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**selldoor** · 08-20-2012, 02:51 PM

Re: Bush LCD TV no power *HELP!*

Voltage at Big cap is too low - should be around 325 vdc - all your dc voltages are low
is your meter ok - check battery.

**retiredcaps** · 08-20-2012, 03:16 PM

Re: Bush LCD TV no power *HELP!*

Originally posted by beemerbruser View Post

On primary side.
Measured 230VAC coming to board
Measured 230VAC on the rectifier
Measured 300VDC at filter cap C101.
Measured 9V at VDD of IC101 (SG6742MRSY). Not sure if this is correct as I suspect it should be 12V-16V. If so, what should I be doing next?

You are correct in your assumption that the voltage of IC101 VDD should be around 12-16V.

The datasheet says

15.5V is typical with a range of 14.5 to 16.5.

My spatial mapping skills are weak at best, but underneath that top right hand corner heat shield might be an electrolytic cap in the 47uF 50V range that is your startup cap. It might be bad without visible signs of bloating. Since those caps are only around 33 cents, I would replace it first to rule out a bad cap. Use something like Panasonic FC series.

Since you are also in Europe, you might/probably have PFC circuitry involved which would boost the DC voltage across the big cap to around 400VDC.

As I said my knowledge is limited

Your post is easily 98% better than most of the posts asking for help.

**retiredcaps** · 08-20-2012, 03:19 PM

Re: Bush LCD TV no power *HELP!*

Originally posted by selldoor View Post

is your meter ok - check battery.

The Fluke 170 series (175, 177 and 179) will have a low battery icon indicator, but will still be accurate. When the battery is below a certain threshold, it will then display "batt" and not take any more measurements.

Refer to

https://www.badcaps.net/forum/showpo...2&postcount=21

**tom66** · 08-20-2012, 03:25 PM

Re: Bush LCD TV no power *HELP!*

I have an el-cheapo DMM at work (some Mastech brand.) Low battery icon comes on, display gets very dim (invisible looking straight on), but if you look at an angle, reads exactly the same (+/-1 digit) as the Fluke 179 which I use for proper stuff.

It is very surprising to see a high quality Delta PSU, with good Chemicon and Rubycon caps, in a Bush. Is this LED backlit? Bush TVs, in my experience, are built down to a very low price. The Bush brand is owned by Home Retail Group, i.e. Argos. Despite the low build costs, they are usually only £10-15 cheaper than comparable Samsung TVs (which are okay, if you replace the caps.)

**beemerbruser** · 08-20-2012, 03:27 PM

Re: Bush LCD TV no power *HELP!*

Hi, thanks for quick post.

I was always under the impression that around 300V DC was normal on the big cap. Regardless I've replaced battery & now reading 308VDC. However, this has no bearing on actual fault so any ideas what next? Because I'm not seeing anything on the secondary diodes I assumed there is an issue somewhere on the primary side. The transformer details if this is helps are
MD-1301 (00)
MV-DP9569 DELTA
DCUM1002(02) 2D3

Cheers

**tom66** · 08-20-2012, 03:29 PM

Re: Bush LCD TV no power *HELP!*

Check your mains line voltage - one probe in live and one in neutral - if 308V you should have line of = 217V. Minimum in UK&ROI is 216VAC (max 253VAC).

Call your electric company if it's that low as it's not good!

**selldoor** · 08-20-2012, 03:37 PM

Re: Bush LCD TV no power *HELP!*

@retired caps - good to have you back keeping me in order now the olympics is finished. Id watch the video but its 16 mins and my son is currently "skyping" his girlfriend in Canada of all places so at the bit of bandwidth I can get I reckon it will take a couple of hours so I'll just take your word for it..

@ BB Something is not right what voltage do you get on the~~ pins on the bridge rectifier. Also can you quote voltages to two places 300.01 12.02 etc.
All yours end in 00?

EDIT
Sorry you say 230vac at the bridge - what do you get at the + & -

**beemerbruser** · 08-20-2012, 04:00 PM

Re: Bush LCD TV no power *HELP!*

Firstly, thanks guys for the rapid responses!

@retired caps - see attached pic of under heatshield. Looks like it says "RR 222K 1KV" printed on it . According to the ESR meter it's 0.26ohms. Does this sound ok or should I remove & test ooc or just replace regardless?

@tom66 no it's an LCD 1080p & yes I was surprised too by the quality of components used. If only it would work though!

Line voltage is ok 223.8V

@selldoor 311.6V at the + & -

Attached Files

**tom66** · 08-20-2012, 04:05 PM

Re: Bush LCD TV no power *HELP!*

Originally posted by beemerbruser View Post

Firstly, thanks guys for the rapid responses!

