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Discussion Starter #1
I've got a Mitsubishi WS-55819. Convergence started going out sporadically about a year ago, but we use the set less than an hour a day on average, so it took a while to be bad enough for me to want to dig in and fix.

Pulled the board and replaced the convergence ICs using hi-temp solder (after hearing of so many cold solder flow issues). All pads were perfect and very well protected from each other. The new ICs came from MCM Electronics based on recommendations of another forum - although I see on here that it may be a problem. The fuses F9A04 and F9A05 were okay and I checked all the smaller resistors near the ICs and the two 330 ohm resistors on the +24 and -24 convergence circuits.

Reinstalled the board and powered it up. The fuses (F9A04 and F9A05 - Pico 5A) went out immediately.

I pulled the board again and replaced the fuses. I measured resistance between the ground pin and each of the other pins on each IC and compared the values. None of the values appeared to raise a red flag.

Reinstalled the board again and powered it up. The fuses went out immediately, but this time the associated D9A60 and D9A61 diodes blew as well.

I can't find the diodes listed in the service manual's parts list, but I should be able to find some that would work from Digi-key. I've got a couple new ICs from ACME Enterprises and could put them in, but I'd like to know if there's any way to know if the new ICs I already installed from MCM Electronics are good.

What should I do next? If I simply replace the diodes and fuses, I imagine I will not be fixing the cause of the problem. I could install another pair of convergence ICs, but aren't I just wasting the labor and wear-and-tear on the pads if the problem is elsewhere?

Is there a way to know if the ICs are the cause of the fuses and diodes going out? What would happen if I remove the convergence ICs and try to run the board after only replacing the bad fuses and diodes?
 

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Your post was moved to the proper forum to maintain forum organization and to make information easier for others to find in the future.

First, read the first 10 posts in the convergence repair thread where you originally posted your message.

What makes you think the two diodes are damaged? This would be very odd. Pull them out of circuit to test them if you think they are bad, but I would be very surprised if they are.

You can run the set with the convergence chips removed and verify that the supplies to the chips are intact and that the signals to the chips from the convergence generator do not have excessive d.c.
 

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Discussion Starter #3
Thanks for moving my post to the appropriate forum. Being new to the forum, I didn't realize this was here.

The reason I suspected the diodes were "bad" is that when I first pulled the board I measured them with a cheap multimeter (no diode testing function) and read low resistance in the positive direction and high resistance in the negative direction on each diode. The last time I pulled the board I was reading high resistance in both directions across each of them. Your comment and the lack of finding reports of bad diodes elsewhere has me hopeful that maybe it was a test condition error. When I get back to the board I'll desolder one of the legs of each diode and measure them again - this time hopefully with a multimeter that has a diode test function.

If it were you, would you just replace the convergence ICs with the pair I got from ACME Enterprises? Or would you first try running the set without the MCM Electronics ICs to confirm that they were probably the cause of my blown fuses?

Thanks!
 

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I would not assume anything and check the supplies and resistors carefully. It is very odd to have both fuses blow. I would check for solder bridges and for any poor connections or improper connections.
 

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Discussion Starter #5
Recalling the first time I pulled the board, I remember seeing and hearing a spark jumping from the heatsink to the "Conv-Gene" cage when it tipped from removing the last screw - I wasn't ready for that tip. I had thought the spark was just going to ground, but perhaps it caused the failure of the fuses? Since then I've been very careful to prevent contact between the heatsink and the cage.

I've also taken a couple small shocks from capacitors, but I didn't think those would be damaging to the board.

How should I go about "checking the supplies" carefully? Do you mean anything downstream of the fuses? I've measured all the resistors to make sure they match the schematic. Are you speaking of continuity checks and resistance measurements only?

Thank you.
 

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The positive and negative supply voltages should be present at the ICs and should be clean with little ripple or noise. You can check the voltage with a DMM but to see noise or ripple you need a scope.

There should not be voltage on the heat sink nor the cage on the conv gen. These are both grounded. The caps in the power supply to the chips can hold a charge, and should be discharged with a resistor or light bulb before servicing if they do not discharge themselves. Not doing so is an easy way to blow a new chip.
 

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Discussion Starter #7
Okay, after re-checking, I believe the diodes are okay. :whew:

I neglected to bleed off the charge in the capacitors prior to installing the IC's, so now I'm suspecting they may have been toasted because of that.

Now, if everything appears to be okay other than the fuses and convergence IC's, should my next step be to remove the current IC's and install new fuses and try to run the TV like that prior to installing the new IC's?

Or would you go ahead and install the second pair of new IC's and a couple new fuses? (as long as the supplies and resistors check out, of course)
 

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Discussion Starter #8
I guess the diodes are fine. I replaced the fuses and carefully desoldered the convergence IC's. I just got done putting the board back in without the IC's installed to help determine if something else was causing the fuses to fail.

