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tezza
March 1st, 2009, 12:32 AM
Another disk drive adventure (and yes I have read the sticky).

I think I know what happened to these drives but I’d like to know exactly what’s wrong, even if it might be hard to fix. Someone out there might know.

The Apple haul (http://classic-computers.org.nz/blog/2008-9-04-a-load-of-old-apples.htm)left me with a total of six Disk II-type drives. Of the drives, three worked, one I got working (speed alignment), and the other two were broken. Two of the four working drives were nice TEAC models.

One of these TEAC drives stopped working a while ago. The disk would spin but wouldn’t recognise, read or write to any disk. Yesterday I had a close look at this drive with aim of finding out what’s wrong.

Having a working drive, I thought I’d try to isolate the problem by swapping the cables and circuit boards one at a time between the two drives. Doing this revealed the problem was most likely on the main circuit board, as a board swap fixed the broken drive.


http://classic-computers.org.nz/blog/images/2009-03-01-teac-apple-drive-bottom.jpg

Photo 1: Drive from bottom showing main (green) circuitboard

However, as I was doing some more testing, the second drive suddenly failed and exhibited exactly the same symptom as the first? I found that not only do BOTH drives now fail to recognize disks but it you use them to boot good disks, they usually corrupt them!

What do I think is wrong? My theory regarding both drives is that the disk index timing light is no longer working. I deduced this because…

First reason. When I’ve pulled away the sensor board (but left all its cords attached) I can’t see any light at all through the index hold when the disk is spinning, or when a drive tries to boot WITHOUT a disk inserted. The disk index timing bulb should be lit, yes?


http://classic-computers.org.nz/blog/images/2009-03-01-teac-apple-drive-top-index-hole-sensor.jpg

Photo 2: Index hole sensor

http://classic-computers.org.nz/blog/images/2009-03-01-teac-apple-drive-top-index-hole-sensor-board-removed.jpg

Photo 3: Index hole sensor circuit board removed showing timing light (upper right)

Second reason. A piece of software I used for tuning disk timing, doesn’t work at all for the two faulty drives. They spin, but there is no timing registered (see photos). On a good drive, timing is registered just fine. I figure the disk index timing light is used to determine speed (am I correct in assuming this?).


http://classic-computers.org.nz/blog/images/2009-03-01-speed-test-good-drive.jpg

Photo 4: Timing software on a working drive.

http://classic-computers.org.nz/blog/images/2009-03-01-speed-test-non-working-drive.jpg

Photo 5: Timing software on a non-working drive (no speed indicator appears)

How has this happened and what exactly is wrong? I don’t know exactly what’s wrong I have a suspicion as to what might have caused it. At one stage during the testing yesterday I accidently plugged in the drive incorrectly. It’s really easy to do this with the Apple II disk controller, putting the plug in the wrong layer of pins. I should have listed this in the list of design flaws.


http://classic-computers.org.nz/blog/images/2009-03-01-apple-disk-controller-plug-mistake.jpg

Photo 6: Opps. How NOT to plug in a Disk II to a Disk II controller card

Now I’m not sure if this caused the second drive to fail or not as I was juggling a few things at the time. But it was soon after that I noticed it had gone the same way as the first one! And, when I think of it, the reason that FIRST drive may have stopped working is that I’d done the same thing a few months ago. I remember doing it once before (I know, slow learner) and although I didn’t directly connect the dots at the time, it could have been that mistake that zapped the first TEAC.

So, my theory. Through incorrect plugging on both drives, I’ve zapped something on the circuit board which controls the disk index timing light. With the light not functioning, the drive doesn’t recognise a disk is present.

Do these deductions seem reasonable and if so, does anyone know EXACTLY which IC or component might be damaged?

Tez

david__schmidt
March 1st, 2009, 04:57 AM
I think I know what happened to these drives but Iíd like to know exactly whatís wrong, even if it might be hard to fix.
After reading this through, I think so too. ;-)


However, as I was doing some more testing, the second drive suddenly failed and exhibited exactly the same symptom as the first? I found that not only do BOTH drives now fail to recognize disks but it you use them to boot good disks, they usually corrupt them!
Yep. Been there, done that myself.


What do I think is wrong? My theory regarding both drives is that the disk index timing light is no longer working.
Did you ever see an "index timing light" actually working? I ask because Apple never used them. Woz's design doesn't use the disk index hole; it is completely and utterly ignored. That's the difference between "soft sectors" and "hard sectors."


The disk index timing bulb should be lit, yes?
Unless the disk electronics does it on its own, maybe so... even so, I doubt a timing "light" would use visible light anyway. More likely UV.


Second reason. A piece of software I used for tuning disk timing, doesnít work at all for the two faulty drives. They spin, but there is no timing registered (see photos). On a good drive, timing is registered just fine. I figure the disk index timing light is used to determine speed (am I correct in assuming this?).
No. Disk timing is determined by the software writing and reading bits to the disk.


