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SE/30 with dead ADB ports

dogcow

Member
I've picked up a mint SE/30 but it's poorly :( The ADB ports dont work at all, I've tried just the mouse plugged in, and just the keyboard and any combination of mouse / keyboard / both into either port, but nothing. Is there a fuse on the motherboard somewhere or is it a bit more of a hassle to fix it? It's a shame as otherwise this machine is like new. Any ideas?

 

wally

Well-known member
Well, right next to the ADB connectors is UL11, the magic ADB chip, F1, a 1 amp fuse to +5V, a surface trace to L1 inductor network pin 3, the other end of the inductor is pin 6 opposite side L1, goes to ADB pins 3 +5 out.

Check F1 first. If good, check continuity inductor pin 3 to 6. If inductor is blown pins 1,8 are a likely spare. Pin 1 is the one next to the fuse.

ADB ground is filtered by L1 pins 4,5

ADB signal is filtered by L1 pins 2,7

Avoid damaging UL11 with static-touch the nearby ground rail first.

Look carefully at nearby Q3, a surface mount 2N3904 that can get eroded to crap by leaking fluid from C13. Also all surface traces near C13.

Check underneath to make sure that R31 470 ohms, R32 4.7K , R33 27 ohms are intact.

C72 .01 uf and C73 33 pf need to not be shorted.

Check soldering of ADB connector blocks.

There are several artwork layouts so your mileage may vary...

[:)] ]'>

 

Unknown_K

Well-known member
Yes the ADB ports are fused, I remember digging my manual out for a forum member with a dead IIfx ADB port in the last forum. He ended up putting a fuse in and it worked fine.

 

John8520

Well-known member
Yes the ADB ports are fused, I remember digging my manual out for a forum member with a dead IIfx ADB port in the last forum. He ended up putting a fuse in and it worked fine.
That would be me! (or at least you helped me with the very same problem on my Mac II)

 

phreakout

Well-known member
Being that I am kinda skeptical regarding the whole "fuse" issue, is there anyone out there who can verify with pictures here that the fuse exists?

The reason being is that I had the same issues with my dual 800K Floppy SE last year. The SE booted fine, but both ADB ports were dead in the water. I tested the heck out of that logic board in every possible connection. In the end, I decided to replace the logic board.

Luckily, MacG4 had an SE/30 logic board for sale and saved me from junking the old friend. I coiuld understand either the capacitors, resistors, Bourns filter ICs and ADB chip going bad, but when the fuse was mentioned, I never was able to find it.

I don't want to turn this into a flame war, just to verify that the fuse exists on every SE, SE FDHD and SE/30 logic board and where to find it.

Thanks,

73s 8)

 

Unknown_K

Well-known member
I just looked at my "Guide to the macintosh family hardware: 2nd edition" and only the mac II line has the 1A fuse on the 5V section of the ADB line (because they have keyboard power on).

The SE and SE30 do have a 470 Ohm resister in series on 5V line on the ADB data line (PIN 1 on the connector) you might want to look at.

The ADB signal is described as: Bidirectional data bus used for input and output. It is an open collector signal pulled up to +5 V through a 470 Ohm resister on the computers main logic board.

 

wally

Well-known member
Being that I am kinda skeptical regarding the whole "fuse" issue, is there anyone out there who can verify with pictures here that the fuse exists?...
I don't want to turn this into a flame war, just to verify that the fuse exists on every SE, SE FDHD and SE/30 logic board and where to find it.

Thanks,

73s 8)
I can only speak for the two SE/30 boards I have before me. The fuses are unlike conventional ones in appearance. One style is a surface mount rectangular metal plate sandwich, the other looks identical to a molded case cylindrical axial lead plastic capacitor without body markings dull yellow-orange color, through hole mounted with leads. My SE/30 boards both have a coordinate marking system silkscreened top side along the front and PDS connector edges, and the fuse is between location L12 and L13, marked F1. It is between the filter inductor package and the board edge along which the PDS parallels. And yes, I have verified with an ohmmeter and by following the traces to the filter inductor that this is how my SE/30 ADB connectors get +5.

 

dogcow

Member
Thanks folks, I'll pop some pictures online of the motherboard once I get an hour to get inside the machine.

 

wally

Well-known member
Macbuk's F1 position is identical to my boards, but my parts don't have color codes or that body color. They do have a resistance too low to easily measure. Anyone know if fuses come in green, color coded???

I've looked at some images of SE boards and I do not see any fuses either.

By the way, I figured out why the warnings on not doing hot ADB connects and disconnects. That filter block is a multi-section common mode choke, fine magnet wires wound together on a ferrite toroid. Disconnecting the current causes an inductive spike that can puncture the wire insulation and short multiple ADB signals together, hence Larry Pina's discussions on testing for shorts. The other SE/30 I/O ports are RC or C filtered, no inductance other than strays from wiring, so no substantial inductive spikes.

 
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