Coolant Leak on Mitsubishi WS-A65 CRT RPTV

[SurrealMustard]

Yep, got a CRT rear projection HDTV to work on. Basically, after transporting it, fixing the cold solder joints on the convergence ICs, and cleaning the lenses, I got it all put back together and everything worked great for about two days. I had just ascertained a non-malfunctioning Xbox 360 to put this thing through its paces and was all ready to get started, but when I pushed the power button on the set, it just clicked right off and started blinking the power light. Removing and restoring power has not changed the condition and holding "menu" and "input" does not provide any kind of an error code.

Before I go any further, I need to clarify that this is not one of the digital Mitsubishis with the DM that always breaks down and causes the "blinking green light of death".

Anyway, I cracked it open this morning and found that coolant had inconveniently dripped from the red tube onto one of the white ribbon connectors going between the mainboard and the power supply (first two pictures). After removing the board and thorougly cleaning it up (third picture showing burnt, but clean, ribbon), I was hoping that it might be fixed, but it is unfortunately still doing the same exact thing. Further inspection of the rest of the set has revealed no other obvious coolant leaks or stains.

Any ideas as to where to troubleshoot next?

(If it helps, the "WS-A65" is one of the V20B chassi models (similar to a WS-65311).)

[dick_barton]

Re: Coolant Leak on Mitsubishi WS-A65 CRT RPTV

Has the ribbon continuity where you have the burn mark? Are you sure that the burn mark wasn't already there due to heavy current passing through that connection wire prior to your repair.

[SurrealMustard]

Continuity and burns

Has the ribbon continuity where you have the burn mark? Are you sure that the burn mark wasn't already there due to heavy current passing through that connection wire prior to your repair.

Continuity is good on the pins close to the burn. And looking back at my footage from working on it days ago, the burn definitely wasn't there.

[dick_barton]

Re: Coolant Leak on Mitsubishi WS-A65 CRT RPTV

Is there an error reset that may need to be cleared because it detected a fault when the coolant leaked?

[SurrealMustard]

Re: Error resets

Is there an error reset that may need to be cleared because it detected a fault when the coolant leaked?

The A/V reset button on the front has no effect. As for other possible methods of resetting errors, I scoured both the service guide and training manual (both attached), but couldn't find any mention of it anywhere (the only error messages that it'll report are ones that cause the set to shut down, like short circuits and deflection failures). It does says that the light is supposed to blink three times when power is connected to indicate that the microprocessor has initialized (I've seen what that looks like, and those blinks are a bit longer; what it's doing right now is a bit more abrupt), so it would almost appear as though something is happening to prevent that, but it's hard to say for sure.

[SurrealMustard]

fluctuating 9 volt standby problems!

This is weird. With everything plugged up normally, 9VS is fluctuating between 2 and 8.5v randomly. Unplugging the signal board causes it to come up to fluctuating between 24 and 30 volts.

Specifically, I'm testing across D9A30 (as shown in the attached picture from the service manual), but it looks the same from any other 9VS test point in the set.

Any ideas?

[SurrealMustard]

annoying connector

I decided to remove the power board to get a better look at it, but am having trouble with this one white connector over by the high voltage area. It doesn't seem to want to push, pull, or twist. Any ideas as to how to get it off?

[Moreno83]

Re: Coolant Leak on Mitsubishi WS-A65 CRT RPTV

You mean the white cable right? The white connector is to hold the cable in place!

I have not seen this before but just looking at that cable im sure it's shrink wire preventing either the cable showing the solder connections or for preventing something to get in/out.

You can always remove that shrink wire and add a new one later. My bet is that you will see some solder!

[dick_barton]

Re: Coolant Leak on Mitsubishi WS-A65 CRT RPTV

I believe that Moreno83 is correct and it is probably soldered to the top of the transformer.
The schematic in post #6 shows a transformer giving 9Vs but in the photo post #7 it looks like a line output transformer used in CRT sets that provided the 10-30K for the crt tube?

Just had a look at the manual
Post #7 is the EHT transformer (T5A51)
I also believe that Moreno83 is correct and it's a sleeve that should pull upwards.

Can you unclip the lead from the other end which fits into the crt tube.

[dick_barton]

Re: Coolant Leak on Mitsubishi WS-A65 CRT RPTV

Looking at your schematic post #6, D9A31 is an 8.2V zener and assuming you need 1.5V across the led of PC9A50 (pins 1 & 2) then total voltage = 9.7V and the zener should regulate the voltage to that approximate voltage.
Have you checked what dc voltage you have across the zener and the diode (pin1-2)

[SurrealMustard]

Troubleshooting data

You mean the white cable right? The white connector is to hold the cable in place!

I have not seen this before but just looking at that cable im sure it's shrink wire preventing either the cable showing the solder connections or for preventing something to get in/out.

You can always remove that shrink wire and add a new one later. My bet is that you will see some solder!

Yep, "cable" was indeed what I meant . If it's permanently attached, I'll explore disconnecting it from the other end before cutting and splicing, but if it comes to that, I guess that's what'll have to be done.

