CPC464 grey border black screen etc.

[pledg]

I re-seated/soldered the gate array and the Z80 sockets with no effect still same garbled screen except it now has a BLACK BORDER? (see pic)


I've been swapping RAM and re-flowing sockets but no effect.


It feels so close but yet still so far!

I'm now looking into IC125 and the ROM chip...

[VincentGR]

I have a 6128 with a problem like yours.
Black screen was caused by the Z80 socket, it was corroded.
Now I am in the black border - grey screen and all chips are fine.
I don't have the specific 114-115 LS although I have a bunch of other LS chips 

[pledg]

Update.


New ROM eeprom installed but no difference to main or donor boards.


Couple of questions, easy one first:


1.Can a faulty AY chip stop the 464 from starting?


2. I've been continuity testing (AGAIN) the RAM to buffers, gate array and Z80 and AY chip. My donor board has the 40010 array installed so I'm checking continuity back through the 40007 array socket via the different pin outs of the 40010 array. It all seemed fine only one dry solder. Question is interrupt pin 10 going into pin 16 on Z80. Taking this up to the 40010 array pin 32 I can't get continuity. Am I understanding this correctly or miss reading something?


Many thanks...

[gerald]

1.Can a faulty AY chip stop the 464 from starting?

No, but it would make the keyboard unusable.

2. I've been continuity testing (AGAIN) the RAM to buffers, gate array and Z80 and AY chip. My donor board has the 40010 array installed so I'm checking continuity back through the 40007 array socket via the different pin outs of the 40010 array. It all seemed fine only one dry solder. Question is interrupt pin 10 going into pin 16 on Z80. Taking this up to the 40010 array pin 32 I can't get continuity. Am I understanding this correctly or miss reading something?

What you're missing that the 40010 has a 4.7k serie resistor between pin 32 and Z80 pin 16. 

Now, from the picture you posted, you should concentrate on the RAM subsystem which include
- the GA/Z80/row/column mux : IC109/IC104/IC113/IC105
- data buffers/latch : IC115 / IC114
- all the RAM device
- GA and CRTC

The fact that you have a properly set screen/border mean that the ROM is properly programming the CRTC, but crash when trying to use the stack.
If your ram are on socket, can you take a picture will all of them removed ?

[pledg]

Thanks for your help, I didn't have the schematic just the pin outs but I see now it goes through r144!


Also found a broken trace/ring on pin 5 of IC104 which has been successfully bridged.


Still double checking other IC's then I'll try a power up.


If that fails I'll post a pic of the RAM out of the sockets.


Thanks for your help.

[pledg]

Update!


So having had enough of continuity testing the RAM and IC's etc. I thought I'd take another look at IC125 which on my boards is a TC74HCU04P chip. On one of my 2 boards this chip is dead so I'm having to swap it during testing.


Part of its circuit are resisters R143, R144, R145 all of these had blown so have been replaced! The donor or 2nd board I have has exactly the same fault so I'm swapping those out too.


I believe this circuit controls the crystal clock so is fundamental to operation.


Fingers crossed for an imminent start-up but I'm not counting chickens just yet!!!!

A replacement IC125 or TC74HCU04P seems hard to come by! Is it known by any other names. I noticed a TC74HCU04N is that compatible?

Cheers

[TotO]

Any 74HCU04 IC with the same through-hole pins package are compatible.
TC is the brand and N/P are the IC package. (i.e. "D" is not compatible, because SMD)

[pledg]

Thanks...

[pledg]

.

[Bryce]

Update!
Part of its circuit are resisters R143, R144, R145 all of these had blown so have been replaced! The donor or 2nd board I have has exactly the same fault so I'm swapping those out too.

I have to question that statement, because it's almost impossible. How exactly were these resistors blown? Physically damaged or burnt to a crisp?If they were burnt, then every single chip on the PCB is most likely destroyed. For example: The highest normally possible voltage across R145 is 5V which would give a current of 5mA  or 25mW. But this resistor is a 1/4W resistor, so you would need at least 10 times the voltage for a prolonged period to destroy it. If there was more than 50V across this resistor at any time, then the rest of the board is fried too.The story isn't much different for R143 or R144, they would need at least 16V across them. Lower than 50, but the end effect for the board would be similar.

