Dead Neovo X-174

[johnboy183]

Have just inherited one of these monitors which shows no sign of life at all, not even a green led on the on/off switch which it should display. On opening it I found a surface mount Elna cap 470uf 16v wide open at the top with electrolyte sprayed out onto the coverplate of the circuit board. Not having any of this type I replaced this and the only other similar cap with two through hole caps of equivalent specs but can still get no life at all from the monitor. I can get a reading of 12v on one lead going from the logic board to the seperate inverter board ( there is no power board as such as the power is supplied from a 12v external power supply) but no other reading at that connector (ie no 5volt). The only other thing I have found is that the fuse on the inverter board appears to have failed but the caps on the board are fine and even temp wiring across the fuse produces no life.
As I have not seen one of these monitors before and there is little on the forum or net on faults with them just thought i would ask if anyone has had similar faults on one to point me in the right direction. Unfortunatelly cant get a photo of the thing at the moment to post but will try.
Also can anyone point me to a simplistic explanation of the direction of power flows from the on/off switch/LED throught the inverter and back as it were as I still dont fully understand the backlight control mechanism?
Many thanks for any help offered - it is very much appreciated.
Regards
Johnboy183

[PlainBill]

Re: Dead Neovo X-174

Johnboy (sounds like one of the Waltons),

The power LED is usually controlled by the controller on the logic board. There are two control lines from the logic board to the inverter. One turns the CCFLs on and off; the other controls the brightness.

PlainBill

[johnboy183]

Re: Dead Neovo X-174

I have made a tiny bit of progress (I think!) on this problem. I cant measure 5v on any point on the board or connectors. Starting at the power input I can register 12v through the sytem but also find there is a 5 pin LM2596 Simple switcher power converter 5 pin chip near the power input that according to the data sheet takes in 12v and ouputs the 5v needed. Measuring on the pins the input does show 12v going in but none of the pins show 5v coming out (one is quoted as a feedback, one as GND, one as ON/OFF and one as 5V)
Is it likely to be a failed switch or is that too simple a conclusion and some other connected component is preventing the switch from operating?
The LM2596 is near the bottom of the photo. Any advice or other components to check would be very welcome (ignore the two sideways mounted caps as they are the temp solution to the two faulty caps found)
Thanks
Johnboy183

[johnboy183]

Re: Dead Neovo X-174

Hopefully with photos this time as it failed on the earlier post

[PlainBill]

Re: Dead Neovo X-174

I have made a tiny bit of progress (I think!) on this problem. I cant measure 5v on any point on the board or connectors. Starting at the power input I can register 12v through the sytem but also find there is a 5 pin LM2596 Simple switcher power converter 5 pin chip near the power input that according to the data sheet takes in 12v and ouputs the 5v needed. Measuring on the pins the input does show 12v going in but none of the pins show 5v coming out (one is quoted as a feedback, one as GND, one as ON/OFF and one as 5V)
Is it likely to be a failed switch or is that too simple a conclusion and some other connected component is preventing the switch from operating?
The LM2596 is near the bottom of the photo. Any advice or other components to check would be very welcome (ignore the two sideways mounted caps as they are the temp solution to the two faulty caps found)
Thanks
Johnboy183

By the looks of things, you're using a universal adapter. What is it's current rating?

If the adapter has enough current capacity, it could be a defective switching regulator, or it could be a problem with the inductor. Also, there is another unknown component between the inductor and the regulator. What is it? (Diode?)

As a suggestion, turn the flash off (to avoid glare), take the pictures in a well lit room (to shorten the time it takes to take the picture), and steady the camera with a tripod or other stand to eliminate jitter. Lastly, turn down the resolution on the camera one step or use editing software to reduce the resolution to a maximum of 2000 x 2000 pixels. That way you won't have to conceal them in a RAR file. Remember that I'm and old fart and fundamentally lazy. I don't like to have to jump through hoops to look at pictures.

PlainBill

[johnboy183]

Re: Dead Neovo X-174

Thanks PlainBill. I dont think the "?diode" is marked but I will check tomorrow as its now 11.15pm in the UK and like you I am an old fart and need my sleep ! whatever happened to being young and being able to burn the candle at both ends?
Thanks again
regards

[PlainBill]

Re: Dead Neovo X-174

Thanks PlainBill. I dont think the "?diode" is marked but I will check tomorrow as its now 11.15pm in the UK and like you I am an old fart and need my sleep ! whatever happened to being young and being able to burn the candle at both ends?
Thanks again
regards

That's for young kids. Old guys like us have to use stealth and trickery.

