Bauhn 65" 4K TV Power Supply - Blown Ceramic Disc Capacitor

[bdc]

Hi, I'm new to trying to repair electronics. Recently my TV had a loud pop and no longer powered on, I immediately saw the fuse was blown on the power supply and ordered some new ones. I replaced the fuse and it immediately blew the replacement fuse (can see the blown replacement circled in blue). I then noticed there was the blue circular object (circled in red) that had exploded, I'm not sure if this exploded after I replaced the fuse or if I just missed it the first time I looked at the board (unfortunately I didn't take a pic of the board then).

The problem I have is that I can't find a schematic for the power supply (I've searched under Bauhn, Polaroid and Makena which all appear to use the P.SWP.198HM.1 board for their power) and the little blue capacitors don't have any writing on them (the larger ones do) to tell me what to replace it with.

Shame I didn't take the TV back for a replacement when I first got it, as it rarely turned off on me right from the start and I've since learned that this is often a capacitor issue.

Can anyone help with either locating a schematic, or help me with some recommendations for replacements capacitors? Looks like I can order a replacement board from AliExpress for about $60USD so that's an option too, but I'd prefer to try and fix it myself first.

[maneatingmonkey]

Hey, do you still have the TV/board? The value of that cap is 101K (100 pF with 10% tolerance), rated for 1KV. But it is more than likely you will have some failed MOSFETs and possibly other components too. I can walk you through how to find them. I also have the same board with different components that have exploded and are illegible. In return you can help me identify them 

P.S. Don't buy a replacement board from AliExpress. It's for the Polaroid/Makena variants which have different configurations of components installed to the Bauhn variant (e.g. missing coil L504 and cap EB502 on the bottom right of the board, as well as the middle white connector CNB2).

[KevinA]

Have you asked Bauhn Australia if they will supply schematics?

[bdc]

Yes I still have the board, if you still have yours and would like to work on trying to fix them I'd be happy to give it a go.

I only have a soldering iron though so I expect I probably need to buy a multimeter to help you out? I've been meaning to buy one anyway but I don't want to buy absolute crap like I did with my first soldering iron.

[sean0118]

Those little blue capacitors might need to be Y class safety rated, but most of the replacements available will be anyway. A voltage rating higher than 1kv is okay too.

It's likely the MOSFETs under the nearby heat sink are shorted out too, as maneatingmonkey suggested. It should be fixable but you will need a multimeter.

[Gyro]

The little ones are most likely part of the snubber networks.  Y rated ones are required where they bridge the primary-secondary isolation barrier. You can see a several of them a little further down and up the left side the board where there is the thick silkscreen marking on the board. The only things that cross it are the transformers, opto-isolators and Y caps. These are bigger (still blue) and more bulbous due to their higher isolation voltage safety rating.

[pescado99]

Hi (if this thread is still live...:-), I just picked up 'free on Marketplace', Bauhn 65" ATVS65-0716. All 5V and 12V voltages on the main PSU seem OK, but backlight voltages are only about 3V. I tried to test with some stacked 9V batteries (gave me 70V DC), but I can't see a backlight. The main PSU has no signs of damage. Did you have an success with this repair? Cheers and advance..

[sean0118]

Hi (if this thread is still live...:-), I just picked up 'free on Marketplace', Bauhn 65" ATVS65-0716. All 5V and 12V voltages on the main PSU seem OK, but backlight voltages are only about 3V. I tried to test with some stacked 9V batteries (gave me 70V DC), but I can't see a backlight. The main PSU has no signs of damage. Did you have an success with this repair? Cheers and advance..

It's pretty common for backlights to fail, which sends the power supply into protection mode. Your power supply might be okay, assuming it's LED can you take the backlights out and look for shorted or open LEDs?

Does the TV stay on or switch to standby after a few seconds? If you shine a torch at the screen can you see any picture?

Be careful with the stacked 9V batteries as that voltage is getting high and can supply a lot of current.