How has this happened and what exactly is wrong? I donít know exactly whatís wrong I have a suspicion as to what might have caused it. At one stage during the testing yesterday I accidently plugged in the drive incorrectly.
Bingo! That's it. If you are off by one row (horizontally or vertically) you will have released magic smoke. I can point you to particular chips to replace on the original Disk ]['s analog board, but I have no idea with those fancy SMD chips on your TEAC drives.


Photo 6: Opps. How NOT to plug in a Disk II to a Disk II controller card
Ummm, indeed. That's what happened. Drives will spin, but they will write garbage to your floppies now.


Do these deductions seem reasonable and if so, does anyone know EXACTLY which IC or component might be damaged?
If this were a Disk ][ drive, I'd point you to the 74LS125 on the analog board. I have a sleeve of them for that exact reason.

chuckcmagee
March 1st, 2009, 06:21 AM
All the soft sectored floppy drives that I know of use a SINGLE index hole as a signal for the start of the track. I have never heard of a drive that used no index hole whatsoever.

Of course, saying that I am weak on Apple knowledge would be generous. I did upgrade a IIe to a IIe enhanced, that count, huh huh?

patscc
March 1st, 2009, 06:50 AM
david__schmidt said...even so, I doubt a timing "light" would use visible light anyway. More likely UV
Usually IR is the light of choice. Assuming it's a IR diode & photo diode/transistor on the other end, are there any voltages across the parts ?
I couldn't find the original part numbers of the drives in the post, does anyone have them ?
Of course, if someone has a link to the schematics...

Are you getting anything on pin 16 (data read)


chuckcmagee said...I have never heard of a drive that used no index hole whatsoever.
C64's ignored it. I wanna say most GCR-format's ignored it, but I won't swear to it.
patscc

david__schmidt
March 1st, 2009, 07:14 AM
Usually IR is the light of choice.
Right, of course. Wrong end of the spectrum...


All the soft sectored floppy drives that I know of use a SINGLE index hole as a signal for the start of the track. I have never heard of a drive that used no index hole whatsoever.
And now you have. :-)

tezza
March 1st, 2009, 08:57 AM
>Did you ever see an "index timing light" actually working? I ask because
>Apple never used them. Woz's design doesn't use the disk index hole; it is
>completely and utterly ignored. That's the difference between "soft sectors"
>and "hard sectors."

You know, I remember reading something like this on the web ages go. Before posting my message I googled trying the find that infomation and couldn't find it. I did find a lot about hard vrs soft sector that implied nearly all 5.25 inch diskettes used soft-sector with a single index hole (as opposed to hard-sector with many holes). Nowhere could I find info that explicitly stated the Apple II drives didn't use the index hole! I started to think I'd imagined it and posted the above anyway, knowing someone would correct me if I was wrong.

I'm sure you are right. This morning I peeped inside one of my other Apple II drives and found no index sensor whatsoever. It just wasn't there! Obviously it wasn't needed.

How DO Apple drives keep track of their sector beginnings then?

Anyway, thanks for the comments so far. Certainly something on the board is cooked from the mis-plugging. There was no smoke and nothing looks damaged. All the ICs are non-socketed but I'm up to de-soldering and replacing if only I knew exactly which one was a goner.

Tez

Terry Yager
March 1st, 2009, 09:06 AM
All the soft sectored floppy drives that I know of use a SINGLE index hole as a signal for the start of the track. I have never heard of a drive that used no index hole whatsoever.

Of course, saying that I am weak on Apple knowledge would be generous. I did upgrade a IIe to a IIe enhanced, that count, huh huh?

Apples ain't exactly my long suit either, but they don't use the hole, and neither do C= drives. That is why people are able to easily flip their SS disks over and use the other side just by notching the edge to make them writable. I want to add Atari 8-bit machines to the list too, but my memory is fuzzy about that at the moment.

--T

Dwight Elvey
March 1st, 2009, 09:20 AM
Hi
The begining of sectors are marked by special sequences of data
on the Apple or Clock and data on normal soft sectored.
While many newer PC drives need to see the index to go
ready, I've covered the index hole on many disk used in
older drives without any problems of reading or writing. Formatting
always used the index hole on PCs to my knowledge through.
Dwight

dorkbert
March 1st, 2009, 09:39 AM
That drive looked more like an MFM drive than an Apple one. First time I've seen one like it...

tezza
March 1st, 2009, 09:53 AM
>The begining of sectors are marked by special sequences of data
>on the Apple or Clock and data on normal soft sectored.

Ah, I see. Thanks Dwight.


That drive looked more like an MFM drive than an Apple one. First time I've seen one like it...

