Sharp TV no longer powers on

[mattbatt]

Hello,
I have inherited my fathers old TV it's a Sharp LC-60LE831U. It was powering on and off randomly until IC7905 blew it's top (TY264PN) I replaced it and the TV still didn't power up. I traced down that the 2.2 ohm fusible resistor R7914 was blown so I have replaced that and still no joy.
I am measuring 164VDC on the two outside legs of the rectifier.
On the TY264pn using pin 3 as ground I am measuring
1) 0.5VDC 8) 0.0VDC
2) 0.0VDC 7) 0.0VDC
3) GND
4) 0.0VDC 5) 164VDC

There is no voltage going to the mainboard connector. There are no blinking lights on the front.
Please help me troubleshoot this TV.
Thanks,
MattBatt

[dskall]

Re: Sharp TV no longer powers on

Need good pictures of front and back of power board

[mattbatt]

Re: Sharp TV no longer powers on

Darn it I forgot to put the powersupply model numbers in the first post
Delta DPS-183BP A
RUNTKA798WJQZ
Jimmy took better pictures than I can.

When I get home from work tonight I can try taking some.
No caps look blown.

[mattbatt]

Re: Sharp TV no longer powers on

OK I took some pictures let me know if there is an area I can highlight further.

Thanks for the help

[CapLeaker]

Re: Sharp TV no longer powers on

So I am guessing you have no 5V STBY voltage. Check if the 5V STBY rail is shorted (secondary). If you have juice going into the TY264pn, but nothing coming out, may be a good chance it is bad, needing to be replaced.

[dskall]

Re: Sharp TV no longer powers on

I was unable to find spec sheet for TY264pn

[R_J]

Re: Sharp TV no longer powers on

Here it is

[dskall]

Re: Sharp TV no longer powers on

Where did you find it?

[neilc6]

Re: Sharp TV no longer powers on

Check R7918 as well.

[mattbatt]

Re: Sharp TV no longer powers on

r7918 is also good
this is where I bought the replacement chip from
http://www.newark.com/power-integrat...8?ost=TNY264PN
They have a PDF up on the page https://cdn.badcaps-static.com/pdfs/...09355ebacf.pdf

[budm]

Re: Sharp TV no longer powers on

BTW, if you leave the DCV meter (set to 20VDC range) probes connected to standby Voltage output pin and GND and then power up the board, do you see the meter shows any activity at all?
I wonder if the Optoisolator on the EN pin may be damaged when that IC blew up, also the bypass cap on BP pin.

[neilc6]

Re: Sharp TV no longer powers on

The shopjimmy repair kit for a similar power supply replaces IC7905, D7908, R7914 and R7918.

http://www.shopjimmy.com/sharp-rdenc...repair-kit.htm

[mattbatt]

Re: Sharp TV no longer powers on

So I am guessing you have no 5V STBY voltage. Check if the 5V STBY rail is shorted (secondary). If you have juice going into the TY264pn, but nothing coming out, may be a good chance it is bad, needing to be replaced.

That was one of my thoughts as well, unfortunately I am leagues of my depth of understanding circuit boards of this complexity. Where is the 5V regulator?

[mattbatt]

Re: Sharp TV no longer powers on

Alright so next up on the test block is D7908 which has the symbol of a zener Diode. It has "P6KE 150A" printed on it. I looked it up it's a TVS diode (new to me).
Removing it from the board and using my diode test it reads 0.6V forward bias and OL reverse bias. In resistance mode it reads OL in forward bias and 13.743 Ohms in reverse bias.
The next component in series with the chip is R7909 a BYV26E which is reading 0.5V forward bias and OL reverse in diode mode on the DMM
I suspect these might be bad since I can follow the positive bus from the capacitor bank to R7914 (bad replaced) - D7908 (?) - D7909 (?) - IC7905 (bad replaced).

This is the best labeled board I think I've ever seen.

[mattbatt]

Re: Sharp TV no longer powers on

Does anybody have a suggestion on which way I should look next?

[dick_barton]

Re: Sharp TV no longer powers on

Removing it from the board and using my diode test it reads 0.6V forward bias and OL reverse bias. In resistance mode it reads OL in forward bias and 13.743 Ohms in reverse bias.

The diode test is correct in 0.6V and OL but are you sure it's 13.7 ohms and not Megohms?

Can you give the voltages at the connector marked PD

[budwich]

Re: Sharp TV no longer powers on

certainly not an expert, but based on your first post which I assume was done after the replacement of the switching regulator IC, based on my very quick read on the attached spec, your reading of pin 5 prevents the IC from turning on because it is below the turn on spec which at power up should be above 200v... of course, the value you read might be ok after start up... but perhaps you need to monitor that point a few times to see if it reaches the threshold.

[mattbatt]

Re: Sharp TV no longer powers on

The diode test is correct in 0.6V and OL but are you sure it's 13.7 ohms and not Megohms?

Can you give the voltages at the connector marked PD

Yep totally screwed that one up it's Megaohms sorry about that.