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Apple ii europlus

DRAM, like most TTL compatible devices has a small pull up current ( around 5 to 10 milliamps ). This means you can trace it down by shorting the DOUT or Q to ground. You should be able to trace it down that way, running your RAM test.
Dwight
 
Dwight Elvey said:
DRAM, like most TTL compatible devices has a small pull up current ( around 5 to 10 milliamps ). This means you can trace it down by shorting the DOUT or Q to ground. You should be able to trace it down that way, running your RAM test.
Dwight
Click to expand...

cheers

actually managed to locate the faulty chip with a bit if basic.

need to diagnose the problem with the slots, cant get a working interface and drive to boot. The Apple is recognising that its there, the drive spins and steps to track 0, then nothing.
 
KC9UDX said:
Bad or dirty head, or misalignment or speed problem.
Click to expand...

Its a working interface and drive and prodos floppy, checked before and after in my main machine and gives no problems (this unit is just a solitary board running on an ATX PSU and an arduino-PS/2 keyboard interface)

Seems like the system can talk to the interface but is not getting anything back, does the interface do a DMA transfer ?

Have booted the machine with galaxians from an audio file, so the machine is all but working, just not with the disk interface. Might be a PCB/Mechanical issue, but it all looks ok.

Probably time to break out the logic analyser if I can find it.

Crying shame, found our Schlumberger S635 in circuit tester I used for Z80 board level diagnostics years ago in a skip at work last week, PC needed to operate it, long gone. Also some 8086/80286 ICE machines were scrapped too.
Why do we throw away history :(
 
usual chips going wrong are the 74LS125 on the Disk II Analog board (seen this a hundred times) usually the drive spins but does nothing and the ULN 2003 (the stepping motor won't move)

Those can go bad when the cable is not connected properly to the Apple II
 
bibilit said:
usual chips going wrong are the 74LS125 on the Disk II Analog board (seen this a hundred times) usually the drive spins but does nothing and the ULN 2003 (the stepping motor won't move)

Those can go bad when the cable is not connected properly to the Apple II
Click to expand...

However, the Disk and the interface (and the floppy too) have all been tested on another Apple II so they are working fine.

Just working through the drawings to try and work out where the fault could be

So far it looks like F12 produces I/O strobe but that also selects the ROM's, so unlikley. H12 produces I/O select and H2 produces DEV select only so will test them next. Could be B6 & B7 not going high impedance on when requested on a interface write cycle but that should also affect a RAM write too.

Wish I had a complete, full system drawing, rather than the bit by bit drawings from the reference and Gayler's guide
 
Interesting developments



Voltages all appear to be correct and dont dip or otherwise during device access.



DEVSEL and I/OSEL are active in the slot, all address and data lines appear active.

I then put the card in slot 1 and did PR#1 and prodos booted (well, it came up with a screen wanting 64k, so near enough), dos 3.3 boots (with a few complaints) and once running i can catalog the disk.

So, noisy bus i'm thinking now. Does RA01 terminate the I/O interface bus ?

The waveforms are messy, but no worse than most signals on machines of this vintage, but its hard to tell. Im probably getting reflections and that will be hard to see.


Two steps forward at least.
 
Ok, I'm confused.


With it almost working, I though I would try another Disk II interface I had about that didnt work in my working machine, and it worked in slot 6, boots fine, Apex diagnotics running on it with no errors.
Put the original interface card back in the main machine, works fine in there

So I seem to have some incompatability between two machines and their Disk interface cards. One motherboard is a Europlus and the other is a US ][+. I dont think there is a significant difference except a crystal and a couple of pads made/broke ?

Both interface cards came from the US, though they do look very different. One is much lighter and omits all the gold fingers that are not used, while the other is a much darker green and has every connector finger present, though I dont think they are essentially any different. They both appear to have 16 sector PROMS (though one is missing the yellow p5/p6 stickers) as they both read the same disks without error.

Well, I should not complain too much as they are working, but I would like to know why.



Also posted Applefritter
 
Back to this board after getting the TRS80 and Microvax up and running.

Can now get it to boot fine (never found out why one working disk interface didn't like this machine) and I have been using it to diagnose a Disk II i got for £5

New problem is my Vergecourt RAMEX 16 memory card has gone flakey. Tends to work when turned on, but fails after about an hour of use.

One chip, one of the multiplexors 74LE153N has a broken pin. Was really floppy when removed and snapped when touched. This could easily be the fault (I hope) and a spare on order.

The second, is a 74121N, a monostable multivibrator.

Now, this one tests as ERR in my chip tester, and I have a new one on order,

but I wonder do these ebay chip testers successfully test this chip (given a possible need for external RC network) ?

and, what is this potentiometer for ? http://www.quartdepomme.fr/quartdep...cards_(Updated)/Pages/Memory_RAM_cards.html#1

Cant find a circuit diagram. It might be the external timing circuit, but that would be odd to leave to the vagaries of a crappy carbon track, though I suppose if the manufactures had a problem with timing and had to trim each one, it might have been required.
 
Gary C said:
Back to this board after getting the TRS80 and Microvax up and running.

Can now get it to boot fine (never found out why one working disk interface didn't like this machine) and I have been using it to diagnose a Disk II i got for £5

New problem is my Vergecourt RAMEX 16 memory card has gone flakey. Tends to work when turned on, but fails after about an hour of use.

One chip, one of the multiplexors 74LE153N has a broken pin. Was really floppy when removed and snapped when touched. This could easily be the fault (I hope) and a spare on order.

The second, is a 74121N, a monostable multivibrator.

Now, this one tests as ERR in my chip tester, and I have a new one on order,

but I wonder do these ebay chip testers successfully test this chip (given a possible need for external RC network) ?

and, what is this potentiometer for ? http://www.quartdepomme.fr/quartdep...cards_(Updated)/Pages/Memory_RAM_cards.html#1

Cant find a circuit diagram. It might be the external timing circuit, but that would be odd to leave to the vagaries of a crappy carbon track, though I suppose if the manufactures had a problem with timing and had to trim each one, it might have been required.
Click to expand...

I don't trouble shoot with a chip tester so couldn't tell you how they handle oneshots. Your memory problem is likely a thermal issue. Use some cold spray on them one at a time to find the problem part.
Dwight
 
Cheers.

I will replace the chips tomorrow. Hopefully the cracked leg was causing the problem, but as it was strong enough not to get left in the socket, I would have though it was intact enough to work so your probably right about it being a dram.
 
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