2 dead monitors, blueh h94w and amw x1700ds

[rephlex]

Hi, I have two monitors with PSU problems and I was wondering if anyone had any ideas on what could be wrong with them before I replace all the capacitors.
The blueh monitor works for a few minuites before cutting out. The monitor has to be left for a while before it will work again (cool down?). The voltages are OK until the screen cuts out, at which point the 5v rail drops to 4.6. Runnning the monitor off an external 5v PSU solves the problem.
The board has ILPI-068 written on it.

The other monitor doesn't turn on (not even the LED). I left the monitor at work so I haven't tested it loaded but unloaded it has approxamately the correct voltages, but produces (on 14.5v rail) 13.5v for one sec, 14v for one sec, 14.5v for one sec, and then drops back to 13.5v. This could just be due to being unloaded though.
The bord is a Digital Decode Ltd. PI-SB01

None of the components look damaged and I have done basic resistance tests on both of them (FETS, caps, diodes, transformers etc.) and they all seem to be ok. I don't have an ESR meter at home but I could test the caps when I'm at work on Monday. Nothing seems to be getting particularly hot either.
Does anyone have any ideas on what to test?
Thanks, Nick

[seanc]

Re: 2 dead monitors, blueh h94w and amw x1700ds

Digital Decade LTD?

They manufacture the PSU boards in the "AMW" monitors I've repaired. Always been bad caps.

What are the monitors brand & model?

[rephlex]

Re: 2 dead monitors, blueh h94w and amw x1700ds

The one with a digital decade pcb is from an AMW x1700DS-A1 and the other monitor is a Hyundai BlueH H94W

[seanc]

Re: 2 dead monitors, blueh h94w and amw x1700ds

Yep, I have one of those here. Are you sure there are no bulging caps on it? You'd be wise to replace all of the caps anyway since they're usually Capxon, I suspect it would be fine afterwards.

I'm guessing you're in the UK, adding your location to your profile would be helpful. Someone may be able to offer their services or a few parts if nearby.

[rephlex]

Re: 2 dead monitors, blueh h94w and amw x1700ds

I am quite up for fixing these monitors myself but I just wanted to make sure that if I spent £20 on capacitors there would be a chance I would fix the screens. The caps in the AMW are mainly elite and on the hyundai they are su'scon and samxon.
I've been doing quite a lot of work on ethernet over AC adaptors with dodgy caps and I've found that the (bad) caps they came with (jackcon) are OK provided they arn't subjected to too much ripple. They had a CLC filter for the 3.3v and only the first C needed replacing with a low ESR version to get them working reliably

[seanc]

Re: 2 dead monitors, blueh h94w and amw x1700ds

Elite caps, interesting.
I'd suggest you post top and bottom pics of both boards. I can compare it to my AMW and someone else like PlainBill can probably chip in some very good advice.

[rephlex]

Re: 2 dead monitors, blueh h94w and amw x1700ds

Here are the images of power supplies. The slightly burnt resistor on the Hyundai board (top center) is where I discovered how the feedback from the 15 or so volts from the backlight works. It has a zenner and a resistor designed to pull up the 5v if the 15v gets too high. I was running the 5v off a bench supply so the resistor got quite warm quite fast. That section still works though.
Also I have started changing caps on the Hyundai board on the 5v rail. I've put in a Nippon Chemi Con (large, left hand side) and a Sanyo (near burnt resistor). It hasn't made any difference though.
Bottom of Hyundai
Top of Hyundai
Bottom of AMW
Top of AMW

[rephlex]

Re: 2 dead monitors, blueh h94w and amw x1700ds

I measured most of the larger (1mF) caps from the AMW today - the 16v ones all had roughly the same results, as did the 25v ones. I've posted the worst performing caps below.
(@125Hz)
25v, 1000uF
tan d: 0.057
cap: 951uF
esr: 66.55mOhm

16v, 1000uF
tan d: 0.096
cap: 993uF
esr: 123.8mOhm

datasheet for these caps states a tan d of 0.18, but no esr values. They look OK to me - does anyone have any other ideas about what might be wrong.
Thanks!

[PlainBill]

Re: 2 dead monitors, blueh h94w and amw x1700ds

I measured most of the larger (1mF) caps from the AMW today - the 16v ones all had roughly the same results, as did the 25v ones. I've posted the worst performing caps below.
(@125Hz)
25v, 1000uF
tan d: 0.057
cap: 951uF
esr: 66.55mOhm

16v, 1000uF
tan d: 0.096
cap: 993uF
esr: 123.8mOhm

datasheet for these caps states a tan d of 0.18, but no esr values. They look OK to me - does anyone have any other ideas about what might be wrong.
Thanks!

Those readings indicate the caps are bad. I'd expect ESR values below .03. I just pulled a 1000uF 16V Nichicon HE and checked it's ESR. I got readings of .02 - .03. However, that's not the likely cause of the problem with the power supply. The picture shows a small electrolytic (C1P?) between the SMPS transformer and the power FET. There may be another on far side of the SMPS transformer. Check (or just replace) them.