When I plugged in the set and turned the power on, it stayed powered up and the fuses didn't blow. The CRT's didn't come on (which I think may be expected with no convergence IC's???) and when I checked for an error code it reported "1-2", which the service manual says is "no error".

Two questions.

1) Are the CRT's not supposed to come on when the convergence IC's are not installed?

2) Should the next step be to install the new IC's (from ACME Enterprises) and try it again? Or are there important troubleshooting steps I should perform first?

Thank you.
 

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Discussion Starter #9
I checked all the 150 Ohm and 3.9 Ohm resistors on the convergence IC circuits and didn't see any red flags at all.

I discharged the two (C9A68 and C9A74) capacitors before installing the new ACME Enterprises SDK392-570 convergence chips. I also secured the heatsink and clamps to the board and to the chips before soldering to minimize stress on the pins.

I installed the board back in the TV tonight and plugged it in. Before powering it up I ran the diagnostic check and got the "1-2" no error code :)duh: duh - since I hadn't even turned the set on yet - but, hey, after all this hassle I was quite trepidatious about turning it on). Hoping beyond hope, I hit the "On" button on the MX-700 remote and watched as the green power light lit up for about 2.5 seconds and then clicked off!

Well, now I'm at a loss. I can fully empathize with people I've seen trying to unload these TV's with "Firewood For Sale" ads. :wits-end:

I hate to give up on this thing, but what choice do I have? Pleas for help from anyone in the Seattle area have been met with the sound of crickets. I can't fathom paying an anonymous authorized Mitsubishi repairman $250 to knock on our door and simply tell me that it'll cost at least $500 to repair this thing. :spend:

I know most people would love an excuse to kick this thing to the curb and replace it with one of the new sets, but we really like this set and hoped to get many more years of use out of it for the $2700 we originally dropped on it. For us it's also furniture as we have the Mitsubishi A/V rack that's perfectly matched to it.

I really, really, really don't want to just throw this set away!

Anyway, the only thing I can think of is that maybe, just maybe all those little 3.9 Ohm, 2 Watt resistors have been compromised by 7-1/2 years of getting hot and I wasn't able to detect that by measuring their resistance in situ without power. If by some small chance that is the case, can I get by without ordering even more convergence chips? Is it possible that the four new IC's I've burned through have been unharmed and simply replacing the resistors and fuses might do the trick? I sure wouldn't want to subject the board to all the heat necessary to remove and reinstall these chips if I didn't have to.

Please help me save my set. :help:
 

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Discussion Starter #10
This morning I desoldered one leg of each of the twelve 3.9 Ohm resistors on the convergence IC circuits and they all measured within tolerance (±10%?).

I've carefully inspected (with good light and 4X magnification) all the traces on the board and all the solder connections and cannot find any suspect areas.

Since I haven't replaced the Pico 5 Amp fuses (I'm down to last 2 until I order more), today I hooked up a power supply to the fuse side of one of the diodes (D9A60) and the ground (Pin 1) of the convergence chip on the same circuit (IC8C01). I slowly dialed up the voltage until I got to 24V without seeing any surges in current or signs of a short, so it appears the problem is beyond the PCB-POWER board.

That may explain why when I hooked everything up with the convergence chips removed it reported no error but also no picture.

Looking at the schematic, I'm wondering if the most likely thing that is trying to pull more than 5 amps through the fuses is downstream of the "GREEN/BLUE DY" or "RED DY" connectors. Do these connectors carry any kind of significant power? Or are they just signal carriers?
 

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Chances are that you had bad ICs or blew them. Just about the only thing that will blow the both fuses on the convergence supplies would be the ICs. It is possible to have a bad yoke, but that is rare in these sets.

If you have no pix, it is not because the ICs are removed. You should see picture with no convergence correction. The problem needs troubleshooting with the fuses intact and the chips removed to determine why you have no pix.
 

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Discussion Starter #12
Thank you so much for taking the time to reply, Leonard.

I know for certain I had at least one bad IC before I started this whole exercise, because when I clipped the pins off IC8C01, what was left of pins 1 thru 4 fell right out of the body of the IC.

But I'm completely befuddled. What are the odds that I'm still contending with bad ICs when I've replaced the pair twice with chips from vendors that are deemed reputable by most people on these forums? How many times would you replace the pair of chips and fuses before suspecting that the problem is elsewhere?

On all four of these new IC's, I've measured resistance between each of the pins (most focused on pins 4, 5, 8, 10, 12, and 17 because they carry power) and pin 1 (ground) and found nothing inconsistent, unexpected, or out of the ordinary. I measured them before and after the fuses blew, with no notable difference.

Perhaps a bad yoke is unusual, but based on the countless hours I've read online about convergence chip issues, I think it's safe to say I'm dealing with something quite unusual.. In fact, I've yet to find a single account of a story like mine.

