Toshiba 27df46 wont turn on

mrdouble · Joined: 10 Oct 2010 Posts: 6

Hi guys,
First post and I did read forum rules so hopefully I wont get flamed for idiocy.

Ill try to make this short and sweet

My 27 in TV died so I replaced it with a 42 in lcd. Thing is, no one likes the new tv but me so im trying to fix old one.

So, I fired up my oscope and mistakenly thought I could evaluate the signal coming out of Q502.. I was wrong. I replaced it only to find the same symptoms which is to say it wont turn on.

Right now im thinking maybe D523 is bad as the drop across is is 2.6v and it should be 18. Right? its a MTZJ18B which as much as I read is a 18v zener. If this diode is indeed bad, best i can see I havnt found a reseller =(

If I remember right in most good PS circuits, if UV or OV is detected there is a circuit that will prevent any switching to occur. I'm hope ing this is the issue.

I have included a blown up PS page https://home.comcast.net/~mrdouble/toshiba%20ps.pdf

Was also wondering what is B501_1 thing and why C507_3 is marked with ZZZ?

ALSO. I have the full Service Manual would it be benifial to upload it to you guys as I paid like 17 bucks for it. Wasnt sure it posting it was allowed

Thanks in advance
Mike

minnie · Joined: 18 Aug 2005 Posts: 2880 Location: Hell

To forward bias a diode is only .6 to volts DC. Unless it's a zener diode. Let me think on this one but I would suspect a bad diode. Check/replace C504 22@50, C113 2.2@50, C633 10@35. Then suspect D523.

jts1957 · Joined: 24 Nov 2008 Posts: 2476 Location: Far, Far Away

Raw b-plus 159.4 Q502 drain. 5.3 volts is the switching circuits b-plus for Q502 gate and Q514 collector. D523 is between this point and circuit ground.
B501_1 is a ferrite bead. Acts like a coil.

Check R501, F502, Q502 and Q514

You should be able to upload SM into service manuals database.
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mrdouble · Joined: 10 Oct 2010 Posts: 6

Thank you for the quick responses. Seems wife went out and bought a new exterior door, Guess who get to replace that.

Ill let you know what I come up with later this week Smile

mrdouble · Joined: 10 Oct 2010 Posts: 6

Ok, I had it fixed.. HAD

It seems Q514 was bad, I replaced it and turned it on.

After confirming everything was working, I decided I wanted to check the Q502 signal with my O-scope. When I did, I shorted the gate to source with the probe. I ended up cooking Q514,Q502,R44,R521,R530, fuse F502,And R542.

I guessing when I shorted out Q502, it pulled to much current across R542, which popped that which force all power through remaining paths.

My real question is now.. Is where do I order these parts. Like the .18 Ohm 1 watt metel oxide resistor. I know I can go to Digikey if I want to buy 2500 of them. I would really like to buy all of it at 1 place to save money on shipping.

Thankyou

jts1957 · Joined: 24 Nov 2008 Posts: 2476 Location: Far, Far Away

You ARE using a isolation transformer?

There's also Mouser. Both will sell you "1" if it is "In Stock." How important is composition of resistor?
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jts1957 · Joined: 24 Nov 2008 Posts: 2476 Location: Far, Far Away

You ARE using a isolation transformer and a sharpened probe-tip?

There's also Mouser. Both will sell you "1" if it is "In Stock." How important is composition of resistor?
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mrdouble · Joined: 10 Oct 2010 Posts: 6

No on both, Probe is standard plunger tektronics type .

Well, I appreciate the offer but since I have like 10 components id like to replace id like to find somewhere to buy all my parts.

I went to toshiba and they said they don't sell part directly and that they use this distributor but when I click on the link there are no parts available