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How to discharge the photo-flash capacitor of a DSLR (here K-30/K-50/K-500)
Posted By: photogem, 06-16-2019, 02:33 AM

Several times now we had discussions about how to discharge the photo-flash-capacitor of a DSLR body when one for example needs to replace the solenoid.

1. Pentax bodies with pop-up flash which will open without the battery inside the camera:
K10D, K20D, K7, K5 series, K3, KP, K1 (Samsung GX10/GX20)
K-30, K-50, K-500, K-S1, K-S2, K-70

2. Pentax bodies with pop-up flash which will open only with batteries inside the camera:
*ist DS/DL (Samsung GX1/2), K100D, K110D, K200D, K-01 (!), K-m, K-x, K-r

Which means that with all cameras in Pos. 1 you can discharge the flash-condensor by just taking the battery out and wait 24-36 hours (I have never measured the time
because I always discharge it anyway, it is the safer way to go.
But with all cameras in Pos.2 you have to open the pop-up-flash with the battery inside! (Li-Ion with K-01 and K-r, NiMH with the others)

Which means the photoflash-capacitor will charge and can give you a nasty shock.

But also if you don't want to wait and work right away, you need to know how to discharge the condenser properly.
Particular with the Pentax K-30/50/500 you can get a a nasty shoch but as well with the K100D, K200D and others..... I just haven't opened one of them for a long time now so I can't remember the spots where you don't want to touch at all. But with the K30/50/500 it is here (marked with red dots):

Because I have replaced now so many solenoids and anyway play safe, I built myself a little device which allows me very quickly to discharge this capacitor:

I use a 60W/240V standard lightbulb (so the old type with filament, no LED etc!) A 1-1.6 kohms/10W resistor will do the same but you can't see the discharge,

I find that the strong short illumination is much more useful. One could also use a Voltmeter, but it has to be the oldfashioned type with a needle and yet it will take several minutes to discharge, not a good idea either.

It is important to find out the positive=plus-pole of the capacitor because touching this one and the metal of the k-mount (which is minus/-) of your body is sufficient, here shown on a K-500:

Capacitors have their minus (-) pole marked with a long stribe along one side The capacitor of the K-30, K-50 and K-500 have the plus-pole towards the front (K-mount side)!:

The lightbulb illuminates quite strongly when you discharge it (mine is protected against shock because I use it regular):

There have been several times when I believed the photoflash-capacitor should be discharged but because of this error and having also received this surprise of a shock (not dangerous to a healthy person but very unpleasant and particular having the danger that while unscrewing or soldering the solenoid you slip off with the tool and do very bad damage) I now always test with the lightbulb: Often it illuminated but a shorter time.

Flash-capacitors are built to work very fast so they charge and discharge very fast. They might not fully charge if one is fast but the residual voltage is enough to do damage.

There are capacitors which are difficult to reach, for example K-S1, K-S2 and K70. But with those you can wait those 2-3 days because their pop-up-flash opens without battery inside.
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06-16-2019, 02:44 PM   #2
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One word of caution - well a few actually. Discharge an electrolytic capacitor and it's safe, right? Well, not necessarily. I didn't believe this until I saw it with my own eyes... An electrolytic capacitor has some ability to recharge itself after it has been discharged. Really. It has something to do with charge stored in the electrolyte which migrates back onto the plates. I've discharged electrolytic capacitors, then hooked a voltmeter up to verify safety. To my shock, I saw the voltage slowly rise from 0 back up to some significant value. Guys who work on vacuum tube guitar amplifiers (high internal voltages) discharge the caps, then leave a clip lead attached to both leads on the cap. Prevents nasty (and dangerous) surprises.
06-17-2019, 02:15 PM   #3
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I don't agree with you at all.

This is not a (vintage!) valve-/ tubepoweramp with ancient electrolytics or... allthough of highest quality... paper-in-oil capacitors ... which *CAN HAVE* have what is called dielectric absorbtion (DA). Usually DA is the case with capacitors of inferiour quality of if they aged. Pentax had always used high quality photoflash capacitors, often Rubycon which are some of the very best ever made (for audio and particular those Japanese Rubycon "Black Gate" electrolytics were the cream of the crop, no other manufacturer ever was able to produce such a high quality).
I also found ELNA caps inside some Pentax, not bad at all either (the equivalent were ELNA Cerafines for audio).

I have discharged many high-voltage capacitors in my life... DA never was a problem.
And I never ever came across DA after I discharged a Pentax photoflash.
06-18-2019, 11:35 AM   #4
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QuoteOriginally posted by photogem Quote
This is not a (vintage!) valve-/ tubepoweramp with ancient electrolytics
New tube guitar amps are very much alive and well, and they use new manufacture electrolytic caps, not ancient ones. Current flat-screen TV's use electrolytic caps in their power supplies; I've repaired them. Do a quick search on 'photoflash capacitors' and you'll see that the most common ones are electrolytic. There are many quality levels and price points. I wasn't trying to say that an electrolytic cap will always recharge itself, only that some can. I've seen it. Since most of us are not capacitor experts, it pays to err on the side of caution when working with a device capable of storing dangerous (to humans) amounts of energy. Leaving a clip lead connected across the cap's terminals continuously drains the charge in case DA is present.

