[alijafary509]

Few weeks ago I bought online an old flash gun Philips 25CB. I was very excited about my first flash gun capable of bouncing up to 90 degree and having three power level setting. When I received the flash, I hurriedly inserted three freshly charged cells and turn it on. I waited for few seconds to let the flash fully charged. There was no response. I tried couple of times pressing test button but all in vain. Unfortunately flash was dead! I was very disappointed. I called to the first owner of the flash to file a complaint but his cell phone was powered off. After thinking a while about the current situation, I decided to give it a try to repair. In short repair was very straight and simple as I was excepting. I reassemble the flash inserted the cells and turn it on. This time it started charging with a whistling sound and after 5 seconds ready lamp was lit. I pressed the test button and there was a very powerful flash illuminating the whole room.

As I was already searching on the internet about using old flash gun on new DSLR, I was very conscious about the HIGH TRIGGER voltages on hot shoe that could FRY by gear. I set my DMM at auto range and measured the voltages of the only pin of the flash gun hot shoe. I was shocked looking at the screen of the DMM. It reads 150VDC. The excitement of the successful repair vanished by this measurement. According to available information on the internet, it was not safe to use this flash on my Pentax K-r. Being an electronic engineer, I was not going to let the flash go unserved so easily. So, I decided to modify its circuit and made it work.
I was completely in dark about how flash actually works. Some further searching reveals that camera triggers the flash mounted on the hot shoe by shorting the central contact pin of the flash to ground. I shorted the flash contacts to verify my freshly gained knowledge and it worked. My next thought was “what is inside the camera which does this job????”

I further searched on the internet to get service manual of my Pentax K-r for an exact answer of my question but could not succeed. At that moment a thought flashed into my mind. How much damage a 1.2V cell can cause to my camera??? Hold on I know we are talking about HIGH VOLTAGES but don’t forget our main power source is three or four 1.2V cells assemble in parallel to increase current capacity. To discharge the Xeon lamp in the flash we need 1000V to 4000V. To get such high voltage from a DC power source, an oscillator circuit oscillates the DC power which drives a step up transformer. The stepped-up voltages are then stored in a bulky capacitor which ultimately became our main power source to discharge the flash. All flash guns use the same principle. A friction of this voltage appears on the hot shoe contact.

Does only high voltage enough to destroy or damage an electronic circuitry? The answer is NO. We need a power source capable of delivering high current to damage a component as well. According to electrical law “stepping up voltage reduces the current in the safe friction it is stepped up”. Means when we step up 1.2 volt to say 1000 volt, we actually do almost 1000 times step up ultimately reducing the current capacity 1000 times. In my case I used 2100mA three cells in parallel thus total current capacity of 6300mA which reduces to 6.3mA after step up procedure. Most of the current flows in trigger plate to discharge the Xeon lamp. When I measured how much current flow between the hot shoe contacts, I was astonished to know that it was merely 130uA. So little current even at 150V is not enough to damage an electronic component. Now, I was not worried at all putting my flash gun on my Pentax K-r hot shoe. I made my first flash mounted on the camera and waited for any smoke or any other abnormality. Nothing happened. I made couple of further shots to test the camera and flash. Everything was working fine.

The last words, for electronic switching inside camera we have three options to use. A
1. BJT
2. FET
3. MOSFET
In my opinion a MOSFET is the most probable solution to be used for HSS. Even a small signal MOSFET can handle 350V plus 500mA current safely. In my opinion, high trigger voltages are not a problem as long as it belongs to a flash gun. So, keep enjoying old flash guns you got without any worry next time.

“THIS IS ALIJAFARY SAYING YOU KEEP FLASHING”

[Antanico]

Hello,
Is this your flash? http://www.fotos-fotoheray.de//ebay/131120108645.jpg
Can you clarify what are these aptions and where you set them up?
1. BJT
2. FET
3. MOSFET
Thanks
Ant

[alijafary509]

Hello,
Is this your flash? http://www.fotos-fotoheray.de//ebay/131120108645.jpg
Can you clarify what are these aptions and where you set them up?
1. BJT
2. FET
3. MOSFET
Thanks
Ant

This is the same flash but this is not mine.
BJT, FET and MOSFET are hardware components used by the manufacturer not a setting in the camera. Hope it will clarify now.

