quick look and have worked out that either a 4007 or a 40010 from him should work out at about $32 Aus including tracked and insured postage.

I just found that today whilst surfing for Amstrad parts, so looks like I will definitely be fixing it anyway

Too bad for you you did'nt take the monitors :

- the colour one provide much better image for vintage games graphics than any LCD display currently available, unless you add some expensive video pre-processing hardware. The GBS 8220 is definitely not of these ones. Also remember all vintage graphics were designed for CRT screens, not for the now "pixel perfect" LCDs.

- the green monitor is really good for any serious activity on the CPC. The monochrome image is crispier than on the colour output and, if your are in any serious programming, provide less eye-strain

I realise CRT's look better, had my c64 running on one last week. Unfortunately I don't really have the room for it, mostly due to a retro computing habit getting a bit out of control . I am only really interested
in games on it so a Monochrome monitor won't cut it. If I had grown up with one it might be a different story.

I'd guess the Gate-array too. However, it may not be actually damaged. Remove it from the socket and clean the pins of the IC and the socket with isopropanol and it might solve the problem.

Either a problem in the GA or in the ROM. Check / clean them first. 

The only socketed IC's are the Z80 and the Gate Array (ULA). I already tried reseating the Z80 but will remove, clean, and try the ULA tonight.

Just out of curiosity, is the 40010 ULA any better than the 40007? this board has provision for either, so if the ULA proves to be faulty then I could remove it
and fit the 40010, in a socket of course.

[Bryce]

Only when reading/writing to it's registers.

CRTC generates an address the gate-array reads the data from that address and outputs it as pixels.
CRTC address is also used for ram refresh, gate-array doing the read performs the refresh.

And aren't those registers used when setting modes and colours?

Bryce.

[gerald]

Just out of curiosity, is the 40010 ULA any better than the 40007? this board has provision for either, so if the ULA proves to be faulty then I could remove it
and fit the 40010, in a socket of course.

There are slight differences between 40010 and 40007.
   - they do not have the same pinout, so put it on the right socket 
   - the 40010 have a minor display difference in mode 2 where the display start one pixel clock earlier.
   - the 40010 consume less than 40007

If you can choose, go for  a 40010

[arnoldemu]

And aren't those registers used when setting modes and colours?

Bryce.

No, the colours and modes are registers inside the Gate-Array.

For CRTC you control the size of the display, it's position and the timings (vsync and hsync).

[Bryce]

Ah, good to know. That's where my lack of programming knowledge lets me down

Bryce.

[imperious]

I removed, cleaned, and reinserted the 40007, made no difference unfortunately. Unless there is a real chance of it being the 74ls244 (I can get one in Jaycar just 3 minutes away by car)
I will order a replacement ULA.

I also did some resoldering on the Rom, Audio, Video IC's.

The smudging effect around the characters on screen definitely changes colour at switch on. It can be pink (might be light red), red, dark blue, light blue. The Yellow always stays the same though.

[gerald]

I removed, cleaned, and reinserted the 40007, made no difference unfortunately. Unless there is a real chance of it being the 74ls244 (I can get one in Jaycar just 3 minutes away by car)
I will order a replacement ULA.

I also did some resoldering on the Rom, Audio, Video IC's.

The smudging effect around the characters on screen definitely changes colour at switch on. It can be pink (might be light red), red, dark blue, light blue. The Yellow always stays the same though.

Did you check/clean the socket ? D0 is on pin 24.

[Bryce]

I removed, cleaned, and reinserted the 40007, made no difference unfortunately. Unless there is a real chance of it being the 74ls244 (I can get one in Jaycar just 3 minutes away by car)
I will order a replacement ULA.

I also did some resoldering on the Rom, Audio, Video IC's.

The smudging effect around the characters on screen definitely changes colour at switch on. It can be pink (might be light red), red, dark blue, light blue. The Yellow always stays the same though.

Blindly ordering and swapping parts can be an expensive passtime. Do you have any test equipment, even a cheap multimeter to test what's actually broken?

Bryce.

[imperious]

Blindly ordering and swapping parts can be an expensive passtime. Do you have any test equipment, even a cheap multimeter to test what's actually broken?

Bryce.

Sorry, I should have mentioned that I'm an electronics Technician, with over 25 years experience. I have a Multimeter and Oscilloscope. I do consider having spare parts to be a worthwhile expense,
especially with this hobby with 30+ year old IC's that can die at any moment.
Just let me know what You want me to test. It's midnight here, so it will be another 17 hours or so till I can check anything.     

[Bryce]

Ok, then I don't need to explain how to test these things: I'd start by testing the bits going to the GA to see if any bits are stuck at a particular value. Same with the outputs of the 244.

Bryce.

[imperious]

OK, Had a bit of a poke around the Data lines, inputs and outputs of the 244 looked the same, nothing seemed to be stuck
at a zero or a 5v level anywhere.
Is it normal for VCC2 on the 40007 to be about 3.5v? The two 6 ohm resistors are ok. The +5v rail is good at 4.97v.

[gerald]

OK, Had a bit of a poke around the Data lines, inputs and outputs of the 244 looked the same, nothing seemed to be stuck
at a zero or a 5v level anywhere.

Did you check that all data bit are toggling on the 40007 itself ? You can safely remove the heatsink for the test.
Board schematic are the wiki

Is it normal for VCC2 on the 40007 to be about 3.5v? The two 6 ohm resistors are ok. The +5v rail is good at 4.97v.

Yes !

[imperious]

The Data looks the same on the 40007, ls373, ls244, and D0 on IC120. Nothing jumps out at me as unusual.
I did get a 74ls244 from Jaycar and was going to socket all chips on the 40007 side of the D0 line but it took me ages
to remove IC120, so will order a solder sucker from Ebay as desolder braid takes too long.

I've ordered a 40010 from Cent Pourcent as well as a tape drive belt. My cpc has this motherboard File:Z70200 MC0001A TOP.JPG - CPCWiki

[imperious]

Thanks to everyone who helped, and especially Richard at "Cent Pour Cent" who reposted the ULA and drive belts I ordered due to the 1st package getting lost somewhere in
the mail system.

The ULA was the culprit and all is fine now with a 40010 in place instead of the original 40007 (board has provision for either).  I put 2 copper heatsinks on it for
good measure. The original owner was a smoker and despite cleaning it still smells of it, although only if You get close enough.  It looks a whole lot better though.
I did the 200x speedup and used a car cassette adaptor to load some games which works well mostly.
Also captured StarWars via my GBS8200 and Vga to hdmi adaptor into my Avermedia card on my PC. The video is a bit less sharp due to processing for Youtube.
For sure the CPC looks very good on my LCD monitor, far better than nearly all my other 8 bit machines.  The stereo sound also is very nice to have.

[Audronic]

Well done


Ray

[Bryce]

Congratulations.

Bryce.

[VincentGR]

Good news!