Vestal power Board Repair 17pw26-1

[garrymc123]

Hi there i replaced some caps on this power board but when i was doing a voltage test on the outputs after the recap i accidentally touched too pins together ( Which i have marked out with a circle ) now the board will not start up i Believe i have shorted the earth with the 12v line .can any one point me in the right direction on what to check which maybe i shorted when touching the pins together .

any help much appreciated

[diif]

Re: Vestal power Board Repair 17pw26-1

I have one of these on my bench in front of me. Check Q827 for a short.

Pin 5 is ground and pin 6 is 12v. It goes across a jumper then a 0 ohm resistor then another jumper to the centre pin of Q827, the other sides of the diode are ground.

[R_J]

Re: Vestal power Board Repair 17pw26-1

See if this helps

[garrymc123]

Re: Vestal power Board Repair 17pw26-1

cheers guys i will check this out after work today and will let you know the outcome .thanks again

[garrymc123]

Re: Vestal power Board Repair 17pw26-1

Hi Guys Checked q827 for short and its fine also checked Q828 and its fine also what other components can i check would the 0 ohm resister read as 0.001

thanks in advance

[Dannyx]

Re: Vestal power Board Repair 17pw26-1

When you say the board will not start up, does that mean you get no output AT ALL ? Not even 5vSTB ? Check all diodes after the switching transformers, though I doubt they would die that easily...

[garrymc123]

Re: Vestal power Board Repair 17pw26-1

thanks dannyx for your help i mean u can hear the board starting up then it shuts down and just keeps doing this ..before i accidentally shorted the pins it would stay on

[Dannyx]

Re: Vestal power Board Repair 17pw26-1

Sounds like something's shorted then....grab your meter and start probing around: start with the large parts like diodes and transistors and work your way to smaller ones like ICs and diodes (that's how I do it at least). I once had a relatively similar issue where the PSU did not output anything despite no major semiconductors being shorted and it all boiled down to a tiny SMD cap which was shorting the VCC and GND of one of the switching ICs. Check those as well.

[garrymc123]

Re: Vestal power Board Repair 17pw26-1

thanks guys i think i have found the problem at J132 there is a zero ohm resister which comes from q827 but it has no connection when tested with the multi meter

[stj]

Re: Vestal power Board Repair 17pw26-1

it's burned, look closely.
raising the question - why did it burn??

[Dannyx]

Re: Vestal power Board Repair 17pw26-1

thanks guys i think i have found the problem at J132 there is a zero ohm resister which comes from q827 but it has no connection when tested with the multi meter

Yeah, I can definitely tell there's a burn mark in it. Provided it burned out when you shorted the pins and nothing else failed, THEORETICALLY replacing it should solve the issue. Be bold and try it out

[garrymc123]

Re: Vestal power Board Repair 17pw26-1

Thanks guys after replacing the resister ( Jumper ) it now stays on so i will continue with the voltage tests and hopefully it will work ..i will let you know the outcome ,,

thanks again for all your help much appreciated

[garrymc123]

Re: Vestal power Board Repair 17pw26-1

Hi i put power board back in tv and now the power board shuts down when its connected to the video board so i did a couple of quick tests i and i found out that some of the small smd caps have both ends connected to ground when tested with the multi meter ..any ideas guys

[Dannyx]

Re: Vestal power Board Repair 17pw26-1

Hi i put power board back in tv and now the power board shuts down when its connected to the video board so i did a couple of quick tests i and i found out that some of the small smd caps have both ends connected to ground when tested with the multi meter ..any ideas guys

That's a pretty bad symptom: shorted SMD caps can sometimes mean something else is shorted in parallel with them, more often than not, the main IC. SMD caps seldom fail on their own...you might get lucky. Try pulling them out one by one (preferably remembering where they go) and see if the short disappears. If it doesn't, the IC they're connected to has failed.

I got lucky a couple of times, for instance I once had a TV that wouldn't power on because of a shorted SMD cap on the bloody internal DVD drive ! Now THAT'S some dum luck I wrote a whole thread about this freak discovery.

[garrymc123]

Re: Vestal power Board Repair 17pw26-1

Thanks dannyx i will try that and see what happens i thought i would double check voltages again from the power board and i noticed on PL816 PIN 27 it says it should be 30v but im only getting 24.48v on that pin and thats with the video board disconnected i also checked it at D881 and its the same voltage but only on one leg of the diode at the capacitor side i get nothing at the transformer side.

thanks in advance

[Dannyx]

Re: Vestal power Board Repair 17pw26-1

It's impossible to measure the output a SMPS transformer with a regular DMM - the frequency is much too high for the meter to be able to catch anything, that's why you won't see anything at the transformer side (anode) of the diode. 24v is a tad low, but what I'd call acceptable nonetheless. The main board is your main concern right now, since you're saying you have shorts there and it also kills the PSU when you connect it....most definitely the main culprit at the moment. One way you can test PSUs, if you don't have an adjustable load, is to use some car lightbulbs rated for 12v and 24v (or 2 12v in series) and hook them up to the corresponding outputs of the PSU and see if it's still stable. If it is, the problem is most likely someplace else.

[R_J]

Re: Vestal power Board Repair 17pw26-1

If you have a short on the main board I would expect the voltage on the power supply to be low, How about a couple pictures of the complete main board, both sides or maybe a model number of the tv, or numbers from the main board. maybe there is a schematic of the main board around
Can you trace the short on the main board back to a particular pin on a plug that goes to the power supply?
What do you consider the Video board? The main board or the T-con board
That +30 goes to two different plugs PL816 (27) & PL817 (5-6)

[R_J]

Re: Vestal power Board Repair 17pw26-1

I see the part number on the picture of the board
I looked up a manual for a Vestel 17MB35-1, it looks like the +30 volts supplies the audio circuit, the area you pictured around U124 looks like the audio out circuit, you may have a shorted audio output ic.
Which smd caps measured short? C527 or C528??

[Dannyx]

Re: Vestal power Board Repair 17pw26-1

I once had an audio amp shorted on a monitor, to the point where it put a hole in the circuit board (it war arcing because it was powered with a 12v adapter so it didn't know it's supposed to shut down due to a fault on the board). I simply took a dremel and effectively cut the PCB where audio IC was and that at least got the monitor to turn on. You may have a similar scenario here as well....obviously you'll probably want to replace the IC if it turns out it's faulty rather than removing it entirely...what good is a TV without speakers (unless you're using it as a monitor or via an external amp or something).