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Discussion Starter #1
Hi All,

First post on the forum, and asking for help as is usual.

I have a Sony Kp-44px3u rear projector TV that I don't want to send to the skip just yet. The LED blinks 3 times repeatedly which from the service manual indicates it has an OVP problem.
I have read several threads saying it's the STK392-560 convergence IC's etc and check fuses so that's what I have done.
Some probing on the G card showed 4 fuses blown. The +/-15v and the +/-19v picofuses specifically.
This seems to agree with the usual diagnosis of STK's blown so I have desoldered and removed them.
Also now I have replaced the 4 fuses that were blown but the two +/-15v ones are still blowing even though the STKs are removed.

If I replace the +/-15v fuses again and disconnect the connector to the D board they do not blow, indicating it is the D board that is blowing them.
Also with the D board connector (CN6009) disconnected I now get the LED flashing 8 times indicating horizontal protection, which may or may not be reasonable, I don't know.

So my questions :
1. Is there typically anything else on the D board that would cause the +/-15 picofuses to blow ?
2. Is it expected that the TV will work without the STK chips ?, I think it should just have a distorted picture ?
3. Any further advice ?

I don't mind spending time on this TV as it's a bit of fun to get these things working and any help is appreciated. I have the service manual and know my way around a schematic etc but not too familiar with TV systems but know enough what to touch and what not to touch ).

thanks !
 

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Plain ole user
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Please read the first ten posts of the convergence repair sticky in the DIY Repair forum VERY carefully.

http://www.hometheatershack.com/forums/diy-repair-maintenance/5600-crt-based-rptv-convergence-repairs.html

Blown fuses occur for one of two reasons. Either something internal shorted and pulled too much current, or something on the source side created a surge and took out the fuse, with or without damage on the other side of the circuit. Because you have multiple supply lines with open fuses, I am guessing either a power surge or a failure in the primary of the power supply caused the open fuses. I would start by measuring the load side of the fuses to see if there is an obvious short to ground on one of the lines, and check the likely components that might be damaged in each supply circuit.

You can run these sets with the convergence ICs out of circuit.
 

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Discussion Starter #3
thanks lcaillo, I was hoping you'd pop by with a reply.

Yes I have read the entire 31 pages of posts in the thread you have linked. Thank you for putting all the effort into all those.
I will take a closer look to the power supply G board but in order to be sure the G board is working correctly I need to know if it's got an on mode. I know with SMPS there is a feedback mechanism to control the frequency of the primary getting switched.
So will the G board generate its voltages with all the connectors to the other boards pulled ?
Or does the G board need an enable input to be high or low so the board will start up ? Similar to how a desktop pc's power supply starts up.

thanks for any assistance.
 

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Discussion Starter #4
ok, some progress.....

Following lcaillos advice I metered out between ground and the +/-15v lines on the D board.
The +15v had 1.2ohms between it and gnd.

After some elimination I found D8002 which is a 19v Zener was shorted out.
I removed the diode and powered up the telly and it turned on. The 15v line is at 15.4 so I think it's safe to leave the zener removed for the time being as it's effectively out of circuit anyway at that voltage.

The screen is dominantly red with horizontal lines banding across it. But after 20secs or so the TV switches itself off with the red led blinking repeatedly on the front with no discernible pattern.
The picofuses on the D board beep out ok and the resistors are all measuring low resistance ( 1.2ohms in circuit, is this acceptable ?).

Is all this normal now that the STKs are also still removed ?
I'm considering putting the STKs back in but am hesitant as why did the +/-19v fuses in the G board go in the first place ?, should I chance it ?

any further advice is appreciated
 

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Plain ole user
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Refer to the schematic and the specific resistors to know what the readings should be.
 

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Discussion Starter #6
thanks lcaillo,

Would the constant red screen and self power off collaborate bad resistors even though the STKs are removed ?
Or do I have a bigger problem with one of the CRTs failing in some way ?
I have also tried turning down the HV pots in the front of the TV but to no avail.
 

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Those are not HV pots, they are screen (G2) controls, and if not adjusted carefully an cause retrace lines and blanking. None of this has anything to do with convergence, the STKs, nor the related resistors. CRT aging can lead to difficulty adjusting balance between the CRTs and retrace lines being present.
 

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Discussion Starter #8
ah ok.

With that I popped back in the two STKs and the TV is still powering up with red screen and then switching off after 20secs or so. All fuses are holding at least though.
So it seems the fuse problem was a blown zener diode in the D board, if not related to the usual STK issues.

Where to look from here to solve the new problem then ?

thanks for your help, I realize that these newbie questions must be annoying.
 

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Some sets will shut down with the screens not adjusted properly. Most sony sets just blank the image.
 

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Discussion Starter #11
thanks for this info.

I've just noticed the front LED is blinking 24 times. Didn't bother counting this far up before !!!
The service manual error code 24 is audio protection so I pulled the AU power connector on the G board and now it's staying on. More progress !!
 

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Discussion Starter #15
Could it be the red CRT is shorted ? or perhaps its CR board is faulty ?
If the CR board is faulty can I swap it with the CB or CG board to see if the problem moves ?, or is this a bad idea...
 

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More likely either the crt is worn out and the AKB circuit can only get enough output by increasing the bias or you could have a problem on the drive board.
 

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Discussion Starter #17
I found out why the Audio section is not working and causing the TV to shut down. Amplifier IC is blown.
This TV is a tough one to fix.

How can I diagnose if its the CRT or the drive circuit ?, is there any swap I can do with the other 2 to prove one way or the other ?

thanks for any advice !
 

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Plain ole user
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On most sets you can swap the drive boards but it is often difficult because of the wiring.
 

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Discussion Starter #19
Had a look at doing that on mine but not able as the connectors don't match the same on each. However I took each off and touched up all the solder joints. On powering on now I get no picture and the TV starts blinking the LED 5 times. Think this indicates a drive failure. IKP or something. Double checked my work and no solder bridges or anything so don't know have I created a new problem or fixed the last one.....
 

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Check the drive components on the CRT boards and try removing the spark gaps if it has them. Sometimes those went bad.
 
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