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Norman 200B schematics or service info

David DiCarlo , Sep 28, 2012; 02:46 p.m.

Does anyone have the schematics or service info for a Norman 200B portable strobe? My unit does not always supress the afterglow and I'd like to attempt to fix it. thanks, david

Responses

Frank Skomial , Sep 29, 2012; 03:02 a.m.

When I was prototyping strobe designs, and drove flash tubes to destrution on purpose, either by applying too much energy, or by applying too high voltage, eventually some flash tubes at the end of life experienced longer light decay, ... perhaps what you call afterglow ? In most cases, near the end of tube life, the light intensity outut dropped drastically, and sometimes instantly. (excluding extreme loading that blows the tube instantly)

If I understant what your aftergow means, perhaps you just need to replace the flash tube (xenon bulb), if flash works otherwise. Other flash electronic components, (except a thyristor if there is one), should not cause the flash tube to glow longer, as it would be more of abrupt failure.

I would try flash bulb replacement first.

I do not know Norman 200. However, if the flash output variation is done by a thyristor (case when flash light duration decreeeses with smaller energy fraction setting), and you use partial power setting controlled by the thyrisor, other than tube components could be responsible, e.g the thyristor not shutting down fast enough.
Does the afterglow happens at full power discharge, or at fractional ratio setting ?

David DiCarlo , Sep 29, 2012; 08:11 a.m.

According to the repair person I spoke to, he said the more likely thing is that the controller board was going and not the flash tube. But then a controller board service makes him more money than selling a replacement flash tube, so I may have just answered my own question...

The after glow, when it occurs, happens at any power setting. There is no fractional ratio on the 200B - it uses a switch and a bank of capacitors to control the flash power. Very granular (50, 100, or 200 W-s) but simple and easy to implement. Nothing fancy like modern continuously variable power flashes of today.

There does appear to be some electrode plating some on the inside of the tube where the electrodes enter the tube. It's directional. I don't know enough about flash tube to know if that's normal or evidence of impending demise. I found a reference to 800 W-s bulbs that fit the LH2 head, which allegedly would give faster flash pulses and costs just as much as a normal 200 W-s replacement one.

In any event, I just traced out the wiring of the flash head, so I now understand what the connections through the cable are and are doing. If I can't locate schematics, I can continue to reverse engineer it myself. I'd just prefer not to...
There are definitely two SCRs (one 16A and the other an 8A) on the board inside, three 741 op amps, three TIP-29 TO220 packaged transistors and two TO-3 transistors (undoubtedly the inverter switches) on the board. All the rest are passive components, two of which are trim pots.

Frank Skomial , Sep 29, 2012; 09:06 a.m.

The metalic electroplating inside side of the bulb is normal and used to feed the polarization voltage to the tube through the siver like conductive coating or paint. Other type tubes use a mesh of wires instead. It is to feed the high voltage polarization pulse to start the avalanche of current flow through the tube.

Since the flash is so simple, when the huge avalanche of current starts flowing through the tube, the flash controller has no ability to quench this or make a longer discharge, until capacitors are discharged. The 16 and 8 Amps SCRs are perhaps used there to control the capacitor loading process, and not the huge current discharge instance.

David DiCarlo , Sep 29, 2012; 09:17 a.m.

Actually, an SCR is what controls this flash. While it's true that the tube won't shut off until the voltage drops below some value, an SCR will not turn off until the current flowing through it goes down to a low enough level. In the circuits I've seen with a variable output, the main SCR initiates the flash and another one shunts a capacitor across the first SCR which siphons off current to the point where the first SCR shuts off.

All in all, though, SCRs are relatively slow. Current flashes use IGBT transistors which can turn on and off pretty much at will. IGBTs are what allows Nikon's wireless optical remote control to work - their protocol sends out a series of extremely short lower power flashes to control the remote flashes.

If I get brave enough, I might build an IGBT controlled pack, either from scratch with a bank of caps or by gutting this 200B. But it'd be a rather ambitious undertaking...

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