| Attachment | Size |
|---|---|
 Apple ii Pictures | 3.84 MB |
Hey Guys,
I recently bought an Apple ii, it doesnt work, no beep, no video.
Ive already checked the voltages on the peripheral card slots, they were wrong.
It obviously had been repaired before with jumpers.(Photos included in the PDF)
I reseated every chip and checked the continuity on all jumpers, but it didnt work.
Thanks in advance for your help, Denis
[quote=deni85]
Hey Guys,
I recently bought an Apple ii, it doesnt work, no beep, no video.
Ive already checked the voltages on the peripheral card slots, they were wrong.
It obviously had been repaired before with jumpers.(Photos included in the PDF)
I reseated every chip and checked the continuity on all jumpers, but it didnt work.
Thanks in advance for your help, Denis
[/quote]
Denis,The Motherboard looks to be in very good physical condition.
Do all tests with no boards installed. Insure there is a full 48K of RAM. (as pictured)
I would start with the power supply, specifically at the connector which supplies the board.
Check for: +5, -5, +12, and -12VDC. Insure the voltages are correct before pulling chips.
Pending the failure of the supply, (or not) this might give us a direction on what you should do next.
Personally, I would un-do the modifications made to the Motherboard. Not sure what those do.
I would also try to match each 8-chip bank of memory. It's a good practice to keep each row of memory
the same. Not mandatory, but good practice.
If you're lucky, it might be the supply itself.
Note: I notice pin 6 of Slot 0 appears to have a damaged pin. Insure it is not touching another pin.
Hey thank you for helping me out, I really appreciate your help!
The power supply seems to be working, no issues there,
but some traces on the pcb seem to be damaged
One thing, it is a ][+ motherboard, not a ][. You can tell that by the ROM chips. All the sockets are full. A ][ will normally have two sockets empty (sometimes have other chips there like the Progammer's Aid #1 or 3rd party. But the part #s for the chips are those of the Applesoft ROMs and Autostart F8. So that means ][+.
Anyway, for repairing, I'd suggest starting here at this link:
https://mirrors.apple2.org.za/Apple%20II%20Documentation%20Project/Books/
There are a couple of books on repairing ][+. The Chilton's and Sam's books are good ones to check out.
Those traces look intentionally cut to me, when the mods were done.
I wonder what purpose those mods serve. Interesting.
If you want to reverse the mods, you can probably scrape the coating off the cut traces with a knife and bridge them back with solder.
That contraption hooked to the video output is probably an RF modulator for hooking the machine an old-skool TV set that only had an RF input, if you weren't aware.
Edit: If they chopped up that board just to bypass a burned out gate on that '245, instead of replacing the chip, I'll nerdrage. Lol.
The modification was done to replace the (hard to find) 8304 buffer IC with a more common 74LS245. Unfortunately they are not pin compatible and thus the need for the ugly motherboard modification.
Your first post says that the voltages on the slot connectors were WRONG but later you say that the power supply is OK. Is that correct?
[quote=jeffmazur]
The modification was done to replace the (hard to find) 8304 buffer IC with a more common 74LS245.
[/quote]
The same with the 74LS367 in the socket beside the 6502 where the 8T97 was. Press this chip right into the socket!
Regards,
Ralf
Thanks!
[quote=jeffmazur]
The modification was done to replace the (hard to find) 8304 buffer IC with a more common 74LS245. Unfortunately they are not pin compatible and thus the need for the ugly motherboard modification.
Your first post says that the voltages on the slot connectors were WRONG but later you say that the power supply is OK. Is that correct?
Yes, the voltages on the slot connectors were wrong, but the power supply is OK
Good grief. 8304 aren't THAT hard to find. And it would be better to make an adapter socket that fit into the board than hack the board itself!
[quote=softwarejanitor]
Good grief. 8304 aren't THAT hard to find. And it would be better to make an adapter socket that fit into the board than hack the board itself!
So do you assume that the board is not working because of the hack?
No, I wouldn't assume that. I would guess the board probably was working with the hack at some point. I was just saying that the hack was probably not necessary, and that it was done in a poor way. If the board were mine, I'd get a proper 8304 and reverse the hack. But I wouldn't assume that would fix the board. There may very well be something else wrong with it.
+1 on Softwarejanitor's reply. Undo the hack.
Find out why the connector voltages are wrong. There are no voltage regulators on the A][ motherboard so it could still be the supply failing. (under load)
FYI: 8304 here: https://www.ebay.com/itm/282106996683/
Also, what is that white blob at the front right of the motherboard near the 74LS74/74LS02/Q5?
Make sure that hasn't eaten into the traces also (if it was something corrosive).
[quote=deni85]
Yes, the voltages on the slot connectors were wrong, but the power supply is OK
[/quote]
What voltages were wrong on the connectors? How did you determine that the power supply is OK? If the voltages at the power connector are OK, then the only way the slot connectors could be wrong is due to burnt traces.
I suspected that pin 49 shorted pin 50, the voltages were wrong on all connectors. I checked the power supply using my multimeter.
[quote=Polymorph69]
Also, what is that white blob at the front right of the motherboard near the 74LS74/74LS02/Q5?
Make sure that hasn't eaten into the traces also (if it was something corrosive).
[/quote]
which one do you mean?
[quote=macnoyd]
+1 on Softwarejanitor's reply. Undo the hack.
Find out why the connector voltages are wrong. There are no voltage regulators on the A][ motherboard so it could still be the supply failing. (under load)
FYI: 8304 here: https://www.ebay.com/itm/282106996683/
[/quote]
ill definitely try that out, thank you!
If you tested the power supply with no load, that may not rule the power supply out as being faulty. A weak power supply may not hold voltages correctly under load, or once it heats up.
This white blob:
White Blob.jpg
Thanks
Where are the gerbers?
[quote=macnoyd]
Where are the gerbers?
[/quote]
There is a download link in the middle of that web site.
Looking at the photos it appears that there are incorrect chips is row B. I can see 74LS138, 74LS367 and 74LS283, these don't belong there and will cause the system not to boot. I would check each location and make sure the correct part is installed.