Indeed. It's a generic MFM drive modified for use in Apples. Notice the backplane on the right which plugs into the standard connectors. That plus a few strategic re-wirings and track cuttings/connections on the back of the main board turns it into an apple drive.

It seems these were not that rare. I own a full-height TEAC drive of a smiliar nature, which I use for my System 80. In that case I bought it as a never-been-used Apple drive and had to "de-modify" it back to it's original state for use. The seller provided the de-mod instructions which is why I risked buying it for the S80. It was easy to restore and works on the System 80 just fine.

Tez

MikeS
March 1st, 2009, 10:23 AM
Looks like others answered the questions while I was typing mine, so excuse the repetititon:
---

Yeah, it ain't a problem with the index sensor; as mentioned elsewhere Apple and Commodore drives just looked for special preamble sequences on disk to mark the beginning of a sector and did not use or need any index holes in the disk. That is why you could 'flip' diskettes to use the other side; if the drive did look for index holes then the hole on the disk would be in the wrong place and this trick obviously wouldn't work.

But this has nothing to do directly with the issue of hard- vs. soft-sectored diskettes; this refers to whether the controller is using hardware (and software of course) or *only* software to locate the beginning of a *sector*; most soft-sector controllers (other than Apple & CBM) still need an index hole and hardware to find the beginning of a *track* (cylinder). Of course since Apple & CBM drives don't have *any* index sensing hardware, they are by definition soft-sector systems and can use either hard-or soft-sector diskettes, even upside-down if you disable the write-protect sensor or add a WP notch on the disk.

Soft- and hard-sector only refers to the disk controller and the disks (one index hole vs. multiple holes, usually 11 or 17); unless the disk *drive* sees multiple index holes as a speed error, disk drives don't care. Of course Apple & CBM drives are incompatible with 'normal' drives for other reasons.

And besides, even if the drive did have index sensing hardware it would probably use IR so you wouldn't see it directly anyway without using a video camera sensitive to IR.

Good luck with the repair, Tez; those drives are much easier to damage than 'normal' drives because they carry +5 and +12V on the interface cable; still, the damage might just be one of the output drivers so try tracing the signals back from the interface to the drivers.

tezza
March 1st, 2009, 10:45 AM
Good luck with the repair, Tez; those drives are much easier to damage than 'normal' drives because they carry +5 and +12V on the interface cable; still, the damage might just be one of the output drivers so try tracing the signals back from the interface to the drivers.

Thanks. It looks like I'm not going to be able to hold out much longer from getting that oscilloscope, does it. :)

Tez

MikeS
March 1st, 2009, 11:48 AM
Thanks. It looks like I'm not going to be able to hold out much longer from getting that oscilloscope, does it. :)

Tez
... or you could buy our pal Philip another case of beer...

If they are a modified 'standard' TEAC model, you might find a relevant or at least useful schematic in one of the manuals on the TEAC web site.

http://www.teac.com/DSPD/support/floppy_drives/floppy_drives.htm

Good luck!

tezza
March 3rd, 2009, 01:14 AM
Thanks for that Link Mike. Unfortunately it doesn't have those particular TEAC drives. They are model FD-55E-02-U units. If anyone has any manuals/schematics on these I'd love to hear from you.

The good news is that Philip Avery is going to load me his Oscilliscope for a while to do some of this diagnostic work. The bad news is I'm going to need a crash course on "Digital Electronics for Dummies" before I can use it. (:

Tez

chuckcmagee
March 3rd, 2009, 02:55 AM
Thanks for that Link Mike. Unfortunately it doesn't have those particular TEAC drives. They are model FD-55E-02-U units. If anyone has any manuals/schematics on these I'd love to hear from you.

The good news is that Philip Avery is going to load me his Oscilliscope for a while to do some of this diagnostic work. The bad news is I'm going to need a crash course on "Digital Electronics for Dummies" before I can use it. (:

Tez

Almost my entire adult life, I couldn't really afford an oscilliscope. Then, when prices got more reasonable, I had forgotten to even look at them anymore. So, recently I finally finally purchased one. Of course, 2 days later a super deal for a much better one shows up on ebay. Now I have 2. I will be using the fancier one some time soon to figure out my Tandy TL/2 video out problem. Looks like the horiz sync is either totally gone or wacked out. I haven't put the scope on it yet to see << real soon now >> as everyone likes to say.

IF you are poor and really disparate, one can use those old analog VOM to check signals. TTL goes from +5 to around 0 volts so if you have a train of binary ones followed by zeroes (alternating), the analog guy should give you a reading around 1/2 of +5 or 2.5 volts. The " a/c averaging " on the old deflection needle actually comes in useful at times. Of course, if the signal was around 2 hz then the needle would swing wildly back and forth.

As we all know, a scope is much easier to get useful info out of.

MikeS
March 3rd, 2009, 08:28 AM
Hmm, like too many places TEAC seems to have reorganized their web site and the useful (for us) stuff is impossible/hard to find.

