InFocus LP350 power supply dead - Help!

[plutonium239]

Hi there -

I got an InFocus LP 350 that suddenly stopped working. When I switch it on it simply does nothing - no lamp, fan, LEDs, anything - silence of the lambs. So suspect is of course the power supply. Took the projector apart, inspected power supply - MagneTek 3979-03-100 - no charred parts, blown resistors or anything else looking wrong - spick and span. Measured the fuse and it is shiny and intact. Measured electrical connection from the plug prongs through fuse and switch well into the power supply's guts. When I switch it on and hold my ear close to the transformer between primary and secondary stage I can hear it chirp quietly about 4 times a second.

So I am wondering if any of you got an idea what might be wrong or what to check or can recommend a place I can turn to for advice,

Thanks in advance!

Markus

 

[mbates14]

Check your 4 secondary SMD rectifiers on the output of the power supply. you probably got one on the 12V output shorted.

replace it.

 

[plutonium239]

Wow thanks a lot!! One of the rectifier diodes (CR500) was indeed shorted, and I replaced it (could not get the original part IR3J (Schottky rectifier 3A/100V), so I used an NTE579 (Schottky rectifier 3A/90V)). The diode did not fit in the original location, so I attached it to the reverse side, extending it with wires. Now the projector powers back up, yey!

However, the projection lamp does not come on, and after three seconds the green LED starts flashing amber. I measured resistance of the lamp unit and it is infinite. However lamp looks spick and span, no melted filament that I can see. I removed insulation from internal lamp wires and measured resistance directly on the bare wires (to ensure the connector is not defective) - still infinite. Does this mean the lamp unit is broken and needs replacement? Is the flashing amber LED normal for a broken lamp?

Thanks!!!!

 

[ywh]

mbates14 is great!

 

[mbates14]

Wow thanks a lot!! One of the rectifier diodes (CR500) was indeed shorted, and I replaced it (could not get the original part IR3J (Schottky rectifier 3A/100V), so I used an NTE579 (Schottky rectifier 3A/90V)). The diode did not fit in the original location, so I attached it to the reverse side, extending it with wires. Now the projector powers back up, yey!

However, the projection lamp does not come on, and after three seconds the green LED starts flashing amber. I measured resistance of the lamp unit and it is infinite. However lamp looks spick and span, no melted filament that I can see. I removed insulation from internal lamp wires and measured resistance directly on the bare wires (to ensure the connector is not defective) - still infinite. Does this mean the lamp unit is broken and needs replacement? Is the flashing amber LED normal for a broken lamp?

Thanks!!!!

you still have a problem in the power supply unit.

Does the lamp attempt to come on? do you hear a sort of "pulse" action? if none, you need to check and replace the L6561D nearest to the black dope transformer that the lamp wires come out of, and check and replace the open start capacitor underneith the black dope transformer. 100nf 400volt. they are tall rectangular boxy like. they can be red, white, or somtimes gray in color. Only way to find these open, is a good old tenma analog ESR meter. the needle will move up SOME on a good one, and move up barely, if at all on a bad one.


A real simple way to rule out the L6561D circuit, is when the projector powers up and fans come on, does the color wheel spin up also? if not, suspect L6561D and associated circuits. if so, suspect the charge-pump lamp start capacitors. or the picofuse.

Once you get this fixed, you may, or may not notice when the lamp starts, it starts real weak, and then shuts off. starts again real weak, and then shuts off. This is caused by shorted turns in the inductor on the lamp boost-up converter circuit. You probably wont have this problem, but if you do, thats why. only solution is to rewind the inductor, but thats a pain in the A$$ because i have tried, and they usually overheat on me and die. because i cannot wind them "perfect" need a machine or a darn good hand to do that.

 

[plutonium239]

Thank you so much for all that great info, mbates14! Both the L6561D and the capacitor look fine from the outside. How do I know if the L6561D needs replacement?

Most and foremost I am confused by the lamp unit though, since I cannot measure any electrical connection through it (infinite ohms = open) even though it looks perfectly fine. Shouldn't I measure the filament's resistance (a couple ohms) between the connectors?

Thanks!!!

 

[mbates14]

ok. it seems you dont understand how the lamp technology works.

These lamps do not have filaments.

There is 2 electrodes inside the lamp. it takes an extremely high voltage pulse, about 2kv or so depending on the lamp, to throw an arc. the arc causes the gasses to ionize and allows a current to flow between the electrodes to complete the halogen cycle. When this occures, an excess in current will start to be drawn. the sensor circuits pick this up, and shut off the lamp ignition, and begin to enter driving mode, where it supplies a constant current DC/AC source depending on the lamp. this allows the gas to continue to ionize, and allow the elements to heat up. and the lamp to continue to "warm up"

current is monitored during operation of the lamp. if the current rises or drops below a certain "threshold" the lamp cuts off and power supply tells projector that the lamp is impending failure. its out of "spec".

Through the life of the lamp, the electrodes begin to "wear away" and the high pressure inside the quartz will allow those deposits to plaster themselves to the wall of the lamp.

if the lamp looks clear, the lamp is in perfect shape. as the lamp wears, the glass becomes more foggy as the electrodes wear away. and when they wear away, the current begins to drop off some. until it reaches the point where the power supply will not keep the lamp running.

Also over time, the quartz begins to weaken. and this allows the high pressure gasses to continue to thin out the walls of th elamp, and the lamp can someitmes die in an explosion.

 

[mbates14]

Thank you so much for all that great info, mbates14! Both the L6561D and the capacitor look fine from the outside. How do I know if the L6561D needs replacement?

Most and foremost I am confused by the lamp unit though, since I cannot measure any electrical connection through it (infinite ohms = open) even though it looks perfectly fine. Shouldn't I measure the filament's resistance (a couple ohms) between the connectors?

Thanks!!!

You dont, you just replace it. i explained everything in my post for testing the capacitors.

also, somtimes when the L6561D fails, theres a small SMD 22 ohm resistor that drives the power MOSFET. this can open during the sign of failure. NOT ALWAYS. so dont rely on that to answer the question.

 

[plutonium239]

Thanks so much again for the input. I tested all capacitors around the lamp transformer with my oscilloscope's component tester, they all seem good, and so seem the semiconductors around it (show curves that make sense). I also replaced the L6561D. It still does not work. So I am giving up at this point, and are selling it on eBay:


InFocus LP350 Projector PART/REPAIR, SP-LAMP-LP3e, case

So if any of you fellow geeks wants to try your luck, you're welcome!

Thanks again, this forum rocks!!!!

 

[rnox]

lp350 510-1430-04 psu.

r508, r511, r535 resistors blown. Anyone have values?

Also blown and replaced:
d500, d501, d507 = bav99
cr503 = ir3j
u3 = viper100a
u4 = opto
d2 = tl431

 

[sujatapatil]

I got an InFocus LP 350 that suddenly stopped working. i inspected power supply - MagneTek 3979-03-100 - no charred parts,
i want following Smd resistance value & Circuit Digram i pdf format
R513,R514,R515,R517,R516
So I am wondering if any of you got an idea what might be wrong or what to check or can recommend a place I can turn to for advice,

Thanks in advance!

Sujata patil