Also, if any of these resistors or the 74HCU04 were non-functional, you wouldn't get that square screen you show above.

Bryce.

[pledg]

Yes of course you're right I think tiredness had set it by that point!


Resistors were fine...

[pledg]

Having checked and rechecked continuity I started looking at the RAM again! I have 16 4164 RAM modules enough for both boards.


Looking at the random readings from pin 2 and 14 with the logic probe I started pulling and swapping anything that didn't give a reading. I got to a state where all but one were giving a reading from pin 2 and 14.


I then popped in one of my salvaged original 4264 RAMs and the usually garbled screen flickered with interference and the tape drive started to play. I'd accidentally pressed the play button down whilst moving it.


I then connected up the keyboard but was getting no beep on pressing the delete key. The tape head was obviously working as it was picking up noise but without a tape.


I'm wondering whether the 4164 RAM I have is not compatible in some way?


Any thoughts...

[pledg]

Let me just put this out there!


The board I'm working on when I received it had a 40008 array socketed in the 40007 slot! Earlier in the post I think the outcome of this was that the pin outs are different to the 40007 and should the 40008 have been in the 40010 socket?


I've put a working 40007 into this socket.


I saw another post that offered a change in resister layout if swapping from a 40010 and 40007 arrays on a dual board! Can anyone confirm this?


When I was getting confused with resistor values earlier in the post I was looking at the CPC464 schematics that show the 40007 array pinouts.


When you have a 40010 on a board there are resistor changes to the published schematic. Particularly R144 which on CPC464 is 330ohms and on the 40010 should be 4.7k???


I'm still struggling to find a decent image of the 40010 schematic.


Could my struggles be that the board is not actually set up for running a 40007 hence the garbled screen?

[Bryce]

My suspicion is that you damaged a track while removing the old RAM. Have you checked that all RAM pins are connected to where they should be?

Forget the Gate Array, if it the pinout wasn't correct the square frame wouldn't be appearing on the screen.

Bryce.

[pledg]

I'll give those a final check before throwing the towel in and shipping it off to you  

[pledg]

Success!!!! 


After probably a 30+ year sleep the AMSTRAD CPC464 lives!


Firstly a big thank you to everyone who contributed to this thread and put up with the inane ramblings of a complete electronics beginner.


I'll do a final post detailing what was changed on this board to get it up and running soon. I'm just a little loathed to go poking around in it for the moment but now it's working I can use it as a test machine to get my donor board up and running also.


I popped the case back on and all works as it should apart from 1 key the right hand shift key. How lucky was that! at least there's two of them! I'd already changed the tape drive belt and that seems to be running okay. I don't have any tapes so I'll give the audio in mod a go. Although I certainly won't be drilling a hole in the side or rear of the case!!!



Cheers


Paul.

[VincentGR]

Congtatz Paul 

[Bryce]

So what was the issue?

Bryce.

[pledg]

Well before posting a definitive answer I would like to work back through some components I swapped out.


I suspect it had the wrong power supply put though it causing multiple failures!


Now it's working I can say I enjoyed the experience of repairing it. 


Pledg

[Bryce]

Well before posting a definitive answer I would like to work back through some components I swapped out.


I suspect it had the wrong power supply put though it causing multiple failures!


Now it's working I can say I enjoyed the experience of repairing it. 


Pledg

But obviously, the last thing you swapped out is what brought it back to life! So what was that?Please don't tell me you were swapping multiple parts each time. Never do that, it will only confuse the process.

Bryce.

[pledg]

Well the final fix that brought the system back to life was swapping RAM chips and testing the i/o signals with the logic probe. I discovered that from a newly purchased set of 8 4164 RAM chips two were faulty!

[pledg]

Confirmed faulty on main board:

40008 Gate Array
RAM
IC112

Confirmed faulty on donor board:
40010 Gate Array
Z80
RAM
ROM 40009
IC108 Video
IC114 (visibly blown damaged)


IC125 (can't confirm which board had the failed chip I unfortunately mixed them up!)


Replaced anyway:


C101
X101


Pledg.