NEC LCD1700v ... feeling clueless

[PJsmith]

So I've got this NEC LCD1700V monitor that blacks out 1 second after turning it on...a bunch of web searching turns up that it's probably the Inverter, and more specifically probably the Capacitors on the inverter.

I'm pretty handy, so I figure I'll swap out the caps myself.

Only problem is, I can't seem to look up the correct replacements anywhere. I went to the Digikey site and either I don't know something I need to, or I'm doing something wrong.

I've attached pictures so my questions are easier to follow, but I sure could use some help/input from anyone obliged to lend a hand.

1. I assume that I'll need to replace both Radial capacitors (one is bulging on the top, the other probably not far behind). These say NKcon, 180uf, 30V 105deg. I can't find these

2. I don't see any problems visually with the other capacitors (the blue, what we used to call wafer, ones in pic #2). This is a dual inverter, so there's 8 of those bad boys. These simply say 3kv, 3 9k, which I assume is 3900pf, correct? Can't seem to find these either.

3. What am I missing in this project (besides needing to check discharge before handling)?

Thanks so much in advance for anyone that can walk me through finding these!

P


3.

[kc8adu]

Re: NEC LCD1700v ... feeling clueless

i use 220@35 panasonic fc.
a bit big but they work fine.

[PJsmith]

Re: NEC LCD1700v ... feeling clueless

i use 220@35 panasonic fc.
a bit big but they work fine.

This is sort of why I have this problem. Maybe I don't know all of the shorthand just yet, but...

I assume you are just speaking of the radial caps? Oversizing them by this much won't be an issue?

Also, should I just abandon the idea of changing out the blue ceramic caps in picture 2? are they unlikely to be contributing to my problem?

Thanks again!

[kc8adu]

Re: NEC LCD1700v ... feeling clueless

the blue hv caps are usually burnt when bad.they are not lytics and cannot be replaced with them.leave them alone.
oversize wont hurt anything.
if too big lay them on their side when you install them.just have to clear the shield if any.
may as well do the psu while its open too.

[retiredcaps]

Re: NEC LCD1700v ... feeling clueless

I have the same issue with the OP and I'm sure it is not the PSU because I have tried 2 of them and I get the same 2 seconds to black. The PSU is external AC/DC adapter brick

The caps on the logic board all look good, but I have no ESR tester so I can't be sure.

There are 2 caps on the inverter board that I need help identifying.

It is grey and says ".15K 250". The series is R79. Sorry for the poor light (sun is down).

I found this datasheet and wondering if I have the correct part. The full datasheet is at

http://www.kemet.com/kemet/web/homepage/kechome.nsf/file/R79%20Series/$file/F3301_R79.pdf

but I took a snapshot of it in the pic below. I measured the cap and it is identical to the datasheet, but looking for confirmation.

So I've got this NEC LCD1700V monitor that blacks out 1 second after turning it on...a bunch of web searching turns up that it's probably the Inverter, and more specifically probably the Capacitors on the inverter.

[PlainBill]

Re: NEC LCD1700v ... feeling clueless

I have the same issue with the OP and I'm sure it is not the PSU because I have tried 2 of them and I get the same 2 seconds to black. The PSU is external AC/DC adapter brick

The caps on the logic board all look good, but I have no ESR tester so I can't be sure.

There are 2 caps on the inverter board that I need help identifying.

It is grey and says ".15K 250". The series is R79. Sorry for the poor light (sun is down).

I found this datasheet and wondering if I have the correct part. The full datasheet is at

http://www.kemet.com/kemet/web/homepage/kechome.nsf/file/R79%20Series/$file/F3301_R79.pdf

but I took a snapshot of it in the pic below. I measured the cap and it is identical to the datasheet, but looking for confirmation.

That's the part, however it is unlikely that cap is responsible for the problem. Unlike electrolytics, these tend to be very reliable.

PlainBill

[kc8adu]

Re: NEC LCD1700v ... feeling clueless

wrong thread!
disregard.

