issue with DISK II controller

[4ez...@gmail.com]

Hi all. I was hoping to pick your brains on an issue I'm having with a Disk II interface card #650-X104. Basically when it's connected to a DISK II drive the "IN USE" led is always on and so is the drive motor. Otherwise loading software from the floppy seems just fine.

The drive the card is connected to acts this way no matter whether it's in slot 6,5,4 etc. If another card and drive are setup as the bootup drive (i.e. slot 6) and this is another slot (i.e. slot 5) with another drive it's still doing it.

The DISK II drive it's connected to is a known good (which works fine
on another controller card of the same) and the cable is correctly attached to the pins.

Where should I be looking here to fix this? ....
Electrolytic Capacitor
PROM P5
PROM P6
or one of the 74LS chips?

My guess would be it's one of the 74LS chips, but which one and why? Sure, I could replace them all without great cost but wouldn't learn much that way.

Also, if anyone could tell me a modern equivalent for the PROM chips that are on the DISK II controller that would be great. Thanks!

[James Davis]

Apple Disk II Schematic:

ftp://public.asimov.net/pub/apple_II/documentation/hardware/schematics/APPLE_DiskII_SCH.pdf

Look for "MOTOR ON" in the lower right quadrant.

[James Davis]

You can find chips here:

http://www.reactivemicro.com/index.php?cPath=1_31

[4ez...@gmail.com]

Thanks, it would seem the 74LS132 is the one I'm going to try replacement for. I know Jameco has those. The other link for the PROM chips doesn't seem to be a match and all the ones listed are not in stock.

[James Davis]

Sorry about the chips link. It was suggested in another post.

You should check MOTOR CONTROL resistor R5 and capacitor C2 (bottom, center of schematic), first/also.

[waynej...@gmail.com]

If you have another working card that you've tested the drive on then why not swap chips until you've either found the bad chip or eliminated chips as the problem>

[4ez...@gmail.com]

On Sunday, May 21, 2017 at 9:22:45 AM UTC-7, waynej...@gmail.com wrote:
> If you have another working card that you've tested the drive on then why not swap chips until you've either found the bad chip or eliminated chips as the problem>

The thought occurred more than a few times and the temptation is there. Afterall, it's only eight chips on the controller card.

What has kept me from doing it so far is I'm trying to learn how someone else (perhaps even with more experience) might troubleshoot this, and why they went the route they did. Just as James Davis showed me a link to a schematic I didn't know was in Asimov (I've been there before), I'm going to learn stuff doing it 'the hard way'.

Ultimately, I might do a chip swap. But touching a working controller card is not where I would begin. I'm thinking it's better to just get them new from a trusted supplier.

[roger....@gmail.com]

The Disk II drive enable signal is normally high. When it goes low the drive motor and In Use LED should come on.

Check the voltage on the drive enable for both Drive 1 and Drive 2 on the controller card and take it from there.

[James Davis]

Have you checked in the Apple II troubleshooting Technical Notes or in any Apple II Repair books for Disk II controller card data?

[4ez...@gmail.com]

On Sunday, May 21, 2017 at 1:11:12 PM UTC-7, James Davis wrote:
> Have you checked in the Apple II troubleshooting Technical Notes or in any Apple II Repair books for Disk II controller card data?

Not sure if I have. I've been looking all over in various places:

this newsgroup
Apple Fritter
appleii-box.de
Asimov

Sometimes it's hard to zero in on certain things even when they are right there in front of you.

Mostly when it's close to what I'm saying is happening it's caused by when someone didn't correctly attach the Disk II ribbon cable.

Funny thing is when I bought this controller (with the issue) recently off eBay it looks to be in great physical shape and no signs of apparent damage.

If I had the skills, knowledge and tools I could check the resistor and voltage, etc. but I don't. I have checked capacitors out of circuit, but that's about it.

I'll give it another week or two of research before I throw in the towel and do a chip swap.

[James Davis]

Don't know where you are, but do you have a local Apple Dealer? If so, they may be able to repair it for you. If not, we have one here, Computer Center of Hayward <www.cooh.com>, that has Apple II Service: (510) 733-1846; Showroom: (510) 733-1843; Fax: (510) 733-1855.

