Disk II rainbow cable, false write protect and other problems

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CWJ_Wilko's picture
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Disk II rainbow cable, false write protect and other problems

Having some issues with an older Disk II unit, rainbow ribbon cable.

Problem 1: No matter what disk I use in the drive, MECC Computer Inspector says that the write protect switch is down.

Problem 2: It will only read from a disk with the disk drive housing off (strange). Specifically it is able to read with the housing half slid back. Once it covers the first of the big capacitors and the inductors, reading is unreliable. There are no visible shorts, in fact, turning the housing upside down and placing it on top of the drive (without touching the analog card) produces the same unreliability.

The analog card is (C) 1978 but is different to others that I've seen pictured before. It has a small square hole in the PCB, and the inductors are cylindrical and exposed, rather than curled 180 degrees and covered like on my other drive.

I have a strong feeling that the analog board needs some TLC, but at this stage I feel like I've tried everything that has been listed before, so looking for a new direction.

This is what I have tried so far.

- Swapped analog card with a known good drive, which worked. This means the write protect switch, female card port and ribbon cable are okay?
- Tested write protect switch with multimeter, looks good.
- Head clean with 99% isopropyl, no change, same symptoms.
- Swapped 4x ICs from known good analog card into bad card. No change, symptoms remained.
- Replaced electrolytic caps on bad card, no change, same symptoms.
- Replaced R12, no change, same symptoms
- Speed test and adjustment, 299rpm exactly and well within recommended tolerances

Also using it in combination with the good drive sometimes delivers unexpected results. Most of the time the symptoms remain the same, but sometimes when the bad drive is 1 and the good drive is 2, both drives will read their write protect switches as off, no matter what disk you use. If they are swapped, then write protect will be stuck on, on the bad drive only.

Sometimes when trying to boot Prodos it will shoot up a message -Unable to load PRODOS-.. Other times the disk will fail to boot and dump me into the monitor.

I've read pages and pages of documentation, with no luck so far. Does anyone have any tips?

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Re: Disk II rainbow cable, false write protect and other ...

CWJ_Wilko, I have a couple drives with the same analog card (hole in it)

One thing I did not notice you mention was the Disk II controller card. I see from your first troubleshooting item that you swapped, I think, the analog card with one from a good drive and that worked?
To me that says it is the analog card, especially if you swapped the ICs on the card (as you mention later) and that did not solve the problem.

I mention the Disk II card simply because you don't mention it.

If you have not already, make sure to check this website for more possible solutions/procedures.
Zan

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Re: Disk II rainbow cable, false write protect and other ...

Hello CWJ_Wilko,

to be more precise read the page and it´s follow up pages at:
http://www.appleii-box.de/H084_1_AppleIIDiskService1.htm
hint for the search:
if the problem is related to one drive only the problemis located in general at the drive-,
is the problem also has influence at the second drive too the problem is more general
located at the controller.

if the writeprotect switch is O.K. the problem is located eiter at the
analog board of the diskII or at the controller. Hint:
There is a screw at the outside of the DiskII frame to adjust precise
position of the writeprotect switch.

speedyG

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Re: Disk II rainbow cable, false write protect and other ...

Thanks all for the suggestions. I have scrubbed all the chip contacts clean with isopropyl and a pencil eraser, no change. I have also removed and reseated all the chips on the Disk ][ Interface Card, no change.

For sake of simplicity with the ongoing troubleshooting, I'll call the working good drive 'Singapore' and the problem drive 'America', from the place of manufacture on the analog card.

Just to clarify, I have tested the actual write protect switch in the America housing with a multimeter, and the circuit is good. This is also evident by swapping the analog boards over.

Singapore always worked with my Disk ][ Interface Card, no problems whatsoever, which makes me want to rule out the card.

However, I can't deny that plugging both America and Singapore into the card caused both drives to have write protect issues, depending on the configuration. I'm looking for a cheap replacement Disk ][ Interface Card, so I can at least rule it out.

But I still think the problem originates on the America analog card, mostly because when the housing is placed over the card, it immediately has read write issues.

I'm thinking it must be magnetic interference of some kind, the metal in the housing is affecting one or more components on the board. The housing is not physically touching the board, but it somehow affects the performance. Moving the housing over the top of the drive while running will cause a variety of read write issues.

The AppleBox website is a fantastic read but doesn't really tell me where to look next. Read/write tolerances are a maybe but that's beyond my comprehension, I've never picked up an oscilloscope.

And to come full circle, even with the housing off, I'm still having write protect issues no matter what configuration I use.

I'm on the lookout for a cheap Disk ][ replacement in the meantime, but being in Australia it can be hard to source these things cheaply.

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Re: Disk II rainbow cable, false write protect and other ...

UPDATE:

I've switched the 74LS125 ICs once more, I think the original chips are now back in their original boards. I have now returned to a semi-functional configuration, where both drives are now reading and writing, but both are ignoring their write protect switches (always off).

America also seems to be running better with the housing back on, but I'll have to check it again after I've powered off for a few hours.

So just by switching that IC and nothing else, I'm getting completely different results across BOTH drives. I'm tempted to buy two new 74LS125, now under the assumption that at least one or both chips are acting up. Does this sound about right?

Also still looking at a new interface card, just in case.

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Re: Disk II rainbow cable, false write protect and other ...

