Wg k4900 deflection

sgreen2k

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What is the best way to remove Q302 and Q303 from the heat sink? The screw is really stuck in there. It would seam easier to de solder the heat sink as well so it would be easier to remove and install. I just have a pencil iron. What you'd you use to de solder the heat sink?
 
Any reason you are replacing the deflection transistors? Its incredibly rare for them to fail. have you checked they are actually bad before going through the hassle?
 
I am troubleshooting vertical collapse. Don't they have to be removed to test them? Is it possible when testing with a multimeter they could still be bad? I figured if I had to pull them to test, I might as well replace them and ordered 2.
 
I always pull the whole heat sink when I replace these, yes those screws are on there very tight and it is impossible somtimes to get a good grip to remove them, as Ian said these are a pretty low failure item, reflow solder around that area, maybe you might get lucky! also check to make sure none of the pots are broken.
 
you can test them in circuit.

use my video to help you.



the 4900 is known for cracked solder joints, traces and cracks in the PCB.

it can be a hard one to track down VC issues on.

look all over and use your meter on continuity and beep out the traces.

if you hit a brick wall and need it fixed, your welcome to send it in.

Peace
Buffett
 
Negative on base positive on emiter and multimeter set to diode.

Q302 - .070
Q303 - short

When you say middle are you talking about the base? Because on mine it goes base collector emiter. Using the collector as the negative I got

Q302 - neg collector pos base .525
Q302 - neg collector pos emitter .525

Q303 - neg collector pos base .471
Q303 - neg collector pos emitter. 431
 
I think i was doing that wrong. NPN Transistor should have a positive base and measure the collector/emitter with negative.
Q302 - Pos base to neg emitter .0
Pos base to neg collector .525

Q303 Pos base to neg emitter .070
Pos base to neg collector .470

I'm guessing they are both bad? I'm still wondering how i'm going to get them out.
 
red lead on B

black on C and E.

you should get .460ish range on both in circuit.

Peace
Buffett

This way its
Q302 - 0 / short
Q303 - .070

When i got the chassis the fuse was blown. I checked the rectifier diodes (all were ok) and installed a new fuse with a fuse holder. It turned on and I found out it had vertical collapse. My guess is that someone plugged in something while the monitor was on and the chassis grounded on the frame. I noticed a couple of square 1/2" quark board pieces under the chassis when i pulled it out.

Thanks for you guys help. Ill post back after the new transistors are installed.
 
sounds like they are shot.

those quark pieces are there from the factory.

you can ground that chassis to the frame pretty easy if the 2 screws are not installed.

it slips around a lot for sure.

Peace
Buffett
 
Update:
I installed the transistors. Kinda got better? I guess it wasn't going to be the quick fix i thought it was.

I found D302, D303 to be bad. thats what shorted out Q302.
I also found a hair line crack? near C314 and the heat sink. I'm not sure if i caused this while messing about with the transistors. Going to replace D302/D303 and jumper the crack and Ill update with results.
 

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be sure to test D302, D303 out of circuit.

i have seen them test bad in circuit before.

i have also had to replace them once in a great while.

yup, get that crack taken care of.

cracks are hard to spot on the 4900 since the green mask will cover them.

Peace
Buffett
 
I think i hit the wall. With the jumper and D302/D303 replaced it made no change. Adjusting the pot in the back this is the widest it will go besides a line down the middle. I'm not sure what else to try.
 

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other than looking for more cracks or out of spec parts, there is not much else to do.

that has always been the fixed for VC on the 4900 for me.
95% cracked traces/pads.
5% bad parts.

if you want to send it in, shoot me a PM.

Peace
Buffett
 
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