PlainBill

[johnboy183]

Re: Dead Neovo X-174

Hi,
the power supply you see is a PC Power supply adapted to provide a test bench supply and i have only used it this time as the 12v input pin socket on the Neovo is a size I dont have on any of my conventional 12v bricks. Dont exactly know the amps output to hand but the symptoms remained the same when I earlier used a 12v 4amp power brick with the wires simply soldered to the inputs ( the monitor is quoted as needing a 12v 3.3amp input).
The "?doide" is indeed a diode (D1 according to the markings on the board). Given my electronics prowess is limited to simple experience and commonsense plus a multimeter and caps tester can you tell me the best way to test the diode in question and the inducter or is it simply substitute and eliminate until the fault becomes obvious and the 5volt is restored?
regards
Johnboy183

[PlainBill]

Re: Dead Neovo X-174

Hi,
the power supply you see is a PC Power supply adapted to provide a test bench supply and i have only used it this time as the 12v input pin socket on the Neovo is a size I dont have on any of my conventional 12v bricks. Dont exactly know the amps output to hand but the symptoms remained the same when I earlier used a 12v 4amp power brick with the wires simply soldered to the inputs ( the monitor is quoted as needing a 12v 3.3amp input).
The "?doide" is indeed a diode (D1 according to the markings on the board). Given my electronics prowess is limited to simple experience and commonsense plus a multimeter and caps tester can you tell me the best way to test the diode in question and the inducter or is it simply substitute and eliminate until the fault becomes obvious and the 5volt is restored?
regards
Johnboy183

It appears the external power adapter is more than adequate for the task. Pity, that would have made an easy fix.

The first step is to make sure pin 5 of the regulator is connected to ground. This controls the regulator. If the solder joint broke, the regulator will probably turn off.

Testing the diode is fairly easy if you have an ohmmeter. Measure the resistance across the diode using the 200 ohm scale or a similarly low scale. I would expect it to be greater than 10 ohms. Also, check the inductor for continuity. If the resistance across the diode is very low (less than 1 ohm), measure the resistance from each side of the inductor to ground. The short is on the side which shows the lowest resistance. (It is frustrating to replace a diode and a regulator only to discover the problem was a shorted capacitor.

PlainBill

[johnboy183]

Re: Dead Neovo X-174

Have done that now (if I have done it as you described that is!). The diode shows 173 on the 200ohm scale and the inductor shows continuity. the ground pin on the LM2596 has good contact as have the other pins. Can't see any physical signs of poor traces, shorts or burning in the vicinity. Does that leave me with a dead LM2596 switcher do you think?
I have a 1501-50 switcher on another board that is physically identical and according to its datasheet is a similar device for similar voltage input and outputs but cant find them linked togther as equivalents on any sites as yet.
regards
Johnboy183

[PlainBill]

Re: Dead Neovo X-174

Have done that now (if I have done it as you described that is!). The diode shows 173 on the 200ohm scale and the inductor shows continuity. the ground pin on the LM2596 has good contact as have the other pins. Can't see any physical signs of poor traces, shorts or burning in the vicinity. Does that leave me with a dead LM2596 switcher do you think?
I have a 1501-50 switcher on another board that is physically identical and according to its datasheet is a similar device for similar voltage input and outputs but cant find them linked togther as equivalents on any sites as yet.
regards
Johnboy183

That's a dilemma. The symptoms point to a dead IC, but the question in my mind is 'What killed it?' I'm not fond of substituting parts, but the AP1501-50 certainly appears to be an equivalent part. The only other suggestion I have is to hook up an external 5Vdc supply to the output of the LM2596 and see if the monitor comes to life. If one of the processor chips releases it's magic smoke, well, it's now unrepairable for sure.


PlainBill

[johnboy183]

Re: Dead Neovo X-174

Obviously telepathy works across the Atlantic as I was just rigging up a wire to try that when your post came through. Have connected a 5v to the output terminal of the LM2596 and for the first time have a green led appearing at the switch - and no magic smoke. I can also measure 5v at some of the points I would have expected it but so far no video or backlights. Also the on /off switch when pressed does not put the power off but looking at it I would assume attaching the wire has overidden the functions of the switcher and that is why. It may well be that as the switcher appears to be the problem then its other functions are interrupted and that is why no other functions are happening as one of the pins carries the feedback another ground and a third is on/off. It sounds logical to me but that may just be a simpletons view!
Cheers

[PlainBill]

Re: Dead Neovo X-174

Obviously telepathy works across the Atlantic as I was just rigging up a wire to try that when your post came through. Have connected a 5v to the output terminal of the LM2596 and for the first time have a green led appearing at the switch - and no magic smoke. I can also measure 5v at some of the points I would have expected it but so far no video or backlights. Also the on /off switch when pressed does not put the power off but looking at it I would assume attaching the wire has overidden the functions of the switcher and that is why. It may well be that as the switcher appears to be the problem then its other functions are interrupted and that is why no other functions are happening as one of the pins carries the feedback another ground and a third is on/off. It sounds logical to me but that may just be a simpletons view!
Cheers

Ordinarily the regulator is never switched off. As I recall, pin 3 (and the tab) is ground on this regulator, pin 5 is control - low to turn on. The fact that the monitor is not responding to the buttons may be due to the external 5V supply, or there may be other problems.

PlainBill

[johnboy183]

Re: Dead Neovo X-174

Have replaced the LM 2596 switcher with the 1501-50 and the LED lights up and I can get 5v on most points now but still no video or backlights. Have now tested the 4 transistors 2SD2097 and find all four shorted! Obviously there has been some heavy event that has hit this monitor at some time. Have ordered the transistors (quite cheap on Ebay) so will try them when they arrive. This has now become a challenge!
Johnboy183