Riddled TV Repair Forum

SteveS · Joined: 22 Aug 2010 Posts: 13 Location: North Carolina

Ah, now I get it.

I've already put it back. I'm going to have to wait until tomorrow to remove it again. The soldering iron is starting to give out and I'll pick up one on the way home from work. I don't want to make a bigger mess of it than I already have.

Thanks for the help. I think I'm still having fun Razz

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SteveS · Joined: 22 Aug 2010 Posts: 13 Location: North Carolina

Q486 removed from circuit.

Q486 B-C open/.640v
Q486 B-E open/.641v
Q486 E-C open/open

R486 - 12 Ohm
R487 - 383 Ohm
R489 - 20 Ohm

I had to lift a leg of D486 to get a good reading.
D486 .710v/open

This part of the circuit all looks good.

Should I do the same exercise against Q490?

JTS1957 · Joined: 21 Jan 2009 Posts: 1331 Location: Far, Far Away

Just for grins, substitute another 1000ufd 16 volt for C626.

SteveS · Joined: 22 Aug 2010 Posts: 13 Location: North Carolina

Placed Q486, and D486 back in circut. Replaced C626 1000uF 16v with a new Cap 1000uF 25v, with no effect. Voltages at Q486 still in the .5v to 1v range.

I'm going to chase this further down the circuit.

Here's my plan:
Remove L3401 and measure at Q486-E
Remove Q490 and measure at Q486-E

Hopefully I'll be able to determine if something is causing the voltage at Q486 to be low.

JTS1957 · Joined: 21 Jan 2009 Posts: 1331 Location: Far, Far Away

Do you have a external power supply available? Car battery would do in a pinch.
Can you put your own 12 volts on Q627 Collector?

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SteveS · Joined: 22 Aug 2010 Posts: 13 Location: North Carolina

Attached an external 12v 1A supply briefly.

Relay clicked on immediately when 12V was supplied, and stayed on like power was good, rest of set did not act like it was powered on. Pushing the power button had no effect.

Q486, and R486 got hot enough to smell bad before I removed power.
Did not notice any other parts in the general vicinity that got hot, but I may have missed some.

Voltages were ~1V at Q486.

Checked Q490, voltages there were ~1v. Q90 and surrounding parts did not seem hot.

L3401 is cut at this point, so the sound chip is disconnected.
The RGB transistors connected to the picture tube have their emitters connected to 9V (which looks like it is driven by Q486) and Q490 which supplies 5V (currently measures ~1v) is also connected to Q486.

JTS1957 · Joined: 21 Jan 2009 Posts: 1331 Location: Far, Far Away

Can you put 9 volts on Q486 emitter, then 5 volts on Q490 emitter? It would be more informative to know if the supply you're inputting is being drawn down excessively.

SteveS · Joined: 22 Aug 2010 Posts: 13 Location: North Carolina

I'll work on doing that tomorrow. I'll need to dig up supplies for 9v and 5v. I know I have both around in the spare parts bin somewhere Wink

SteveS · Joined: 22 Aug 2010 Posts: 13 Location: North Carolina

I applied external 9V to Q486-E and the set powered up.
When I removed the external 9V the set stayed powered up, and appeared
to be functioning normally.

Powering the TV off and then on again without external 9V and it is still working. Did this a couple of times, and it still works. Not sure how long it will stay like this though.

JTS1957 · Joined: 21 Jan 2009 Posts: 1331 Location: Far, Far Away

I WAS expecting you to see some change, but everything working, and staying working I wasn't.

Chances are 50/50 it will still start/play if you leave unplugged a couple days for everything to discharge.
I've seen some 6.3 & 10 volt lytics test shorted installed in set but test fine removed and then work fine when reinstalled (but I put a fresh one in later), so I guess a sudden application of voltage might have a similar effect?