Most of the SMPS controllers worh the same way. At start up they draw power through a high value resistor; a small electrolytic (10-47uF) stores energy while the SMPS starts. There is a tertiary winding on the SMPS transformer that feeds a diode with another small electrolytic storing the energy. This provides run current. The symptoms indicate the startup cap is becoming discharged before the run cap has enough energy stored to maintain operation.

One other point - I've ignored this thread until now because I hate dealing with the confusion caused by two power supplies from two different monitors in the same thread Add the confusion of the designation changing and I just click on 'Previous Thread'.

PlainBill

[seanc]

Re: 2 dead monitors, blueh h94w and amw x1700ds

Did you measure the smaller 220uf? Mine had failed.

[rephlex]

Re: 2 dead monitors, blueh h94w and amw x1700ds

More test results, I did this @ 1kHz as I thought that it would give more accurate results with SMPSs (above 4kHz most of the elite caps become inductive). I don't think any of them have failed as such, but they are just not low ESR types and don't work well with HF power supplies. I've ordered replacement Panasonic ones that should arrive on Monday so I will see then if that really was the problem.

Make Size Voltage C(uF) ESR tan d
Elite 10uF 50v 8.73 3.82R 0.211
Elite 1mF 25v 939 35.6m 0.211
Elite 1mF 25v 943 35.5m 0.210
Elite 1mF 16v 964 87.6m 0.533
Elite 1mF 16v 957 87.3m 0.526
Elite 1mF 16v 965 85.4m 0.518
Elite 470uF 16v 441 190.7m 0.528
Elite 220uF 25v 208 434.5m 0.569
Elite 220uF 25v 209 406.3m 0.533

---------- other caps I tested at the same time ----------
Pana FC 100uF 100v 84.6 166.2m 0.088
Pana FK 1mF 6.3v 932 77.6m 0.455
Nippon CC 1mF 16v 945 110m 0.652
OS-Con 100uF 16v 103 56.1m 0.037

[leops]

Re: 2 dead monitors, blueh h94w and amw x1700ds

hi, I'm new in this forum but really interested to that considering I have the same Hyundai model LCD with same problem. This monitor is working fine for a few seconds and after is switching off automatically. Some time is working fine for indefite time until I'm not switching off the on/off button. In that case could create again the same problem or continuing to work fine. Anyway when the issue is coming I have to leave the monitor ON and disconnect the power, wait some seconds and reconnect the power. Do you have idea what could be the problem? I have already resoldered all strips. Thank you. L

[retiredcaps]

Re: 2 dead monitors, blueh h94w and amw x1700ds

Anyway when the issue is coming I have to leave the monitor ON and disconnect the power, wait some seconds and reconnect the power.

Post pics of your boards like the ones in post #7 using the manage attachment feature. Please do not post inline. The smallest board change is significant.

[leops]

Re: 2 dead monitors, blueh h94w and amw x1700ds

hi retiredcaps
thanks for your reply
my board is the same Hyundai than rephlex posted on the middle of this post, bottom and top. Exactly the same. Could that helps?

ciao
Leops

[PlainBill]

Re: 2 dead monitors, blueh h94w and amw x1700ds

hi retiredcaps
thanks for your reply
my board is the same Hyundai than rephlex posted on the middle of this post, bottom and top. Exactly the same. Could that helps?

ciao
Leops

Here's the problem with using the pictures of another monitor, even if it's identical. Some months ago I tried to help someone who had a 'two seconds to black' problem. He indicated the caps looked good. We exchanged over a dozen messages, and made many measurements before he finally provided pictures. In the pictures it was obvious that several caps had bulging tops and had vented. He DIDN'T know what he was looking at. Based on that experience, if pictures of the actual monitor are not provided, I will ignore the thread.

PlainBill

[leops]

Re: 2 dead monitors, blueh h94w and amw x1700ds

ok plain I'll post pictures. I have to open again the monitor leave me today. Thanks
Leops

[leops]

Re: 2 dead monitors, blueh h94w and amw x1700ds

As required I have posted hyundai monitor fotos. Hope this helps

Thanks a lot
Ciao
Leops

[Th3_uN1Qu3]

Re: 2 dead monitors, blueh h94w and amw x1700ds

Try to place the camera on something stable, the photos are blurry. We're also going to need some pics of the solder side of the board.

[leops]

Re: 2 dead monitors, blueh h94w and amw x1700ds

I'll try again to do it and amount the board from the chassi to take pics on solder side. do you see something strange from these?

[Stagdriver]

Re: 2 dead monitors, blueh h94w and amw x1700ds

I have been working on the Hyundai Blueh board.
My symptoms are that the screen operates fine for ten minutes, then flickers and i lose the backlight, after a while presumably whilst something cools down a bit comes back on but flickers and goes out again over and again.

I examined the board and no caps were showing signs of stress but changed them all for good quality low esr anyway. No improvement whatsoever.

i do notice though that the pcb itself has signs of heat around the schotty's an near the top left invertor transformer.

I attach photo of front and rear and notice that on rear there are a pair of fets with a tell tale heat colouring on the pcb front side.

Has anyone else had similar problems to this, my money is on a dodgy coil winding, but perhaps the fets?.. Any suggestions greatly appeciated.
Cheers Stagdriver

Hope the images uploaed ok