HP L1706 No Power

[killian6pk]

This monitor is a 2006 model. When I plugged it in there was not power evident. No LED or anything.

When I opened it up it had 3 bulging 470uf 25v caps all were Suscon. I changed all of the caps on the board, but not the large black cap 100uf x 450v. Checking the ESR it read 0.52esr and 107.5 capacitance. That was in circuit.

There was also two (I think they are transistors) marked Q on the circuit board. They are just like the old 5707's on the BenQ boards that were always burning up. I can't find a data sheet on these by the number on them. I checked them with the ohm setting 1-2 and 1-3 and 2-3 all were OL either way I placed the probes. There was also some heavy dark brown overheated areas where these two were on the board. I am assuming that they are toast. Does anyone happen to know what the part numbers are for these transistors? The numbers written on them: top line 4GPO3G7 (the O could be a Q) second line is 641016. Neither identifier turned up a data sheet.

If anyone has an idea I could use it.
Thanks

[matthmal]

Re: HP L1706 No Power

test the fuses and bridge rectifier to see if they are blown up.

[killian6pk]

Re: HP L1706 No Power

Fuses are good. I will check BR and see what reads. Can I check it with the power off? What reading should I be looking for?

[matthmal]

Re: HP L1706 No Power

test the voltage on the big cap with power on 600VDC and BE CAREFUL.

could 4GPO3G7 be 40T03GH or 40P03GH ?

[killian6pk]

Re: HP L1706 No Power

I figured out the part number is 40T03GJ they are NChannel Enhancement Mode Power Mosfets 30v, 28A, 31.25W. The ones in my Power Board are TO251J packages. I have looked on Digikey, Mouser and Ebay and can't find these in that style. Ebay has them that have a screw hole to put them on a heat sink. I am afraid that they are so large they won't fit on the board. I am thinking of getting the SMD part in the TO252H package which is made to solder to the board with the back down on the board. This package is similar to the 3 legged fet with the tab at the top where the tab and middle leg are the same. I would have to run a large cut off diode pin through each hole and solder it on the back of the board then solder each pin to the a leg of the SMD part. Anyone got any ideas on this. Any better ideas also would be appreciated.

This monitor is a 2006 model. When I plugged it in there was not power evident. No LED or anything.

When I opened it up it had 3 bulging 470uf 25v caps all were Suscon. I changed all of the caps on the board, but not the large black cap 100uf x 450v. Checking the ESR it read 0.52esr and 107.5 capacitance. That was in circuit.

There was also two (I think they are transistors) marked Q on the circuit board. They are just like the old 5707's on the BenQ boards that were always burning up. I can't find a data sheet on these by the number on them. I checked them with the ohm setting 1-2 and 1-3 and 2-3 all were OL either way I placed the probes. There was also some heavy dark brown overheated areas where these two were on the board. I am assuming that they are toast. Does anyone happen to know what the part numbers are for these transistors? The numbers written on them: top line 4GPO3G7 (the O could be a Q) second line is 641016. Neither identifier turned up a data sheet.

If anyone has an idea I could use it.
Thanks

[killian6pk]

Re: HP L1706 No Power

test the voltage on the big cap with power on 600VDC and BE CAREFUL.

could 4GPO3G7 be 40T03GH or 40P03GH ?

There is not going to be any power until I get these two Power Mosfets figured out and reinstalled. As to the part number see my post above. I have the part number figured out and have a datasheet for it, however I don't think the mosfet package if being made anymore. I am trying now to figure out a way to use the same part in a different style package. Anyone got any ideas on how I might accomplish this besides what I have thought of in the post above?

Same goes with the Bridge Rectifier someone in a previous post wanted me to test. Can't do that one either until the mosfet problem is answered.

If you look at the picture of the top of the power/inverter board near one end of the inverter transformer you can see a dark brown overheated area on the board. That is where these two mosfets are installed. You can see them in the picture.

[budm]

Re: HP L1706 No Power

OK, what you need to do is to get the power LED to come on when you hit the power switch, so I would remove those two MOSFET's from the board for now so it will eliminate the heavy load from the power supply for now for you to be able to take the DC readings on those caps you have replaced. There is a SMPS IC that drops down the DC voltage down for running the logic board, need P/N.
This board only has one output winding on the power transformer that feeds the Common Cathode rectifier (3-pin TO-220 case style) on the heat sink, the output feed that large filter cap just right above the transformer (it is sitting in the middle between the rectifier diode and the 5-pin SMPS IC. I expect 12~18vdc on that cap when you apply 120vac to the board, it is an always on power supply so the voltage should be there the minute the 120vac is applied to the board.
BTW, the board turn brown due to bad caps which allow AC ripple to get to the inverter output circuits and causes it to run at the wrong frequency which caused the MOSFET's to run hot. It was probably has bad caps for a long time that just got worst.