What are the symptoms of a "bad yoke"? What symptoms would be expected to lead up to one?

As for the no pix condition despite having good fuses and no convergence chips, what signals determine whether or not power is made available to the CRT's? It seems like it would be a separate issue - likely one that came about when I first pulled the board. After all, the set appeared to be working perfectly other than what might be expected by an intermittent open on some of the IC lines.

When I inspected all the traces and solder joints on the board, the two least solid-looking joints (they still looked to have good adhesion) were pins 14 and 15 on the big transformer (T9A50?) near most of the fuses (F9A04 and F9A05 are still the only ones that have blown). In addition the first time I pulled the board out, I believe the first connectors to be strained just a bit were PCB-SVM (a 7-pin connector with pins 1 (110V) and 4 (12V) carrying the most strain) and PCB-CRT (a 8-pin connector with pins 1 (220V) and 3 (12V) carrying the most strain).

Along this line of consideration, is there a condition where the lack of power to the CRTs could cause the fuses F9A04 and F9A05 to fail? Or is their sole purpose to protect the IC's?

I feel like possibilities are narrowing down somewhat. I sure do appreciate your input on this! :yes:
 

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As I have said before, the no pix condition is not likely related to the convergence problem, other than that you may have created it when trying to service the convergence problem.

I would review every connection in the set to verify their integrity, verify all power supplies, and trace back from the CRT to find why you have no pix. That will require an understanding of the requirements for an image on a CRT, at minimum a DMM, and possibly an oscilloscope. The details of such troubleshooting are beyond the scope of this forum.

If you started with a convergence problem and now have something more, it is a pretty safe bet that you did something to change the conditions.
 

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I assume you mean the coils in the supply lines to the ICs. If they go bad they open, so you would not expect a fuse on the line with the open coil to blow, since there is no load. The chips and the other supply side may blow because of the voltage being unbalanced at the chips. If both fuses are blowing, you likely have bad ICs. That is the one thing that ties both sides together.
 

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Discussion Starter #16
I was thinking of the coils driven by the convergence IC's (through the "GREEN/BLUE DY" and "RED DY" connectors on the PCB-POWER board). They're the ones shown in the upper left corner of the attached image from page 67 of the service manual.

Unfortunately, I'm better at following schematics than I am at understanding what the circuits actually do and how to verify them. At this point I'm really just trying to evaluate whether or not it would even be worth paying a pro to fix it or bringing it to a recycling center and getting a new set. If I felt real confident that this set could be fixed for $500 or less, I'd definitely go that direction. On the other hand, if it's much more than that I'd probably cut my losses at this point and move on. That's why I'm still taking stabs at how extensive the problems might be.
 

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Those are the convergence yokes. Yes, it is possible to have a short there, but I still doubt that you would blow both fuses if that was the case.

Again, the first thing to do is verify the power supplies are working by putting in the fuses, removing the ICs, and doing some testing. Make sure that there is not excessive d.c. on the inputs to the chips and that the +/- supplies are present at the chips.
 

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Discussion Starter #18
Those are the convergence yokes. Yes, it is possible to have a short there, but I still doubt that you would blow both fuses if that was the case.
Just to confirm then - your thinking is that in order for both fuses to blow in the moments before shutdown, one of the ICs is more likely the culprit than anything downstream? If so, I puzzled as to why I can't detect any shorts within any of the four new chips I installed. :scratchhead:

Again, the first thing to do is verify the power supplies are working by putting in the fuses, removing the ICs, and doing some testing. Make sure that there is not excessive d.c. on the inputs to the chips and that the +/- supplies are present at the chips.
Myself not being an electrical guy, I hope you understand I'm feeling quite uneasy about poking multimeter leads around inside the set when it's powered up. :nono: Is there any advice you can give to help me stay safe in doing that? :hide:

Thank you!
 

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If you are not confident in what you are doing, you should not proceed.
 

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Discussion Starter #20
If you are not confident in what you are doing, you should not proceed.
Well, I came up with a way I was comfortable with. I took out the IC's, soldered in new fuses, and soldered 2-foot long leads into pins 1 (GND), 4 (-24V), and 5 (+25V) of IC8C02. I've confirmed that there was great continuity between pads 1, 4, and 5 of each IC position on the board.

So, I reinstalled the board with new fuses and the IC's removed, carefully plugging in all the connectors and replacing all the screws. When I plugged in the power cord, it sounded completely normal, but when I pressed the power button on the front panel, nothing happened.

The "Power ON LED" never even flashed, indicating that the microprocessor is NOT functioning.

I double-checked the automotive-type fuse on the Main PCB and it was fine.

Does this tell me anything useful? Any idea what I should check next?

Thank you!
 
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