Fix your SB600 (by David Hilos)

[Txnoob]

Thank you for the note.
So I turned it on and set a timer for three minutes. It whined and at around a minute and a half the display said "Bat stby" and stopped whining.

The batteries felt slightly warm.

This was done twice.
1. With Alkaline Batteries
2. With freshly charged 900mah NiMh batteries

Oh I failed to elaborate on the discharge circuit.

After burning quarter watt resistors a few times (held with pliers fortunately), I made a circuit to discharge the capacitor, with 8 in4007 diodes, 2k 5 w resistor, two Leds and a 98ohm resistor.

The circuit was found here.
http://www.jestineyong.com/wp-content/uploads/2016/01/discharge-tool.jpg

 

[one eye jack]

Yes...but did you press test button to fire flash?

 

[Txnoob]

I did not previously.

So repeated the steps.
1. Installed batteries
2. As it whined, pressed the test button
3. The flash fired
4. Repeated test firing a few times
5. The whining continued and eventually saw the "Bat Standby" sign

 

[one eye jack]

I did not previously.

So repeated the steps.
1. Installed batteries
2. As it whined, pressed the test button
3. The flash fired
4. Repeated test firing a few times
5. The whining continued and eventually saw the "Bat Standby" sign

Technically SB600 is working! "Bat Standby" sign I think is the standby function (custom function) which is on by default. I think this indicate capacitor is fully chardged and monitor circuit cuts off charging to conserve battery. See pg.7/54 of repair manual. Do note that the cap is charged to 330V so be careful. There is a discription of the flash circuit on page 43/54 of adobe reader.

Now it's left to check it TTL flash is working or not,refer to user manual.LCD backlight will turn on if any button is pressed. Cheers!
With alkaline batteries minimum charge cycle is 3.5 sec. and 200 flashes per fresh battery set.

 

[Txnoob]

One eye Jack,
Checked the standby mode. Set it to Auto.
Oh yes the 300V cap will be accorded due respect.

I read the description of the circuit. I understood some of it.

Testing the TTL.
Took a few pictures, of course,no way to tell if the flash is ready.

The flash didnt have the metered output. That's to say the ready light blinked thrice after firing, and a value -1.7 flashed on the LCD, detailing the amount of misfire/underexposure.

So here are my thoughts:
1. The pressurization (oscillator) circuit is functioning - As evidenced by the charge in the condenser
2. The triggering circuit works - as evidenced by the test fires
3. TTL metering works, as evidenced by the flash telling me that the shot was under exposed.

So my suspicions, based on what I understand so far.

1. The cut off circuit that stops the oscillator on detecting adequate charge may not be working
2. The detection circuit that tests for the charged capacitor may be at fault
2. The condenser is dying

I'm not confident enough to probe for faulty SMD components yet. The easy and lazy thing to do is:

1. After discharging the condenser, pull it off the board and test it. I do have an ESR meter.
2. If the condenser is good, then conclude that one cannot always win again at the gods of silicon and let it rest, till such time that I get the itch again!

 

[one eye jack]

We tend to think the worst has happened but it could be something simple.From your description, ready light not available but can be because capacitor can not be fully charged because capacitor is bad so test esr which may account for underexposure but it can be the flash tube as it is heavily used (many shots). Take capacitor out of the circuit to test.

 

[Txnoob]

True. It probably is something simple.
I checked the capacitor off circuit, and it's at 1126 mfd (expected 1000 mfd) at perfect zero ESR. So that's a good cap.

I'm tempted to change the xenon lamp. But, seeing that it's the charging circuit that's at error I'm hesitant.

The circuit boards have various markings of TP. Which I believe denotes test points. After manufacturing they mush have a method to test the board.

Maybe I'll have to buy me a good magnifying glass and start testing each component in the board.

 

[one eye jack]

True. It probably is something simple.
I checked the capacitor off circuit, and it's at 1126 mfd (expected 1000 mfd) at perfect zero ESR. So that's a good cap.

I'm tempted to change the xenon lamp. But, seeing that it's the charging circuit that's at error I'm hesitant.

The circuit boards have various markings of TP. Which I believe denotes test points. After manufacturing they mush have a method to test the board.

Maybe I'll have to buy me a good magnifying glass and start testing each component in the board.

Before considering changing xenon tube first you have to determine if the charging or pressurizing circuit can charge up to 330V.
Then check voltage detection circuit is working correctly (cut off when high voltage is reached). Finally the flash control circuit
for exposure. The test points are indicated on the schematic. Start at the battery section and proceed from there. Yes a magnifying glass is good for smt components.

 

[weimng]

Can this thread work for sb800 too? My sb800 fires by itself randomly whether it's on or off the hotshoe

 

[one eye jack]

Can this thread work for sb800 too? My sb800 fires by itself randomly whether it's on or off the hotshoe

This is a different problem. I would suggest cleaning the electrical contacts of camera and flash hotshoes with alcohol/methanol from hardware shop (NOT THINNER!) but if it does not work send to Nikon service center . I suspect it's the flash's hotshoe electrical wiring or hotshoe itself since you said it fired when not on camera hotshoe.

See this link for similar problem:

D700 flash / hotshoe issue with SB800.

https://www.flickr.com/groups/756291@N24/discuss/72157630172381878/

d700 and sb-900 going crazy firing on it's own

https://www.dpreview.com/forums/thread/2810639

D700 Hotshoe Flash Firing By Itself

https://www.dpreview.com/forums/thread/2690793