[kditraglia]

Hello,

I recently picked up this tv from craigslist for dirt cheap as it was not working and the original owners just wanted to get rid of it, and being the poor college student thats interested in electronics I decided to pick it up and take a crack at repairing it.

I have been browsing these forums for the past couple weeks and found a lot of very useful information(seriously this is one of the most informative and well kept web sites I've ever visited).

Anyway so far All I've done is taken it apart and poked around inside a little bit, I removed the power supply and glanced over it to see if there were any glaring problems, but it looks to be in pretty good shape (theres a little corrosion on some of the solder, but I don't think that is breaking the connection?). I put the power supply back in and tried to turn it on again, and it actually was able to turn on(I think this is mostly because I noticed the solder on the on switch was very loose and I don't think I was even pressing it before when I was testing), but then immediately turned off after about 4 seconds. No fuses are blowing, but it will turn off after 4 seconds every time I try to power it on.

I read in the DIY sticky thread that the convergence boards will send signals to turn the tv off if something is wrong, so my next plan of attack was to take them out and see if the tv will power on to try to narrow down my problem. I am making a thread on the problem if anyone has any words of advice or know of any common problems with this model (I understand its quite old). I will keep it updated as I figured more out.

Thanks in advance for any advice and keep up the great work!

 

[lcaillo]

You may have a convergence output problem, but there are lots of things that can cause shutdown. You will notice dozens, perhaps hundreds, of ring cracks on solder joints in this set if you look very closely. Before doing much troubleshooting, I would resolder any that I can find, as this is the most common source of problems on this and other Pioneer RPTVs.

 

[kditraglia]

Thanks for the quick reply

Would you expect to see cracked solder on the power supply itself, or on some of the other boards? I am looking at the power supply now and everything seems to be well fastened in. Is there something else I should be looking for, my definition of cracked solder would mean the component can jiggle around a little bit.

 

[lcaillo]

The power supply, deflection, and convergence areas are the most prone to problems from bad solder joints, but they are present throughout the set. You will not see components jiggling. The cracks are very fine and cause problems by increasing the resistance in the connection. It can be less than obvious if you don't know what you are looking for. I use a magnifier and resolder the majority of joints on these boards.

 

[kditraglia]

OK, I touched up all the solder connections on the power supply, I just had a quick question about the convergence. If I take out the entire convergence board should the TV be able to power on, or do I have to just take out the 2 convergence chips connected to the heat sinks, but leave the board in place? I am just trying to narrow down the problem, I'm thinking if it turns on without the convergence board in I can replace the ICs check the resistors and touch up the solder on that board and hopefully all will be well.

And again, thanks for the help thus far.

 

[lcaillo]

I don't think it will run without the board, but I am not sure. Most sets will run without the ICs with no problem.

Don't underestimate the amount of soldering that needs to be done in these sets. The vast majority of them that I have fixed have required no parts other than a big roll of solder.

 

[kditraglia]

OK, I have identified what has to be the convergence board (it has an STK4277 SL attached to it). I wanted to take out the deflection board out and touch up the solder connections on both these boards at the same time, so I grabbed the next biggest board inside (was a real pain to remove), but doing a quick google search on what I removed it is actually the audio/video assy. I'm thinking its probably in good shape just from looking at it(and all the components are very small so it would take some very precise soldering to even attempt to touch it up). So my question is what exactly am I looking for to give away that something is the deflection board, theres a board thats connected to all the inputs on the back, and a smaller board hanging off the side of that one. Also there are 3 small boards attached to each of the R,B,G projectors, and of course theres the power supply. Am I missing something or is one of those the deflection board, I'm not really sure what I'm looking for.

 

[lcaillo]

Power and deflection are on the same board in this set, IIRC. One high failure part in these is the vertical output IC, which is often damaged when solder joints start coming apart.

 

[kditraglia]

I touched up a lot of the solder points on the convergence board and started testing the resistors and they all look to be in good shape. Theres several resistors connected to most of the pins of the convergence IC that are marked at 330 ohms, and half of them are reading 300 ohms, the other half 330 not sure if thats enough to be concerned about but they are out more than 5%.

Is there a way to test the convergence IC without taking it out of the board to see if its live or not? If not I suppose I will take it out and see if I can power on the tv without it.

Also how can I identify the vertical output IC and are there any tricks/signs to tell me if it is bad or not?

 

[lcaillo]

The only way to test an IC like this is to run it, monitor the inputs and outputs and see if it works. If it is pulling the set down, you can remove it.

I suggest having the service literature for any repair. This is how you can identify parts if you do not have the skill and knowledge to do so without the documentation. One way to identify the vertical output is to find the yoke wires and trace back to the chip.

 

[kditraglia]

OK, I resoldered all the connections on the PSU/Deflection board as well as all the connections on the convergence board. I removed the convergence IC and tried to power on the tv and get the exact same behavior of shutting off after about 5 seconds. I have been trying to locate the literature on this tv, but haven't had much luck probably because its so old I can't find any website that carries the service manual for this.

Doing what research I could on the vertical output IC I think I have an idea where it is (theres a small transistor looking chip with a little metal head off the top of it, it somewhat resemebled a picture I found of one). There is also a 47uF capacitor right next to it which I also read should be replaced when replacing the IC. So my question now is does the chip I am looking at sound like it could be vertical output IC(it looks like the letters on it wore off so its really hard to identify it, I could take a picture of it if it would help). Where can I purchase another one, how much do they cost ~? Should I also replace that capacitor? Is there a way to test whether it is faulty without the service manual? Do you know of anywhere I could get a service manual for this model of TV?

Thanks again for all the help!!

 

[lcaillo]

Capacitors shold be tested for capacitance and ESR. This has nothing to do with having the manual. You need the manual to determine what parts are and where they are in the circuit. Your questions regarding parts require going to the manual and doing some research. This is beyond the scope of the forum.

There are a number of suppliers for parts and service manuals listed in the sticky in the DIY forum and in the Parts Supplier reference list. You can also get the manual from Pioneer, though it will likely be very expensive from them.

 

[kditraglia]

OK, I finally got a copy of the service manual but I still haven't been able to get this thing up and running. One thing I did notice is there was a resistor completely fried(was reading 0 resistance). I have a screenshot of where it was located and I replaced it and the new one does not seem to be getting fried when I turn the tv on, but it still doesn't stay on longer than 5 seconds. Hopefully that is a clue to what part is failing.

Also now that I have the manual I can make some measurements of the output voltage at certain points to try to pinpoint what is actually failing, but I was wondering if thats possible by just plugging it in and measuring, or I have to actually do the measurements in the quick 5 seconds that I can keep the tv powered on?

Again thanks for the help, and I'm sorry if this is getting too specific than you would want for this forum, but I am just looking for some general advice to steer me in the right direction given what I am seeing.

 

[lcaillo]

When resistors are "fried" they fail by opening or increasing their resistance. If you read 0 ohms, you are reading a short, or a lower resistance than your meter (or the range setting) is capable of resolving. An open resistor will read a high or infinite resistance.

There are many possibilities with these old sets. At this point I have given you all that I can without resorting to step by step troubleshooting, and this is beyond the scope of the forum.