Bestview HD17A - lines, patterns or "no signal"

[Th3_uN1Qu3]

I got this in today. The symptoms have been going for a while, basically the display would be all funky and it would take many restarts to get it going. This is the type with external power brick, i posted about a similar one, Likom HD17A if you remember, the one with STONE caps that got stuck in service mode. On this one all caps are Samxon but of a similar form factor. Two Hermei and two small Teapo caps on the inverter. Anyway, all the caps are good.

Power supply was found with the primary 68uF, 400v Su'scon cap bulged. That's no wonder considering its location - it is right in the middle of all the heatsinks. The power supply is also quite small. That cap got cooked good. So as a result, this thing saw quite a bit of 50Hz ripple. I'd known about this monitor for a few months, and i'd insisted i take a look at it, but it seems some people only act when it's too late.

All voltages are okay except 1.8v which is 1.8v only when the thing is off, or when i get the no signal message. When it does the funky patterns, 1.8v starts as low as 1.2v and varies between 1.6 and 1.7v. Btw the patterns are quite psychedelic, i filmed a minute of them, i'll post it if you want it.

My laptop recognizes it (but only as a "generic monitor"), my computer does not recognize it at all. The VGA cable i am using could be bad tho, i'll check it out tomorrow as the only other monitor i can try it on is in mom's room and mom's sleeping now. Regardless, the thing turns off after a few seconds whether i get the no signal message or not. I assume this is normal "no signal" behavior. This isn't two seconds to black, the inverter is controlled by a 5v signal from the logic board, and that goes out when the screen turns off. I cut the wire for that signal and hardwired it to 5v, and indeed, the lamps stay on, but the screen goes white - so the panel gets shut down.

I believe the logic chip has suffered permanent damage. I'll talk to the guy with the Likom monitor tomorrow, after i gave it back to him he said i can keep it, but he never came to give it back to me again. If i remove the EEPROM from this logic board and put it on that one, i should end up with a working board. This one also has an audio amp and speakers while the Likom doesn't, but the speaker grilles are on the back of the monitor so i don't think anyone is gonna miss them.

[Th3_uN1Qu3]

Re: Bestview HD17A - lines, patterns or "no signal"

Nice one... Soldered a random Rubycon cap on the bottom of the one after the 1.8v reg and guess what? Now i get the no signal message every time and 1.8v is stable. Now i sure hope my cable is bad and it's not anything else.

[Th3_uN1Qu3]

Re: Bestview HD17A - lines, patterns or "no signal"

Cable turned out to be good so i tried the monitor on the other laptop (using the same crappy cable) and it works. Go figure. Btw, ever seen separate "Brightness" and "Backlight" controls?

Edit: Tried the Eizo CRT (but with the same cable) on my dv9000 and it says it doesn't get horizontal sync. I guess you can add the VGA out to the list of failures of the dv9000... but what about my main computer with the HD3870, as that wouldn't even detect this LCD? I'm quite sure the HD3870 didn't just fail overnight, the second output worked a few weeks ago. I have another CRT that has a built-in VGA cable (not removable). I'll try that one, and if that works it means the cable is indeed bad, maybe the dv5's VGA output defaults to sync on green and that's how it gets around the missing hsync signal.

Edit 2: The other CRT also complains about missing hsync signal on my dv9000. So its VGA output has failed. I wonder what's up with the HD3870 tho.

[Th3_uN1Qu3]

Re: Bestview HD17A - lines, patterns or "no signal"

The monitor works on my HD3870 too. It was a matter of CCC conflicting with the Windows display properties panel. I also found a cap that fit snugly in the power supply - it's 47uF instead of 68uF but it appears to work fine. It is a Samxon 105C cap. I also made a ghetto cooling mod to it - i glued a piece of perfboard to the top as a template and proceeded to drill a lot of holes. This should keep the new cap from suffering the same fate as the old one. I'll post a pic tomorrow.

So, summary:

• Just because a cap is after a linear not a switching regulator, it doesn't mean it cannot fail.
• If a linear regulator displays fluctuating voltage, that doesn't mean the reg is bad. Change its output capacitor first.
• Even if the cap seems alright, but it just doesn't work while a new one does, replace it with the next higher value if it fits. Linear regs are way more tolerant of output capacitors than switching ones, and chances are the absolute minimum value was used at the factory.