Speedlight SB-28 fires at its own will

pkr1979 · Mar 24, 2024

Hi all,

I just got a Speedlight SB-28 from eBay Im trying to use with a F100 and an F4 (Ive got an SB24 I use with these cameras without any issues). However, the SB-28 fires randomly, and I have to admit after skimming the manual Im not really any wiser. Any ideas, or is it simply broken and potentially unfixable?

Cheers
Peter

Nitroplait · Mar 24, 2024

I have two SB28s and in my experience they have been very robust.
I have used them on a number of Nikons over the years (not the F4) and on many other camera brands but have never encountered the random firing you describe.
They are also very inexpensive now so it doesn’t make much sense to consider paying for repairs.

If there are traces of battery leaks in the battery compartment, that may be the culprit of intermittent issues, I have experienced that with other flash units.
Cleaning the contacts may help but it is not unlikely the leaks may have migrated into the electronics and there is nothing worth doing in that case.

I would advise to request a refund and find another that works. The SB 28 is a great versatile unit as it is also useable on all cameras in Auto or manual modes. Good luck.

koraks · Mar 24, 2024

pkr1979 said:
the SB-28 fires randomly

Take a multimeter and test for continuity between the hot shoe center contact and the hot shoe pin that contacts with the metal side rails on the camera hot shoe (i.e. GND). You should read a high resistance. If it reads low, there's a short circuit inside the flash unit. To be clear: I'm talking about taking measurements on the flash unit, not the camera. The flash doesn't have to be turned on and doesn't need to have batteries installed. In fact, it's better to measure with the flash unit turned off.

ic-racer · Mar 24, 2024

I believe the SB-28 fires through a semiconductor circuit via IC2. Does it fire on its own when not connected to a camera, otherwise I suspect a camera issue. When connected to the camera, you indicate it fires at random intervals? How much time between the flashes? Does it fire as soon as the ready light comes on? Does it fire when the shutter of the camera is released? Does it do this in all modes?

I'd look for oxidation, or poor connections, etc.

koraks · Mar 24, 2024

ic-racer said:
I believe the SB-28 fires through a semiconductor circuit via IC2.

You mean "I2C"?

In any case, it seems like the SB28 has a fairly normal trigger method: simply through the center contact. The only oddity is that it can go in sleep mode and then needs to be woken up before it fires. If you trigger the center contact, apparently the first trigger will wake up the flash and only the second will fire it. There's a separate 'wake' contact that can be used instead of the double-clutch approach. See here: https://camtrapper.com/viewtopic.php?t=12147

Of course there's also TTL but that's a separate issue from the trigger process itself, I think.

ic-racer · Mar 24, 2024

If we are looking at the same schematic, IC2, ICF-M5296 3FP, which, I believe is a custom made IC. Looks like the IC recieves its signal from the middle flash contact via pin CX2, process the signal and TG1 and TG2 (pins 37 and 38) are the output which trigger the spark coil's discharge capacitor. Probably not much to 'repair' in that circuit, what do you think?

koraks · Mar 24, 2024

ic-racer said:
schematic

Ah, I see. no I wasn't looking at a schematic, could you link please? I'll have a look. I still think an accidental short circuit somewhere is most likely, e.g. due to damage to isolation on wires near the mount.

ic-racer · Mar 24, 2024

koraks said:
Ah, I see. no I wasn't looking at a schematic, could you link please? I'll have a look. I still think an accidental short circuit somewhere is most likely, e.g. due to damage to isolation on wires near the mount.

Do you know this site? The SB-28 service manual is there. Also, the SB-24 manual has the troubleshooting algorithm (below) which was not duplicated in the SB-28 service manual.

Nikon Service Manuals, Repair Manuals, Part Lists -free download-

Nikon Service Manuals, Nikon Repair Manuals, Nikon Part Lists -free download-

ss-it.de

ic-racer · Mar 24, 2024

We had a thread on this recently, but those Nikon service manuals are good up to the point where you need to put the 5" floppy in your computer to adjust the camera or flash...

BCM · Mar 24, 2024

I had one that did this only when connected to a camera. Note that it did this regardless of the camera type. There was a short in the base wiring and the load (torque) of the flash on the flash mount would randomly cause it to fire.

koraks · Mar 24, 2024

ic-racer said:
Do you know this site?

Great, thanks - no, I didn't. I have very little Nikon gear, so I guess I never looked for it. It's great though!

ic-racer said:
those Nikon service manuals are good up to the point where you need to put the 5" floppy in your computer

LOL! I can try, but I'm not sure it'll spin up in the DVD drive...

BCM said:
There was a short in the base wiring and the load (torque) of the flash on the flash mount would randomly cause it to fire.

Exactly, I'm thinking along those lines, too.

Using the schematic a little more, I can see the following possible causes for a forced trigger that can't be stopped:
* Short circuit in the wires connecting Cx with internal circuitry; I'd look in particular at the wire that goes from the hot shoe towards the PCB.
* Fouling of the external synch terminal or multiple flash terminal with a material that's sufficiently conductive to pull Cx low.
* Fouling of the flash test button, causing it to stick or bridge the contacts.

I'd start by wiggling the flash test button to see if that helps any; if it appears to stick or depress with difficulty, start cleaning there. Also clean the ext. sync etc contacts. If that doesn't help, then start opening the unit and look for a wire contact problem in the base of the flash. If that also doesn't help...sit down on floor & cry.

pkr1979 · Mar 24, 2024

BCM said:
I had one that did this only when connected to a camera. Note that it did this regardless of the camera type. There was a short in the base wiring and the load (torque) of the flash on the flash mount would randomly cause it to fire.

Sounds like mine - did you get it fixed? If so, how?

BCM · Mar 24, 2024

pkr1979 said:
Sounds like mine - did you get it fixed? If so, how?

If I remember right, I pulled apart the body and re-soldered the connections. I was also fixing a remote trigger that had been dropped and another Nikon flash at the time so forgive me if I'm in error. I do remember that the plastic around the base had a crack and I used epoxy to repair that. It is possible that the mechanic issue was causing the electrical as there certainly weren't any obvious issues like crossed wiring.

pkr1979 · Mar 30, 2024

BCM said:
If I remember right, I pulled apart the body and re-soldered the connections. I was also fixing a remote trigger that had been dropped and another Nikon flash at the time so forgive me if I'm in error. I do remember that the plastic around the base had a crack and I used epoxy to repair that. It is possible that the mechanic issue was causing the electrical as there certainly weren't any obvious issues like crossed wiring.

Thanks.

pkr1979 · Mar 30, 2024

koraks said:
Great, thanks - no, I didn't. I have very little Nikon gear, so I guess I never looked for it. It's great though!

LOL! I can try, but I'm not sure it'll spin up in the DVD drive...

Exactly, I'm thinking along those lines, too.

Using the schematic a little more, I can see the following possible causes for a forced trigger that can't be stopped:
* Short circuit in the wires connecting Cx with internal circuitry; I'd look in particular at the wire that goes from the hot shoe towards the PCB.
* Fouling of the external synch terminal or multiple flash terminal with a material that's sufficiently conductive to pull Cx low.
* Fouling of the flash test button, causing it to stick or bridge the contacts.

I'd start by wiggling the flash test button to see if that helps any; if it appears to stick or depress with difficulty, start cleaning there. Also clean the ext. sync etc contacts. If that doesn't help, then start opening the unit and look for a wire contact problem in the base of the flash. If that also doesn't help...sit down on floor & cry.

Thanks man.

Speedlight SB-28 fires at its own will

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Speedlight SB-28 fires at its own will

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