problems CPC 6128 bewitched ?

willow3411 · 17:57, 19 May 23

Goodnight all !
I'm back with other problems...
I have a CPC 6128 Old which has keyboard problems (keys appearing without doing anything).
So I don't panic, I disassemble my keyboard, clean it as usual and put everything back together.
Same problem (see photo).
I unplug the keyboard and there is the same problem!!
the letters and abbreviations scroll across the screen.

This happens after about 30 seconds...

I changed the AY, added the 2.2K resistors, redid the welds, changed the Z80, the 40010.
always same problem.
Has anyone had this problem before?
thanks in advance
attached the pictures
thanks in advance
willow3411

Rabs · 08:49, 20 May 23

My understanding is that the AY IO port is normally pulled high and the PIO scans for a key press by pulling the lower part of port C low, which is decoded using a 74145, and port A is read via the AY.

Noted that you have used an AY-3-8912AP hence the resistor SiL network where the AY-3-8912 has internal pull up resistors.

I guess I would check that the AY IO port is indeed pulled high and then check resistance between the 74145 ouput and the AY IO port.

willow3411 · 16:04, 20 May 23

Quote from: Rabs on 08:49, 20 May 23My understanding is that the AY IO port is normally pulled high and the PIO scans for a key press by pulling the lower part of port C low, which is decoded using a 74145, and port A is read via the AY.

Noted that you have used an AY-3-8912AP hence the resistor SiL network where the AY-3-8912 has internal pull up resistors.

I guess I would check that the AY IO port is indeed pulled high and then check resistance between the 74145 ouput and the AY IO port.

Hello,
thanks for the lead.
the 74145 is the IC101?
I have 5v on the AY.
I can't find the resistor you're talking about?
I did not understand when you speak to me of port A on the AY? is it pin 1?

Thanks
Willow3411

Rabs · 16:51, 20 May 23

Ah, sorry.

If you look at my 6128 I have an original AY-3-8912 and hence the resistor network below it is not needed.

You cannot view this attachment.

You can see from the schematic how the PIO (8255), AY and 74145 are connected.

And if I measure the voltage on AY pins 7 to 14 (the IO port), I see about 4.8V.

You cannot view this attachment.

I guess as you are seeing random text without the keyboard attached then the AY IO port may be floating or a problem, or there is some sort of odd path to the 74145.

eto · 17:59, 20 May 23

If no keyboard is connected, there should be no connection between the PIO/74LS145 and the AY, so my understanding would be, that the problem must be related to the AY side of the keyboard matrix.

Did you check that the resistor array is working properly and that it's definitively in the right orientation?

willow3411 · 18:13, 20 May 23

Quote from: eto on 17:59, 20 May 23If no keyboard is connected, there should be no connection between the PIO/74LS145 and the AY, so my understanding would be, that the problem must be related to the AY side of the keyboard matrix.

Did you check that the resistor array is working properly and that it's definitively in the right orientation?

Hi,
what resistor network?
the one I added under the AY?
and indeed I have the problem without a keyboard connected.
the 74ls145n has been changed.
I actually can't find the resistors that can be a problem.

willow3411 · 18:15, 20 May 23

Quote from: Rabs on 16:51, 20 May 23Ah, sorry.

If you look at my 6128 I have an original AY-3-8912 and hence the resistor network below it is not needed.

You cannot view this attachment.

You can see from the schematic how the PIO (8255), AY and 74145 are connected.

And if I measure the voltage on AY pins 7 to 14 (the IO port), I see about 4.8V.

You cannot view this attachment.

I guess as you are seeing random text without the keyboard attached then the AY IO port may be floating or a problem, or there is some sort of odd path to the 74145.

hey,
ok i will test this.
thanks

eto · 18:16, 20 May 23

Quote from: willow3411 on 18:13, 20 May 23the one I added under the AY?

yes, that one.

eto · 18:17, 20 May 23

Quote from: willow3411 on 18:15, 20 May 23
Quote from: Rabs on 16:51, 20 May 23Ah, sorry.

If you look at my 6128 I have an original AY-3-8912 and hence the resistor network below it is not needed.

CPC 6128 PIO and AY.jpg

You can see from the schematic how the PIO (8255), AY and 74145 are connected.

And if I measure the voltage on AY pins 7 to 14 (the IO port), I see about 4.8V.

Amstrad CPC Keyboard Schematic.JPG

I guess as you are seeing random text without the keyboard attached then the AY IO port may be floating or a problem, or there is some sort of odd path to the 74145.
hey,
ok i will test this.
thanks

You do have a 8912A - that one will need the resistor array. But if it's in the wrong direction or malfunctioning or has some kind of shorts, it might cause issues.

willow3411 · 18:58, 20 May 23

Quote from: eto on 18:16, 20 May 23
Quote from: willow3411 on 18:13, 20 May 23the one I added under the AY?
yes, that one.

ok this resistors it's Good

willow3411 · 18:59, 20 May 23

Quote from: eto on 18:17, 20 May 23You do have a 8912A - that one will need the resistor array. But if it's in the wrong direction or malfunctioning or has some kind of shorts, it might cause issues.

