CurtPalme.com Home Theater Forum

HK-Steve

Well yesterday was an interesting day,
I got my EMI tape in and started to play with my LVPS. Installed the tape onto both 1/2's of the LVPS chassis.
Then I got to doing a few upgrades as planned.

Finished, checked everything, installed and sat down to watch some TV to test all was OK.
10 mins in, a HUGE POP. Then the lights and power went out.

Hmmmm, seems I have a little problem.

So I open the LVPS, find some nice burn marks on the heatink for the 390v
I get to removing the board from the chassis and find it has nothing to do with the shielding, Cool

I replace the 3x transistors, 1 is clearly blown, black powder and burns all over it.
The screw and the heatsink tape is also covered, and pit marks from the arc.

Re-test all the surrounding parts, all clear.

Re-install, and then found no HV
Pulled the HVPS and found the fuse blown, replaced then re-installed.
Fired up the projector and all was well.

Now I can get back to hooking up the scope to see if there are any improvements with the EMI tape installed.
I will post some pics a little later of the damage.

Cheers
Steve

Nashou66 · Joined: 12 Jan 2007 Posts: 16171 Location: West Seneca NY

So what caused those to pop? I have a bad LVPS here from way back when and I blew those same parts but something eles i never figured out. That was when i was a greenthumb so maybe now I'll go back and explore it, but working with 390vdc is not something i want to do. I was thinking putting that tape on the outside, it make no difference right?

Glad you got her working again!

Athanasios

HK-Steve · Posted: Wed Oct 14, 2009 1:30 pm Post subject:

Not sure what caused the POP,
just seems to have arc'ed through the screw to the heatsink.
Had to replace around 20 parts all up.

The other thing I don't understand is about the use of hotmelt glue in the LVPS.
Yes I understand for the inductors so they don't move, vibrate or create dry joints.

But when you see the heatsinks covered in hotmelt, I would think that it would make the heatsinks worthless for the cooling of the transistors they are attached to.

The other thing I found in the HVPS is the white powder/dust (this is unmodified at this point)
I know this is normal, but it seems some HVPS are worse than others for this.

Cheers
Steve

Nashou66 · Joined: 12 Jan 2007 Posts: 16171 Location: West Seneca NY

Steve can you pm me the list of the parts, Mine had the same thing happen but i was the one who shorted it, I have the large mosfetts and one Ic I cant remember but what else should I look for?

Yeah on yours it looks like maybe the heat sink insulator too maybe failed?

Athanasios

HK-Steve · Posted: Wed Oct 14, 2009 1:54 pm Post subject:

For the parts I replaced, It was just luck more than anything, as we don't have a schematic for the LVPS

I replaced Q1, 2, 3
R3, 4, 5, 67, 66, 65, 76, 77
D2, D10
U5, U6, U4

Think that was it. so it was 16 parts.

Let me know how you go.

Cheers
Steve

dturco · Posted: Wed Oct 14, 2009 2:59 pm Post subject:

Wow, I just pulled my HVPS and it looked exactly like yours Steve. I have some video noise showing up in my picture since the last round of upgrades, it's really annoying, the picture is deep and rich at times, then it looks full of wavy lines and static sometimes. I thought the HVPS was the place to start looking for bad or bulging parts so I pulled it apart for an inspection. I thought it was going bad because of that dust in there. I guess not.

Edit: I have taken the neckboards to Mike Parker and on his test machine and his 9500 this noise isn't there, just on GOZER.

So the LVPS is next but looking at yours I'm hesitant to do this and cause myself grief.

Also what does one need to start testing for noise? I assume a scope of sorts but I don't have a clue about them and I'm getting nervous about casually pulling things to look at, as it increase the chances of damage by just being in there.

And no, I will not put down the tools. Laughing

Nashou66 · Joined: 12 Jan 2007 Posts: 16171 Location: West Seneca NY

Thanks Steve I'll have to look at them.

Athanasios

Nashou66 · Joined: 12 Jan 2007 Posts: 16171 Location: West Seneca NY

Dave, the whole Power supply(LVPS) has mostly crapy macon caps. I'd replace all with either Nichicons or the Panasonic FM and FC series. And Steve, Im surprised you have not re-caped your LVPS with the Nichicons you like so much.

Athanasios

PaulB · Posted: Wed Oct 14, 2009 3:56 pm Post subject:

I picked all the hotglue off the heatsinks when I first opened up the LVPS. They obviously can't work properly with all that glue on them.

I thought it was just my LVPS that had been assembled by someone with a glue fetish Shocked

Glad you fixed it Steve and thanks for the pictures/info, good material if it happens to anyone else.

1031 · Joined: 22 Mar 2006 Posts: 657 Location: Finland

HK-Steve · Posted: Wed Oct 14, 2009 5:31 pm Post subject:

Hey Everyone,
As Jarmo said, the voltage has punched through the heatsink tape,
It is like the screws were done up too tight and the tape has gone so thin that it broke down under the voltage.
Don't look at me, it was like that when I got here Laughing

PaulB,
Man hat stuff is so hard to pick off,
How did you get it off?? any tips on the best way other than a screw driver or knife??

Athanasios,
You really don't want to know what I have in there, or do you??
Everything has been replaced, the pic is before the last set of mods done on the same day Thumbs Up

after it was up and running, the evening and today has been lots of changes.
Like this

dturco,
The HVPS is pretty good for parts not failing, it is more the potted section which give all the trouble.
Having said that, there are certainly many parts which can be upgraded to improve the stability and quality of the output voltages.

Cheers
Steve

HK-Steve · Posted: Wed Oct 14, 2009 6:09 pm Post subject:

This is some of the ones taken out for replacement over the last day and today, some are LVPS and HVPS,
Do you know Which are from Where?

I am sure you will all get it right, pretty easy actually.

Cheers
Steve

mp20748 · Posted: Wed Oct 14, 2009 6:37 pm Post subject:

HK-Steve · Posted: Wed Oct 14, 2009 6:56 pm Post subject:

Hmmm, interesting Mike,
I will agree and dis-agree with you on this one,

as some of the heatsinks are just full of glue in the middle, not even touching the circuit board, or strengthning the support for the transistor to prevent movement or dry joints.

Appreciate your input.

Cheers
Steve

PaulB · Posted: Wed Oct 14, 2009 7:18 pm Post subject:

PaulB · Posted: Wed Oct 14, 2009 7:35 pm Post subject:

Nashou66 · Joined: 12 Jan 2007 Posts: 16171 Location: West Seneca NY

Tom.W · Joined: 09 Mar 2006 Posts: 6635

Steve is as normal as I am.

Ahhhh Never mind .................................................................... ! Mr. Green

tse · Joined: 03 May 2006 Posts: 1014 Location: Sweatbucket, Fl.

The blow up looks like it was initiated by insulator failure. I never did like the idea of using thermal compound with flexible type insulators. I don't think any of the manufacturers recommend that.

Half of the LVPS main output section is a forward converter. The filter inductors do most of the filtering so cheap caps do a good job. The other part of the main section is a flyback converter where the caps do all the filtering. A cap upgrade in this section might do some good.

The white powder in the HVPS is the release agent that eases taking the potted section out of the mold. It might not look nice but doesn't hurt anything.

Scott

macgyver655 · Joined: 22 Aug 2007 Posts: 8508