Another Disk Drive Diagnosis

[tezza]

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 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.

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?

Photo 2: Index hole sensor

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?).

Photo 4: Timing software on a working drive.

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.

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]

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.

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, 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?).

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 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.

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]

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]

light

light

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]

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]

>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]

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]

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]

The odd looking drive

The odd looking drive

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

 

[tezza]

>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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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