[James Davis]

On Sunday, May 21, 2017 at 6:50:05 PM UTC-7, James Davis wrote:
> Don't know where you are, but do you have a local Apple Dealer? If so, they may be able to repair it for you. If not, we have one here, Computer Center of Hayward <www.cooh.com>, that has Apple II Service: (510) 733-1846; Showroom: (510) 733-1843; Fax: (510) 733-1855.

Sorry for the typo. It is <www.ccoh.com>.

[4ez...@gmail.com]

Thanks, James. I'm not in that area. But I would think for the cost it would be cheaper to buy another card from eBay. Otherwise I may just get the chips from Jameco and hope I don't have to also replace the PROMs.

[Michael J. Mahon]

It is *extremely* unlikely that the PROMs are bad, and the other chips are
readily available and inexpensive.

--
-michael - NadaNet 3.1 and AppleCrate II: http://michaeljmahon.com

[James Davis]

Just came across this card for sale at the Apple II Store:

https://www.ebluejay.com/ads/item/5878641

[4ez...@gmail.com]

Thanks for the tip! Neat projects you did!

[4ez...@gmail.com]

On Monday, May 22, 2017 at 5:25:58 PM UTC-7, James Davis wrote:
> Just came across this card for sale at the Apple II Store:
>
> https://www.ebluejay.com/ads/item/5878641

Thanks, got plenty of those but it's not for the DISK II drive and I'm actually not looking for another controller.

I will probably be getting the logic chips from Jameco. Even though Michael Mahon states it's extrememly unlikely to be the PROMs, and I believe him, I am still interested to know of a modern replacement (if there is one) for the PROM's. Unfortunately Mouser, Jameco, and Digi-Key can't help me.

I told them I was looking for a DIP-20 and
some models from the era I'm told which work for this are:

6309 Shottky (256X8)
TBP28L22N Texas Instruments (256X8)

Somewhere in the future when I have the knowledge, I know I can make my own compatible interface card. The design doesn't look that complicated, but for me it is a little beyond my reach. Just a little. :)

[gid...@sasktel.net]

I kinda had a similar problem where the lights were on but nobody was home. One thing you could try before delving into replacing chips is, take an erase and erase the crud off the contacts of the card. It could be just enough to prevent one or two pins from making contact.

Rob

[Michael J. Mahon]

You may be surprised to hear that the Disk ][ Controller card is widely
regarded as one of the most elegant designs in the microcomputer universe.

It is, as you might guess, a Steve Wozniak design, with an extremely clever
and reliable logic state machine running at 2MHz. This state machine
effectively recovers the data clock from the disk head signal and buffers
it for just enough cycles for the Apple II RWTS routine to read it.

Steve also played lots of tricks to reduce the number of vias
(plated-through holes) on the card to just two.

His design allowed 50% more data per track than the standard single-density
scheme and replaced virtually all the digital logic in the disk drive with
a faster software solution. And the controller was much less costly to
manufacture when the standard data separation IC was quite expensive.

Check out Sather's chapter on the disk controller in "Understanding the
Apple ][" or "Understanding the Apple //e", both available as PDFs. It's a
terrific case study in elegant design (where elegance = function / chip
count).

[Michael J. Mahon]

The symptom suggests that a flipflop or buffer has failed. Without any
/Device Select, the controller is apparently selecting the disk, regardless
of software.

[James Davis]

On Tuesday, May 23, 2017 at 4:17:46 PM UTC-7, Michael J. Mahon wrote:
> The symptom suggests that a flipflop or buffer has failed. Without any
> /Device Select, the controller is apparently selecting the disk, regardless
> of software.

4ez: That is the MOTOR CONTROL section at the bottom, center of schematic.

