Yet Another Black Screen (YABS)

namaman · 08:38, 07 April 25

I keep coming back to this question...I've tried about 6 different 74LS32s as replacement for IC112, but why only one produces a video image (but with garbled characters)? The other 74LS32s produce no image and possibly no video output at all.

McArti0 · 08:39, 07 April 25

Confirm IC112 pin4 connections to Z80 pin20
Confirm IC112 pin5 connections to Z80 pin21

5V between Pin14 and Pin7 of IC112

McArti0 · 08:44, 07 April 25

Quote from: namaman on 08:38, 07 April 25I keep coming back to this question...I've tried about 6 different 74LS32s as replacement for IC112, but why only one produces a video image (but with garbled characters)? The other 74LS32s produce no image and possibly no video output at all.

74LS32 has 4 OR-gates. The one that has a working gate 1,2,3 pins(Can write to CRTC, 8255,GA) has a broken 4,5,6 ( reading all IO always)

namaman · 08:48, 07 April 25

Quote from: McArti0 on 08:39, 07 April 25Confirm IC112 pin4 connections to Z80 pin20
Confirm IC112 pin5 connections to Z80 pin21

5V between Pin14 and Pin7 of IC112

Yes
Yes
4.8V

McArti0 · 08:51, 07 April 25

Quote from: McArti0 on 08:44, 07 April 2574LS32 has 4 OR-gates. The one that has a working gate 1,2,3 pins(Can write to CRTC, 8255,GA) has a broken 4,5,6 ( reading all IO always)

Buy new IC112 and IC110 I don't believe them.

McArti0 · 08:53, 07 April 25

Do you have a breadboard?

namaman · 09:00, 07 April 25

Quote from: McArti0 on 08:51, 07 April 25
Quote from: McArti0 on 08:44, 07 April 2574LS32 has 4 OR-gates. The one that has a working gate 1,2,3 pins(Can write to CRTC, 8255,GA) has a broken 4,5,6 ( reading all IO always)
Buy new IC112 and IC110 I don't believe them.

I have tried new 74LS32s...dont work.
I could remove IC110 as I have spare 74LS132.

I do have a breadboard somewhere maybe.

McArti0 · 09:07, 07 April 25

"I have tried new 74LS32s...dont work."

OR gate is simple like wire.
If pin 4 is always Hi then pin6 is always Hi.

namaman · 09:26, 07 April 25

Quote from: McArti0 on 09:07, 07 April 25"I have tried new 74LS32s...dont work."

OR gate is simple like wire.
If pin 4 is always Hi then pin6 is always Hi.

I have tried MANY different 74LS132 ICs in the socket...only one 74LS32 works and produces a corrupt image on the monitor. The other 74LS32s don't seem to work at all.
I have removed the 74LS132 at IC110 and socketed it and replaced it...no change :-(

namaman · 09:33, 07 April 25

Wait...Wait!!!!
Maybe it's working!!!!!

McArti0 · 09:35, 07 April 25

Quote from: namaman on 07:14, 07 April 25pin 6 ic112 (red)

Quote from: namaman on 07:34, 07 April 25
Quote from: McArti0 on 07:27, 07 April 25Ok What is IORQ pin20 doing at this moment?
not much at about 4V (a little noisy)

Show it on an oscilloscope pin6 IC112 and z80 pin20.
Next
Show it on an oscilloscope pin6 IC112 and pin4.

namaman · 09:45, 07 April 25

Thank goodness for that!!!!
I thought I was going crazy.

So I replaced IC110 and it didn't fix the problem, but then I thought I should change IC112 again in case it's some weird chip combo thing happening..and it works.

So... the 74LS32 (IC112) I was using was actually bad, but in combination with the 74LS132 (IC110) which was also bad, produced a picture (albeit a corrupted one)!!!!
Where as, if I replaced the 74LS32 with a good working one, in combination with the bad 74LS132, it wouldn't produce a picture...thats a frustrating symptom.

so to put it another way... two broken ICs kind of worked, but one broken IC and one good IC didn't work...jeeez!