[retiredcaps]

Re: NEC LCD1700v ... feeling clueless

I will reflow the joints at the transformers as you suggest. A couple of them look suspect under the jewelers loupe.

I may also change those two 180uF 30V caps.

Now that it is sunny, I added clear pics of the inverter board and logic board for those who stumble on this thread in the future.

your nec is really a benq,acer,aopen,ect.
bad caps and bad solder joints at the transformers.
also bad 2sc5706/07

[retiredcaps]

Re: NEC LCD1700v ... feeling clueless

I just reflowed the solder joints at the transformers and I still get the same 2 seconds to black.

This inverter board has no 2sc5706/07, but I'm assuming the D1804 at Q6, Q7, Q11, and Q12 does a similar function? This 1700V was made in Oct 2002.

BTW, F1 and F2 fuses check out okay for continuity.

I will try to replace the 180uF 30V caps next.

your nec is really a benq,acer,aopen,ect.
bad caps and bad solder joints at the transformers.
also bad 2sc5706/07

[Dgtech]

Re: NEC LCD1700v ... feeling clueless

I have a stupid question. Only cause I havent seen it listed, have you checked F381? It is a round red component on the processor board. Also, I would definitely change out the Capxon caps on this processor board without a second thought. Just to keep my sanity, i change them. If they are good, I have a bin labeled " Good Capxon caps" for the lesser $$ repairs.

[Scenic]

Re: NEC LCD1700v ... feeling clueless

I have a bin labeled "Good Capxon caps"

syntax error (invalid argument)

[retiredcaps]

Re: NEC LCD1700v ... feeling clueless

Your question is valid and I checked all the fuses on the logic board including F381 for continuity (buzz/tone) and they all pass with my friend's multimeter.

Getting 680uF 25V in 10mm x 12.50 mm is very hard. The cap right below FB330 has to fit underneath the sturdy metal lip. That cap may have 1.5 mm of clearance. The other 680uF 25V caps could maybe go to 16mm, but it would be very close once the shield is put back on.

I found some old stock Rubycon that are size 8x12mm, but are 85C and marked T0248 (year 2002 week 48) at

http://cgi.ebay.ca/20-680uF-25V-680u...item4aa1cc639b

Now I know the fit and I have seen pediaparts before in listings, but these caps are 8 years old and only 85C while the original Capxon are 105C.

A search at digikey doesn't show anything with 10mm x 12.5 mm or smaller.

PS. I'm not at a point yet where I'm comfortable measuring anything with live voltage. Everything I'm doing right now is while power OFF and consulting Electronics for Dummies while doing DMM measurements. So I'm doing easy fuse checks.

I have a stupid question. Only cause I havent seen it listed, have you checked F381? It is a round red component on the processor board. Also, I would definitely change out the Capxon caps on this processor board without a second thought. Just to keep my sanity, i change them. If they are good, I have a bin labeled " Good Capxon caps" for the lesser $$ repairs.

[retiredcaps]

Re: NEC LCD1700v ... feeling clueless

Okay, I worked on this a bit more each time I learn something. I checked the 4 transistors (D1804) on the inverter board they test okay.


Tested all 4 D1804 with diode check function on multimeter.

pin 1 = base (COM and black lead)
pin 2 = collector
pin 3 = emitter

All 4 show

pin 1 to 2 = 0L (black lead on pin 1, red lead on pin 2)
pin 1 to 3 = 0.707v (black lead on pin 1, red lead on pin 3)

Now I'm trying to test the transformers on the inverter board, but I cannot identify them properly?

The only markings I see are

2X657026B (from pic)

TAD585-1 Rev A (from pic)

06 2XX (on the side)

The transformers are 1 inch long = 2.5cm and 3/4 inch wide = 2 cm.

It has 6 legs on one side and 4 legs on other side. I can't figure out which are the primary and secondary legs.

I can't find anything via google or datasheets?

