5.25 unidisk repair

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Joined: Jul 5 2016
Posts: 30

Hi all,

Recently I managed to damage two 5.25 unidisks. In both cases after I reassembled the drives I notice the disk spins but the drive head no longer moves.

Using a 3rd working drive I was able to narrow the issues in both cases to the unidisk analog board.

I started by looking at the drive that has the same board as my working one - luckily the ic's are socketed so I was able to rule them out quite easily by swapping them over.

Next using Sams ComputerFacts - Disk Drive Apple II as I guide I checked the voltages at the transistor (Q2) and found E - 11.9 / B - 0.63 / C - 0.62 which according to the documentation doesn't sound right.

I would like to change the transistor however I don’t know what an available equivalent would be – the existing part no is B1080

Any assistance would be greatly appreciated.

Cheers

AttachmentSize
unidisk pcb 1.jpg1.98 MB
unidisk pcb 2.jpg1.61 MB

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speedyG's picture
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Joined: Nov 16 2011
Posts: 2406
Re: 5.25 unidisk repair

Hello dc99,

unfortunately you published the wrong part no. .....
That number is a internal number for ordering from factory...

at the other hand in the Disk II there are on different PCBs different types of Q2.

Just for short here a list of the used transistors in the DISK II
followed by transistors that possibly might serve as replacement transistors.
Restricted as "possible" because some of them do NOT have same pin outlining !

I'm crating an additional page in my site at the chapter about the DISK II
where i will add drawings from the replacements and their pin outlinings
so that choice of replacement will be explained. That page will be completed
tommorow on 4th of Dec. and i will then place here a link to that page.
So i'd recommend to wait till that page is complete.

here the brief preview of the list:
MPSU51 Si PNP 40V hfe50 possible replacements: MPSU55, MPSU56

2N3906 Si PNP 40V hfe100 possible replacements: 2N3905, 2N4403, BC212, BC307, BC557

2SC2785F Si NPN 60V hfe >200 possible replacements: 2SC2458

2SA1175F Si PNP 60V hfe 200

2SB596-0 possible replacements: 2SB633, 2SB703 TIP41C, BD244B

UPDATE: The new replacementpage is online:
http://www.appleii-box.de/H084_8_AppleIIDiskService8.htm

speedyG

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Joined: Jul 5 2016
Posts: 30
Re: 5.25 unidisk repair

Thanks for the reply speedyG.

Sorry I should clarify that while I am using the Disk II guide this is a Unidisk PCB so the labels are also different. ie. Q2 on this board is the equivalent component of Q1 on the Disk II PCB.

For clarity I have attached a photo of the board and highlighted the Q2 transistor which is marked 'B1080'

Cheers

speedyG's picture
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Joined: Nov 16 2011
Posts: 2406
Re: 5.25 unidisk repair

nevertheless the page is now ready. See update above !

Thanks for the correction of the link.

speedyG

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Joined: Jul 5 2016
Posts: 30
Re: 5.25 unidisk repair

Thanks for the link speedyG. I've re-uploaded the photo of the Unidisk PCB and it's now working.

Can I just confirm that the B1080 on this PCB is the equivalent of MPSU51 -> MPSU55 -> MPSU56

Cheers

speedyG's picture
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Posts: 2406
Re: 5.25 unidisk repair

After view of the picture this update:

B1080 is not the complete Number....
Many "eastern manufacturers" cutted off ( truncated )the first 2 alphabetic letters "2 S"
resulting to irritation.....
the complete Typnumber is:
2SB1080.

answer to question:
similar but not same....

i will update my above mentioned page this evening with the relevant datasheet
and list alternate devices.

UPDATE: 2SB1243 as replacement for 2SB1080 added.

speedyG

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Posts: 30
Re: 5.25 unidisk repair

Hi speedyG,

Thanks for the quick update however I noticed the item you added on your website is 2SB1085 not 2SB1080.

Cheers

speedyG's picture
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Joined: Nov 16 2011
Posts: 2406
Re: 5.25 unidisk repair

Hello dc99,

thanks for the correction.

In fact i slipped down one line in one of my old transistor crossreference books.
The data for the 2SB1080 was not availiable there - but a remark displayes statement
that the 2SB1080 is identical to the 2SB1243.

I corrected the entry in the page.

speedyG

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Re: 5.25 unidisk repair

Hi speedyG,

I am just following up about your book which indicates that 2SB1080 is identical to the 2SB1243

I found some specs on both (see below) however they appear quite different. Unfortunately I don't have the knowledge to determine what are key factors in selecting a substitute transistor nor if the information below is sufficient to make that decision so any assistance for those more knowledgeable would be great.

Previously I raised if 2SB1080 is a substitute for MPSU51 (MPSU55 -> MPSU56) which is used in the disk II pcb - I still wonder if that is the case given the two boards appear to use practically the same componentry.

