Yet Another Black Screen (YABS)

[namaman]

I'm not so sure it's going to be that easy...

Anyway, is that IC120 the IC117 for the first four RAM chips?

Cheers 

[Audronic]

Yep 120 to 117 
Bit 0 to Bit3

Kep Safe

Ray

[namaman]

Hey...check it out!!!!
I was able to replace all RAM with know good RAM and it works...well, kinda...the keyboard doesnt work :-(
So thats next on my list of fixes. 

So far: Z80 dead, RAM dead, ROM dead.

Thanks to everyone for sticking with me so far, especially McArti0 for all his troubleshooting suggestions.

Stay tuned as I investigate the keyboard...

[McArti0]

Is the keyboard not working on both ROMs?
Does DiagROM only hang when detecting CRTC?

[namaman]

yes...keyboard not working at all for both ROMs.
The Diag test stops there...and thats it.

[McArti0]

Check pin32 GA(40010) it should be 300Hz interrupts

Pin18,20 AY - Quick Hi,Lo series 50 times per second.

Grounded one or more Pin19,20,21 8255 at start CPC
This changes the brand name in the welcome text.
It proves that the 8255 works at all.

Grounded pin 7-14 AY. Should be serial 10 chars on screen at one pin.

[Bryce]

Hey...check it out!!!!
I was able to replace all RAM with know good RAM and it works...well, kinda...the keyboard doesnt work :-(
So thats next on my list of fixes.

So far: Z80 dead, RAM dead, ROM dead.

Thanks to everyone for sticking with me so far, especially McArti0 for all his troubleshooting suggestions.

Stay tuned as I investigate the keyboard...

If that much was broken it must have got an over-voltage or reversed voltage. That would have damaged the AY too, so I would just go ahead and swap it.

Bryce.

[namaman]

Check pin32 GA(40010) it should be 300Hz interrupts

Pin18,20 AY - Quick Hi,Lo series 50 times per second.

Grounded one or more Pin19,20,21 8255 at start CPC
This changes the brand name in the welcome text.
It proves that the 8255 works at all.

Grounded pin 7-14 AY. Should be serial 10 chars on screen at one pin.

Does it matter what ROM I have installed? 
I'll give those a try tomorrow. Getting late here now.

I also just tried swapping in another known good CRTC and the Diagnostic test still hangs at the CRTC test.

[McArti0]

firmware ROM.

[namaman]

Also I recall seeing this video from Noel:

*see the 19min 50second mark

I wonder if my PIO is dead too?

[namaman]

Bryce.

I think you are probably correct. 
I forgot to add to the list of dead parts the CRTC...but surprisingly out of all the RAM that was desoldered only two RAM chips were dead, the rest tested fine.

[McArti0]

You have a working GA. That's a lot of luck.

[McArti0]

I wonder if my PIO is dead too?

First tests....

[namaman]

Check pin32 GA(40010) it should be 300Hz interrupts

Pin18,20 AY - Quick Hi,Lo series 50 times per second.

Grounded one or more Pin19,20,21 8255 at start CPC
This changes the brand name in the welcome text.
It proves that the 8255 works at all.

Grounded pin 7-14 AY. Should be serial 10 chars on screen at one pin.

yes...
- 300Hz on pin 32 of the GA.
- On the AY, Pin 18 pulses (see photo), pin 20 seems dead.
- Grounded one or more Pin19,20,21 8255 at start changes nothing on the boot screen.
*one addition here, Grounding PIN 19 causes the screen to slowly roll as if Vert Sync is slightly off.

"Grounded pin 7-14 AY. Should be serial 10 chars on screen at one pin."
Not exactly sure what this means.

* Dammit...something just pooped itself on the system as I was testing. Just checked its not the RAM, or the GA, or the Z80, or the CRTC, those all look fine I think...more investigation needed

[namaman]

...Well, not sure what was going on there, but I suspect a marginal 74LS32 @ IC112 (I was getting a complete blue screen, and sometimes just randomness). I actually piggybacked it with another, and the system suddenly booted again, removing the piggyback IC and the system continues to boot as before. Unusual.

[namaman]

Grounded pin 7-14 AY. Should be serial 10 chars on screen at one pin.

I tried individually grounding those lines, but nothing changes on screen. No characters appear.

