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Another Disk Drive Diagnosis

tezza said:
Ok, here are those high-resolution pictures. Images are about 2MB each.

Hope you can spot something significant in them.

Tez
Click to expand...

No, not really. I was looking for something like a 244 or 245 or 373 buffer that would take the hit if it was plugged in wrong.

I'm pretty sure I have one of those drives for the Apple ][/+ and I'll put it on my list of things to look at when I get the chance.

Being off my feet for two weeks has REALLY put me behind in work, so, just hang on to them.

It's quite possible that the drive I have suffered the same fate as your, so, I'll take the chips off the main board and run them through the chip tester to see if I can give you an idea of what goes when you do that.
 
buffer

buffer

Tezza, that 74LS367 buffer on the adapter board might be blown. I wonder if you could take the drive, sans adapter board, and hook it to a PC since it's got the standard 34-pin interface. (Okay, I didn't read the entire thread, so if someone already suggested it...)
patscc
 
patscc said:
Tezza, that 74LS367 buffer on the adapter board might be blown. I wonder if you could take the drive, sans adapter board, and hook it to a PC since it's got the standard 34-pin interface. (Okay, I didn't read the entire thread, so if someone already suggested it...)
patscc
Click to expand...

That's a reasonable line of thought. I don't think it's the apator board though. When only one drive was broken, I switched those boards and there was no difference. Only when I switched the main board did the broken drive spring to life (and the non-broken one stopped working). Then of course I plugged the working one in incorrectly and that was the end of that. :(

However, there is also another reason why testing the drive in another machine wouldn't be easy. If you have a look closely, you'll see a number of cut tracks, jumpered points and bridged connections all designed to fool the standard TEAC into thinking it's a Disk II drive for an Apple. The plug in adaptor board only does part of the job.

Tez
 
Druid6900 said:
It's quite possible that the drive I have suffered the same fate as your, so, I'll take the chips off the main board and run them through the chip tester to see if I can give you an idea of what goes when you do that.
Click to expand...

I'd certainly be interested to see what you get.

Tez
 
Success!

Success!

ok, with some help from Philip Avery's loaned oscilloscope, I made good progress on these two broken drives today.

I've found a Hex Inverter IC on the mainboard wasn't working in both drives (probably zapped). Pins 1 and 2 were set high when only pin one was suppose to be.

Anyway I replaced this IC on both drives. One drive now works perfectly. The other drive still dosn't work as it seems there was a second problem lurking in one of the units. I've islolated that problem to the clip-on planar (the backboard which plugs into the TEAC drive card), as swapping the planars carries the problem with it.

Comparing the Hex 3-state Buffer/Bus driver ICs (74LS367AP) on that planar during a disk boot shows a difference. That IC on the good board shows pins 1 to 7 all low (0 volts). The IC on the non-working board shows Pins 5 and 7 showing about 1 volts? According to the IC connection diagram detailing the logic in the IC, given the signals coming it, those pins should be low. They are showing 1v and yet the pins on the working board show 0. This means it could be faulty, yes?

I want to replace this IC, but I can only find 74LS367AN ICs among my spares, not a 74LS367AP. I suspect there is a significant difference. Is there? Or can I use an "N" instead of a "P".

I feel I am nearly there with these drives. With an oscilloscope, the experience I've built up over 18 months and a skim through "Electronics for Dummies" which I got hold of a few days ago, things are finally starting to gel was far as understanding how logic circuits work.

Tez
 
N vs P is *usually* just a difference in the package; I'd say go ahead and use it (but of course <fill in usual disclaimer, etc.>)
 
N suffix usually means plastic dual in link package (P-DIP) package, but some manufacturers use P. You should see that different manufacturer logos are on the parts you are looking at. The parts should be completely interchangable. One tip about removing bad soldered in chips. Cut the leads from the package. Then you can remove one leg at a time, which is much easier than trying to remove the whole package at once. If you think that there is any chance that you'll have to change the chip in the future, put a socket in there, if it will fit.

Regards,
Mike WIllegal
 
tezza said:
Comparing the Hex 3-state Buffer/Bus driver ICs (74LS367AP) on that planar during a disk boot shows a difference. That IC on the good board shows pins 1 to 7 all low (0 volts). The IC on the non-working board shows Pins 5 and 7 showing about 1 volts? According to the IC connection diagram detailing the logic in the IC, given the signals coming it, those pins should be low. They are showing 1v and yet the pins on the working board show 0. This means it could be faulty, yes?
Click to expand...
1V should be low enough to register as a logical 0, but if the fact that there's a difference could itself indicate a problem (e.g. that the output is stuck at 1V and doesn't go high when it should). If you have a replacement, it's definitely worth a try.

tezza said:
I feel I am nearly there with these drives. With an oscilloscope, the experience I've built up over 18 months and a skim through "Electronics for Dummies" which I got hold of a few days ago, things are finally starting to gel was far as understanding how logic circuits work.
Click to expand...
Yep, sure beats swapping ICs and hoping for the best, doesn't it? ;-) Nice find on the inverter - you're doing a great job.
 