[BrokenYugo]

70V may not be enough, the purpose built testers for this are usually around 300V open circuit. It goes without saying, but any attempt to power the LEDS directly needs to be done with a current limited supply, 20-30 mA is plenty and considerably less will work.

[pescado99]

Hi brains trust. A quick update. I noticed that the back light flashes very very briefly on power up (almost too fast to see). So the backlight is (assumed) OK. On cold startup the voltage on the multimeter across the top -ve [CNB801] and bottom +ve [CNB805] back light pins jumps to 84 V, then decays immediately. After about 30 seconds it's down to 30V or so. So I'm thinking the PSU is the culprit (plus you can see the LCD without the backlight, so T-Con and Mainboard are almost certainly OK). On inspection, two SMD resistors on the back of the PSU (near top left stamped '154', part number [RB328] and another stamped '154', part number [RB125] to the left of the big capacitor)seem to show some heat affect, or it could be the factory soldering?? See pics. None of the caps have popped or are raised. I've never changed out SMD parts, but have been soldering basic electronics for 40 years. Does anyone have a circuit diagram/schematic for this PSU 'P.SWP.198HM.1'? Also, I assume I can't test components on the board because they could be affected by other components in series/parallel?

Yep, Also, 8 x 9V batts = 70 volts, not enough to light up the LED's though (had a pretty dodgy connection though).

Cheers and thanks in advance.

[pescado99]

Hi all, received an email from the helpful folk at Tempo. Repeated below. So I'm not getting a circuit board from Tempo, and everyone says don't buy the 'P.SWP.198HM.1' power supply on-line, it's for a Polaroid or Makena (pics online show it's similar but definately not the same). So it's up to me to fix. I haven't had a response from this group, so I'll start replacing the 2 x dodgy looking soldered SMD resistors (both labelled '154', which should mean150 k ohm) with standard quarter watt - which should work. If it's anything else I'm probably stuck. I really need a circuit diagram. Thoughts anyone?
_______________________________________________
Thank you for your email and apologies for the late response.
Unfortunately, we don't have a circuit diagram for this unit.
We apologise for the inconvenience.
Kind regards,
Marcus
Kind Regards

Tempo Group of Companies
Australia | Asia | Europe | North America
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E: info@tempo.org
 |    W: www.tempo.org

[sean0118]

I'll start replacing the 2 x dodgy looking soldered SMD resistors (both labelled '154', which should mean150 k ohm) with standard quarter watt - which should work. If it's anything else I'm probably stuck. I really need a circuit diagram.

I suspect the resistors are probably okay and don't need replacing, I think that is just flux from soldering. Do you have a multimeter yet? What resistance are you measuring across each one in circuit?

I'm pretty sure you'll have shorted transistors somewhere, most likely under the heatsink near the blown capacitor. If you find a shorted transistor and assuming it's a MOSFET you also need to look at the components that drive it's gate pin (it sometimes takes out the IC which drives it for example).


With regards to the schematic you could ask on the badcaps forum, there's lots of tv repair technicians on there. They could help diagnose the fault too but they will want lots of close up photos of each side of the PCB:
https://www.badcaps.net/forum/forumdisplay.php?f=31


Good luck, it should be fixable, could be a few components which need replacing though. 

[pescado99]

Thanks, yes I have a multimeter. I haven't checked the badcaps site. I'm sure I'll have to take them (trannys and caps) off the board to check values. I thought the same thing about flux, but everything else looks perfect (no caps are obviously bulged or blown). Will start to check out the transistors. Tempo got back to me - "we no longer support this product" what garbage, the TV is 5 years old.  Will start to check the resistor values one by one - that should be easy enough . Pretty keen to get this going...

[sean0118]

You should be able to test the transistors in circuit, at least to check for shorts. Are you able to take the heat sink off to see part numbers? There could be diode arrays under there too which are in a similar package to the transistors.

[pescado99]

Many thanks, will go through it systematically when I find time to check the board. I haven't lifted off any heat sinks yet.. a job for tomorrow