Electronic Gurus wanted...

About a year ago I tried to resurrect a flash unit that had been sitting in storage for about 5 years. It was a Metz 76 MZ5. I hardly ever used that flash and as a matter of fact, I was about to send it for service, because the TTL was not working. Unfortunately I had to move around that time, so the flash unit stayed in storage for more than 5 years, until I decided to get my stuff from storage about a year and a half ago.

 

To keep things short, I recharged the battery that was miraculously still working, then I plugged the battery to the flash and turned it on. I knew I had to reformat the Capacitors, so I turned down the power and slowly began to hit the TEST button to fire off the flash. Everything seemed to be going well, but at around the 4th push of the TEST button, the flash made a very loud POP and all the little lights went off ! I figured the flash was done, so I put it back in its box and placed it on a far corner shelf in my closet, never to be seen again...

 

Today I decided to investigate what exactly happened to that flash. After figuring out how best to open it up, I saw what looked like a mini explosion on the main electrical board. I'm not an electronic expert , but it looked like a Resistor and a "Capacitor' were severely damaged but everything else was intact.

 

The soldering of those units did not seem that complicated so I figured I could replace those two items and get the flash going again. unfortunately, I don't know what parts these are. The Resistor is completely fried away and what looks like a capacitor has no markings on it. I tried calling Vilatec the distributor of Metz products in NJ, but they said they do not support Metz products anymore and do not have any parts. Can anybody tell what those parts are by viewing the picture below ?

 

I suspect someone can help, but you will need to get clear photos that show the part numbers or copy and add those to your note.

Which are the parts that have failed? I'm struggling to see any obvious signs of damage in the photo.

 

Resistors have a color band code for value and tolerance, and most poly film capacitors, such as those pictured in blue use an alphanumerical code for the value and tolerance with the working voltage stated.

 

Clearer photos of the bodies and any markings on the parts in question would be helpful.

 

Edit: I now see the damage to the grey capacitor and adjacent resistor. My suggestion is to remove them from the board and clean with isopropyl alcohol so that hopefully you can reveal some markings which disclose value. Barring that, you would need to find a schematic for you flash unit and determine which parts in the circuit failed, so that you know what the appropriate replacements would be.

The picture might not be too clear, because I took it with my iPhone. The parts in question if you can see them, are right in the center of the image. There is a Black cube with a smaller grey cube in front of it. There is a blackened hole where the "capacitor ?" failed on the smaller grey cube with a "K" on the top. In front of the grey cube there seems to be a resistor, but it is blown away and I can't read the markings on it. In front of the resistor you can see the blackened wires where the explosion happened. There are NO markings on the black or grey cubes that show damage that is why I was asking ? The board seems to be intact, but underneath it, there are dark marks where the explosion occurred just as you see on top.

If you can't make out any markings and don't have any technical paperwork on the flash, then you are pretty much SOL. Electronic components cannot be visually distinguished in this situation, as capacitors and resistors may have the same external characteristics while varying in capacitance, resistance or voltage rating, in addition to other factors.

 

Your only other option would be to persuade someone with the same model of flash to disassemble it in order to see what undamaged components look like, or even better, measure as, out of circuit.

If you can't make out any markings and don't have any technical paperwork on the flash, then you are pretty much SOL. Electronic components cannot be visually distinguished in this situation, as capacitors and resistors may have the same external characteristics while varying in capacitance, resistance or voltage rating, in addition to other factors.

 

Your only other option would be to persuade someone with the same model of flash to disassemble it in order to see what undamaged components look like, or even better, measure as, out of circuit.

 

I sent an email to Metz.com. I was just hoping that one of you "seasoned" photographers might give me a clue.

The capacitor is only damaged because the resistor next to it has burned it. The capacitor is probably still functional. The resistor is, literally, toast. Too badly charred to even guess at its ohmic value.

 

However, I strongly suspect that replacing the resistor won't cure the fault. There's obviously an overload or short circuit downstream of it. Possibly a diode or other active component.

