games flitting between CPC MODEs

[Devlin]

I made a tweet with a video about this:

https://twitter.com/magic_bane/status/1152296561390555137


For some reason after my CPC has been running for a while it will randomly flit between display modes - it causes audio glitches too(not captured in the video) and I am not sure what part is going funky here.


Any thoughts as to what's wrong and how I might be able to fix it?


thanks in advance

[VincentGR]

1. Try cleaning the motherboard and sockets, re-seat all chips.
2. Wait for more advanced answers from someone else 

[dragon]

The more easy test you can do is if you have another cpc swap the gate array(same gate array) . They are in socket, you don't need any soldering.


And same for z80. But it can be ram.

[robcfg]

Actually, you have to be careful, because the 40010 is not compatible with the 40007 and 40008, that's why the boards have two different slots for Gate Arrays.

[VincentGR]

Actually, you have to be careful, because the 40010 is not compatible with the 40007 and 40008, that's why the boards have two different slots for Gate Arrays.

Off topic question, will this need any extra modifications or you just plug it?

[robcfg]

If you find the same part number it just plugging it in.


If the ga is a 40010 and you have a 40007/8 to try, you need to solder a socket and a capacitor as far as I remember.

[Devlin]

I don't have any spare known working hardware to test against -


My 464 has PT NO Z70100 on the mainboard, is that relevant?
The Gate array is a 40007 chip.


Would it be prudent to replace the thermal goop with something a bit more modern?

[gerald]

I don't have any spare known working hardware to test against -


My 464 has PT NO Z70100 on the mainboard, is that relevant?
The Gate array is a 40009 chip.

40009 is the ROM 
On a Z70100 mainboard the gate array is always a 40007 and is under the heatsink.
https://www.cpcwiki.eu/index.php/Mainboard_Versions#CPC464_version_1_.28original.29

As a 1st, just reseat it on its socket.

[Devlin]

40009 is the ROM 
On a Z70100 mainboard the gate array is always a 40007 and is under the heatsink.
https://www.cpcwiki.eu/index.php/Mainboard_Versions#CPC464_version_1_.28original.29

As a 1st, just reseat it on its socket.

Caught that just before you posted! corrected for later reference.


I've reseated the 40007, and am testing it now to see what happens.

[Devlin]

Caught that just before you posted! corrected for later reference.

I've reseated the 40007, and am testing it now to see what happens.

It's still happening after that. Thought it might have been heat related - but it never got hot enough that I couldn't keep my finger on it (so that ruled out overheating causing glitches)


I confirmed it wasn't power right away - the power supply is supplying a steady voltage.


Assuming it's the Gate Array - What options do I have regarding replacements?


Can I use a newer thermal paste (like the stuff I use on my PC) to replace the old stuff if that might help?

[Devlin]

There's been a development (this might help narrow down what's wrong)


I've noticed now on power-on sometimes holding del that the beep you get when it can't delete any more sometimes sounds like it's going at warp speed, and keyboard inputs are counted several times from a single quick press.


While testing earlier (with monte carlo casino since it seems to be the most reliably noticeable for catching the glitches) I noticed that the game stopped registering that it was mid spin and the second and third reels just kept spinning forever. First time i'd ever seen it do that.


Could this potentially be a Z80 issue?

[robcfg]

I wouldn't discard that the chips are good and you may have some corrosion/damaged tracks/broken solder joints on the pcb.


Maybe some pictures of the pcb (both sides) could help diagnosis.

[Devlin]

top side of board - clicky through for full size

[Devlin]

clicky through for full rez



I had intended to upload original images as attachments to avoid web services nuking the quality but it wouldn't let me upload directly so here's imgur links.

[VincentGR]

The only weird thing I see is above Z80, although tracks seem OK 

[Devlin]

The only weird thing I see is above Z80, although tracks seem OK 

What's weird about it?


I reseated the Z80 and cleaned the socket - Seems to have helped but I don't trust it. Is there a tape-loading(CDT) program that can test the Z80 that I can use?

[VincentGR]

Looks like there is something like bubbles on that pcb area.
Dunno how it is affecting the traces or how will it be under the socket.

[Devlin]

Looks like there is something like bubbles on that pcb area.
Dunno how it is affecting the traces or how will it be under the socket.

I don't think that's going to be much of an issue. C64s can get a lot, lot worse in that regard.

[gerald]

Looks like there is something like bubbles on that pcb area.
Dunno how it is affecting the traces or how will it be under the socket.

Don't worry, that a side effect of the way solder mask was applied 30 years ago  .

[Devlin]

After a few days I'm discovering it's been behaving solid (even in this vile british heatwave), so for the time being I'm going to declare this case closed, BUT I'd like to know what I can do if this persists.