• Please review our updated Terms and Rules here

Apple IIe no video issue

Your HGR graphics AND your text characters are missing one bit. Notice the side by side @ @ in your photo vs mine:
AT_text.jpg
Yours has a black line gap where mine is solid between them. So there is a bit missing regardless of the video data fed into the video rom UF4. The text character data is pre-determined
by the ROM character font in UF4 and data is fed to the shift register LS166 which you replaced. The shift register clocks the data serially into the video signal. The data being fed the shift register
is missing a bit, therefore UF4 is defective. I would bet your life savings on it :)

Larry G (SpeedyG ???)
 
I considered D3 as a possibility until it was determined that the text character fonts are also missing a bit. Those characters are represented by data values in the video ROM sent out the data lines to the shift register. I was also puzzled how
the hires video could also be routed THRU the ROM chip. Reading Winston Gayler's description of the Apple II shows two different shift register paths for text and graphics but looking over and over the IIe schematic and block diagrams, I did not see another shift register path to the video output. I remember reading how the IIe was redesigned with less chips needed than what the II used so aux type functions / chips could be added. From skimming thru Jim Sather's Understanding the IIe, it appears that BOTH text and hires graphics are routed thru the ROM to it's data outputs. I still don't understand how that is done. I learned from Sather's book that the 8 data out pins of the ROM 9-11, 13-17 are 5V high when display is black so it wouldn't be an open pullup resistor either. I'm betting one of those pins is remaining high. A scope could prove it. If someone knows a different way this is accomplished, please chime in.

Larry G
 
Bend the pin up do it doesn't go in the socket and measure it with a common multimeter. Stuck zero will be 0V, stuck one will be Vdd. Anything else would indicate a screen full of random patterns or characters, and a working ROM.

I'm not saying you're wrong, I don't have time to fully investigate. But I've seen pass-through ROMs and I don't think that is one :)
 
I do not have a EPROM programmer, but I wish I did.

I thought about changing D3 but it's not socketed, so it would be easier to change the ROM, if I can find one.
 
Powered off, with an ohmmeter you could measure the video ROM in-circuit pins 9-11, 13-17 to pin 24 Vdd and see if there is one pin with a lower resistance than the others. They should all be the same around 3.3k because of the pullup resistor.
Then check out of circuit they should all be very high resistance because essentially they are open collectors. Can check to pin 12 ground also.
 
retrogear said:
Powered off, with an ohmmeter you could measure the video ROM in-circuit pins 9-11, 13-17 to pin 24 Vdd and see if there is one pin with a lower resistance than the others. They should all be the same around 3.3k because of the pullup resistor.
Then check out of circuit they should all be very high resistance because essentially they are open collectors. Can check to pin 12 ground also.
Click to expand...

All these look OK.
 
>All these look OK.
My gut tells me it can't be the video ROM but I don't see another path. I scoped the data lines feeding the shift register out of my //e video ROM and I do see bits changing in HGR mode as I fill the memory with bit sequences like 01, 02, 04, etc so maybe ??? At least it's socketed ... You could ohm out the IC pins to the PCB solder pads to be sure you don't have a bad socket or just ohm the pins to the next circuit points they feed like the corresponding pins of the LS166.

Larry G
 
Enhanced?

Enhanced?

I just had a totally off the wall thought. Is your //e enhanced? Would you possibly have an unenhanced video rom with enhanced other roms / 65c02 or vice versa mismatch ? A new video rom was part of the enhancement kit
 
I can send a programmed 2732 for free for your case, just give me a link to the BIN image. Prior shipping I can verify its operation on enhaced/non-enhaced //e computers. On the other hand if you can read your present ROM somehow I can burn it and verify its operation at my place, because the cause of your faulty motherboard could be elsewhere.
 
retrogear said:
I just had a totally off the wall thought. Is your //e enhanced? Would you possibly have an unenhanced video rom with enhanced other roms / 65c02 or vice versa mismatch ? A new video rom was part of the enhancement kit
Click to expand...

They are interchangeable. It wouldn't cause a problem.
 
"Would you possibly have an unenhanced video rom with enhanced other roms / 65c02 or vice versa mismatch ?"

Good thought, but it is correct.. 342-0265-A
 
george said:
I can send a programmed 2732 for free for your case, just give me a link to the BIN image. Prior shipping I can verify its operation on enhaced/non-enhaced //e computers. On the other hand if you can read your present ROM somehow I can burn it and verify its operation at my place, because the cause of your faulty motherboard could be elsewhere.
Click to expand...

That would be appreciated.

http://mirrors.apple2.org.za/Apple%20II%20Documentation%20Project/Computers/Apple%20II/Apple%20IIe/ROM%20Images/

Apple IIe Enhanced Video ROM - 342-0265-A - US 1983.bin

I do not know of a way to read it, though. Any ideas?

Thanks.
 
Last edited:
Ok, I 've programmed and tested successfully one 2732 EPROM. Send me your address as a PM and I will ship it tomorrow morning from EU (it is 8pm LT now). It takes approx. 3 weeks to travel from my location to the US...
 
You must log in or register to reply here.
Back
Top