Bush LT24M3 Monitor/TV (24" 1080p)

[tom66]

Next project is a Bush LT24M3 1920x1080 (full HD) TV/monitor which I won on eBay for £5.50 + £8 postage. I've been on the look out for a good HDMI capable 1080p 22-24" monitor for a while so I snatched this one up.

I plan to use this with my Raspberry Pi which I received a couple of weeks ago and haven't played with much due to my sister using the 42" for Skyrim 24/7.

Anyway the fault is that the power LED flashes, but the display doesn't turn on. I believe it to be a Vestel chassis, probably using a 17PW26 PSU of some kind, which typically means bad caps.

To be continued (when I receive it & get some free time to look at it) but in the meantime anyone have any ideas?

[tom66]

Re: Bush LT24M3 Monitor/TV (24" 1080p)

Finally got the monitor, took some time to get it here.

When plugged in the screen flashes white briefly then goes dark. There is no image on the screen (just white screen, like T-con is off), so I don't think it's 2 seconds to black.

After some minutes of pressing the power button, it then powered up and gave a perfect picture. Screen good, backlight fine and everything seemed to work. So I'm thinking it's something intermittent.

Took it apart (quite easy.) No bad caps from visual sight, and all check okay ESR. Full of CapXon and JH caps, ugh. Pulled plenty of JH from an old LCD TV so I know they don't last. And we all know about CapXon. So I'll probably do a preventative recap on it anyway.

5VS (standby 5V) is 5.1V. However the 5V main rail only reaches about 1V when it flashes; so something isn't letting it rise high enough, possibly a bad PMOS switch. This unit doesn't have a real standby supply, it just switches the 5V and 12V rails on when it gets a PSON signal.

Amazing how thick these newer LCDs are (I'm used to 10mm panels, this thing is a good 50mm.) Maybe this is how manufacturers are forcing OEM "super slim" TVs to be expensive LED based panels? I'm wondering if they are using a different type of CCFL, as it's only got two bulb connections which is a low number for a 24" monitor.

[Rtech]

Re: Bush LT24M3 Monitor/TV (24" 1080p)

It is unusual for a 24" to have just 2 B/ls,I would have expected with those connectors they would have 2 live and one return each,so feeding 2 lamps on each socket.

[tom66]

Re: Bush LT24M3 Monitor/TV (24" 1080p)

Just two wires on each socket as far as I can see.

Just now the soldering heating element on my Aoyue 968 died. Perfect timing!!! I have a mains "fire starter" iron and a gas/butane iron, so I might end up using one of those.

Look how thick this panel is... The T-con is mounted diagonally!

[tom66]

Re: Bush LT24M3 Monitor/TV (24" 1080p)

I managed to get the soldering iron working again, but it needs a new element soon.

Anyway, I did some probing and I've found a suspect LDO.

AM1117-ADJ
Input = 5.1V (standby)
Output = 0.56V
Adjust = 0.33V

The output *must* be at least 1.25V for all 1117-series regulators and the adjust being at 0.33V (~26% of 1.25V) suggests the output should be ~2.12V or probably 1.8V or 2.5V. (Just an approximation, but it shows the regulator is probably faulty - it could be drawing more current through the adjust pin or introducing current into it, causing inaccurate results.)

I'll do some more probing and see if I can get it to work again. I suspect it was my cold room that gave it an extra burst of life, so I'll borrow some freeze spray to confirm my suspicions. I've already seen walking wounded LDOs before (which intermittently work), on a Samsung T-con board.

[tom66]

Re: Bush LT24M3 Monitor/TV (24" 1080p)

Oh, and I figure the 5V main rail is possibly rising, but it's too fast to capture; it rises briefly to ~3V on my meter, but then goes out. I wish I had a nice Fluke with analog scale meter now; but it looks like I'll have to get out the scope.

[tom66]

Re: Bush LT24M3 Monitor/TV (24" 1080p)

Okay, so I can get the monitor working when I freeze-spray the suspected LDO. So I will replace that device.

I made a video on how I diagnosed this fault:

http://www.youtube.com/watch?v=qfL0Kv3DVkg

[budm]

Re: Bush LT24M3 Monitor/TV (24" 1080p)

Hi Tom,
The output should be 0.33V + 1.25Vref = 1.58v, so 1.5V is about right.
By the way 5.5 Pounds for the 24" monitor? Cheap!

[tom66]

Re: Bush LT24M3 Monitor/TV (24" 1080p)

Hi Tom,
The output should be 0.33V + 1.25Vref = 1.58v, so 1.5V is about right.
By the way 5.5 Pounds for the 24" monitor? Cheap!

