Strong Switcher "Main Mod" Error Failure Mode

[Ryan Gallagher]

Thanks Tony. I think I'm leaning towards caps/fuses first repair attempt. We have 3 functioning and 4 with issues. If I can get up to speed servicing these we may be good for a while for our single screen.

I was already headed down your advice path in my datasheet comparisons for replacement caps. Size and leg pitch seem to be the gotchya to avoid, all the rest is easily searchable on Digikey etc.

As far as the fuses in these. Are they generally slow-blow or fast-blow ceramic fuses? I'm guessing fast-blow based on the ceramic look... but minimal markings on mine other than the rating.

[Tony Bandiera Jr]

Thanks Tony. I think I'm leaning towards caps/fuses first repair attempt. We have 3 functioning and 4 with issues. If I can get up to speed servicing these we may be good for a while for our single screen.

I was already headed down your advice path in my datasheet comparisons for replacement caps. Size and leg pitch seem to be the gotchya to avoid, all the rest is easily searchable on Digikey etc.

As far as the fuses in these. Are they generally slow-blow or fast-blow ceramic fuses? I'm guessing fast-blow based on the ceramic look... but minimal markings on mine other than the rating.

For fuses, the 3 character marking (AGC, 3AG, MDL, etc.) will tell you if it is fast acting or slo-blow.

In the 1/4 x 1.25 inch fuse sizes, ceramics marked ABC are fast, and MDA are slow. (Cooper fuses) Other manufacturers may use different markings.

[Mark Gulbrandsen]

This is the very first switcher I worked on back in 2004. It's very important to use the exact same fuses in a switcher that were originally in it. Exact equivalent fuses are also ok. Having repaired hundreds of them from all over the US, most issues are blown transistors and switching transistors. I NEVER had a single control board failure. There are also diodes on the inside area between the heat sinks that fail. It is important to check all of the semiconductors on those two boards. The most that fail are the 1 to 3K switchers, later de-rated at the top end to 2.5 kw. Theaters still ran 3kw lamps in them. The larger rectifiers are the same, there are just more switching and rectification modules in them. If you have any V-1 switchers throw them in the trash. Semiconductors are NLA for those. You will also usually find burnt up wiring in them. See Photo.

Also write which color transformer lead goes to which terminal, up on the heat sinks, or take pictures. If you hook em up out of phase and turn it on, Austin will no longer exist.
You may see a crack in one or more of the semis as in the picture. No worries. Be sure to replace All OF THE heat sink mounted SEMI'S, and use brand new insulators with a very light schmear of decent heat sink compound on both sides of the insulator! ! !
Also, be sure SG-405 inrush current limiters are installed. Some older units have other types that eventually fall apart or crack. Check all the PCB mounted diodes on the boards that are behind the heat sinks. Occasionally one or more of those can short out. I never had a unit with bad capacitors. Replacing all of them will be expensive, but I always tested them with a meter for shorts. Lastly... The first turn on should be done from at least three blocks away just for safety's sake. If there is no mushroom cloud, then you may approach the rectifier.... Just kidding.... They have always worked fine after a rebuild.