DC Power Supply help

[dj7934]

Hi,

I have an AC to DC power supply. From what I can tell it has two outputs. First, a high voltage (350VDC) and second a lower (12VDC) output. I'm getting about 170VDC on the high output and 0.1VDC where I'd expect the 12 volt output. The application is an older DLP projector. The high voltage output supplies a mercury lamp ballast -- with an input specification of 350VDC (that's where the assumption of what to expect on the high side came from.) The rest of the components (control panels, cooling fans, etc. seem to need 12VDC.

So, the device failed slowly -- first intermittently -- sometimes would power on, others would not, then failed completely.

I'm interested in learning to see if I can repair it myself as a learning experience since the age of the equipment doesn't justify new parts of professional repair and I just have a general interest in learning about electronics and have done some smaller (less complex) repairs/projects in the past.

So, I'm looking for ideas if anyone is knowledgeable and willing to provide suggestions. My first suspect, is what would cause some output, but not what is expected.

I posted a couple photos of the circuit also.

Thanks in advance for any helpful thoughts.

 

[ADRT]

I would try replacing the large electrolytic capacitor on the board. It's comin in power supply's for these to fail and cause issues like you are explaining. I recently repaired an lcd tv power supply that was having the same issues. Sometimes it would power on and other times it would not. I replace the large cap in the supply and the owner states that it has worked great since.

 

[dj7934]

Thanks. That guy was my first suspect, so I ordered a replacement a couple of days ago. The one I removed seemed to test OK, so I'm not very optimistic, but I'll swap it when I receive the new one and post an update. Thanks again!

 

[dj7934]

So, I'm curious about the (largest of all) coil type component pictured below. I've shown it from the top and bottom and numbered the terminals appropriately. There's continuity between terminals 2 and 4, in either direction but NOTHING between any of the other terminals in any direction. I'm not sure what this component is and/or whether the check for continuity/resistance is valid/important/significant. The other similar looking components show continuity -- one (the far right one in the first image of the first post) has 2 terminals and shows continuity the other one (with the center insulator) has continuity between the terminals associated with each "side" of the insulator.

It makes sense that a single coil would have continuity between at least 2 terminals, but I'm not sure what to make of the rest of it.... 4 terminals complete continuity between 2 and 4 but seemingly nothing (resistance or apparent gates) providing connection between any of the other terminals. Can anyone help me understand it?

Dan

 

[dj7934]

Well, I received the large cap and swapped it out (observing the polarity of the original). Didn't seem to make any difference at all in the output from either output connector on the circuit and the projector still doesn't power up. One thing I believe may be important is that the low voltage circuitry seems non-functional, so it's not that the "lamp" won't power on. Even the control panel backlighting doesn't work and panel buttons (to turn on the lamp) are working. I know the fuse is good and would expect more voltage from the small red connector, even before power on.

I researched earlier today and, from what I can tell, the large coil component mentioned in my last post seems like some sort of choke that, from what I understand, would be likely to cause this issue.

Any other ideas from the group that you can share?

Thanks in advance.

Dan