[killian6pk]

Re: HP L1706 No Power

Ok I will check into these readings and get back to you.
So do you think the mosfets I took out are actually toast or was I testing them wrong when I tried to check them on the ohm scale?
I see the SMPS IC you are talking about, but I can't see the number so I will have to desolder it from the board unless I can find it in the Service Manual. The board location is U851.

[budm]

Re: HP L1706 No Power

No, I just want them out off the circuits so we will not have heavy current draw from inverter circuit in case there is problem in the inverter circuit that causes the power supply to stay in shutdown mode.
The IC is for the buck regulator.

[killian6pk]

Re: HP L1706 No Power

OK, what you need to do is to get the power LED to come on when you hit the power switch, so I would remove those two MOSFET's from the board for now so it will eliminate the heavy load from the power supply for now for you to be able to take the DC readings on those caps you have replaced. There is a SMPS IC that drops down the DC voltage down for running the logic board, need P/N.
This board only has one output winding on the power transformer that feeds the Common Cathode rectifier (3-pin TO-220 case style) on the heat sink, the output feed that large filter cap just right above the transformer (it is sitting in the middle between the rectifier diode and the 5-pin SMPS IC. I expect 12~18vdc on that cap when you apply 120vac to the board, it is an always on power supply so the voltage should be there the minute the 120vac is applied to the board.
BTW, the board turn brown due to bad caps which allow AC ripple to get to the inverter output circuits and causes it to run at the wrong frequency which caused the MOSFET's to run hot. It was probably has bad caps for a long time that just got worst.

I took the SMPS IC out and this is what the numbering is: 1st Line AC
2nd Line 1506 3rd Line 0646CL

I put the SMPS IC back in and checked the Power. The LED lights up. The large filter cap was at 12.16VDC. The 100UF 250V large cap was at 172V and the Bridge Rectifier DC output was 173V and the AC output was 124V.
Should I put the two fets back in or are they no good? I have the info on the fets in an earlier post.

[budm]

Re: HP L1706 No Power

So with the two MOSFETs removed, now you do get the 12VDC and the power LED is not on and you can also turn it on and off?

[killian6pk]

Re: HP L1706 No Power

So with the two MOSFETs removed, now you do get the 12VDC and the power LED is not on and you can also turn it on and off?

Yes the two mosfets were removed. The power LED turns on and off with the switch. It appears to stay on untill turned off. This is just with the Power board and the key board connected together. I did not have the backlights pluged in to the PB.

[budm]

Re: HP L1706 No Power

I would check those two MOSFETs real well again, I thing they are causing the power supply to go into shutdown mode due to too much current draw due to bad MOSFETs or due to shorted transformer,or the PWM that drive the MOSFET's GATE stuck on.

[killian6pk]

Re: HP L1706 No Power

I would check those two MOSFETs real well again, I thing they are causing the power supply to go into shutdown mode due to too much current draw due to bad MOSFETs or due to shorted transformer,or the PWM that drive the MOSFET's GATE stuck on.

I am not sure I tested them properly. How should I test with them out of circuit?

[budm]

Re: HP L1706 No Power

Can you find the spec sheet of the PWM 18-PIN (or 20-pin) IC in that inverter section so we can see how it is being used?
Also what resistance do you get between Source and Drain using Ohm mode?

[killian6pk]

Re: HP L1706 No Power

Can you find the spec sheet of the PWM 18-PIN (or 20-pin) IC in that inverter section so we can see how it is being used?
Also what resistance do you get between Source and Drain using Ohm mode?

The only IC I can find in the inverter section is on the bottom of the board. It is a 16 pin IC. It's number is BIT3193G. Here is the address for the Data Sheet:

http://www.alldatasheet.com/view.jsp...hword=BIT3193G

One of the FET's reads (OF) between D&S on ohms scale
2nd FET starts out at 14.8 mohm and slowly drops to around 10.4 mohm

[budm]

Re: HP L1706 No Power

Try putting the MOSFETs back in to see if it will cause the power supply to go into shutdown, if it does, I would take a chance on replacing them, you do not have the Ringer to test the inverter transformer so you do not really have much choice here.

[killian6pk]

Re: HP L1706 No Power

Try putting the MOSFETs back in to see if it will cause the power supply to go into shutdown, if it does, I would take a chance on replacing them, you do not have the Ringer to test the inverter transformer so you do not really have much choice here.

Put the mosfets back and fired it up and it has been running for about 45 minutes with no problems. I am going to leave it running for a couple of hours just to make sure. I think we may have saved another one from the burial grounds. I was really glad to see those mosfets did not have to be replaced, because they are no longer available in that package size. Would have been a really hard work around to get any of the currently available packages to fit in that space. Thanks Bud Have a cold one on me.

[budm]

Re: HP L1706 No Power

So I wonder why it starts working again, may be I should not ask since it may stop working again just to get back at me.

[killian6pk]

Re: HP L1706 No Power

So I wonder why it starts working again, may be I should not ask since it may stop working again just to get back at me.

Yep, never ask questions, just be thankful it works. Maybe the recapping was all it needed.