Neotec NT-500 - dead *FIXED*

[lilshawn]

i have a NT-500 (27'' NT-500DXB7/P7) chassis in a buck hunter that went dead...no power at all... no power light... no chirping nothing...sent it back to manufacturer to be fixed...returned with some caps replaced...still not working - exact same problem dead. said they had it working....sure.

sent this chassis back again... came back with a few more caps replaced and maybe the SMPS chip/fet, it's hard to tell for sure....still deader than a doornail...insist that they had it running on the bench for several days. Neotec sent a new/used chassis and it worked fine.

so i have this chassis sitting around and would like to see if i can get it running again...

problem is, there is a real lack of documentation on this unit, the schematic is terrible,, but i'm hoping someone who has had some experience with is model can help me out.

EDIT

some "poking around" on Friday had led me to believe that there is something wrong with the SMPS section of this power supply.

seems i'm getting 83.3 volts dc on one of the coils of the primary side of the main transformer and -84.0 volts on the other.

i get nothing out of the secondary side.

isnt this supposed to be 100+?  

there is a 140 volt output on the secondary side of the transformer so i'm sure the "b+" is run off the transformer, not directly from the SMPS like most monitors    as this transformer is the only thing "Bridging the high voltage line" i have swapped out the transformer from another chassis, so i'm stumped.

i have a PDF of the schematic if anybody would like to take a stab at it.

[lilshawn]

no ideas anybody??

[lilshawn]

[lilshawn]

well seems the SMPS driver chip went bad. It was causing the switcher MOSFET to stay partially on instead of pulse. thats why there was voltage on the primary side of the drive transformer and not the secondary side.

replaced  KA3842 IC chip (dip8)

[Level42]

Although nobody responded (Neotec's are pretty new and not so often in the classic cabs) this is good info to know.

Apart from your problems how did you like the Neotec ? What brand tube is in them and what chassis (is it really branded Neotec ?)

[lilshawn]

most of the Neotec monitor tubes (i believe i'l double check )are "Thompson" tubes if they are "round" front versions (EDIT TO INCLUDE flat flatface tube variant is LG/Philips # A68QCU770XV3N). They seem to be plagued with the same problems, most likely due to a bad choice in design and/or caps. The Chassis are actually manufactured by Neotec, thus supporting documentation is a little scarce. This chassis bears NO resemblance to anything else out there so i'm believing it's an in-house design.

there is about 5 caps in the power system that feeds the rest of the computerized control systems. (EDIT: c525 c527 c 519 c501 c502) They are jammed in between 3 power regulators and their heat sinks. the caps blow and the SMPS  starts loading down till the FET blows and the SMPS control chip goes with it.

another issue is the vertical IC (ic301) goes... takes out R623A/B (go way out of spec) replacing all ensures reliability.

lastly the transistor that controls the power to the electronics (Q501 (HSB772) in with the aforementioned caps) tends to heat up, till it burns off the board...leaving a nice dime sized charred hole in it's place. replacing it with an NTE185 and attaching a small aluminum heatsink to it to help dissipate heat really helps. this is a transistor that simply switches the monitor 15 and 12 volt supplies off/on using the monitors CPU. if you like, you can "bypass" this transistor and just have the monitor stay on. (jump across the emitter and collector (pin 2-3) but be warned if you press the power button, the computer and monitor will do some weird things since it will think it's powering down, but the monitor will stay on. in our applications it stays on 24/7 and gets powered off when the main power switch kills AC, so i doesn't matter to us, but your application might not work here.

I think the main problem is that It appears to use both a standard and an SMPS power supply, making diagnostics a PITA. Up-capping the voltage when replacing the blown caps is definitely recommended.

we only have a handful of maybe 7 or 8 these monitors and have had problems with even less.  but the ones we have had to fix have all had the caps in that section blown out, and 2 that have had a main power feed resistor cook the trace off the board. This chassis is the second "resistor" blown chassis. the resistor was repaired and later on the caps and the SMPS blew out. I'm almost inclined to think it may be related. The other chassis (resistor repaired about a year ago) is still operational.

I'm almost tempted to begin just replacing the resistor, SMPS chips, and the caps when (and if) the units come in the shop.

Other than the issues, the tubes (offered in curved and flat versions) seem alright. Found commonly in Big Buck Hunter cabs with curved monitors and BBH Pro with flat along with WG d9200's. Seems they started out with the neotec monitor, and later changed to WG. Reason unknown. (possibly due to supply issues or different manufacturing plants using different monitors during the BBH Pro run. We have had more issues with the WG's than the Neotec's. The chassis have a wide variety of screen controls to get a nice square picture (tilt rotation keystone pincushion etc) you can adjust the RGB from the control panel which is a bonus on some cabs, since the neck cards are often buried up inside the cab where you can't even see them.

supports 640 X 200 CGA, 640 X 400 EGA, 640 X 480 VGA, 800 X 600 S-VGA and HORIZONTAL: 15.75, 24.8, 31.5 ~ 38 KHz
VERTICAL: 45 ~ 90 Hz scan frequency and has both VGA connection and standard RGB pin header.

[jlzeller]

What is the model number/location of the FET you describe?