You may want to measure pin 5 to pin 7 with an ohmmeter, they may be shorted. Probably not but since they are both at 1V it is worth a shot.

Mike
 
Thanks for those replies. Yes, I always clip the legs off these small ICs first and then extract those and clean the holes. I'm not sure if I can squeeze a socket in this time as the planar is squeezed up against the back. There's not much room!

>1V should be low enough to register as a logical 0, but if the fact that
>there's a difference could itself indicate a problem (e.g. that the output is
>stuck at 1V and doesn't go high when it should). If you have a replacement,
>it's definitely worth a try.

Yea...I'm not convinced it IS the 74LS367AP. I piggybacked one of these replacement ICs on the old lugs before I removed them and that also showed 1v on those pins? However, it seems to be the only IC of the three on that board that shows a difference compared to the other one? The only other thing on there are a couple of capacitors and a few resistors. Swapping the cables doesn't make a difference so it certainly is something on the board.

Anyway, as I've started IC replacement I need to complete it. I found a second spare IC, so I'll use that. I haven't measured it over the old lugs as I removed them before I discovered I had a second replacement of the same type.

>Yep, sure beats swapping ICs and hoping for the best, doesn't it? ;-)

Indeed. I found the book helped to integrate a lot of the scattered bits of knowledged I had already picked up and suddeny lots of things started to crytallise. A sort of "oh I get it!" kind of moment. Having the scope helped cement it.

Tez
 
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Can you find what pins 5 & 7 are connected to? It's quite possible that something on those lines is trying to pull up the '367s outputs.

Conversely, what are the inputs (4 & 6) connected to? You *may* be able to pull them up with a resistor and see if the outputs follow.

Sounds like you're getting there for sure; we're all enjoying watching you become a real techie!
 
Tez,

I have to apologize for not getting back to this thread. I DID look at the Teac drive I had that was modified for an Apple ][, but, it was a different model and totally different board, so, it wouldn't have helped much.

I also found another 4 "modified for Apple" drives which I haven't had time to test and got two more 3rd party 1/2 height drives in the last pile of XT/AT stuff I got.
 
No worries Druid, I've cracked it.

The problem with the back planar on the second drive was indeed the 74LS367A. I inserted the replacement and it's all good now. As usual, I've written up the repair in my blog.

Thanks guys for all your help.

>Sounds like you're getting there for sure; we're all enjoying watching you
>become a real techie!

LOL! I've got some way to go before I can graduate as one of those valued vintage venerables. I'm further down the techie path than I ever thought I'd be though.

I'm now tempted to take another look at that heat-related faulty Apple clone, working from the CPU out while I've still got the scope!
 
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Well, I did move my scope out where I could use it. Haven't actually turned it on and hooked it up yet. Like I said, I went from only Volt Ohm Meters to 2 scopes (and bunches of VOMs) here recently. Only took me about 40 years to finally get a scope. My first project will be to look at the horiz sync signal on one of my Tandys. Fairly sure I will see NOTHING in the way of a signal as the monitor doesn't display the text in a readable form.
 
Cracked it!

Cracked it!

tezza said:
No worries Druid, I've cracked it.

The problem with the back planar on the second drive was indeed the 74LS367A. I inserted the replacement and it's all good now. As usual, I've written up the repair in my blog.

Thanks guys for all your help.
Click to expand...

Geeze Tezza, at this rate I'd do well to leave my scope with you, and send all my faulty stuff over for you to fix! :-D

Great progress.

Philip
 
Lol! Thanks.

Yea, it's starting to all make sense now.

Next challenge is that Apple II+ clone. Then there are the last 2 broken Apple drives to check. These ones never worked. I did look at them initially, but they are worth a revisit.

The there is the grumpy old Osborne. Works, but it has "issues" (dicy PSU I think. If I can find the capacitor resposible, I'll be happy).

Then there is that Mac SE, which has a video problem. Then a couple of PS/2, neither of which are working for various reasons.

When did you say you wanted this scope back? :)

Tez
 
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