Apple II+ pure white screen?

[zezba9000]

So have an Apple II+ I'm trying to get working.

The issue I'm running into is the screen is PURE WHITE.  But why?  Its like the CPU is idle doing nothing.

#1 I built a new PSU using a PICO & 1705 voltage regulator to get -5v. (All voltages test correct)

#2 I replaced the 3904 transistors but not the A13 one yet. (No change)

#3 I only have a single row of memory chips in.

#4 There is no beep.  PWR LED doesn't work but 5v power is going to LED correctly.

Anyone ever seen this before and know what a might be wrong?

 

[bibilit]

Ram chips are not in the right place.

First row should be populated first, then second and third row

 

[zezba9000]

Ram chips are not in the right place.

First row should be populated first, then second and third row

Thanks.  Now I have white vertical lines. So maybe its some bad ram. Reset all chips so replacing ram will be next.

 

[bibilit]

Can be, but commonly with bad ram you got garbage on screen.

 

[zezba9000]

Ok so maybe people can help me identify the voltages on these caps, if they differ at all.  Are they all 50v?

I now replaced all the electrolytic caps & transistors on the board and one of the ceramic ones.

Also have a single row of NEW memory. Using old memory also doesn't change anything. So its probably not ram.

I now get this on the screen.



Replaced power light with LED.



Here is a picture of all the ceramic cap types. Are they all 50v?  If so why do they differ?



So I also re-seated all chips on the board as well.  Unless someone has a better idea I was going to replace all ceramic caps but need to be 100% sure I'm replacing them with the right ones.

 

[bibilit]

Don’t think your issue is related with capacitors. 

Garbage screen is either Ram or Rom related. 

 

[zezba9000]

Don’t think your issue is related with capacitors. 

Garbage screen is either Ram or Rom related. 

Well pretty sure its not RAM as both original ram and new ram produce the same result.

What ROM chips should be replaced or investigated first?  Sucks they're so expensive.  Are there new 3rd party ROMs for Apple II+ ?

 

[bibilit]

Without another unit to swap, hard to say. 

Yes 3rd new units are available, not very expensive. 

 

[zezba9000]

Without another unit to swap, hard to say. 

Yes 3rd new units are available, not very expensive. 

Do you have a link?  I can't seem to find 3rd party solutions when doing google searches.

 

[zezba9000]

Without another unit to swap, hard to say. 

Yes 3rd new units are available, not very expensive. 

So read you only need the F8 rom to use ASM.

I removed every rom but the F8 ram and the same issue happens. Remove the F8 rom as its block garbage.  So it might be the "341-0020-00" / F8 ROM.

But I can't find a 3rd or first party one anywhere.

EDIT: ok looks like I found one here: https://jesperalsed.com/vintageapple/product/341-0020-00-2/

 

[bibilit]

https://www.ebay.de/itm/Apple-II-plus-and-europlus-ROM-replacement-board-replaces-D0-D8-E0-E8-F0-F8/283900202214?hash=item4219c54ce6:g:VY0AAOSwJ4peOVLS

i have bought this one, all in one Rom set, tested ok. 

 

[zezba9000]

https://www.ebay.de/itm/Apple-II-plus-and-europlus-ROM-replacement-board-replaces-D0-D8-E0-E8-F0-F8/283900202214?hash=item4219c54ce6:g:VY0AAOSwJ4peOVLS

i have bought this one, all in one Rom set, tested ok. 

O awesome, didn't know you could replace all ROMs with just the first slot.

I'll get that thing, tnx!

 

[zezba9000]

So bought a working board of the same model.

I went through and replace all chips one at a time till I found the bad one.

It wasn't a bad ROM FYI.

Is this a memory controller chip?  Picture shows good chip from other board but thats where the bad one was.

Funny thing is its the LAST chip I tried replacing... wow I have bad luck LOL.



It now works!!!  So I will buy a replacement chip and have two working boards.



Also do people put heatsinks on some of these chips that get a little hotter?

 

[zezba9000]

So I'm going to get these and see if they work.

https://www.amazon.com/gp/product/B08CCLXC15

 

[bibilit]

Logic chip... good work.

yes those chip can do a lot of strange things when bad.

 

[desiv]

Funny thing is its the LAST chip I tried replacing... wow I have bad luck LOL.

That is why, whenever I find a bad chip, I always replace 2 more, just so the one that fixed it wasn't the last one I tried.

...

Sorry..  Couldn't help it.. ;-)

Great find!!!!

Love reading these threads!

 

[zezba9000]

This is what my custom PSU looks like inside

 

[zezba9000]

Anyone know if China is the only place to buy these: https://www.ebay.com/itm/Floppy-Disc-Drive-Emulator-with-Disk-ii-interface-for-Apple-ii-iie-iic-Laser128/143672823651

Who designed these?  Where is the official store?

I need to get a SD disk drive card.

 

[zezba9000]

Also any suggestion for a JoyStick interface card?

Got frogger running from .wav / tape.  Everything working good so far.