dukane optoma

[yonu]

Ok guys have another problem no this time it isn't user stupidity

while teaching today my fathers projector blew the fuse so I changed the fuse it blew the new one so i removed the internal power supply from the unit and and hooked it up and it blows every fuse that is installed it appears that it is a voltage regulator on the psu board I have incuded a couple of images and i will take some better photos when my good camera is done charging

[japlytic]

Re: dukane optoma

They look like rectifiers or MOSFETs.
One at a time, remove a burnt-out component attached to the heatsink, and note its location and markings on the component.
It would be helpful if you have the model number for the projector.

[shadow]

Re: dukane optoma

The components that are 'sparking' seem to be MOSFET's. These components tend to fail short. That is that when they fail, most of the time the connections are shorted together. You can do a quick test to see this is the case with a multimeter. It is advisable to take the components out before testing, however I am not sure if it is absolutely critical. If the MOSFET's are shorted, then any fuse will blow because excessive current would flow.

The next question is has anything else failed due to the failed MOSFET's?

[yonu]

Re: dukane optoma

it is a dukane optoma ezpro 550

and i will remove the 2 end ones how can I tell if they are bad I would assume witht he sparking that they will be burnt

Thanks,
yonu

[yonu]

Re: dukane optoma

ok now to sound stupid the mosfets ar ethe black thaings correct if so that is the problem I removed the heatsink and one of the legs had melted completly off of it will post a image in a moment

[davmax]

Re: dukane optoma

When testing MOSFEt's it is best to disconnect the two outside leads. Having said that , testing in situ can still be a good indicator. It looks like you have four MOSFET's, two driving each output transformer. Usually only one of a pair fails so you can simply compare the ohmmeter on lowest ohm range(multimeter setting) readings of each device to find the failed one. If you place the positive meter lead on the metal tab of a device then probe the two outer leads with the negative meter lead you should be able to determine if a device is shorted. If both outer leads read a short the device is failed. However check and compare all devices for a differences. If sparking occurrs check the insulation of each device to the heatsink. Place the an ohmmeter lead on each device tab (one at a time) and the other where the heat sink is attached to the PCB (a metal contact) a high to infinite resistance should be found, this unfortunately depends on the circuit and the infinite resistance that it is supposed to be can only be obtained by disconnecting the MOSFET. If this insulation has a failure then it must be fixed.

[yonu]

Re: dukane optoma

here is the image

[yonu]

Re: dukane optoma

thanks I think i found the problem I think the one that burned out was the problem however is it normal for a MOSFET to actually burn off a leg like that?

[davmax]

Re: dukane optoma

Your picture definitely confirms that these are MOSFETs, see the IRF number as the part number. The other device to the left appears to have black on the PCB.

Clearly a very heavy current has caused the lead to burn out. This is usualy protect by the fuse. If the fuse has been upgraded this protecion is lost and the lead burns up.

You will need to replace both MOSFETs and clean up the PCB because the black is conductive. Check for any other affected components.

When replacing always check that the device is completely isolated from the heatsink with the insulator using an ohmmeter on the high resistance range, replace the insulator if there is a risk.

Check the soldered joints and PCB track to the transformer that is part of that circuit.

[yonu]

Re: dukane optoma

should I go ahead and replace all 4 mosfets or ust the those 2 and what is the best way to clean up the board?

[japlytic]

Re: dukane optoma

Use metho to clean up the board and replace all four MOSFETS (all four look like they have blown). The MOSFETs are IRFP450 - 500V 14A, with an ON resistance of 0.33 ohms - rds(ON) is 0.33 ohms.
You should also check the components connected to the MOSFETs too.

[davmax]

Re: dukane optoma

I am unable to see that the second pair of MOSFETs is blown. Clearly the two that are visible need changing. As these are two seperate circuits, two devices to each transformer, the others do not need changing unless they are blown.

[yonu]

Re: dukane optoma

thanks guys am getting ready to go pick up the mosfets now as far as i can tell eveything that connect to them is fine will let you know if that does the trick

[yonu]

Re: dukane optoma

well I guess I am at a standstill until I can fidn the mosfets online our local electronics store wand $16.99ea and said it will take a week to get them

tanks again and will let you know if that works when i get the new ones

[yonu]

Re: dukane optoma

hey should these work

http://cgi.ebay.com/IRFP450-MOSFET-N...QQcmdZViewItem

tyhey have the same number of the mosfet but they are saying they 500v

Thanks

[davmax]

Re: dukane optoma

Same part number MOSFET should be just fine and at a good price. Get four at that price.

[yonu]

Re: dukane optoma

actually at that price I am going to by about 10 or so incase i need them for something else later

Thanks

[yonu]

Re: dukane optoma

ok I got the mosfets intoday and I got ehm changed however upon the first time switching on the power rather than Blowing the fuse and sparking it threw the main breaker and blew the fuse any ideas would be great on what to look at next.

Thanks

[yonu]

Re: dukane optoma

sorry about the double post

[yonu]

Re: dukane optoma

ok upon further checking with a ohm meter it turns out that every leg on this mosfet and the 2 circled legs have a reading to the center pin of the other 3 mosfets so if anyone can make a suggestion to find out what is causing this it would be great

Thanks again