[namaman]

I have ordered a 8255 PIO, a YM2194F Sound chip, and some AY-8910 to AY-8912 adaptor boards.
I hope thats all I'll need to get this machine up and running again.

I guess it's time to desolder the 8255 and the AY-8912...

[McArti0]

yes...
- 300Hz on pin 32 of the GA.
- On the AY, Pin 18 pulses (see photo), pin 20 seems dead.
- Grounded one or more Pin19,20,21 8255 at start changes nothing on the boot screen.
*one addition here, Grounding PIN 19 causes the screen to slowly roll as if Vert Sync is slightly off.

- GA working.
- Pin 18 AY, 8255 working at Write
- pin 20 AY ? ? ? 8255 not working at Write?
- Pin19,20,21 8255 not working at Read !!!
- https://www.cpcwiki.eu/index.php/LK_Links
- PIN19 realy not Pin22? its to 60Hz/50Hz Vsync switch

[McArti0]

I guess it's time to desolder the 8255 and the AY-8912...

First test IC112 Pin6

Test pulse 74LS145 between +5V and Pin2

If Pin2 pulses then cross on working CPC Pin2  LS145 to READY permanently. This should stop CPC at Open AY. Grounded Pins 7-14 AY should be show Lo on Pins 21-28 AY. (Pin 7-Low -Pin 21 Low etc)

[namaman]

Arrrrgh!!!

I mentioned previously I started having intermittent issues, but always seemed to be able to recover...somehow. I suspected the 74LS32 at IC112.
...Then suddenly I couldn't boot at all. I replace IC112, but still no change.

Two steps forward, one step back!!!!

Here is a video of what I'm getting now. Kind of a pulsing on the screen. Also seems like some signals are also pulsating at the same rate. No change if ROM is removed. 
I have checked the GA (in my 6128), Z80 (in my 6128), and CRTC (in the Apple II 80 column card), and they still all seem to work in those systems.

Oh dear...What to do now. 
I checked the voltages, and the clocks, and again those seem fine.
Frustrating.

[Bryce]

Arrrrgh!!!

I mentioned previously I started having intermittent issues, but always seemed to be able to recover...somehow. I suspected the 74LS32 at IC112.
...Then suddenly I couldn't boot at all. I replace IC112, but still no change.

Two steps forward, one step back!!!!

Here is a video of what I'm getting now. Kind of a pulsing on the screen. Also seems like some signals are also pulsating at the same rate. No change if ROM is removed.
I have checked the GA (in my 6128), Z80 (in my 6128), and CRTC (in the Apple II 80 column card), and they still all seem to work in those systems.

Oh dear...What to do now.
I checked the voltages, and the clocks, and again those seem fine.
Frustrating.

That's why bridging and shorting pins should never be used in diagnosis, measurements tell you everything you need to know. It's too easy to accidentally break something else and end up where you are now.

Bryce.

[McArti0]

You have loose sockets. When You unplug and plug Chip in socket, You cannot be sure that all pins are connected.
Bridging and shorting pins with brain is nothing wrong with doing something, you just need to use your brain and know how it works.
If you don't know how to do it, you scare others.

Now 74LS32 is used to Write to CRTC. But not work properly

[namaman]

Bryce, yes, that is indeed quite possible. I think I'll stop that for now.

So after some more playing around, this is where I am at.
I am fairly sure the CRTC, Z80, GA and RAM are all ok.
I started looking around IC112 again. I removed the new 74LS32, and put back the original that I desoldered...I saw more signs of live, and on some restarts I even got a white screen and black boarder!!!...I then I looked in my parts bin, mostly I have one kind/maker (which proves not to work at all) and then I found a third variety of 74LS32 and tried that...this time I was able to consistently get a boot screen, but with garbled or inverted colour text (see image).

Soooo....not sure what is going on and why the various 74LS32 have different outcomes, but I feel I'm starting to focus in on the problem a little bit, or at least I'm in the right area.
Anyway, it's real late here now, so I'll pick this up again in the morning.
Any help or insights would be greatly appreciated.

Thanks again

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[McArti0]

IC112 is Main Source IORD and IOWR signal for CRTC and 8255

GA dont use IC112.

NOW you have problem with WR and RD from Z80. check Your socket.

[eto]

you just need to use your brain and know how it works.

Most people don't know how it works and telling them what to do (especially without explanation why) has a very high risk that they make a small mistake here and there.