Strong Switcher "Main Mod" Error Failure Mode

[Ryan Gallagher]

Anyone familiar with the failure mode on strong switch mode supplies when the "main mod" red error light illuminates?

We were doing an inspection and previewing a couple reels of Clockwork Orange.

We heard what sounded like a lamp strike ping on the projector with a recently made good spare and tuned supply (wired for spot/manual mode).

Lamp stayed on and while we were investigating we noticed the "Main Mod" error light had illuminated, which manual says refers to a main board fuse opening. But manual also says operation should cease when that occurs. The lamp stayed powered for a couple minutes despite the error until it started to waver in intensity and then extinguished. About the same time I turned off the lamp switch we heard another pop from the supply (and it was not the breaker, but I haven't checked the resettable fuse yet).

My co-projectionist thought he smelled the magic smoke at that point but I did not notice it. Having spares I did not try to re-power it, I removed power at that point. We swapped in a spare in 10 minutes and were back to finishing our tech-check (but with a watchful eye on the 2nd spare).

If anyone else has encountered main board fuse errors and has tips for diagnosis or repair i'm all ears.

Seems my supply woes from prior threads are not quite over yet.
Thanks.

[John Eickhof]

what lamphouse model, type, and serial? is it a followspot or is it a projection lamp, the xenon troupers use reverse polarity of the bulb possibly the dc is reversed at the cannon plug on the power supply...check your wiring.

[Mark Gulbrandsen]

If memory serves me there is no fuse on the control board. If there is then it may be a solder in type, but out of over a hundred switcher repairs, I never had a bad control board, it is well isolated from the high power end of things. Otherwise, Replace all the switching transistors, high speed diodes, and all fuses(even if they check good). Check the thermisistors and all the diodes on the switching boards, and check them all by un-soldering one end. The pop you heard was either a high speed diode or switching transistor fail. Note that these pics are of a 1 to 2.5K switcher. The larger switchers just had extra module sections added in, but driven by the same control board...
Also, if you have type one switchers, they are door stops. The main switching semi's for those are long obsolete. Not even Strong can fix those.

[Ryan Gallagher]

If memory serves me there is no fuse on the control board. If there is then it may be a solder in type, but out of over a hundred switcher repairs, I never had a bad control board, it is well isolated from the high power end of things. Otherwise, Replace all the switching transistors, high speed diodes, and all fuses(even if they check good). Check the thermisistors and all the diodes on the switching boards, and check them all by un-soldering one end. The pop you heard was either a high speed diode or switching transistor fail. Note that these pics are of a 1 to 2.5K switcher. The larger switchers just had extra module sections added in, but driven by the same control board...
Also, if you have type one switchers, they are door stops. The main switching semi's for those are long obsolete. Not even Strong can fix those.

Minor correction on my end, the manual says "Primary Board Fuse"... not main board fuse. I would assume primary refers to the high power boards, and not the control PCB. I do see a fuse in your photos, but might have been a symptom of a deeper problem that needs to be diagnosed.

Thanks for the input. Lamphouse is a Super80, I'll share exact switcher model when back in the booth (but it is either a 3-5k or a 4-7k Milspec black suitcase type without the spot/console switch).

After rewiring the pinout on the MS connector for Spot/Manual operation, it had been operating fine for a month, so doubt it is a polarity issue, but will certainly check the others I wired to spot/manual.

Now I have two that are worth fully breaking down to get at the boards for detailed inspection, other just had unstable output. Thankfully I have two more spares standing by due the prior efforts, so not in panic mode yet.

[Mark Gulbrandsen]

Correct! With semiconductors, they usually they blow to protect the fuse... this is definitely true in audio power amplifiers. But in high current equipment, some times the semiconductors hang in there for a few seconds and then both the fuse and Semi are destroyed.

[Ryan Gallagher]

The model details of the bad one since requested.
The one that replaced it is identical except had "R" in the type name.

It appears to have been one of the reconditioned units at one time, according to Film-Tech's label.
Type: 6280107 SN 548
100-150A DC
30-50v DC
3phase 208-240

Film-Tech's label said V1 4.0K, but I believe that type no is the 4-5K unit, at least the 6280107R that replaced it is?
Though if was actually 4K max (perhaps due to being a V1 unit), I could have been pushing it's limits with my 4.0K lamp running at 135A spec.

While not an exact type no match, the 6280110 manual is probably closest in the archive (but for the 4-7K variety with hardwire connectors)
http://www.film-tech.com/warehouse/manuals/6280110.pdf

The MilSpec wiring for Spot/Manual operation Appendix I found previously in other manuals that make reference to this exact unit:
http://www.film-tech.com/warehouse/m...STR6200016.pdf
and
http://www.film-tech.com/warehouse/m...STR6200014.pdf


If it's Version 1 as the film-tech tag says, it may be hard to revive due to parts availability? and maybe not even worth trying if it is a 4K max unit?
Had been in cold storage for 10 years (in our possession), before I rewired the connector and put it into service. It maybe didn't like coming out of retirement.

