my daughter found my old flash (20+ years old) and tried it on her canon T3i. It didn't recognize it and it never fired, but she tried the shutter button. Could this have damaged her camera even if it didn't fire? I have just given her a canon flash and her camera won't fire it, but mine will. If it did damage it, can it be repaired? Any suggestions? Thanks.


3 Answers 3


Unfortunately, it is entirely possible that it did damage the camera. Older flashes have a higher trigger voltage and that may damage the camera. It should be reparable, if that is the case, but it could be somewhat costly.

You can find a bit of an explanation for this online here: Trigger Voltage but it's a little techie. Suffice to say, your best bet is to contact Canon for your next steps.

  • \$\begingroup\$ who knew???? I would have said "No way" off the cuff but it was interesting reading a thoughtful disagreement! \$\endgroup\$ Commented Nov 26, 2012 at 11:02
  • \$\begingroup\$ Thanks! I looked at the trigger voltage guide before asking the question, but all the help out there seemed to be for people who were actually able to use the flash. I wasn't sure where the damage could occur - in the first signal from the camera to try and fire the flash and this somehow resulted in something from the flash overwhelming the delicate electronics, or from something going on as the flash was actually firing. Disappointing day, to say the least. \$\endgroup\$
    – user13717
    Commented Nov 26, 2012 at 17:07
  • \$\begingroup\$ The damage happens at the pulldown FET (transistor). Older electronic cameras used more robust technologies for transistors, newer ones become weaker (as geometry got smaller on silicon) but very new cameras MIGHT have an IGBT transistor for activating the flash. It is usually not the case, so your breakdown voltage is around 16-20 V, above that the oxide between the gate and the source/drain of the transistor gots permanently damaged. It may be that you need to replace only one transistor though... If you cannot do that, you can still try radio triggering, if your camera supports it. \$\endgroup\$
    – TFuto
    Commented Feb 25, 2014 at 10:04
  • \$\begingroup\$ By the way, you tried that flash on another camera, and it worked: well you are still making microscopic cracks on the oxide, and eventually that other camera will be damaged, too. \$\endgroup\$
    – TFuto
    Commented Feb 25, 2014 at 10:06

The problem is that in old cameras, the flash sync was a simple mechanical switch. The flash would present high voltage DC, say 300V, across the switch. When you trigger the shutter, the switch would close, 300V would flow and it would flash.

Modern cpu driven cameras use all semiconductors, and most are designed for at most 5 volts. So an old flash can present 60 times more voltage than the camera can handle.

This potential (voltage) is present any time the flash is charged. If it was off, then there is no need to worry. But if the flash was charged, it could very easily fry circuits in the camera.

  • \$\begingroup\$ Oh, the flash was on and charged. Thanks, now I can picture what was happening. I'll send the camera off for repairs and see what needs to be done. Everything else works fine with it - it just won't fire the external flash. We'll see how expensive it is to fix and go from there. \$\endgroup\$
    – user13722
    Commented Nov 26, 2012 at 20:40

this is what i got as an answer from yongnuo:

will old flash 160v release damage the yongnuo rf-603c ? will Fujifilm FL MX29 damage my receiver? up to what voltage it is safe to use?

Thanks for your email. YONGNUO RF603 can be used with the flashes with the save voltage below 300V. If you are using a photography luminaire, please connect it with a PC sync cable. For we don't have a Fujifilm FL MX29 to be tested with our products, we suggest you to take your camera to a physical store to test it with our products (or borrow from your friends). If the save voltage of the flashes is not sure and the test is in need,we suggest you to use a PC sync cable.

Best regards,


  • 1
    \$\begingroup\$ This is dangerous advice! The P/C sync port delivers the same voltage as the shoe. Some cameras, and possibly the Yongnou trigger, have more shielding for the poor than for the hotshoe, but that is not a guarantee. You can also get cables with added protection — if you don't have one, I wouldn't suggest risking it. \$\endgroup\$
    – mattdm
    Commented Feb 25, 2014 at 9:04
  • \$\begingroup\$ Also, in that scenario, you could make the hotshoe of the receiver live at 160V ... could be unpleasant to touch, or even dangerous in case the flash is actually defective in some way... \$\endgroup\$ Commented Oct 9, 2018 at 23:25

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