neo-tec nt3500 38" monitor wont turn on!!

[rocklite]

hi i have a monitor that wont turn on anymore. it is a neo-tec nt-3500 afaik.

i have been playing with the pots on the chassis pcbs in order to try and make the image better. sometimes when i move certain pots the monitor turns right off and wont start up again until i set them back to where they were. the monitor started to make a lot more noise when displaying brighter colors lately and i have been trying to adjust them again to be quieter.

when i went to turn on my cab today it wouldnt start up at all. it seems to be making a ticking sound. "shwoop-tick, shwoop-tick" it goes. and it just does that instead of powering up. my monitor is connected directly to a "peter chou usp-11-200xt" single block power supply. it used to connect with some bare molex pins but i snipped them off to connect to a grounded power cable to a power bar connected to the wall instead. it was just as noisy this way so i decided to connect with the power supply again. i reconnected it to the peter chou by stuffing the threaded cables into the proper places (molex pins removed). it worked fine last time i saw it but today it wont turn on at all. tried plugging into the wall again but it gave me the same result.

it sounds like its trying to power up. every second i hear this tick/ click/ bweep noise that just repeats in one second.

help. even if you can think of a better place to ask. please help.

[lilshawn]

sounds like maybe you've overdriven the HOT  (horizontal output transistor) by cranking up the B+ too high and caused it to fry.

the HOT is a large 3 legged transistor mounted to a heatsink. you can check it dirty and quick with a multimeter by placing one lead on the middle leg and probing on of the two others. a reading of continuity (zero ohms) or low resistance says it's bad. (should read in the Kohms or Mohms)

do this with the power off of course.

[MonMotha]

Oh boy, you really shouldn't go playing with controls on these things when you don't know what they do.  It's possible to damage components or even create hazards by defeating protection mechanisms like the x-ray protection.

The ticking sound you hear is the power supply attempting to start up, finding that something is shorted and therefore drawing way too much power, then giving up and trying again later.  Likely culprits are the HOT or vertical output IC with the HOT probably being more likely given the circumstances.  Hopefully nothing else got hurt due to the high B+.

It does sound like you've blown up the HOT.  It will need to be replaced, if so.  Before powering back up, you'll also need to make sure that some of the controls are at least in reasonable positions, especially B+ and any HV/x-ray settings, though HV/x-ray settings are often glued into place at the factory.  This may be difficult without some service info, especially if the pots aren't labeled on the board.  Hopefully you marked the original position of everything before you started tweaking them?

[rocklite]

hmm. well there are at least 4 possible ones to test then. i cant reach them all with the multimeter so im going to have to dissconnect the whole chassis board. i disconnected my flyback but i didnt hear a pop. is that a bad sign?

[lilshawn]

no...most newer chassis have system built into them to discharge most of the voltage after a few moments.

you might want to take a wire with an aligator clip at each end and clip one end to the metal frame and stick the other end inside the bellybutton of the tube...it's the tube that has the charge in it, not the electronics.

[rocklite]

its from 1998. by the looks of it. ill try jamming it right in there again though. Yeah I've got a cable i made from two aligator clips and some speaker wire for this.

i dont know what xray protection is so ill look that up.

this was used heavily in an arcade downtown for over 5 years. I'll need to find a cap kit i suppose?

all the pots worked in the position they were in the last time i saw it up. i did not mark where they started out in the first place though... its going to be fun getting this going again. =[ ill mark them now regardless.
 
also a pot on the adjuster pcb is dead so ill need a new one of those too prolly. If you jiggled it, you would get either really bright or really dark and i just played with the flyback and contrast to compensate.

here are some pics. 

"There's my model info."


"I've labeled the pots in case that helps."


"It's the Brightness pot that doesnt work. Figured I had found suitable settings messing around with my pots before."


Uploaded with ImageShack.us

[MonMotha]

Did you adjust R111 (probably B+ adjust) or R429 (X-Ray)?

[rocklite]

yes

[lilshawn]

your x-ray circuit measures the B+... if it gets too high it will send a signal to the SMPS controller chip to shut down the power supply... Xrays are produced from the tube when the high voltage gets really high...it leaks out the backside of the tube and the neck where the glass is thinnest. the thick front glass has lead in it to help block out the xrays. the circuit is designed to shut down the monitor before the xrays get hazardous to your testicles.

maybe x-ray set too low....

or

B+ set too high.

either way, something isn't right.

high B+ can blow the HOT too so maybe you have multiple problems.

PS-

***DISCLAIMER***

I don't advocate the use of x-rays as birth control, and I discourage placing your testicles anywhere near monitors, especially when operating.

[MonMotha]

The behavior of X-Ray circuits unfortunately varies with monitor.  Some simply stop horizontal output (so nothing flyback derived, etc. but the monitor otherwise "runs"), some shut down the power supply, and some actually blow something up to force the monitor to shut down.  I'd check for shorted components, attempt to put the B+ adjust in a reasonable position, and try to crank the monitor up again.  You'll then need to know what to set B+ to as well as where to monitor it.  A service manual would help (and would likely include full tune-up procedures), but is not required.

Sometimes getting these things back up after misadjustment like this involves temporarily defeating the X-Ray protection, usually by cranking the pot all the way to one extreme (which way it goes varies with monitor).  You then get it running, adjust B+ and a few other secondary settings, then you attempt to re-set the X-ray protection.

[rocklite]

I set my multimeter to 20k omh and i read ADJ/r111 at "1.51" it maxes out at 3.00.
checked x-rax/r429 and it reads 4.9 and maxes at 9.34.

i tried setting xrax to full and min and then played with b+ but it wouldnt power on. hopefully its the HOT transistor like ya said. that is right where the noise is coming from. its called "irfpe50". hopefully they have it in stock downtown. when i test it it keeps counting up to about 20 and then goes back to 0.

[MonMotha]

You can't measure a pot like that in-circuit, generally.  You'll get false readings due to the surrounding circuitry.

[rocklite]

ok well i replaced that transistor and it didnt make a difference. the one bolted to the sync above the "ADJ/r111" pot on my image. Any links to good tutorial for testing other possibly faulty parts? Also where might one find the service manual? It doesnt seem to be available on the Neo-Tec site.

[lilshawn]

I've circled the item you need to check out. it is the horizontal output transistor. (HOT)

[rocklite]

thanks! now i just need a new place to order it from. the local place really charges a lot for special orders. any ideas?

[lilshawn]

onesies are often cheaper on ebay... you can get stuff pretty cheap from hong kong... but, you'll have to wait a few weeks for it to show up. you can get small quantities from mouser, but sometimes they will hose you on shipping...to the point where you could just buy locally.

sometimes it's worth the extra $$$ to have it now. but if you have the time, check out ebay.

[MonMotha]

Have you checked MCM?  They've got all sorts of weird TV/monitor related parts not found at more mainstream distys.

[rocklite]

having trouble finding this transistor replacement. i went to the shop downtown but they couldnt order it. it reads; "BU 4530AL PHC0014 B3" on the transistor. is fixing this board my only option? how much should a replacement chassis cost? (50-200?) can i use this tube with another chassis? where might i find a alternative otherwise? thanks.

[rocklite]

any ideas?

[lilshawn]

it's made by philips

usually you can just insert the manufaturer code in front or use a universal code like "2SC" or "2SD" IE: 2SC4530 or 2SD4530

any good electronic supply will have a cross reference they could look it up in to be sure.

also ebay... http://cgi.ebay.com/BU4530AL-BU4530-Power-Transistor-Clearance-sale-/290471866654 this guy is away...but you can watch to see when/if he comes back and order one from him.