Norwood F199 3-seconds image

[vince88]

Just repaired a Norwood 19" F199. This is CompUSA private brand and is identical to Tyris T901DB 19".
Problem: when turned-on, the LCD will display an image only for 3 seconds; green light will stay on, and the image would show with a flashlight. My guess was a fault with some of the backlights.
Opening the LCD is simple: the backshell is fixed to the front bezel by a number of plastic tabs, see pic "tab", and sliding a credit card between the back and bezel does the job to separate backshell from the front bezel. As shown in the "shell" pic, the VESA 75mm plates are just glued to the backshell: not a very good mechanical design ! The LCD panel is Hannstar HSD190ME12 also used in Samsung SyncMaster 913V and Benq Q9T3.
As shown in the "back" pic, the LCD has two main boards [1] a processing board LM1X02N see pic "processing" and [2] a power/inverter UP0401UB12Q07 see pic "power"connecting the the processing board by a 12-pins connector with 12VDC/GND/ON-OFF/BRI. Specs for this UMEC board can be found at .
This board powers 4 CCFLs: CN301/302 and CN303/304; when the LCD is powered up, CN301/302 light up for 3 seconds while CN303/304 fail to light. The Electrolythic caps LTEC are not bulging and seems OK. Inspection of the section of the board relating to CN303/304 shows that [1] capacitor C305 0.33micF 250V is cracked and 'smiling' see pic "C305" [2] both transistors C5706 Q305/Q306 have a weird hole see pic "C5706" [3] transformer UMEC UT35D82 T302 might have overheated. The C5706 are Sanyo's 2SC5706 and I ordered equivalent 2SC5707 marked C5707 from eBay: they come in 4 at $3.99 or bundled with rectifier/caps inside kits called "DELL E172FPB E173FPB HP f1703 f1503 REPAIR PARTS" at $5. NTE equivalent is NTE2668.
I replaced C305 and Q305/Q306, and the LCD works. I believe that the processing board tests the CCFLs, and shuts down if any of the CCFLs is not working

[PlainBill]

Re: Norwood F199 3-seconds image

For the most part, a good analysis. There are a couple of points you missed or got wrong. This particular inverter design is a Royer oscillator, and is favored by a number of manufacturers, including Benq (suppliers of HP and Dell monitors).

The failure is often precipitated by bad solder joints in the inverter transformers. ALWAYS resolder them when replacing shorted transistors.

The other point is minor. The 'logic card' does not sense the action of the backlights. Rather, the inverter controller performs that function, and shuts them down if they are not functioning correctly.

PlainBill

[vince88]

Re: Norwood F199 3-seconds image

TKS PlainBill. I was wondering what caused the failure, considering that [1] both CCFLs on the 'non-working' side were OK [2] inverter transformer is OK [3] there was no overheating traces for either transistors, just punctured cases. I was suspecting initial failure of C305 cap, but I will have a second look at the inverter transformer solder points.

[retiredcaps]

Re: Norwood F199 3-seconds image

but I will have a second look at the inverter transformer solder points.

I have a "like" c5707 benq designed board. When I diagnosed the problem, all I could find was an open fuse. I changed the fuse and forgot to resolder the transformers (a well documented problem on the benq boards).

24 hours later the fuse blew again. I opened it up, changed the fuse, re-checked all the transistors, diodes, etc, but found nothing bad. I resoldered all the transformers and now that monitor is fine (works for 3 straight weeks). The solder joints even under a magnifying glass didn't look "bad", but obviously it made a difference resoldering them.

[PlainBill]

Re: Norwood F199 3-seconds image

TKS PlainBill. I was wondering what caused the failure, considering that [1] both CCFLs on the 'non-working' side were OK [2] inverter transformer is OK [3] there was no overheating traces for either transistors, just punctured cases. I was suspecting initial failure of C305 cap, but I will have a second look at the inverter transformer solder points.

Ahhh!!! You have a valid point. Failure of that cap will result in the transistors shorting. I've seen it at least once.

PlainBill

[lkvee]

Re: Norwood F199 3-seconds image

I also have the F199 which featured a blinking power light, a backlight which flickered instantaneously, and an image which appeared intermittently also.

The big capacitor tested within acceptable limits with respect to capacitance and ESR using ESR Micro 3.1 I didn't test the other caps.

Turns out the transistor 2SC5706 (?) has shorted. I was replace both of them at C303 and C304.

I believe these caps were on the power board:

LTEC PET 5023D - 82uF and 400V
LTEC PET 5013D - 680uF and 16V (x2)
LTEC PET 5013D - 220uF and 25V

The video board on the F199 was made(?) by the gbm Group and features CapXon capacitors:

47uf 16V (x8)
220uf 16V (x2)
100uf 16V (x2)
470uf 16V (x2)

[retiredcaps]

Re: Norwood F199 3-seconds image

The big capacitor tested within acceptable limits with respect to capacitance and ESR using ESR Micro 3.1 I didn't test the other caps.

It is our collective experiences and observations that the largest cap rarely, but not never, fails. Moreover, it is the smaller caps in the secondary section that have high ESR.