2SB1080
Uce/Ucb: -35/-35V
Ic: -2A
N: 10W

2SB1243
Uce/Ucb: -50/-60V
Ic: -3A
N: 1W

Cheers

speedyG's picture
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Posts: 2406
Re: 5.25 unidisk repair

Hello dc99,

the answer is rather simple... the 2SB1243 is stronger than the 2SB1080
and therefor may be used as replacement for the weaker 2 SB1080.

speedyG

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Posts: 30
Re: 5.25 unidisk repair

Hi SpeedyG,

I thought that might be the case but as the original transistor has N 10w and the replacement N 1w I wasn't sure.

Regardless in my case I haven't been able source the replacement part you suggested locally in Australia. Based on your last response am I able to just search for a part that has higher capacity with the same pin arrangement or are there other characteristics that need to be considered.

Cheers

speedyG's picture
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Posts: 2406
Re: 5.25 unidisk repair

Hello dc99,

finally usefull to hear that you are located in Australia.
I have been performing reseach of electronic components in Australia several times
and i still have a list of sources from down under....
I'll check that tommorow and maybe i can pass over a link to a local supplier...

speedyG

UPDATE: Crossreference list page

[img]http://www.appleii-box.de/UFO/2SB1080Crossreference.jpg[/img)

Australian sources:
http://www.x-on.com.au/
http://www.altronics.com.au/
http://www.radioparts.com.au/
https://www.techtronics.com.au/searchcat/COMPONENTS_TRANSISTORS.asp

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CWJ_Wilko's picture
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Re: 5.25 unidisk repair

Hi dc99 and speedy.

Speedy you might want to add Jaycar as another local Australian distributor of electronic components. They don't stock absolutely everything, but they can be useful if you just need one or two odd components. They are a chain store much like RadioShack in the USA, and the only one I can think of that still has electronic components on the shop floor.

Otherwise I normally just go to Mouser, shipping can be a pain but if you have a bunch of stuff you need to order, sometimes you can get free shipping for a big order.

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Posts: 39
Re: 5.25 unidisk repair

Other Aussie electronic component suppliers:

Cheers,
Mike

ggb
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Joined: Mar 13 2012
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Re: 5.25 unidisk repair

There is also rockby.
http://www.rockby.com.au

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Joined: Jul 5 2016
Posts: 30
Re: 5.25 unidisk repair

thanks everyone for the suggestions.

I am familiar with most of those suppliers however I find they generally stock modern parts rather than anything vintage. I've had some success with rockby in the past.

Cheers

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Posts: 1204
Re: 5.25 unidisk repair

Just out of curiosity, why did you disassemble the drives in the first place? I ask because just yesterday I received a couple non-tested drives in the mail that I purchased cheaply, one of which was a Unidisk 5 1/4", that turned out to have some really bizarre issues.

The drive wouldn't accept a disk, and peering in through the slot I could see "something" sticking up where it shouldn't. I took the drive apart (it's amazing what an annoying Chinese puzzle those things' cases are), and what I found was the pulley/carrier that the band from the stepper motor wraps around to move the head was wrenched upwards and stuck in place against a hole in the drive base frame. (I wish I'd taken a picture of it, it's hard to describe in words.) With a lot of finessing and swearing I managed to put things back the way I thought they *should* be, but when I tested the drive after reassembling it I found the drive motor would spin but it made no attempt to move the head when the system was powered on...

Here's the thing, though: I would *swear* that the stepper motor *did* chatter and attempt to move before I took the drive apart to attempt to resolve the physical issue. I found it really finicky to get the analog board back in the proper place and get the cables re-routed correctly, I can't help but wonder if there might be some other connector on the drive chassis itself that's easy to dislodge, or... something else, that's easy to not get right and causes this "spin but no seek" behavior.

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Posts: 30
Re: 5.25 unidisk repair

Hi Eudimorphodon,

I took it apart to clean and service. In my case I am fairly certain I didn't assemble it back properly which allowed the PCB to short. I recommend you have a look at Sams ComputerFacts - Disk Drive Apple II as the design is very similar.

For me the most difficult part is getting the top lid back on. I found it presses against the cord on the back right - A couple of times after reassembly I found the connector dislodge partially so you many want to open it up again and check... perhaps also test it before putting the lid back on so you can see what is happening more easily.

Cheers

Eudimorphodon's picture
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Posts: 1204
Re: 5.25 unidisk repair

Okay, then I suspect I might have shorted the same thing you did. When I first got it together enough to test it I didn't have the front edge of the analog board properly seated in the metal bump-outs in the side rails, so the board was nosing down at an angle, and it's possible the bottom of the board shorted against the metal of the door latch.

Maybe one of these days I'll try to fix it. I'm not too optimistic it'll work properly anyway, though, given how messed up the head positioning mechanism was. I'm pretty curious how it was damaged like that in the first place.