 

It needs a thorough diagnostic and tracing with a multimeter to find the real culprit. And a circuit diagram would really help.

 

I've never seen a Metz schematic released BTW, but Metz flash circuits are generally not very innovative and pretty easy to work out.

 

P.S. Is that the charging socket in front of the blasted capacitor? And is it a figure-of-eight mains socket?

Edited November 12, 2020 by rodeo_joe|1

As an electrical engineer, I totally agree with rodeo joe.

Thanks rodeo(The walking encyclopedia) _joe |1 ...

 

P.S. Is that the charging socket in front of the blasted capacitor? And is it a figure-of-eight mains socket?

I'm not sure what it is ? I have a whole set of capacitors at home, but none of them look like that ???

Edited November 12, 2020 by hjoseph7

I'm not sure what it is ?

If it's not a socket, then my best guess would be that it's an encapsulated inductor (choke) as part of a smoothing CCT.

 

What you've shown appears to be part of a charging cct for the rechargeable battery. The simplicity of the tracks on the PCB leads me to believe that.

 

On longer inspection of the picture, it's difficult to determine where the seat of the fire/blast originated. The capacitor might have blackened the resistor, or vice-versa. Whatever. Those components both need removing and replacing, and the PCB thoroughly de-carbonising. Any black deposit left could 'track' and cause a similar blast in future.

 

That still doesn't get to the actual cause of the blast, which needs further investigation.

 

Warning! Pure guesswork follows:

My best guess would be that the grey capacitor is an X class anti-spike device. Usually 400v/250v ac rated and with low self-inductance. Possibly 10 nanoFarads in value.

 

The resistor remains a complete mystery unless rubbing some of the blackening away reveals some colour bands intact.

The soot and char pattern seems to suggest that the resistor overheated, not the capacitor.

The soot and char pattern seems to suggest that the resistor overheated, not the capacitor.

 

I looked at it again with a lighted magnifying glass. There seems to be a charred hole in the front of the grey cube. Right in front of the grey cube with the 'K' markings on top, there seems to be a Resistor that is burned beyond recognition. Now I have had Resistor explode on me before, but not with that loud sound. The sound was like a gun being fired, really loud !

 

I suspect that something caused the grey cube to explode, which then obliviated the small Resistor in front of it , or it could be the other way around. Maybe the small Resistor blew up and caused the hole in the grey cube ? On the side of the grey cube with the hole in the front, there are markings that look like this: "H40 MKT 400 09" as far as I can tell ?

MKT is (was?) a subsidiary of Philips that manufactures capacitors.

 

If you can show more of the burned board and its relationship to the rest of the flash, then maybe we can get a better idea of its function, and hence the purpose of the resistor and capacitor.

I suspect that something caused the grey cube to explode

My money is on the resistor. The soot and char pattern of both the PCB and presumed capacitor all point in that direction. Very similar situation to the power supply board of my GE electronic air filter I replaced recently and very similar to many situations I've seen during my career in the electronics industry.

Of course the big question still is what caused the resistor to overheat. Failure Analysis 101.

Here are some more shots. I had to break them up so that Photo.net would not flag them. I shot these with my DSLR so they should be a little sharper. There should be 6 pictures total. This is a picture of the bottom board . The wires that lead to it come from the top "mother board" . There is no damage to the top mother board as far as I can tell, so I left it alone.

 

Picture #1, Picture #2

 

 

Edited November 14, 2020 by hjoseph7

Picture #5, Picture #6

 

 

Picture #3 , Picture #4

 

 

Oops something is screwy here ??

Picture #5, Picture #6

 

 

Definitely the resistor, but their probably is another fault responsible for it to overheat.

I sent an email to criscam.com the people in Arizona who use to service Metz flash. Not sure if they will get back to me though...

Most of that board seems like a major waste of fibreglass!

 

I presume that board comes from within the flash head, next to the Xenon tube?

