<Circuit problem?> video output problem

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<Circuit problem?> video output problem

Hello. I am newly to join this forum. 

I have Apple II plus (Rev.4) which I bought I was high school student(38 years ago!).

I kept it for a long time and draw out to share the excellent machine with my son.

First of all, I cleaned the motherboard then reseated ICs and replaced power supply. Now it seems working (system boot, power light on, beep, reading Disk II, reset), but no video. No video, I mean the screen is flashing about 2 times per one second but no message. As I write above system is working, so I can enter command by keyboard in the blind and apple II+ responses good (if I input error command, apple warns with beep sound). My display is LCD I have confirmed that another working Apple II (RFI board)  displays. So I think something is wrong with the video circuit.

Please give me suggestions, comments to find out the problem to check and solve them.

It is hard to express my thoughts and the situation in detail in English, but I will make efforts. If there is something that is hard to understand in my text or more information, please let me know.

Thank you.

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did you try adjusting the

did you try adjusting the video level control back by the video jack? sometimes it has a dead spot

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I tried but there is no change.

Thank you for your reply.

Yes I tried but there is no change. It only changes the brightness of the screen.

I checked several items referring to the “Apple II+/e Troubleshooting & Repair Guide". In the article ”No display - No video" on page 83, only 2N3904 (Q3) is not checked. Does this transistor cause symptom?  If it is a suspicious part, I will replace it. Is there any other checkpoint in the video circuit? I have a simple oscilloscope so I can check the signal.

Thank you.

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I doubt it is the transistor.

I doubt it is the transistor.

When you say the screen is flashing is it a small rectangle about the size of one character or a large rectangle that fills most of the screen?

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It seems to be the symptom “a

It seems to be the symptom “a large rectangle fills most of the screen” as you say.

I will replace the transistor and report the result later

 

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Download "Apple II Circuit

Download "Apple II Circuit Description" from Winston D. Gaylor:

http://mirrors.apple2.org.za/Apple%20II%20Documentation%20Project/Books/W.%20Gayler%20-%20The%20Apple%20II%20Circuit%20Description.pdf

 

Page 220/221

 

SpeedyG

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clumpwork wrote:It seems to

clumpwork wrote:

It seems to be the symptom “a large rectangle fills most of the screen” as you say.

I will replace the transistor and report the result later

 

 

You probably have a faulty character generator ROM,  it seem to be a common failure of late.

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As I mentioned before, I own

As I mentioned before, I own two types of motherboards, Rev.4 and working RFI.

It is regrettable that I can not compare because the type of character ROM installed on each of the two boards is different.

However, because symptom dose not change when ROM is removed, so there is a possibility that the ROM is not functioning (Similarly there may be problems with other circuits?).  For now I look for a ROM that can be replaced.

Speed_G,

I downloaded "Apple II Circuit Description”.  This book is very helpful.

You mentioned “Page 220/221”, but there seems to be no corresponding page.

Would you please tell me the page you recommend I should read?

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I downloaded "Apple II

I downloaded "Apple II Circuit Description”.  This book is very helpful.

You mentioned “Page 220/221”, but there seems to be no corresponding page.

Would you please tell me the page you recommend I should read?

Sorry - correcting myself:

my scan is older larger and has more pages....

at this new smalller scan:

“Page 214    or   Page 215” ( different mainboard revisions  )

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upload a move showing symptoms

Thank you, SpeedyG.

I review the circuit once again with reference to the articles.

 

Here I upload a movie showing symptoms.

https://www.youtube.com/watch?v=Bdeajz28C8Q
I should have shown a little earlier.
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I get this affect on flat

I get this affect on flat panel monitors that are unable to sync with the Apple 2 video signal.

Make sure yours is not the case.

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Does it mean that the refreshing rate

Thank you, Macnoyd.

Does it mean that the refreshing rate varies depending on the generation of the motherboard?

I will try to check on other monitor display.

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The refresh rate doesn't vary

The refresh rate doesn't vary, but the Apple II's Sync signals aren't perfect and some flat panel displays simply don't work as a result.

Let us know your findings.

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macnoyd wrote:The refresh

macnoyd wrote:

The refresh rate doesn't vary, but the Apple II's Sync signals aren't perfect and some flat panel displays simply don't work as a result.

Let us know your findings.

 

That's maybe being a little generous...  It would not be entirely unreasonable to say that the Apple II plays fast and loose with the NTSC standard when it comes to video.  Woz used tricks to generate video using a minimum of parts and while it was good enough to fool most old analog CRTs, some newer devices may not be as sloppy in their tolerances.

