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.
did you try adjusting the video level control back by the video jack? sometimes it has a dead spot
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.
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
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
[quote=clumpwork]
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
[/quote]
You probably have a faulty character generator ROM, it seem to be a common failure of late.
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?
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?
[/quote]
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 )
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.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.
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.
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.
[quote=macnoyd]
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.
[/quote]
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.
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?
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.
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.
videotout1006-1.jpg
videotout1006-2.jpg
videotout1006-3.jpg
Most folks wouldn't have gone that far to solve this issue. Congrat's on your efforts! +1 Nicely done.
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.
rev4_improv.jpg
photo#2 | RFI board , the color is correctly displyed.
RFI_reff.jpg
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.
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).
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.