[Antanico]

This is the same flash but this is not mine.
BJT, FET and MOSFET are hardware components used by the manufacturer not a setting in the camera. Hope it will clarify now.

thanks, Yes I ment the same Similar Flash.
I am still not convinced in risking to fry my Pentax
All the best,
Ant

[Tanzer]

Sorry, but I would beg to differ. High voltage can breakdown an electronic component with very little current. Hence the static electricity precautions (anti-static mat, wrist/ankle bands, grounded furniture,etc) in an electronics lab. You can fry a component with static electricity from your bare hands, at levels you can't even feel.

Of course that kind of static damage mostly happens with fine electronic integrated circuits. It is likely that the components which trigger the flash at the hotshoe are discrete components which can handle more rugged environments.

However, since all newer flashes for many years have been designed with lower trigger voltages, I would not subject my camera to the higher voltages, particularly if the manufacturer says not to do this. Your camera might work for 100 cycles, but then after that, well, who knows.

[Digitalis]

Older pentax DSLR cameras like the*ist were deemed safe by pentax technicians with voltages up to 500v - however I recall some flashes delivering voltages as high as 850v. Most current digital SLR cameras are only designed to handle 5.5v safely, many studio monolight manufacturers have adopted this voltage as standard. Yes is it possible to use a high voltage flash - but it isn't recommended.

Actually an IGBT would deliver superior performance to a MOSFET with Higher current and voltages, IGBT's do appear in high end studio flash monolights but they are yet to be fully accepted into the mainstream.

[MPrince]

thanks, Yes I ment the same Similar Flash.
I am still not convinced in risking to fry my Pentax
All the best,
Ant

I see no point in risking my expensive camera gear, but you, of course, are free to risk yours if you so desire.

If you decide not to risk your camera, you will find this (or something like this) useful:

http://www.bhphotovideo.com/c/product/245292-REG/Wein_W990560_Safe_Sync_Hot_Shoe_to.html

[alijafary509]

Static charge can definitely destry electrostatic sensative devices like MOSFET as long as they are out of circuit. That is why they are delivered with a ring short circuiting the leads together. But when inside a circuit, they beccome as rigid as any other electronic component. They are no more prone to eletrostatic discharge. So, that is not a strong assumption in my opinion.
Moreover, one of my friend is using an old flsah with 250 trigger voltages on his Nikon D90 for the last two years without any problem so far.

BTW, i have taken 175 shots with my Philips flash and Pentax K-r and ccounting is ON......

As long as the manufacturers are concerned, they are all same stating "third part flashes can destroy your camera so always use our designed flashes"

[wombat2go]

I could go chapter and verse but:
Don't do it.

[BrianR]

Here's someone who claims to know of 2 k10d's and one k20d that were frazzled by a vivitar:

https://www.pentaxforums.com/forums/pentax-flashes-lighting-technique/87679-f...tml#post893196.

The official pentax answer in the thread also suggests using a Wein safe sync when using a third party flash. They aren't just saying 'don't do it', so that's nice that they support safe flashing instead of just abstinence.

[alijafary509]

One very simple question why Pentax so reluctant to give a brief reply about exact safe trigger voltages??? One thing is for sure now i am going to tear appart my Pentax K-r to investigate for an accurate answer.

Technically, it doesn't make any sense that an electronic switch could be fried at even 250V because they are quite rigid about handeling the power in sense of voltage and current.

Interesting answer by Pentax about safe trigger voltages: http://support.pentaximaging.com/flashes

[MPrince]

One very simple question why Pentax so reluctant to give a brief reply about exact safe trigger voltages???

Simple answer: Potential liability.

[SOldBear]

The issue of trigger voltage has been going around for years, but noone has come up with a satisfactory answer/explanation.

All camera manufacturers have some sort of warning against high trigger voltage. But none of them, except Ricoh, has ever officially set the limit.

There is the value "6V" floating around, especially among Canonites. But that value came about in an email message from a Canon technician (in Germany, I think) about a particular EOS DSLR model, not even generally for Canon DSLRs.

The only camera manufacturer that has an official statement is Ricoh. This is from GX200 User Guide:

[Pheo]

My wireless triggers will cope with upto 300v.

Problem solved AND you can do off camera flash, which is far more useful

[alijafary509]

Each there is a problem the solution is to spend some more money How pity is that. They think money grow on trees.