Hello CWJ_Wilko,

within the path of the writeprotection switch to the computer there are
also 2 other components. The 74LS323 bus buffering chip and the rainbowcable itself.

The 74LS323 in general won´t get destroyed unless the cable is plugged
with wrong orientation to the controller and in general that mistake
first destroys some chips at the analog board.

A rather uncommen but possible trouble might be the rainbowcable itself.
In some cases - if the cable has been stressed to far - the inner corewire
might be damaged/broken.

If the plastic cover is intact it holds the 2 broken ends of the wire close together inside the plastic cable
but bending the cable might at least parttime interrupt the connection.

The various results depending to various positions of the drive leed my suspect to the cable.
speedyG

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Re: Disk II rainbow cable, false write protect and other ...

Thanks Speedy for pointing me in the direction of the 74LS323, I'll make sure to pick up a replacement for this as well, on top of a replacement Disk ][ Interface Card.

I've ruled out the rainbow ribbon cable as culprit by using the grey ribbon cable that comes with the good drive - same symptoms on America no matter what cable is used. Although I have read on that site linked earlier that the rainbow ribbon cables are particularly susceptible to electronic interference and aren't the most reliable (but they sure are pretty!) The cable looks to be in good physical condition.

All the same I think I'll check continuity of each pin on the ribbon cable.

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Re: Disk II rainbow cable, false write protect and other ...

Hello CWJ_Wilko,

the mentioned site is mine.....
and it contains plenty stuff also at other topics.....
but at least a quite large bunch is related to the DISK II drive hardware
and patching other drives with better capabilities ( more than 35 trcks )
to use the additional tracks with various operation systems....

if problem still remains with the drive and all prcedures still fail
drop another posting.... otherwise if problem is solved it would be
nice to drop a posting feedback too, that problam has been solved and what turned
out to be the problem with this very drive.

sincerely speedyG

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Re: Disk II rainbow cable, false write protect and other ...

I had no idea that site was yours! Good stuff. When I get time I'll run through those potential fixes and see if I have any luck. I'll report back either way.

Thanks again.

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Re: Disk II rainbow cable, false write protect and other ...

I just got a Pair of Older Apple Disk ][s and one of them has the Analog Board with the Hole in It and the strange Inductors...

I got a ProDOS boot failure message once, but I think it was because of the Disk Clamp mechanism not being very tight... I did have the cover off for observation.

I will do some more testing to see if mine acts differently with the cover on...

MarkO

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Re: Disk II rainbow cable, false write protect and other ...

I haven't had the chance to run any further tests, my configuration at the moment is working okay.

Both drives are still ignoring the write protect switch. However the America drive with the rainbow ribbon cable is still refusing to read and write reliably with the cover on.

Strangely even with the cover off, it takes it a few minutes to 'warm up' and start reading and writing reliably. Has anyone had this before? I would have suspected the caps if I hadn't already replaced the three big electrolytic cylinders.

Still very suspicious about the inductors, the insulation on mine is flakey and they are easily adjustable.

I'll likely not trouble myself much longer and just replace the board at the next chance.

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Re: Disk II rainbow cable, false write protect and other ...

Hello CWJ_Wilko,
still remain to the opinion that the cable might be damaged.
To refer to the pictures in the other thread:
the second picture:
the drive with rainbow cable,
the most right cable with black covering is the one that transfers the
write protect signal.

Spotting out the relation between reliability and time of "warmup" is new.

FYI - the analog board at the rainbow cable is very old and very early version.
largest disadvantage is the one missing adjustmentresistor within the
read/write compensation of the MC3470. This was common with the very old drives
while they still have been used at 13 sector mode.

Later drives when 16 sector mode was common - always had the 2 adjustmentresistors.

Can you publish a picture from the bottom side of the drive ?

If there is a variation to the reliabilty of speed turning the disk
maybe somebody replaced the drive spinning belt in former days with a
"weak" replacement belt. Such belts sometimes cause problems like the
explained "warmup phenomenon".

And at one point i agree with your statements:
I also would suspect the left lower coil with the white flaky covering.
The induction of the coil is dependent to the isolation of the windings
within the coil. If the are shortcuts between the windings or at least
lower resistance this will lower the value in µH of the coil and reduce
it´s function. In that case it should be replaced.

For more detailed inspection it would also be usefull to see 2 pictures of the
drive with removed analog board showing once the sideframe with the cable
to the read write head and one showing the side at the writeprotect cable.

While removing the analog board:
there should be a shielding plate between diskkmechanic and the analog board.
See pictures in my site... :
http://www.appleii-box.de/H084_2_AppleIIDiskService2.htm
see first 2 top pictures at the very left side ...... Is it missing ?

speedyG

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Re: Disk II rainbow cable, false write protect and other ...

An update:

I just finished replacing a capacitor in the Apple //e power supply that had gone bad; the //e had been struggling to start from cold with a lot of ticking coming from the power supply, so it was obvious what the problem was.

Not only has that symptom now disappeared, but the America Disk ][ unit is now performing much much better, with fast read-write times with the case on.

I suspect now that the voltages were dropping across my peripherals that caused odd behaviour. I also noticed problems with my Super Serial Card that is setup for hosting a BBS - those are also now fixed.

The write protect switch on both drives is still permanently off, which means that I've still got one problem to solve here. But for the moment, very happy.

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