Photos:


Have not opened after the failure, will have to wait for a slower period when most of the workbench space is not occupied.
But did at least plug it back in one time and confirm the "Main Mod" error is still visible even in standby.
First thing I'll do is get down to the primary boards and check fuses and inspect for cracked/popped components/burns etc.

Cheers.

[Ryan Gallagher]

I think I was confusing "Type 1" as Mark said, and "Version 1" as the tag says. Are Type 1's vastly different looking? externally? Or just an early revision of some models?

[Mark Gulbrandsen]

Seems to me they were all suit case size... Judging by the one they make now for follow spots, they must be at Ver 4 or5.

[Paul H. Rayton]

Not sure if the problem is at this end, or elsewhere, but Ryan's 3 photos are not showing up for me here (Windows 11). I see a blank box and a message, "Invalid file specified" at each image location when I click on it. Can you plz try re-posting the pix? Thks

[Ryan Gallagher]

Weird, the images show up for me on chrome but not on my phone. taken with iphone and mailed to myself then uploaded on a chromebook.

Here they are as attachments.

[Paul H. Rayton]

Thanks -- photos now OK; sadly, I don't have any good answers to your question(s)! Presumably others on here will recognize something there and have ideas.

[Mark Gulbrandsen]

Too many off brand items in the photo chain. Get rid of Apple and Chrome. Get Android and Firefox.

[Ryan Gallagher]

Happy to report the drop in spare has been solid for two screenings thus far. Will circle back to this topic in August when we have scheduled maintenance hours.

[Ryan Gallagher]

If memory serves me there is no fuse on the control board. If there is then it may be a solder in type, but out of over a hundred switcher repairs, I never had a bad control board, it is well isolated from the high power end of things. Otherwise, Replace all the switching transistors, high speed diodes, and all fuses(even if they check good). Check the thermisistors and all the diodes on the switching boards, and check them all by un-soldering one end. The pop you heard was either a high speed diode or switching transistor fail. Note that these pics are of a 1 to 2.5K switcher. The larger switchers just had extra module sections added in, but driven by the same control board...
Also, if you have type one switchers, they are door stops. The main switching semi's for those are long obsolete. Not even Strong can fix those.

Update on this longer term "as I have time" project.

Supply is torn down on a workbench that I don't need for other things constantly. I was immediately able to find two blown ceramic fuses on the primary or secondary boards. I also added to my toolbag a decent ESR meter and was able to identify several capacitors that are likely out of spec and have removed them for replacement. Replacing all larger caps might be the way to go though. The high speed rectifier package legs all appear to meter as expected in circuit. But do you think I need to desolder them all and test again or maybe just replace them all?

I'm torn what is easier if desoldering them all while leaving them attached to the sink is easier, or freeing them from their thermal adhesive and removing them individually. I do have a Hakko desoldering gun, but even the larger nozzle tips were a bit small for the giant capacitor legs/joints, made it work though.

I'm, also tempted to try my luck with an intial repair that only addressed the bad caps and fuses. But it might just pop again and I'd have to tear it all back down.

The "OK" marks in the photos are from a previous repair apparently. I don't think I had finished testing the caps when I took these, all the large blue caps are suspect (puffy tops etc).

[Tony Bandiera Jr]

RE post #6 The "R" after they type number means it was factory refurbished.

On to the post above (posted on my birthday):

Replace all of the blue caps. IIRC they were a brand hit hard by the infamous "Capacitor plague" (And they weren't the best anyways.)

When replacing large electrolytics in something like a switch mode supply, compare the data sheets carefully. (Digi-Key has data sheets available with almost every part on the part's page.) You want to get same or lower ESR, same or slightly higher capacitance, same or higher voltage rating (Watch the physical size), ALWAYS go for higher temp ratings (105c is the common maximum, but knowing Wrong the originals are probably 85c...so replace with 105c rated caps.) And finally, some caps offer a frequency rating go for higher, not less than 100khz in a switcher. All of those tips will help you end up with longer lasting replacements.

And for giggles, check the spec sheets of the OEM caps using the part numbers on the caps.

Mark has dealt with hundreds if not thousands of those switchers, I have done a about 75-100 over my time as a tech.. but I'd never had to replace failed semis..but I had loads of capacitors fail on me.

This reminded me of an old post on the old forums:

https://www.film-tech.com/cgi-bin/ub...=009719#000012 (see the 7th "paragraph" of that post.)

I also did a 7 screen with the older, bigger black case switchers were the failure rate was six of the seven: On commissioning and cutting plates, two were completely dead, one worked for about 20 minutes and died with no drama, two more failed after a few hours.....and one went up in flames right as the owner was standing at the machine chatting with me. Wrong did send out replacements where only one of those was DOA. After that, I went with Christie consoles and LP Assoc. Lamphouses and rectifiers.