Film-Tech Forum ARCHIVE: Strong Power Supply failure

This is topic Strong Power Supply failure in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

To visit this topic, use this URL:
https://ft-forum.com/ft/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=1;t=009043

Posted by Michael Trudell (Member # 3344) on 12-28-2007, 10:56 PM:

Greetings all, hope everyone had a good holiday.

The situation is a Strong Switching power supply, model 628005. AC volts are on pins 2 and 4, muffin fans, lamphouse blower and ignitor work in manual, and AC volts are on 5 and 6 when lamphouse is switched on (switched to local not auto), but there is no power relay operation in power supply, no no-load DC voltage and finally no lamp operation.

This arrived DOA.

After checking out some of Mark Gulbrandsen's posts on typical Strong power supply failures and visually looking over all the components, checking the big fuse etc, I only found a small burned out capacitor (C55) on the motherboard. Before replacing just that and risking some other kind of subsequent implosion (or worse), is there just another motherboard I can replace it with? (p/n 61-72002) Any other comments?

Posted by Mark Gulbrandsen (Member # 72) on 12-28-2007, 11:09 PM:

Michael,

Is this the suitcase model or compact type switcher? I can give you several things to check on either model but need to know which one you have first.

Mark

Posted by Monte L Fullmer (Member # 2797) on 12-29-2007, 02:28 AM:

That's an old black suitcase, circa 1989-1990. I lost 3 of these "05's" in the last two years ..

Michael, look on the manufacture plate and you should see the month and year made.

Posted by Mark Gulbrandsen (Member # 72) on 12-29-2007, 10:35 AM:

Power it up and read the DC across the large blue electrolytic's terminals... What do you get there? It should be pretty high like around 200 or more volts dc. BE careful the charge on that cap is LETHAL! be sure to drain it out with a 1k ohm 5 watt resistor if it doesn't drain down by itself in a short time. Some of the switchers don't have bleeder resistors in them... ditto for a small set of electrolytic caps down on the main board. Its not that difficult to rebuild the main board and all the semicinductors are available off the shelf.

We stock a substantial amount of parts for the "Compact type" switchers but not many parts for the suitcase models. I just order them as needed because there are not many that fail around this neck of the woods... in fact I don't think there are that many of them at all in the mountain states. I do get 4 to 6 compact models in a month for repair though.

Mark

Posted by Michael Trudell (Member # 3344) on 12-29-2007, 03:06 PM:

Thanks for everyone's response. The date of manufacture says 06 97. I am reading a healthy 330 VDC on the capacitor.

I haven't seen the two different kinds side by side but I believe it is a suitcase model, measuring 22" x 19" x 8"

Posted by Phil Hill (Member # 371) on 12-29-2007, 04:04 PM:

That is the "suitcase" model...it is more reliable than the "Compact" model.

The fact you have AC on terminals 5 & 6 of the terminal strip indicates all the primary PS and lamphouse interlocks/circuits etc are OK.

Most likely the problem is with the contactor control circuit (Q2 perhaps) or the contactor coil itself.

Be VERY careful of that 330 vdc on that cap...it holds a charge for a very long time and is lethal!

Posted by Mark Gulbrandsen (Member # 72) on 12-30-2007, 09:19 AM:

Phil,

If he has the 330 voltws dc on the cap that means the main contactor IS pulled in.... Any other thoughts???

I recently had one where the three phase bridge rectifier module had shorted and exploded and the three 50 watt resistors next to the contactor had actually melted their ceramic coating off! The three phase bridge module those rectifiers use is now obsolete but we were able to get some through an electronics parts vendor in England.

Strong will charge you well over 700.00 to repair it... When it may be just a simple repair. My cost to completely rebuild the Compact Switchers is usually under $100.00 in parts.

Mark

Posted by Phil Hill (Member # 371) on 12-30-2007, 11:04 AM:

Those 50-watt resistors are across the contactor contacts to allow the main filter caps to pre-charge so as to avoid a high inrush current when the contactor is energized.

Posted by Mark Gulbrandsen (Member # 72) on 12-30-2007, 12:49 PM:

YEP! And a very dangerous way to prevent inrush... Allows some charge to always be on the cap! [Eek!]

. I can think of at least three safer ways to prevent inrush in these supplies...

Mark

Posted by Phil Hill (Member # 371) on 12-30-2007, 04:32 PM:

My point is there is lethal voltage/current available on those caps whether or not the contactor is closed.

In my opinion, the problem is within the contactor control circuit or the contactor itself.

Posted by Michael Trudell (Member # 3344) on 12-31-2007, 01:23 AM:

There are 3 50 watt resistors that look like they bridge the contactor. I was curious about their function as well. Needless to say, I took all precautions and let it bleed off. There is a bleeder resistor on the cap as well.

The contactor is not closing with 115 VAC on 5 and 6 however. I will check the contactor control circuit when I get back home. All that it looks like is a single-wave rectifier to operate the contactor. I thought it was more sophisticated than that. I am out of town for another week.

as well as replace the little capacitor that is burned on the motherboard.