Macintosh portable backlit m5126 floppy issue

[Joopmac]

A good day to all fellow Macintosh enthusiasts

Special request to the portable experts
Maybe someone can help me with this

I recently acquired a Backlit portable m5126, and had it recapped with tantalum’s

Everything works…!
except for the floppy drives; internal, also swapped with another drive
an external floppy drive, or a floppyemu does not work internal- or external

when I leave the cable of the floppy drive connected, the boot gets slow, especially loading of the finder, and once, in a while, I hear, reading sound from the drive, and the axle is spinning a few times. This is without a disk!

Today I already took the board out again, and cleaned it with 96% alcohol.
now it’s drying, but does anybody have a good idea where I should look to repair?
Also am going to check the voltage with macometer when it’s dried up

I cannot see any broken traces, it’s really pristine
the board was looking really great round the caps

When one inserts a disk, the floppy does get gets ejected on boot, but no floppy with a cross or or question mark

One time at boot, I got the question from the OS, “initialize disk” when I had the floppy emu connected (strange: emu stuck on sector 02 and then resets to 00, never mounts) and a 1.4MB disk in the internal
Drive at that moment
It recognised the 1.4MB as a 800k disk, but cannot initialise it. After reboot the dialog of initialise did not come up again

SWIM trouble?
Can I swap this with swim from
SE or se/30 or LC?

PWMR trouble? Hard to believe, charging and using works brilliantly

Love to hear from you guys, am pretty happy with the working portable
But would be amazing to also have the floppy working…

 

[Joopmac]

Addendum:
Before the recap the Mac would not boot, would bomb while Loading extensions
But at that time I tried a floppy upon boot and greeted me with a floppy with a cross
So this behaviour is definitely changed

 

[alexGS]

I was about to start a thread with much the same problem; backlit Portable, freshly recapped, floppy drive now detects a disk when there is not one there AND same floppy drive works perfectly in another Portable. A different drive has the same fault when tried in the first machine.

I think a stray capacitor pin had found its way across pins of the largest VLSI chip on the right side of the board. However, removing this has made no difference. Cleaning the board seems to make a temporary, slight improvement (it nearly booted off a floppy, where normally it will not read the floppy at all).

I’m about to try swapping the SWIM chip tomorrow. I’ll use one from a PB100 logic board.

 

[Joopmac]

I am very interested in the results

 

[Joopmac]

Any progress? I have a SWIM chip and a socket ready to have it soldered by my friend

 

[alexGS]

Any progress? I have a SWIM chip and a socket ready to have it soldered by my friend

Yes - replacing the SWIM chip restored the correct operation of the floppy drive in the backlit Portable that I was working on

 

[Joopmac]

Update, here I did the same but unfortunately I still can’t read or format disks, so put the Original (Low power? Portable
SWIM back in…
Also it will not eject disks any way from the OS and also a 1.44mb disk is seen as a 800k. At the moment a disk is stuck so going to grab the good old eject pin again

Anybody hints where to look?

 

[daanvdl]

Beside beeping the h*ll out of it between the port(s) and SWIM, it is worth trying to scope out U13C (74AC244) which do buffer these lines:
- Head Select (HDSEL)
- SWIM Read (SWREAD)
- Write Request (W/REQ)

 

[alexGS]

I am very interested in the results

I have an update on that Portable. The disk drive problems returned - thinking a disk was in - not ejecting - reading 800K and not 1.4MB - and were not cured by changing the SWIM a second time. I eventually traced the cause to a single tiny track running underneath a (replaced) 47uF electrolytic capacitor. The via (through-hole) connection had rotted, so pin 16 (HDSEL) of the square VIA (6522) chip was not connected to pin 2 of the third 74AC244 latch (on the right, closest to the 47uF capacitors). Once I made that connection, the disk drive works properly again.

@daanvdl is absolutely right; the rightmost 74AC244 latch is crucial to disk drive operations and last month I replaced all three of those latches with new parts from Mouser (being careful to get the wider package size) - which I thought had fixed it - but I now think it was just that pin 2 connection all along (there had been a history of capacitor leakage). I guess every time I heated the board, it made intermittent contact.

 

[Joopmac]

>pin 16 (HDSEL) of the square VIA (6522) chip was not connected to pin 2 of the third 74AC244 latch (on the right, closest to the 47uF capacitors)

will check this out!!!

did you place the original low-power swim back?
i did test with a swim from a classic, but it seems the backlight was a bit unstable when inserting a disk

 

[alexGS]

did you place the original low-power swim back?
i did test with a swim from a classic, but it seems the backlight was a bit unstable when inserting a disk

Yes; the original SWIM is in there.

I’d been using SWIM chips from Powerbook 100s, since there tends to be a surplus of logic boards over LCDs for those. Interesting to hear about the power instability using a standard SWIM, thanks