Anyway...Huge thanks for all your help and support, and also to Audronic who pitched in some thoughts over the last few days too.

Now I'm waiting for PIO and Sound chip + adaptor board.

You cannot view this attachment.

McArti0 · 10:19, 07 April 25

Quote from: McArti0 on 09:02, 04 April 25Check 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.

And 8255 pin35 (reset) is lo

Pin18,20 This is the same as Pin10,11 8255

Audronic · 10:32, 07 April 25

Well Done

That was some Journey

I am sure a lot of us learned some thing, I did

Thanks

Keep Safe

Ray

namaman · 10:43, 07 April 25

Quote from: Audronic on 10:32, 07 April 25Well Done

That was some Journey

I think the last few days was just a side mission.
The system isn't fully working yet though!

namaman · 00:03, 08 April 25

Quote from: McArti0 on 10:19, 07 April 25
Quote from: McArti0 on 09:02, 04 April 25Check 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.
And 8255 pin35 (reset) is lo

Pin18,20 This is the same as Pin10,11 8255

Pin32 GA(40010) - 0V.
Pin18 AY - Pulsing (but cant read frequency as pulsing is not consistent like a clock).
Pin 20 AY - 0V
Grounded one or more Pin19,20,21 8255 at start CPC - Nothing changes.
8255 pin35 (reset) - Lo.

Audronic · 04:09, 08 April 25

Quote from: namaman on 10:43, 07 April 25I think the last few days was just a side mission.
The system isn't fully working yet though!

Ok

What else is not working ?

Keep Safe

Ray

namaman · 04:41, 08 April 25

Keyboard and sound

McArti0 · 05:32, 08 April 25

Quote from: namaman on 00:03, 08 April 25Pin18 AY - Pulsing (but cant read frequency as pulsing is not consistent like a clock).

Quote from: namaman on 00:03, 08 April 25Pin32 GA(40010) - 0V.

Pin 18 AY pulsing proves that Pin 32 GA is definitely working. (pulsing)

check 8255 pin 14,15,16,17 its scan rows kayboard.

Audronic · 06:07, 08 April 25

Quote from: McArti0 on 05:32, 08 April 25Pin 18 AY pulsing proves that Pin 32 GA is definitely working. (pulsing)

How does that work Pin 32 (Blue Video) ??

Keep Safe

Ray

McArti0 · 06:32, 08 April 25

Quote from: Audronic on 06:07, 08 April 25
Quote from: McArti0 on 05:32, 08 April 25Pin 18 AY pulsing proves that Pin 32 GA is definitely working. (pulsing)
How does that work Pin 32 (Blue Video) ??

Keep Safe

Ray

namaman has GA40010. You must look on 664 or 6128 schem.

namaman · 00:23, 12 April 25

I just have an IBM 5150 Monitor on the workbench at the moment.
Waiting for parts to arrive for the 464 and then I'll replace the PIA first and see if I can get the Diag test to pass, and then will test the sound chip and if dead will build up and adaptor board and install a YM2149F.

McArti0 · 06:13, 12 April 25

You can also see if the 8255 receives the IORD pin5 signal. If Pins 14, 15, 16, 17 are flashing, it means that the 8255 only works as a data receiver, but is unable to send anything to the processor.

Bryce · 13:46, 12 April 25

Quote from: namaman on 00:23, 12 April 25I just have an IBM 5150 Monitor on the workbench at the moment.
Waiting for parts to arrive for the 464 and then I'll replace the PIA first and see if I can get the Diag test to pass, and then will test the sound chip and if dead will build up and adaptor board and install a YM2149F.

The AY is 1000 times more likely to fail than the 8255. I don't think I've ever seen an 8255 fail except in very extreme circumstances.

Bryce.

McArti0 · 16:55, 12 April 25

Quote from: Bryce on 13:46, 12 April 25I've ever seen an 8255 fail except in very extreme circumstances.

Why dont read LK1-LK3 and Vsync...

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Yet Another Black Screen (YABS)