06-18-2019, 04:24 PM   #5
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That's the problem when one forgets what one learned in physics plus the problem when one does not verify:

Take 3 x 9V PP3 batteries, connect them in series and then touch the poles:
You've now got 27Volts/DC and thus the maximum DA which could possibly "hang around" a cheap or faulty photoflash capacitor.

According to modern warnings 60V/DC and 25V/AC and more are potentially dangerous (and this takes medical reasons into account!)

In old days it was double: 120V/DC and 50V AC.

So what you can see on your voltmeter and what happens if you touch lets say 27V .... your turn to try it out and verify it!

The photoflash capacitor stores about 220Volts, maximal DA (of a bad capacitor) is approx. 10% (paper-in-oil caps due to their special construction in tubeamps up to 20%).
You won't even feel a tickle. This you can feel if you touch it with your tongue which is unlikely to happen when you work on a DSLR

To keep the capacitor shortened is a very bad idea because the space around is very narrow, here you are actually prone to do more damage than good.
Aside of it being absolutly useless even if done right.

So opposed to hollywood B-movies you also won't get a shock if you touch a 12V car-battery

Regarding electrolytics in valve-amps: Only very high plate-voltages can cause problems there, particular if amplifiers using triodes such as an 211, 845 or like the Altec 1570 the legendary 811. Yes, then you must be very careful. I have worked with Harold Beveridge valve-amps which feed high-voltage directly to electrostatic speakers as well as valve-amps feeding Stax- and Jecklin-Float ESL headphones. One of them stands right next to me.

It is very thoughful of you that you wish to warn people of potential danger but there isn't any.
06-18-2019, 07:21 PM   #6

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Here, we're also talking about a pulse type shock (which can still be very dangerous if taken through the heart - e.g. defibrillators) but not continuous voltage like the AC line. For that reason, you might get a good shock that is going to wake you right up, but there is usually less risk involved than with the equivalent AC voltage. There can be the possibility of burns since the peak current is high and if concentrated enough (small contact area) will produce tissue heating. Bottom line - DO exercise caution, but it's unlikely that much of a danger is presented AFTER the initial discharge. The discharge energy is proportional to the size of the capacitor and the square of the voltage so 200 volts on the same capacitor will carry 4 times as much energy as 100V. That has to be dissipated somewhere (when the capacitor is shorted) - just a good idea it's into a load. Give it a few seconds, because all the water may not have run out of the pond in that first initial surge. Then it should be rendered safe. If you do take a full shock, chances are, you'll do more damage by knocking everything off your bench and breaking your hand (or some other anatomical item) in the process than from the shock itself.

Last edited by Bob 256; 06-18-2019 at 07:27 PM.
06-19-2019, 09:22 AM   #7
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Again, this is based on theory and not practice.

So lets have some practice:

I checked the voltage on the photoflash capacitor of a Pentax K-30 today:

Test. No.1:

- freshly charged: 330V/DC (so actually the maximum voltage the cap can handle!)
- directly after discharging: 0Volts
and then... as to be expected, after 5 min. it climped up to 12,06V(DC)
I waited a bit longer, measured again, voltage dropped a bit, so I was curious if it would drop even further or climb up again which it eventually did:
- After 90min: 24V/DC

So I took a 12Volt car light-bulb: It wouldn't even light up the slightest (that would have been the pulse, the shock)

Remaining voltage: 0.26 Volts!!

Test No 2:

Same procedure just that this time instead of the I touched it: ZERO, not a tingle.
I made my fingers wet: ZERO again.

The available current is almost NIL. There is no pulse, there is no shock, there is just nothing.

Nothing to worry about.

People who have critical equipment within their body will know what to care about because they are well warned what to do and what not!

Ah... I did the same test with the electrolytic Rubycon Black-Gate capacitors of my DHT valve amplifier: 100 + 100 uF! So quite a bit more capacity.

12,6 V maximum after 3 hours. Lightbulb didn't do the tinest twinkle... remaining voltage again 0,26 Volts

After 24 hours it was down to 0.26 Volts/DC and went down to 0Volts over the next few days.

These tests confirmed what for over 30 years never was a problem:
There never was any residual/parasitic re-incarnating critical voltage which could do any harm to a normal person.

Nevertheless a different option for discharging savely, which came from another member:

- Set your Pentax in its menu C-3-16: Shutter Release while charging flash: Set it on 2 (yes)
- In M-Mode and and time set to 1/200 seconds + flash popped up/open
- take a series of photos (best set it for this) and then immediately switch the camera off!

- Right then the voltage is still too high: I measured 126V/DC!

- But if you wait 1 day, the photoflash-voltage will has dropped down to an uncritical 26 Volts and 2 further days later to almost 0V/DC

Last edited by photogem; 06-28-2019 at 03:13 PM. Reason: added another option

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