 

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the art of redundancy

I was looking at the circuit diagrams of the two motherboards today.

Between RFI motherboard and the one before that, the circuit assembled with the four NOR gates of 74LS02 (A14) looks distinctive. What is the function of the added circuit?

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I searched past forums and

I searched past forums and found the posting (“Apple II Plus color killer circuit “, November 4, 2015 - 11:11am) may also be related to mine.

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Solved video out put problem ... My experiment was successful.

Thanks all. I fixed my apple II+ video output successfully.

I focussed on the difference between the RFI board and the earlier board, in my case the Rev 4. As I wrote in last post the circuit assembled with the four NOR gates of 74LS02 (A14) looks distinctive. So I configured this circuit on the breadboard and replaced it with the circuit of rev 4. 

Your advices has become very useful!!

After all, it is because the LCD display can not recognize the difference between the width of the SYNC signal of RFI (and rev. 7) board and the previous one.

I attach some photo.

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Above and beyond ...

Most folks wouldn't have gone that far to solve this issue.  Congrat's on your efforts!  +1  Nicely done.

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Displaying color problems…video output problem follow-up

 

I thought that it was solved, but I noticed that problems still existed.

It is now displayed on the LCD monitor with rev.4 motherboard, but colors are not correctly assigned. It was only able to display…

photo#1 | rev.4 board with addtional circuit,  the color is NOT correctly displyed.

photo#2 | RFI board , the color is correctly displyed.

Because it seems difficult to understand how to display colors for me,  I continue to learn about circuits with reference to the apple ii circuit description.

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In very simple words:

In very simple words:

color depends to parts of time shift/delay of signal related to base signal timing.

 

check position of "color-trim-adjustment"on mainboard.(variable capacitor trim in row G).

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Thank you  for your advice.

Thank you  for your advice.

I should have written what I tried first.

I have considered that and have tried already.

But, there was not any change.

It may be that there is something overlooking.

Again, I will check again about my attempt.

Thank you.

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circuit symptom?
In my last post, the problem that bothered me was the symptom that the composite video was not displayed with my apple II+. Although this symptom was resolved, a new symptom occurred that a different color was displayed.
I got "Apple II VGA Scaler" from A2heaven and now my apple II+ can display color very sharp. This device solves problems related to the output of composite video.
Therefore it is not necessary to take into considerations of the problem of composite video circuit.
As a result of installing the device, the problem of color assignment became clear.
Here is a correspondence table between color assignment and colors actually displayed. The combination of numbers in parentheses represents 'Bit Positions' that it was written in "The Apple II Crcuit Description" on page 118.
 black       [0 0 0 0]  ->  black       [0 0 0 0]
 magenta     [0 0 0 1]  ->  dark blue   [0 0 1 0]
 dark blue   [0 0 1 0]  ->  dark green  [0 1 0 0]
 purple      [0 0 1 1]  ->  medium blue [0 1 1 0]
 dark green  [0 1 0 0]  ->  Brown       [1 0 0 0]
 gray 1      [0 1 0 1]  ->  gray 2      [1 0 1 0]
 medium blue [0 1 1 0]  ->  light green [1 1 0 0]
 light blue  [0 1 1 1]  ->  aquamarine  [1 1 1 0]
 brown       [1 0 0 0]  ->  magenta     [0 0 0 1]
 orange      [1 0 0 1]  ->  purple      [0 0 1 1]
 gray 2      [1 0 1 0]  ->  gray 1      [0 1 0 1]
 pink        [1 0 1 1]  ->  light blue  [0 1 1 1]
 light green [1 1 0 0]  ->  orange      [1 0 0 1]
 yellow      [1 1 0 1]  ->  pink        [1 0 1 1]
 aquamarine  [1 1 1 0]  ->  yellow      [1 1 0 1]
 white       [1 1 1 1]  ->  white       [1 1 1 1]
looking at this correspondence table carefully, I noticed the following;
 [DL(3), L(2), DL(1), DL(0)] -> [DL(0), DL(3), L(2), DL(1)]   
It seems that the order of combinations of 'Bit Positions' has been changed, at a glance. There may be different perspectives.
 I thought that there was a problem with IC synchronization, I checked the ICs at positions A8, A9, B4, B9, but it does not seem to be faulty.
Are there anything else I need to check? 
I am very sorry that my English expression is insufficient, but It will be a great help if you give me advice.
Thank you.
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