 

If so, there'll be 360 volts D.C. floating around in there, and at many amps. Any short is going to be pretty dramatic.

 

It appears to me that one of the resistor solder pads shorted to another connection, causing the solder to melt and burning out the resistor. Causing collateral damage to the adjacent capacitor.

 

Does the board shown sit adjacent to anything it could have shorted to?

 

Is there charring or damage to something else within the flash head?

 

You need to determine what caused the flashover/short before anything else.

 

Worst case scenario: The flashover put 360 volts down a low voltage part of the circuit and fried a CPU controller or similar.

 

Best case: The damage is localised to that board and whatever it shorted to.

 

But I suspect a single burned out resistor wouldn't result in a total shutdown of the entire flash.

If I had to guess at the function of that board, it'd be that it houses the flash quench capacitor - large blue capacitor housed on the far end.

 

Metz are fond of using a flash control method that involves switching a quench capacitor across the Xenon tube to turn it off. The quench capacitor usually has a value of 3.3uF at 400 volts working.

 

When the flash duration is deemed sufficient, a thyristor or other solid-state switching device couples the capacitor in parallel with the flash tube. This momentarily shorts the plasma in the tube and diverts energy away from it. The plasma is starved of energy and dies, and the light output is quenched.

 

It's quite a clever method, requiring only a switching device to be turned on, and only a small amount of energy to be 'wasted' in charging the quench capacitor.

 

That mysterious black box at the end of the board might house the solid-state switch.

If I had to guess at the function of that board, it'd be that it houses the flash quench capacitor - large blue capacitor housed on the far end.

 

Metz are fond of using a flash control method that involves switching a quench capacitor across the Xenon tube to turn it off. The quench capacitor usually has a value of 3.3uF at 400 volts working.

 

When the flash duration is deemed sufficient, a thyristor or other solid-state switching device couples the capacitor in parallel with the flash tube. This momentarily shorts the plasma in the tube and diverts energy away from it. The plasma is starved of energy and dies, and the light output is quenched.

 

It's quite a clever method, requiring only a switching device to be turned on, and only a small amount of energy to be 'wasted' in charging the quench capacitor.

 

That mysterious black box at the end of the board might house the solid-state switch.

 

I got an email from the criscam.com today, he stated that it could have been the Main Capacitor which caused the circuit burn or, vice versa. Nothing more. Apparently criscam.com does not service Metz flashguns anymore ever since Vistech their distributor based in NJ, dropped the Metz line 2 months ago. He recommended that I invest in a new flash. Hmm at least he could have given me the name of the parts since he has serviced these units before. That's why I didn't send my flash to them in the first place, they are all about money.

 

I also got my hands on the Metz 76 Manual and it states DANGER Never disassemble the flashgun There are no components inside the flash gun that can be repaired by a layperson. Maybe Metz manufactures their own Capacitors and Switches ? Oh well, at lease I still got my 50 MZ5 which I rarely use. Thanks for your help.

Edited November 17, 2020 by hjoseph7

Most of that board seems like a major waste of fibreglass!

 

I presume that board comes from within the flash head, next to the Xenon tube?

 

If so, there'll be 360 volts D.C. floating around in there, and at many amps. Any short is going to be pretty dramatic.

 

It appears to me that one of the resistor solder pads shorted to another connection, causing the solder to melt and burning out the resistor. Causing collateral damage to the adjacent capacitor.

 

Does the board shown sit adjacent to anything it could have shorted to?

 

Is there charring or damage to something else within the flash head?

 

You need to determine what caused the flashover/short before anything else.

 

Worst case scenario: The flashover put 360 volts down a low voltage part of the circuit and fried a CPU controller or similar.

 

Best case: The damage is localised to that board and whatever it shorted to.

 

But I suspect a single burned out resistor wouldn't result in a total shutdown of the entire flash.

There is no charring or damage to the rest of the flash as far as i know ?