Need help of how to bypass the lamp check of Infocus LP725 - diyAudio
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Old 4th August 2008, 04:46 PM   #1
don2kk7 is offline don2kk7  Australia
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Join Date: Aug 2008
Default Need help of how to bypass the lamp check of Infocus LP725

Just got an Infocus LP725 projector from ebay today with a blown lamp, I was thinking about replace the lamp with a 20w led. Right now looking for a way to bypass the lamp check. I've read quite a lot of posts about the same issue but not quite get it, when I'm actually take apart of the projector, I was frightened by the complexity of this projector don't know where to start.

Is there any one who have the experience of fooling the Infocus lp725?
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Old 4th August 2008, 08:48 PM   #2
Shorin is offline Shorin  United States
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I don't have experience with that projector... but I just did my own DIY relamping on an Epson Powerlite.

Just in case you don't know how these typically work, here's an overview of the important stuff in a typical projector:

Power supply
Ballast
Bulb
Mainboard
Optical Assembly and maybe some misc electronics
LCD(s) or DLP stuff

The last 2 things might not be separate boards and stuff but the important part is the power supply and ballast.

A ballast is a big component that may or may not be mounted on it's own board. A ballast is important for starting any metal halide bulb. Florescent tend to need one too. This is because in a gas-filled bulb, you need to generate a spark across the gas or something to make it start. A spark jump takes alot of volts, and the ballast helps to do that. It doesn't use much power once the bulb's started.
It's like matches. You need to apply force to the match head to ignite it, and once it's lit, you don't need to apply any more force.

Anyways, look for the ballast. It makes a buzzing sound when trying to start the bulb, even if the bulb isn't in there. Hope that it's on a separate board... otherwise you won't be able to separate it's operation from the rest of the thing.
I suggest putting the broken bulb in when looking for it. Hopefully you DID save it. I found that the bulb carriage on mine had a little board on it that bridged these two contacts when inserted. It didn't seem to make a difference, but it means something. There was a big 2-wire connector that went to the ballast also.

So if you find that ballast board, find the connections coming out of it. You should find a BIG 2 wire plug going to the bulb, a BIG 2 wire plug coming from another board, and a small-wire multi-wire connector coming from the main board.

Generally the rule of thumb is "look for the control wires". The control wires are the things to trick.

I have seen people do stuff like connect some wires from that control plug, but they didn't explain why.

Others say just find some wire in that and ground it.

In MY case, I had a 3-wire plug coming off of the mainboard. I tested for current between each of the three. I also measured volts. I soon discovered which was the negative return wire.
A few tiny amps flow through the thing when it's trying to start the bulb. My meter put a resistive load on it, so the ballast wouldn't go when the meter was connected.
Then I tried grounding either of the hot wires through my meter while measuring amps. One of them made it work. It wasn't showing any amp reading on my meter though. This was because the measuring scale was putting enough resistance on the line to make it think it was connected.
After I realized what was going on, I realized that I just needed to put a resistor in-line with that pin and then ground it. I desoldered a 42 ohm resistor from a junk power supply and hoped it was enough. It happened to be enough... so joy!

OKAY - that's alot of crap to read but here's what I say you do.

EITHER get a meter that has a 10A load line (this is a common feature for multimeters, get it at RadioShack. Mine was $5 at a discount store) OR get a resistor and wire, and test grounding the pins. However the latter method could be a quick way to getting yourself killed, especially if you pick the wrong wire to test. There is high voltage in many places in a projector. The amps is what kills you though.

A meter is recommended.

If this all goes way over your head, then i've heard that there is such a thing as "diy companies" who could help. There may be some users on this forum who could do it too.
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Old 5th August 2008, 04:56 AM   #3
don2kk7 is offline don2kk7  Australia
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Thanks Shorin, thanks for the detailed reply. It really gives me an idea of what I'm going to do.
I have took the PSU apart and found the ballast there, below is the link to my on-line photo album where u can find all the photos about the projector.
I've go through an post about use opto-couplings to fool the projector, but the funny thing for me is I even can't find the optos. I do find 2 pairs of 4 legged chips on the PSU board which can be found on my web album.
Still going through the PSU, but need leaving for the university soon

Ok to sum up before leave.
The PSU have 2 PCBs, one is the power supply for the main board(the right half), the other half is for the lamp I guess. There are 3 wires form the left half goes to the main board which u can see from the attached photo. So according what you said the 3 wires should be the ones doing the trick.