@retired caps - see attached pic of under heatshield. Looks like it says "RR 222K 1KV" printed on it . According to the ESR meter it's 0.26ohms. Does this sound ok or should I remove & test ooc or just replace regardless?

@tom66 no it's an LCD 1080p & yes I was surprised too by the quality of components used. If only it would work though!

Line voltage is ok 223.8V

@selldoor 311.6V at the + & -

223.8V * 1.414 = 316V. About right then. You just have low line voltage in Ireland. Here I am getting a good 245V (varies by about +/-2V over the day) and at my dad's place (off the beaten track a little) I get 252V almost continuously.

Can you post a pic of the power connector going to main board - of interest is the labels near it.

**selldoor** · 08-20-2012, 04:09 PM

Re: Bush LCD TV no power *HELP!*

Originally posted by beemerbruser View Post

@retired caps - see attached pic of under heatshield. Looks like it says "RR 222K 1KV" printed on it . According to the ESR meter it's 0.26ohms. Does this sound ok or should I remove & test ooc or just replace regardless?

I dont think he meant that one - unless I have missed something - its a small electrolytic - perhaps its the one at C103

**selldoor** · 08-20-2012, 04:16 PM

Re: Bush LCD TV no power *HELP!*

Just been looking at the bottom of the board maybe just the picture but a lot of the joints look a bit ringed. Perhaps resolder all the transformer joints?.

**tom66** · 08-20-2012, 04:16 PM

Re: Bush LCD TV no power *HELP!*

Pretty typical for Delta soldering to be excellent; the rings are support rings added for big heavy components, very nice touch to ensure long term reliability.

**beemerbruser** · 08-20-2012, 04:38 PM

Re: Bush LCD TV no power *HELP!*

@retiredcaps - Attached is more cap pics, C103 & C113. Hopefully these are the ones you are referring to.

C103: 10uF 50V - Readings: 9.32uF, ESR: 0.50
C113: 33uF 50V - Readings: 36.66uF, ESR: 0.06

@tom66 - Attached pics as requested.

Anymore info needed let me know.

Cheers guys!

Attached Files

**tom66** · 08-20-2012, 04:41 PM

Re: Bush LCD TV no power *HELP!*

OK, do you get good 12V at the pin marked 12V? Looks like this PSU only has a single 12V output and no standby mode, pretty typical for a small 24".

**beemerbruser** · 08-20-2012, 04:47 PM

Re: Bush LCD TV no power *HELP!*

I get nothing. That's my problem. Sorry, I should have clarified that at the start.

**tom66** · 08-20-2012, 04:51 PM

Re: Bush LCD TV no power *HELP!*

That's where the fault must be then. But, if the startup cap were an issue, you would get low, unstable outputs, not zero outputs. Check the rectifying diodes for the output side - one may be shorted.

**beemerbruser** · 08-20-2012, 05:07 PM

Re: Bush LCD TV no power *HELP!*

Can you read through my 1st post & see if I've done it right already or are you talking about something else? It's been 15 years since I was in collage doing this stuff

As Retiredcaps has said earlier, I should be getting more than 9V at VDD of IC101. If don't have this then there's hardly any point in trying to take measurements in the secondary.

**tom66** · 08-20-2012, 05:11 PM

Re: Bush LCD TV no power *HELP!*

Originally posted by beemerbruser View Post

As Retiredcaps has said earlier, I should be getting more than 9V at VDD of IC101. If don't have this then there's hardly any point in trying to take measurements in the secondary.

The way a modern SMPS works is to provide a little low current through a high value resistor (330k to 2Meg) to charge up a small cap (10..100uF 16-50V) regulated by a zener diode (sometimes integrated into the IC.) As the voltage reaches a certain point, the switching converter suddenly starts (normally it is using almost no power.) This drains the cap, but the idea is the converter has enough energy in the cap to keep going until the tertiary winding of the power supply (like an additional output) can supply power. The converter has to run for at least 50-100ms so the capacitor must have good capacitance (ESR isn't as crucial for it but still plays a role.) Also, the tertiary power is usually supplied through a low value resistor (1 ohm to 47 ohms) and a diode (1N4148 typically.)

If you have a shorted diode on the secondary, the tertiary winding will get no power, so the converter will never start.

Sort of like a car will start with a dead alternator and charged battery, but won't run for long.

**beemerbruser** · 08-20-2012, 07:08 PM

Re: Bush LCD TV no power *HELP!*

Ok guys bit of an update. Examined the board again & found a small crack on one of the tracks in the primary side, so rubbed it down to expose copper & joined with a bit of solder. Plugged mains back in & it powered up!

So any recommendations for a broken track? A bit of solder joint enough or would a bit of resistor wire be better for the job?

Thanks again folks!

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