In total £16, because it cost £10.50 shipping, not £8. But yeah, very cheap.

I think it is actually 3.3V because when the monitor works it hovers around 3.2V although it's quite unstable. The Vout-Adj measured 0.28V, it should be 1.25V. 0.28V adj with 0.81V out, scale that up, 0.81V * (1.25V / 0.28V) = 3.61V, so about 3.3V.

[budm]

Re: Bush LT24M3 Monitor/TV (24" 1080p)

OK you are getting Adj PIN and output pin reading of 0.28V (not 1.25v).

[tom66]

Re: Bush LT24M3 Monitor/TV (24" 1080p)

OK you are getting Adj PIN and output pin reading of 0.28V (not 1.25v).

Yeah, adjust to output is around 0.28V, and when the monitor fired up I saw a peak of 3.31V.

[tom66]

Re: Bush LT24M3 Monitor/TV (24" 1080p)

I've decided I'll replace all the caps in this monitor/TV as I want it to last me through at least 4 years of university. I'll probably also add a makeshift heatsink to the LDO too, to stop overheating from causing issues. And I am using maybe a slightly better LDO by Texas Instruments instead of "AMS", whoever they are...

Cap replacement bill:

1000u 25V JH Black x1 -> 1000uF 25V Rubycon ZLK

1000u 25V JH Blue x2 -> 1000uF 25V Rubycon ZLK

1000u 10V JH Black x2 -> 1000uF 25V Rubycon ZLK
(the 10V has the same diameter as the 25V - crazy!)

470u 25V CapXon KM x2 -> 470uF 25V Panasonic FM

22u 35V CapXon Orange -> 22u 35V Panasonic MA

120u 400V JH Blue -> 120u 400V Rubycon KXW

The 120u 400V cap was a nightmare to lift of, Megmeet used some stupid glue on it which covered up the rating.

[tom66]

Re: Bush LT24M3 Monitor/TV (24" 1080p)

It's fixed. Still need to recap it for reliability, but it now effortlessly enters and exits standby. Regulator gives 3.32V out.

[budm]

Re: Bush LT24M3 Monitor/TV (24" 1080p)

Great job Tom!
So are you using TO-220 LDO with heat sink?

[tom66]

Re: Bush LT24M3 Monitor/TV (24" 1080p)

Great job Tom!
So are you using TO-220 LDO with heat sink?

No, I did a proper job, replaced it with a TLV1117 because this was the only failed component. I will upload a video shortly about it, after I film the recapping.

One thing I noticed is how much smaller the Rubycon 400V 120uF cap is to the crappy JH one. I guess it's improved technology.

[tom66]

Re: Bush LT24M3 Monitor/TV (24" 1080p)

I declare it fixed. I will edit and upload the video soon.

VGA only supports 1440x900 (or maybe my laptop is limited to that) - but HDMI should be okay with 1080p.

[retiredcaps]

Re: Bush LT24M3 Monitor/TV (24" 1080p)

Is the picture a MacGyver reference?

http://en.wikipedia.org/wiki/MacGyver

MacGyverisms

MacGyver employs his resourcefulness and his knowledge of chemistry, physics,[4] technology, and outdoorsmanship to resolve what are often life-or-death crises. He creates inventions from simple items to solve these problems. These inventions became synonymous with the character and were called MacGyverisms by fans.

[tom66]

Re: Bush LT24M3 Monitor/TV (24" 1080p)

Nope... just a TV program (Stargate SG-1) that I could find. It's hardly a MacGyver - I actually did this properly! For the LG though...

[retiredcaps]

Re: Bush LT24M3 Monitor/TV (24" 1080p)

It's hardly a MacGyver - I actually did this properly!

Just testing to see if the next generation of Europeans actually even knew who MacGyver was!!

You do realize it is the same actor?

However, for some reason, I can't find my roll of duct tape at home.

[tom66]

Re: Bush LT24M3 Monitor/TV (24" 1080p)

Just testing to see if the next generation of Europeans actually even knew who MacGyver was!!

You do realize it is the same actor?

However, for some reason, I can't find my roll of duct tape at home.

Yes of course I know who Richard Dean Anderson is. Coincidental. I just found out what the USB port on this TV is for. It can play video from a USB memory stick - very nice. Actually, the software on this TV is pretty well done - it's just a shame the hardware (PSU mostly) sucks!

I was thinking of doing a dual monitor setup - but there's barely enough space for one monitor on my desk!