Thanks for advance any help will be appreciated
Attached Images
File Type: jpg control wires.jpg (62.3 KB, 306 views)
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Old 5th August 2008, 04:56 AM   #4
don2kk7 is offline don2kk7  Australia
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Default forgot to post the link to my web album

below is the link to my web albums
http://picasaweb.google.com/donghui2k7
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Old 5th August 2008, 01:53 PM   #5
don2kk7 is offline don2kk7  Australia
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I think I'm nearly there after reading this post DIY replacement lamp for projector

I think all what I need to do is to shortcut the red and black wires from the ballast board to the main board, but before I'm doing that I'm worried about the lethal voltage from the ballast. Anyone reckon it will still doing the trick without the power supply to the ballast board?
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Old 5th August 2008, 06:57 PM   #6
Shorin is offline Shorin  United States
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Default almost there!!

You're almost there.

If you read alot of that post, you would have learned that all that stuff about optocouplers. Optocouplers are apparently a way to get a "signal" without being connected to the circuit. There's a light inside those chips and half the leads connect to one circuit and half to another, and there is no connection in between. This pretty much means those 3 wires are probably not part of the ballast PSU circuit, but electrically separated because of the optocouplers.

Don't worry about the voltage here, those 3 wires should be safe. Large amounts of current (amps) is what is deadly and high current needs thick wire.

Either way, get yourself a multimeter so you know what you're doing.

You can do your tests with those 3 wires disconnected from the ballast PSU, or just disconnect the ballast board from the main PSU (look for the big wires, I think it's the 2 twisted ones that go from one side of the board to the other).

Ideally once you get this working, it would be good to leave the ballast disconnected permanently. This would prevent wear on that circuit, and decrease heat I guess. I heard that it could be bad for a power supply (the main one in this case) to not have a load on it... You'd have to put some sort of resistor (or a crap load of resistors) on the old ballast line to remedy this.

I didn't bother, I just left the ballast board disconnected. I'll find out the truth if and when my projector PSU dies.
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Old 5th August 2008, 07:01 PM   #7
Shorin is offline Shorin  United States
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Default warning

Quote:
I think all what I need to do is to shortcut the red and black wires from the ballast board to the main board
I wouldn't do this. Running current/voltage to a place where it shouldn't go sounds like a pretty bad idea to me. I might try it if I didn't have anything else that worked, but I would rather hook up a small amount of voltage to it (a.k.a an itty battery grounded to the case) to try to signal it. Another way would be to somehow vary the current or volts across the jump.

It wouldn't be a big deal if the other wire was DEFINITELY ground.

I would try the grounding method first. It would probably have the same effect.
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Old 6th August 2008, 04:15 AM   #8
don2kk7 is offline don2kk7  Australia
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Thanks for all the replies man.
I'll try to ground the +5 wire tonight after I back from the University. Wish it works.
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Old 6th August 2008, 02:16 PM   #9
don2kk7 is offline don2kk7  Australia
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Did that tonight but still can't tell if it works or not. I have put a led camping head light into the lamp housing, before the pj get started I can see a bright square area on my wall,after I turn on the pj about 5 seconds the bright area turning dim and I can't see any words and whatsoever on it. Don't know if I just screw the whole thing up, I think I suppose to see a pure green picture.
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Old 6th August 2008, 10:46 PM   #10
Shorin is offline Shorin  United States
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Quote:
after I turn on the pj about 5 seconds the bright area turning dim and I can't see any words and whatsoever on it.
It getting dim without you turning that light off means the LCD screen came on. Your lamp may not be bright enough to illuminate the thing.

What I did was i pointed the open bulb chamber at a house light and looked through the lens. That worked well enough, even with my 3-LCD version.

Hook up a video source or a VGA signal to confirm a signal.

I really already knew it was working by the indicators and fans coming on instead of the bulb light blinking.

OH... did you put a resistive LOAD on that ground? It didn't work without that for my projector.
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