[kc8adu]

Re: NEC LCD1700v ... feeling clueless

got mixed up in another thread.
scratch the acer /aopen post.
did you replace those 2 lytics on the inverter yet?
every one i have seen those nkcons on they were open.

[retiredcaps]

Re: NEC LCD1700v ... feeling clueless

I haven't replaced those caps yet on the inverter. I have to find the correct size, but I may put in a couple of temps to test. They are originally 180uF 30V.

Think I can temporarily put in Rubycon MCZ 470uF 25V (the closest values I have) to see if the 2 seconds to black is fixed?

The voltage is slightly under 30V. I have to leave right now, but I can check the voltage across the connectors to see if it uses 5V or 12V or something higher when I get home later.

did you replace those 2 lytics on the inverter yet?
every one i have seen those nkcons on they were open.

[retiredcaps]

Re: NEC LCD1700v ... feeling clueless

DMM shows largest voltage is 19V DC on the logic board. The connector to the inverter also shows 19V DC so 25V should be sufficient. BUT, a batch of United Chemi-con 470uF 35V caps arrived in the mail today so I will use those for temp testing.

Unfortunately, in an effort to remove the old caps, I managed to leave blobs of old solder in the holes and I can't get the new ones in. I will have to investigate how to remove these blobs.

[Scenic]

Re: NEC LCD1700v ... feeling clueless

toothpicks do wonders
(poke through the holes with a toothpick while heating the solder up)

[retiredcaps]

Re: NEC LCD1700v ... feeling clueless

Managed to get the 470uF 35V caps installed, but I still get the 2 seconds to black. So it wasn't the original 180uF 30V at fault.

On the inverter board, I think it is down to the transformers or the CCFLs. By the way, I tried just one CCFL connection at a time and I still get the 2 seconds to black.

I'm also going to check all the ICs on the inverter and logic board to make sure they are all working okay. It will be a good exercise for me to lookup the datasheets and find out what they do.

[Dgtech]

Re: NEC LCD1700v ... feeling clueless

Sometimes when I get a monitor with a similar problem I changed the caps on the inverter board. Here is the interesting part, If you check some of the bad caps with a capacitance meter, they will sometimes read slightly higher than what they're supposed to be. Hmmmm.... If I replace a 180uF cap with a 470 and I get the same result.......????

It would be funny, at least for me, if that 180uF cap that was taken out reads about 470uF. You shouldn't go that high of a change. If it needs 180, put in 180. If you check new similar caps on a cap meter, they will show a difference in uF however not that significant. The tolerances of circuits will allow you some small changes in capacitance but damn, i mean 2.6 times the original capacitance? Not saying it will fix the problem but dont create one trying to fix the original problem.

[retiredcaps]

Re: NEC LCD1700v ... feeling clueless

I don't have a ESR tester. I just tried the 470uF 25V as a temp test to possibly rule out a bad 180uF 30V cap. My original intent was that if the 470uF worked, I would replace the original cap with something closer to 180uF.

I understand what you are saying about the 180uF being too high in capacitance. I will keep in mind that it still could be the caps that are causing the 2 seconds to black.

The 2 local stores here don't have a lot of choices for caps. They don't carry any name brand caps like Rubycon, UCC, or Panasonic. They are the cheaply made ones and are 85C rated.

Sometimes when I get a monitor with a similar problem I changed the caps on the inverter board. Here is the interesting part, If you check some of the bad caps with a capacitance meter, they will sometimes read slightly higher than what they're supposed to be. Hmmmm.... If I replace a 180uF cap with a 470 and I get the same result.......????

It would be funny, at least for me, if that 180uF cap that was taken out reads about 470uF. You shouldn't go that high of a change. If it needs 180, put in 180. If you check new similar caps on a cap meter, they will show a difference in uF however not that significant. The tolerances of circuits will allow you some small changes in capacitance but damn, i mean 2.6 times the original capacitance? Not saying it will fix the problem but dont create one trying to fix the original problem.