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 ).
Do you have the service manual and the procedure for adjusting the screens? If so follow it. If not, feed the set a blank rastar and adjust all of the pots to minimum. Then increase each until you see the CRT light up the background, then back down until the rastar is just black. You may need to use successive approximation rotating between the controls of each to get it to stay out of blanking if the problem is IK blanking due to screen setup.
I have all the pots turned down to the last but it still blinks 5 times after 20secs or so.
If I have a "blank raster" do you think it would stop doing that and allow adjustment ?
If so would a CCTV camera do with a cover over the lens ?, effectively a black level but with all the sync and color burst info the TV needs ?
Also yes I do have the service manual and it mentions "receive the monoscope signal and turn the red VR on the focus pack all the way to the left"
Having another go at this again but have to admit running out of ideas.
Saw some other forum posts mentioning cathode to heater short but there's no shorts on any of the 3 crts between pins 8 and 7.
Also checked for 200v on the neck boards as well.
I'm confused though by " It WILL give you 5 blinks as long as it is in IK blanking, so until you get the three crts balanced it will stay that way "
My questions from this are :
Is there any way to be sure it is just IK blanking and not another problem ?
If it is IK blanking, how can I feed a signal into it and be sure a blank raster is getting through the signal chain when I can't see what aux input is currently selected ?
IK blanking occurs whenever the set cannot balance the return pulses that it uses in the blanking interval to balance the three crts. This can happen for many reasons. Your tubes could be worn out, you could have a drive problem in the electronics, or you could have a set up problem. Start with the screens all the way down, turn them up just until you see the raster light up in each then back down a bit. You may need to adjust each up or down carefully to get a balance that works. Once you get each set to the minimum level that gets the set out of blanking, adjust the drives in the service menu to balance the gray scale. If you can't balance, can't get it to stay out of blanking without retrace lines, or can't get it out of blanking you have a problem with bad crts or drive circuits. Almost certainly, the crts are near end of life in this set, so that would be my guess. Troubleshooting drive problems takes some skill and equipment.
did some more measurements and could see there is no heater voltage. The filaments are not lighting either.
Found a blown fuse on the D board but it blows every time I replaced it.
The heater voltage is daisy chained across the 3 CRT neck boards and if only the blue is connected that filament lights. But as soon as I connected the middle green heater connector the fuse on the D board blows again. Turned out when I was touching up the CR board I had a sliver of solder joining across the heater pins.
So it powers up again now. 5 blinks is gone but the screen is back to being predominantly red. Adjusting the red pot down to minimum shows still red on the screen.
Does this mean the red CRT is gone ?, I checked for a short from cathode to heater earlier and it's open as supposed to be.
I've also lifted the final resistor (R9008) which drives the red CRT and the red picture has disappeared. Doesn't this mean the CRT is ok ?
I have blue and green and actually the picture is looking good (but with no red).
Does this mean the Video Out Amp TDA6118 on the CR board is overdriving the red ?
Perhaps I'll desolder it and swap it onto the CG board and see if the problem moves.
edit >> the problem didn't move by swapping the Video Amp.
Also now I've lifted the video output resistor on both the CR and CG boards and brought a wire across from each to the other CRT. So now the red neck board is driving the green CRT and the green neck board is driving the red CRT. Got that handy tip from YouTube !
Once I did this the screen became full on green. I think this eliminates the CRT as the problem and the real problem is either on the red neck board or some drive signal going to that board.
I have already swapped the video out amp and all the other components seem to measure ok as well on the neck board so not sure where to go next.
Where did you pull the signal from to switch the CRT drive? I would not assume this is a good test without understanding the context of the circuit. Could still just have a CRT with low emission, and/or an AKB failure.
From R9008 on both Red and Green boards. Lifted both of these and put a jumper wire across to the other neck board going into the K of the CRT. See diagram attached.
Also now on double checking the red neck board I found Q9000 with only 25ohms across 2 of its legs ( even after removing it ).. It's a PNP transistor but I don't have any similar so swapped in the same transistor from the green board and soldered in a discrete pnp bc557 which is the only pnp I could find.
The picture attached is now what it looks like. It's quite dim overall and the white balance is not great but the red CRT now at least is not dominating the picture anymore.
mmm, perhaps the bc337 I placed on the green neck board is not a suitable PNP for the job or as you say the CRT is on the way out.
There are some rejuvenation techniques on YouTube etc, have you tried any of these on an RPTV ?
I use a sencore cr7000 or cr70, the best there are for restoration. On these tubes it is a very short lived patch at best. If the tubes are weak there is little to do. The most use these devices are is to determine the state of the tube up front.
yes I've seen that test equipment mentioned. Too bad I can't get a hold of it over here. I hate to leave it at that though. The best I can get the picture is as below. The green text in the service menu looks pretty good but why would the picture not be able to match this I wonder ?
Overall the picture needs all the colours to be be stronger I think. They all seem dull and weak. Is this a CRT aging symptom ? There are some other methods on the web which show how to bring life into an old CRT and I might try one or two of them.
Before I do though would you think there are any service menu tweaks to bring it all back in ?, or should I leave well enough alone ?
If you're ever in Ireland there's a pint in it for you if you bring the Sencore !
ok. did some more tweaks and I think its starting to come good now.
Spent some time twiddling the focus knobs and wound up the colour contrast etc in the menus.
Also ran the heater voltage on each CRT at 9v for a minute and the picture isn't looking bad now.
Think its still got a bit to go though and actually the attached pics don't do it justice.
Must still replace the audio IC that blew though as have no sound still...
Any idea what this dot in the centre of the screen is ?
It stays if I cover either the blue or red lens.
Also I've removed all 3 lenses and cleaned them along with the top of each CRT but the dot stays..
You can see it in the pics in the previous posts as well if you look carefully