Three boards, three times the fun.

[KingHuds]

I have issues with three different LCD boards, 2 power inverters and one logic board, hopefully someone here can help out.

Board #1 is the power inverter from an LT765. Turns on then flickers off after about 2 seconds. Replaced it with a good inverter and it works but I accidentally fried the logic board somehow so it is just all white when on now.






The second board is the logic board I mentioned above. I guess I fried it with a loose connection when I switched inverter boards, heard a high pitched noise and smelled burning and knew something was wrong. You can see the browning on the back.





Third board is from a Proview PL926, same problem as the first turns on then flickers off after a second or two. Im assuming that this is an inverter problem also. I see the browning on the board but not sure what is wrong with it. Please tell me if you need any more pictures of certain parts.

[PlainBill]

Re: Three boards, three times the fun.

The 'two seconds then dark' symptom is either an inverter problem or a CCFL problem. By swapping the inverter you've demonstrated it's the inverter.

The quick clue is that when an inverter gets turned on it turns on the CCFLs at full power, and after a short time starts monitoring the output voltage to the CCFLs and the current draw by the CCFLs. If the voltage is too high or the current draw is too low or too high it will shut down. One possible cause is a bad transformer - either arcing or a shorted turn. One idea someone else had was to try it in a dark room and see if you can see it arcing. Or a ring tester is also good.

If that fails, dig up the data sheet and application note for the inverter controller and see if you can figure out what is causing it to shut down. The troubleshoot from there.

-----

I don't think the discoloration on the controller card is related to the failure. That kind of darkening is the result of anelevated temperature for a long time. Note that on the top side are two high power transistors or ICs. Also, I'd associate a whining sound with an inductor. In the picture the component just above and to the left of the toroid (D9?) looks strange.

-----

On the Proview power supply / inverter combo I would say the same things as on the inverter. Try substituting CCFLs, then start looking for faults on the inverter itself. Another of the ideas I've 'borrowed' is using the CCFLs from a case mod kit as substitutes for the original CCFLs (just hook them up externally). Also use the inverter from the kit to power the original CCFLs.

I'm also trying to wrap my brain around the concept of a dummy load that would allow measuring the output load and current from an inverter. One problem is the frequency and voltage are too high for most AC meters, and the voltage is too high for most scope probes.

PlainBill

[KingHuds]

Re: Three boards, three times the fun.

Where might I be able to find a data sheet for something like that? Or possibly even a replacement board at a higher cost?

Also for the second one you are right there seems to be black melted crap on and under that part, where might i find something to replace it, and would just resoldering that maybe fix it?

I just assumed the last one was inverter failure from my experience with the other monitor, since it just died one day after working fine, I told my friend he could send it in and get it repaired here . But I will try and test the tubes first.

Thanks for the quick reply.

[Bobdee]

Re: Three boards, three times the fun.

there is every chance those caps on inverter are kaput, they are known to dry out and still look good with that inverter,common fault

[KingHuds]

Re: Three boards, three times the fun.

Any way to test them besides recapping it?

[PlainBill]

Re: Three boards, three times the fun.

Where might I be able to find a data sheet for something like that? Or possibly even a replacement board at a higher cost?

Google is a good start. Use the part number of the IC plus the word datasheet.

Also for the second one you are right there seems to be black melted crap on and under that part, where might i find something to replace it, and would just resoldering that maybe fix it?

No, resoldering won't fix it. You'll have to replace it with an identical or equivalent part. That is trivial; IDENTIFYING the part is going to be the difficult task. Plus, it is likely that the fried part was the victim, not the actual failure.

I just assumed the last one was inverter failure from my experience with the other monitor, since it just died one day after working fine, I told my friend he could send it in and get it repaired here . But I will try and test the tubes first.

Thanks for the quick reply.

What is your skill level? Recapping is inexpensive. I have mixed feelings about Frans Solo etc. They charge $30 for replacing a $.50 part. Still, the DO know which part to replace.

PlainBill

[KingHuds]

Re: Three boards, three times the fun.

Ok as far as the first inverter, theres 4 caps I figure I might as well recap it. But not sure what caps to get. The two smaller ones say 105uF, 50V, SS 105C, A3, TEAPO.
The larger ones are 100uF, 25v, 105C, F2043 EVX.

As far as the second, yeah I meant replacing, but I might have found a replacement board, so I will have to see on that one.

I told him to send it there because he really doesn't care about the cost, just time so that was probably faster than me trying to repair it when I don't have a lot of experience re-capping. But the soldering doesn't look too hard.

[Bobdee]

Re: Three boards, three times the fun.

The 2 x 100uf 25V caps are the ones to replace,
The 2 small ones,I have never had to do them
they need to be removed from inverter to test,with capatance or esr meter, the latter will do both, I have had them measure 20+ esr, my meter only goes to 20
bob

[KingHuds]

Re: Three boards, three times the fun.

So I remove the two small ones, then test the other two with an esr meter?

[Bobdee]

Re: Three boards, three times the fun.

Not so, pull the 2 100uf x 25V caps and test with esr meter, for esr and capataince, if bad replace and try inverter again in monitor.
bob

Sorry when I said they need to be removed from board I was talking about the big pair (it wasnt very clear as I can see now)

[KingHuds]

Re: Three boards, three times the fun.

Do I need to test them? Or can I just replace them? I dont have an esr or capacitance meter.

Also just got one more busted inverter, with 68uF and 30v caps, so the same question applies of if i can just replace them.

[KingHuds]

Re: Three boards, three times the fun.

I dont see an edit button so forgive me, but I I got a new logic board also with the other inverter, it is identical to the second one in my first post except the connection to the actual screen. Is there anyway to splice the different connectors so I can use that logic board? I dont know if its even remotely possible, Ill post more pictures if you need those to know.

[PlainBill]

Re: Three boards, three times the fun.

I dont see an edit button so forgive me, but I I got a new logic board also with the other inverter, it is identical to the second one in my first post except the connection to the actual screen. Is there anyway to splice the different connectors so I can use that logic board? I dont know if its even remotely possible, Ill post more pictures if you need those to know.

You've got only 10 minutes to edit a post. Yeah, bummer, been there, didn't even get a tee shirt.

A different connector indicates potential problems. The logic board is customized for the display. It could be as simple as changing a connector on the board replacing both the MX10E processor and the MRT chip (Video processor?)

PlainBill

[Bobdee]

Re: Three boards, three times the fun.

I dont see an edit button so forgive me, but I I got a new logic board also with the other inverter, it is identical to the second one in my first post except the connection to the actual screen. Is there anyway to splice the different connectors so I can use that logic board? I dont know if its even remotely possible, Ill post more pictures if you need those to know.

Phewww, I cant see anyone advising on splicing that connection,
The pins can be removed from connectors and put into diffrent connectors in some cases but you need to know what pin goes where, and thats over my head sorry,
As for caps you certainly dont have to test them just replace with good quality low esr caps,
bob

EDIT sorry Bill I did not know you posted on splicing,I was still doing my one finger typing, and I am realy slow so my grandaughters tells me often

[PlainBill]

Re: Three boards, three times the fun.

EDIT sorry Bill I did not know you posted on splicing,I was still doing my one finger typing, and I am realy slow so my grandaughters tells me often

Yours too, huh? Some things remain constant.

PlainBill