OK,
the resistance network is good and in the right direction 
I will test the rest tomorrow morning
THANKS

willow3411 · 09:14, 21 May 23

Quote from: Rabs on 16:51, 20 May 23You can see from the schematic how the PIO (8255), AY and 74145 are connected.

And if I measure the voltage on AY pins 7 to 14 (the IO port), I see about 4.8V.

Hi all,
So, I did some tests this morning.
I tested with a multimeter the voltage from pin 7 of the 8255 to pin 7,8,9,10,11,12,13 and 14 of the AY.
i have 4.7v
(I don't know if I mentioned it but the failure occurs after 20-30 seconds without a keyboard plugged in).
I'm a little lost with the wiring diagram...
I browsed the WIKI, I read in a post that it could come from a ROM?
I can flash the roms.

willow3411 · 14:58, 21 May 23

hello again,
ok, I can't get it... .
I turn around.
I don't understand where this can come from...
I changed the AY, Change IC101.
measured the voltages as indicated above.
same results...

Rabs · 15:56, 21 May 23

Is the AY good?

Are all the connections/tracks from the AY good?

willow3411 · 16:25, 21 May 23

Quote from: Rabs on 15:56, 21 May 23Is the AY good?

Are all the connections/tracks from the AY good?

thanks for your reponse
the AY is good ( changed )

i'm going to reverified tracks from AY

willow3411 · 17:13, 21 May 23

I just finished retesting all the tracks of the AY.
Everything is OK.
question on ROM 4051 Pin 1 does not beep with ground. it's normal it is connected to nothing (there is no track)

I'm going crazy

I remember the problem comes after a little while (as if there was a component that was heating up, but nothing is heating up)....

willow3411 · 17:17, 21 May 23

I have a silly question....
to test the ROM, can I mount it over the existing one or do I have to unsolder the old one to put the new one (with support obviously)?

Rabs · 20:11, 21 May 23

Quote from: willow3411 on 17:13, 21 May 23
I just finished retesting all the tracks of the AY.
Everything is OK.
question on ROM 4051 Pin 1 does not beep with ground. it's normal it is connected to nothing (there is no track)
I'm going crazy     
I remember the problem comes after a little while (as if there was a component that was heating up, but nothing is heating up)....

Correct pin 1 on a 23256, the 40051 ROM, is not connected.

Rabs · 20:12, 21 May 23

Quote from: willow3411 on 16:25, 21 May 23
Quote from: Rabs on 15:56, 21 May 23Is the AY good?

Are all the connections/tracks from the AY good?
thanks for your reponse
the AY is good ( changed )

i'm going to reverified tracks from AY

Still the symptoms look like an AY issue. Has it been tested as working in another CPC?

Rabs · 20:29, 21 May 23

Quote from: willow3411 on 17:17, 21 May 23

I have a silly question....
to test the ROM, can I mount it over the existing one or do I have to unsolder the old one to put the new one (with support obviously)?

I have never mounted one IC over another, sorry but I am not a fan of this technique.

Also I am not aware of these symptoms being related to the ROM. Maybe someone else knows about this?

Looking at the text you get it seems to repeat and can be associated with a particular row in the keyboard matrix.

You cannot view this attachment.

I guess it could be the PIO giving a false read on port A. Do you get any sound (i.e. if you press DEL)? Port A on the PIO is also used to program the AY.

willow3411 · 14:32, 22 May 23

Quote from: Rabs on 20:29, 21 May 23
Quote from: willow3411 on 17:17, 21 May 23
I have a silly question....
to test the ROM, can I mount it over the existing one or do I have to unsolder the old one to put the new one (with support obviously)?
I have never mounted one IC over another, sorry but I am not a fan of this technique.

Also I am not aware of these symptoms being related to the ROM. Maybe someone else knows about this?

Looking at the text you get it seems to repeat and can be associated with a particular row in the keyboard matrix.

You cannot view this attachment.

I guess it could be the PIO giving a false read on port A. Do you get any sound (i.e. if you press DEL)? Port A on the PIO is also used to program the AY.

Hi,
thank you for trying to solve my problem.
where is the PIO and SLOT A?

It's IC107 Pin 9   no ?

I'm going to test the sound because it's true that I didn't connect the HP

For the ROM problem I read this on the forum by typing 963RUN" in the search bar.
Bryce talks about it

Rabs · 16:57, 22 May 23

The PIO is IC107

Port A is on the PIO pins 4 to 1 and pins 40 to 37.

I have found the post you refer to, https://www.cpcwiki.eu/forum/hardware-related/odd-text-issue-with-cpc464/msg165395/#msg165395, but don't see any outcome.

Maybe @Bryce knows what happened?

willow3411 · 08:05, 23 May 23

i'm going tested IC107

willow3411 · 17:12, 23 May 23

@Rabs
@eto

thanks guys
you took the time to explain and guide me and I found the problem
I focused on the PIO ( IC107 ) and analyzed the signals with the oscilloscope.
and that's what the 8255 delirium as soon as it heats up a bit.
change of IC. put on support and everything is OK !!
A big thank you to you !!

eto · 17:40, 23 May 23

Nice catch. Interesting that a malfunctioning 8255 can have that effect even if no keyboard is connected.

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problems CPC 6128 bewitched ?