[James Davis]

This volume on Asimov might be of assistance to you:

ftp://public.asimov.net/pub/apple_II/documentation/hardware/misc/sams/Sams Apple II Troubleshooting & Repair Guide.pdf

[gid...@sasktel.net]

On Tuesday, May 23, 2017 at 5:17:46 PM UTC-6, Michael J. Mahon wrote:
> <Rob> wrote:

> > On Tuesday, May 23, 2017 at 1:25:52 PM UTC-6, 4ez wrote:
> >> On Monday, May 22, 2017 at 5:25:58 PM UTC-7, James Davis wrote:
> >>> Just came across this card for sale at the Apple II Store:
> >>

> >> Thanks, got plenty of those but it's not for the DISK II drive and I'm
> >> actually not looking for another controller.
> >>
> >> I will probably be getting the logic chips from Jameco. Even though
> >> Michael Mahon states it's extrememly unlikely to be the PROMs, and I
> >> believe him, I am still interested to know of a modern replacement (if
> >> there is one) for the PROM's. Unfortunately Mouser, Jameco, and Digi-Key can't help me.
> >>
> >> I told them I was looking for a DIP-20 and
> >> some models from the era I'm told which work for this are:
> >>
> >> 6309 Shottky (256X8)
> >> TBP28L22N Texas Instruments (256X8)
> >>
> >> Somewhere in the future when I have the knowledge, I know I can make my
> >> own compatible interface card. The design doesn't look that
> >> complicated, but for me it is a little beyond my reach. Just a little. :)
> >
> >
> > I kinda had a similar problem where the lights were on but nobody was
> > home. One thing you could try before delving into replacing chips is,
> > take an erase and erase the crud off the contacts of the card. It could
> > be just enough to prevent one or two pins from making contact.
> >
> > Rob
> >
>
> The symptom suggests that a flipflop or buffer has failed. Without any
> /Device Select, the controller is apparently selecting the disk, regardless
> of software.
>
> --
> -michael - NadaNet 3.1 and AppleCrate II: http://michaeljmahon.com

You can ignore my suggestion if you want, but I believe I am not mistaken in saying that the /DeviceSelect comes through the contact points of the slot. If the contact fails, so will the /DeviceSelect.

It is also free compared to chip replacement.

[Michael J. Mahon]

Since he's tried the card in several slots, I'd be surprised if the edge
connector has remained oxidized. Of course, this connector "pin" may be
damaged...

[4ez...@gmail.com]

On Wednesday, May 24, 2017 at 7:25:40 AM UTC-7, Michael J. Mahon wrote:

The card actually looks really clean around the connectors (shiny gold) so oxidation is unlikely to be the culprit on that part of the card. Elsewhere (i.e. the chips) doesn't look too bad either.

As for the DISK II controller design, and the rest of the story behind it (Shugart and the role the other Steve had, etc), it never gets old to hear or read. Some of it involved in the design (the math part of how things are supposed to work) is beyond me but I get the concepts presented.

Time permitting, I will definitely read up on the sources you and J.D. gave. Thanks again, everyone.

4ez

[Michael J. Mahon]

Congrats on getting a gold plated one--lots of the early controllers just
had a tinned edge connector. ;-)

[4ez...@gmail.com]

So here is how I was able to get the controller card back to working order....

It was my guess that according to the schematic James D. linked, and what I've been hearing from Michael M., the possible 'bad' chip (sidethought: how do they go bad?) would be the either 9334, 556, or the 74LS132. However, in case it wasn't I bought all the other chips that weren't PROMs except the 74LS323 because I couldn't find that from Jameco. Total cost of $3.45 because shipping was free with the amount of my order.

Originally I thought it was going to be the 74LS132 but started by replacing the 9334 with the equivalent 74LS259 because of the order in the schematic. [I'm no expert at this so I'm probably just lucky rather than know what I'm talking about.] I booted the system but the motor was still running even after the program was loaded. Next up was the 556 chip and after booting up the drive was acting normally!

So, it wasn't too terrible for me in the sense that I was able to resolve it without obtaining an engineering degree. Still, one day.... <maybe>. I hope this information might help someone else. Thanks again everyone who answered my call for help.

4ez

[Michael J. Mahon]

Congratulations!

The 556 makes sense, since it is responsible for keeping the motor running
for a few seconds after the drive is deselected (to save spin-up time if it
is soon reselected). So one failure mode for the 556 timer is to keep the
motor on indefinitely.

[James Davis]

On Thursday, June 1, 2017 at 3:34:36 PM UTC-7, 4ez...@gmail.com wrote:
> . . . Thanks again everyone who answered my call for help.
>
> 4ez

You're welcome.

Glad I helped!

James Davis