Hitachi 57F710E Power Issue

[navagator]

I have a Hitachi 57F710E Rear Projection TV that was working great until 3 or 4 days ago. I came in and tried to turn it on and it was just dead. So, I unplugged it and plugged it back in. Nothing, not even the slight click that it makes when you plug it in. So, I removed the power supply board (It's a vertically mounted board, I believe model HA01312) and inspected it visually for bulged caps or burnt or overheated components, anything that didn't look right and couldn't find anything.

I noticed on the bottom of the board there was a row of solder joints with voltages printed next to them(10.5v, Gnd, Gnd, 5.6v, 5.6v, Gnd, 16.5v (not used), Audio Gnd, Audio), which are coming from the large transformer on top. I checked all of these voltages and they're all reading between 12.5 - 12.7 volts AC. I assume this isn't right.

I would really appreciate any help anyone could give me in fixing this issue. It's an old TV but it still has a great picture and I would prefer to fix it if I can.

Thanks

[R_J]

Re: Hitachi 57F710E Power Issue

Check if F904 fuse resistor (2.2Ω/5w) is open. If it is open it is usually because the relay contacts (S901) that normally short it out are bad, You can short the resistor with a wire to test the rest of the circuit but the resistor and the relay should be replaced

[navagator]

Re: Hitachi 57F710E Power Issue

It's closed, I have continuity between the 2 legs of the fuse.

[R_J]

Re: Hitachi 57F710E Power Issue

Do you here any of the relays click when you apply power? there are a few pico fuses to check on the board as well like E940, E941 and others that look like it.
You should have standby voltage across C940, likely around 6vdc, if not check for 160vdc across [- +] of D901 bridge rectifier. If no 160vdc check for 125vAC across K002 and K003 jumper wires, this is the main A/C input

[navagator]

Re: Hitachi 57F710E Power Issue

No, I don'the hear any clicks.

[R_J]

Re: Hitachi 57F710E Power Issue

Did you check for the standby voltage? did you check ALL the fuses?

[navagator]

Re: Hitachi 57F710E Power Issue

There's around 12.8vac at C940, around 2.8vDC at D901, 121.5vac between k002 and k003. I went back to check D901 again because I didn't think I got a very good measurement before and unfortunately I hit a solder joint accidentally I shouldn't have and blew one of the glass fuses, F901, so I guess I'll have to order one of those before I can go any further. Also, I haven't checked any of the other fuses you mentioned yet.

[R_J]

Re: Hitachi 57F710E Power Issue

The voltage on C940 is DC NOT AC

around 2.8vDC at D901, 121.5vac between k002 and k003

If these voltages are correct then D901 must be bad or F902 is open because you can not have 121.5VAC going into the bridge rectifier and only 2.8VDC coming out.

[navagator]

Re: Hitachi 57F710E Power Issue

I'm sorry I was checking D940 instead of C940. I'll check C940 as soon as I can get a fuse.

Thank you for help.

[navagator]

Re: Hitachi 57F710E Power Issue

Could you tell me whether this is a fast or slow blow fuse? I can't see anything on the fuse to indicate this.

[R_J]

Re: Hitachi 57F710E Power Issue

Found it
FUSE F901 51MS 080 L-U I believe it is a Medium Time-Lag Type fuse, 8 amp 250v

[navagator]

Re: Hitachi 57F710E Power Issue

Okay, medium time lag. The blown fuse was a 8 amp 125v, but it didn't have a F, M, or T marking on it.

[R_J]

Re: Hitachi 57F710E Power Issue

I should have said 125v, don't know why I typed 250v

[navagator]

Re: Hitachi 57F710E Power Issue

I found them on Amazon, I'll get them ordered. Thank you.

[navagator]

Re: Hitachi 57F710E Power Issue

The fuses came today, I put one in and plugged it in, but unfortunately as soon as I plugged it in the fuse blew.

[R_J]

Re: Hitachi 57F710E Power Issue

What solder joints did you short on the power supply? Check if D901 is shorted, I suspect it is shorted

[navagator]

Re: Hitachi 57F710E Power Issue

I was looking at the meter when it happened, so I not completely sure. But I was testing the + and - of D901, the bridge rectifier.

[navagator]

Re: Hitachi 57F710E Power Issue

Ok, I did test the rectifier but I did so while it was still in line, I couldn't get downstairs at the time where my solsering iron is. I can remove it though later to test it if I need to.

I touched the + lead of my meter to the - leg of the rect. and the - lead of my meter to one of the AC legs of the rect. I got a reading of 482. Then I reversed this process and got a reading of 0.

Then I touched the + lead of my meter to the other AC leg of the rect. and the - lead of my meter to the + leg of the rect. And got a reading of 0. Then I reversed that process and got a reading of 0 also.

I hope I did that correctly, if so, that doesn't sound right.

[R_J]

Re: Hitachi 57F710E Power Issue

Are you using diode test on your meter? What is 0? 0Ω = a short (same as probes being shorted together)
A bridge rectifier is just 4 diodes in one package, 2 diodes are shorted.

[navagator]

Re: Hitachi 57F710E Power Issue

I'm using the diode test on my meter. It actually reads .482v and .OL and the other 2 readings are both 0v.