Slowly understanding and repairing aquos tv. just have a question

[morgan]

So when a mostfet shorts out does it take a lot of other stuff with it?

i have a sharp aquos lc-30hv4u and one of the n-channel 900v mostfets burned out. i've replaced the 2 mosfets (since i was in there i figured i'd replace both) and fuse so now i get a red light instead of insta popped fuse. The only problem is that when i turn the tv on with the onboard button or the remote the light turns green like it's going to click on but there's no satisfying relay click and the tv doesn't turn on.. if i click the relay myself it just blows a fuse.

I'm thinking i'm dealing with a chain of destruction and not just one part.

if anybody has any thought's they'd be greatly welcomed. (i've got the service manual and i understand about 30% of it but i'm learning)

thank you.

[PlainBill]

Re: Slowly understanding and repairing aquos tv. just have a question

So when a mostfet shorts out does it take a lot of other stuff with it?

i have a sharp aquos lc-30hv4u and one of the n-channel 900v mostfets burned out. i've replaced the 2 mosfets (since i was in there i figured i'd replace both) and fuse so now i get a red light instead of insta popped fuse. The only problem is that when i turn the tv on with the onboard button or the remote the light turns green like it's going to click on but there's no satisfying relay click and the tv doesn't turn on.. if i click the relay myself it just blows a fuse.

I'm thinking i'm dealing with a chain of destruction and not just one part.

if anybody has any thought's they'd be greatly welcomed. (i've got the service manual and i understand about 30% of it but i'm learning)

thank you.

Depending on the application, yes, it could result in a trail of destruction. Does the Service Manual include a schematic?

PlainBill

[morgan]

Re: Slowly understanding and repairing aquos tv. just have a question

it does include a schematic which i can read bits and pieces of.


(not because it's bad quality but because i'm not very good at reading schematics)

[morgan]

Re: Slowly understanding and repairing aquos tv. just have a question

i thought i'd add the schematic for good measure.

http://www.morganhocking.com/powerboard.png

i highlighted the two mosfets i replaced. the q9 (the bottom of the two on the schematic) was the one that was shorted out.

[PlainBill]

Re: Slowly understanding and repairing aquos tv. just have a question

i thought i'd add the schematic for good measure.

http://www.morganhocking.com/powerboard.png

i highlighted the two mosfets i replaced. the q9 (the bottom of the two on the schematic) was the one that was shorted out.

This is a lot more complicated than I am used to. I haven't dug too far into it, but some things are apparent. Q5 and Q9 are the power FETS driving the transformers for the power supply. T1 and T2 are for the 10 volt supply, T3 and T4 are for the 13 volts supply. These are the main supply for the TV.

The key appears to be the circuit at the bottom. IC2 and T6 make up the standby supply, with PC8 providing the feedback for regulation. What's the voltage at CN3, pin 3? The command to energize the relay comes from the main board on CN3 pin 7.

PlainBill

[ecking767]

Re: Slowly understanding and repairing aquos tv. just have a question

I will start by checking out those biasing resistor: R27, R28,R31,& R32. Since there was a short sometime other components are effected. Also check the output voltage you should have +13 volts.

[PlainBill]

Re: Slowly understanding and repairing aquos tv. just have a question

I will start by checking out those biasing resistor: R27, R28,R31,& R32.

That may be a possibility

Since there was a short sometime other components are effected. Also check the output voltage you should have +13 volts.

???? Not bloody likely!!!! Note the information below from his first post.

if i click the relay myself it just blows a fuse.

Then check the schematic. The left side of D1 (the main bridge rectifier) doesn't get connected to the AC line until RL1B (the relay) closes. The standby supply is working; the main supply isn't even getting power.

Morgan,

Which fuse is blowing? It appears we also need the schematic of the operation board - I want to see what is happening to the AC in. And it appears the we have to see the schematic of the main board so we can get an idea of why it's not telling the relay to close.

Also, note Wizards comments in this thread. (It's always a good idea to listen to Wizard).

PlainBill

[morgan]

Re: Slowly understanding and repairing aquos tv. just have a question

Thanks for all the suggestions I'm going through and following them all to see if I can make any headway.

[ecking767]

Re: Slowly understanding and repairing aquos tv. just have a question

I always confirm before and after replacing a faulty component(s) the problem was fix. If there isn't 13volts why short out the relay?? ?? do you have +13 volts??

[morgan]

Re: Slowly understanding and repairing aquos tv. just have a question

That may be a possibility

???? Not bloody likely!!!! Note the information below from his first post. Then check the schematic. The left side of D1 (the main bridge rectifier) doesn't get connected to the AC line until RL1B (the relay) closes. The standby supply is working; the main supply isn't even getting power.

Morgan,

Which fuse is blowing? It appears we also need the schematic of the operation board - I want to see what is happening to the AC in. And it appears the we have to see the schematic of the main board so we can get an idea of why it's not telling the relay to close.

Also, note Wizards comments in this thread. (It's always a good idea to listen to Wizard).

PlainBill

the f1 fuse is the one that's blowing and i would have been more than happy to replace the whole board if the board didn't cost 500 dollars (doesn't seem sensible for a tv from 2003).

i'll post the schematic for the main board this afternoon. after i prod around a bit.

[electroguy75]

Re: Slowly understanding and repairing aquos tv. just have a question

chk the bridge d1 and and surrounding components

[morgan]

Re: Slowly understanding and repairing aquos tv. just have a question

ok. so. heres the main board schematic.
http://www.morganhocking.com/mainunit.png

I pulled the bridge rectifier off and tested it with the dmm and it seems to be in order.. figuring out how to test stuff i don't know how to test has become one of the fun parts of this tv excursion.

[PlainBill]

Re: Slowly understanding and repairing aquos tv. just have a question

ok. so. heres the main board schematic.
http://www.morganhocking.com/mainunit.png

I pulled the bridge rectifier off and tested it with the dmm and it seems to be in order.. figuring out how to test stuff i don't know how to test has become one of the fun parts of this tv excursion.

The last tiem I had to tackle something like this I used a Variac and an isolation transformer to increase the AC voltage slowly. Using a light bulb to limit current would also be a good idea.

As I see it, the best approach would be to isolate each section of the circuit. The problem I'm having is I'm unable to understand parts of the circuit. I THINK the circuit includig Q1, IC1, L3 is related to power factor correction.

Q5, Q6, PC2, T1, T2 and associated components form the 10 Volt regulator. Q9, Q10, PC4, T3, T4 and associated components form the 10 Volt regulator. IC2, T6, and PC8 and associated components form the stand by power supply. I guess Q13, Q14, Q22 and associated components are the high temperature shutdown circuit. Note the temperature rating for F9. But I'm clueless about what PC1 and PC6 do.

PlainBill

[ses4you]

Re: Slowly understanding and repairing aquos tv. just have a question

Anyone have a schematic for this TV. Thanks