Try:
http://www.bitsavers.org/pdf/teac/

Even if those manuals don't match your drive exactly, they're still a great read about floppy drive electronics.

BTW guys, that's oscillOscope...

Good luck! And have a beer with Philip on my behalf; maybe some day we can all share a few in person.

Druid6900
March 3rd, 2009, 12:34 PM
Tezza,

Can you get a high res picture of those chips around the connector on the main logic board?

You probably blew a buffering chip plugging it in wrong. Does a know good drive work on the controller? Check that, because, sometimes Prom5 or Prom6 on the controller is the victim (depending on what connector you mis-plugged into).

tezza
March 3rd, 2009, 04:01 PM
Hmm, like too many places TEAC seems to have reorganized their web site and the useful (for us) stuff is impossible/hard to find.

Try:
http://www.bitsavers.org/pdf/teac/

Even if those manuals don't match your drive exactly, they're still a great read about floppy drive electronics.

BTW guys, that's oscillOscope...

Good luck! And have a beer with Philip on my behalf; maybe some day we can all share a few in person.

Thanks Mike,

Those resources look very useful.

Tez

tezza
March 3rd, 2009, 04:26 PM
Tezza,

Can you get a high res picture of those chips around the connector on the main logic board?

You probably blew a buffering chip plugging it in wrong. Does a know good drive work on the controller? Check that, because, sometimes Prom5 or Prom6 on the controller is the victim (depending on what connector you mis-plugged into).

I will take some high quality photos and attach a link.

The controller is fine. Other drives are A-OK. The problem I'm sure lies on the mainboard. Before I blew the second drive a board swap revealed this.

If only I know WHAT needs replacing. But I guess that's the thing with electronics. The diagnosis is 99% of the work. Once that's done, actually fixing it tends to be easy.

Tez

tezza
March 3rd, 2009, 04:41 PM
Tezza,

Can you get a high res picture of those chips around the connector on the main logic board?

You probably blew a buffering chip plugging it in wrong. Does a know good drive work on the controller? Check that, because, sometimes Prom5 or Prom6 on the controller is the victim (depending on what connector you mis-plugged into).

I will take some high quality photos and attach a link.

The controller is fine. Other drives are A-OK. The problem I'm sure lies on the mainboard. Before I blew the second drive a board swap revealed this.

If only I know WHAT needs replacing. But I guess that's the thing with electronics. The diagnosis is 99% of the work. Once that's done, actually fixing it tends to be easy.

Tez

tezza
March 4th, 2009, 12:14 AM
Ok, here are those high-resolution pictures. Images are about 2MB each.

* Top of mainboard (http://classic-computers.org.nz/blog/images/2009-03-04-teac-apple-drive-mainboard-top.JPG)
* Bottom of mainboard (http://classic-computers.org.nz/blog/images/2009-03-04-teac-apple-drive-mainboard-bottom.JPG)
* Top of back planar (http://classic-computers.org.nz/blog/images/2009-03-04-teac-apple-drive-back-planar-top.JPG)
* Bottom of back planar (http://classic-computers.org.nz/blog/images/2009-03-04-teac-apple-drive-back-planar-bottom.JPG.JPG)

Hope you can spot something significant in them.

Tez

Druid6900
March 4th, 2009, 07:36 PM
Ok, here are those high-resolution pictures. Images are about 2MB each.

Hope you can spot something significant in them.

Tez

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.

patscc
March 4th, 2009, 07:50 PM
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

tezza
March 4th, 2009, 09:43 PM
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

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

tezza
March 4th, 2009, 09:44 PM
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.

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

Tez

tezza
March 22nd, 2009, 12:22 AM
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

MikeS
March 22nd, 2009, 12:59 AM
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.>)

mwillegal
March 22nd, 2009, 04:49 AM
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

cosam
March 22nd, 2009, 04:50 AM
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?
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.


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.
Yep, sure beats swapping ICs and hoping for the best, doesn't it? ;-) Nice find on the inverter - you're doing a great job.

mfortuna
March 22nd, 2009, 08:53 AM
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

tezza
March 22nd, 2009, 10:08 AM
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

MikeS
March 22nd, 2009, 03:36 PM
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!

Druid6900
March 22nd, 2009, 07:23 PM
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.

tezza
March 23rd, 2009, 02:54 AM
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 (http://classic-computers.org.nz/blog/2009-03-23-teac-apple-disk-drive-repairs.htm).

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!

chuckcmagee
March 23rd, 2009, 09:11 AM
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.

pavery
March 24th, 2009, 01:02 PM
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 (http://classic-computers.org.nz/blog/2009-03-23-teac-apple-disk-drive-repairs.htm).

Thanks guys for all your help.

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

tezza
March 25th, 2009, 12:25 AM
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