I believe that Moreno83 is correct and it is probably soldered to the top of the transformer.
The schematic in post #6 shows a transformer giving 9Vs but in the photo post #7 it looks like a line output transformer used in CRT sets that provided the 10-30K for the crt tube?

Right; they are unrelated. I was just trying to get the board out to get a better look at it and this was the last thing standing in my way. Post 6 schematic ≠ post 7 photo.

Can you unclip the lead from the other end which fits into the crt tube.

That's what I'm probably going to have to explore next.

Looking at your schematic post #6, D9A31 is an 8.2V zener and assuming you need 1.5V across the led of PC9A50 (pins 1 & 2) then total voltage = 9.7V and the zener should regulate the voltage to that approximate voltage.
Have you checked what dc voltage you have across the zener and the diode (pin1-2)

I'm getting pretty much nothing across the zener at D9A31 and fluctuating 25-28v on pins 1 and 2 of PC9A50 (this is with the mainboard and signal board disconnected from the power board).

[dick_barton]

Re: Coolant Leak on Mitsubishi WS-A65 CRT RPTV

With all the boards connected do you have all the other voltage that should be present, ie 110v, 206v,17v, 24v, -24v

Is the 9V secondary side loaded and bringing the supply down? Perhaps you could connect an external 9V at that point.

I cannot see how there could be such a high voltage across the opto diode unless the ground was floating. If the diode is not open circuit then it should clamp the voltage across it to between 1.2 1-1.6V

[SurrealMustard]

standby voltage

With all the boards connected do you have all the other voltage that should be present, ie 110v, 206v,17v, 24v, -24v

I don't get any of those, but wouldn't they stay off until the television is powered up anyway?

Is the 9V secondary side loaded and bringing the supply down? Perhaps you could connect an external 9V at that point.

I don't know for sure. All I do know is that when the signal board is added to the equation, that 9VS fluctuates at between 2-8.5 volts instead of 24-29.

As far as an external 9volt is concerned what would you recommend? Is that a good idea with the power supply doing strange things?

[dick_barton]

Re: Coolant Leak on Mitsubishi WS-A65 CRT RPTV

So is the 9Vs the standby supply?

[stj]

Re: Coolant Leak on Mitsubishi WS-A65 CRT RPTV

white wire goes down into the transformer, you cant desolder it - from that end anyway.
it runs at several KV so dont cut it - it's the focus or grid wire.

[SurrealMustard]

stand-by

So is the 9Vs the standby supply?

I think so. On page 23 of the training manual, it says: (along with figure 4 attached to this post)

"D9A30 rectifies AC from a secondary winding of T9A20, generating a 9VS supply. This is the source for all standby supplies in the TV"

white wire goes down into the transformer, you cant desolder it - from that end anyway.
it runs at several KV so dont cut it - it's the focus or grid wire.

You're probably right. Closer inspection reveals that it goes to the box with the electrostatic focus controls and is similarly attached to it. I sure hope that this board isn't too far gone that it has to be replaced instead of fixed because that one cable and connection would make the process into a sizable headache.

[dick_barton]

Re: Coolant Leak on Mitsubishi WS-A65 CRT RPTV

If its an EHT cable connected to one of the CRT's then it may well be that it can be unclipped from the tube.

[SurrealMustard]

ElectroStatic

If its an EHT cable connected to one of the CRT's then it may well be that it can be unclipped from the tube.

If I'm tracing it right, it looks like it's going directly to the back of the box with the screen and electrostatic focus controls, where it is also fixed without an easy means of removal. That said, there's actually a bit of extra slack on it; enough that I could probably flip the board over in the set to do any necessary soldering (hopefully) without having to unplug that pesky cable at all. The position might not be optimal, but it could work. My main concern at this point is finding what is causing this weird fluctuating standby voltage problem.

[dick_barton]

Re: Coolant Leak on Mitsubishi WS-A65 CRT RPTV

Resistor R9A02 limits the input current prior to switch on.

When P-ON base goes high, the relay activates and s/c R9A02 (removes current limiter) and turns on led Pins 5,6 turning on Q9A50 which supplies 20V dc to the EN pin of IC9A50.

Once oscillation starts (minimum of 16V on EN pin to start) the voltage on En pin drops and is replaced with the rectified dc voltage from D9A54

Where does P-On gets its voltage from. Is there another power supply?

[SurrealMustard]

P-on

Resistor R9A02 limits the input current prior to switch on.

When P-ON base goes high, the relay activates and s/c R9A02 (removes current limiter) and turns on led Pins 5,6 turning on Q9A50 which supplies 20V dc to the EN pin of IC9A50.

Once oscillation starts (minimum of 16V on EN pin to start) the voltage on En pin drops and is replaced with the rectified dc voltage from D9A54

Where does P-On gets its voltage from. Is there another power supply?

According to page 32 (and 25) of the training manual, the P-On would come from the control circuitry in the microprocessor on the signal board and end up at Q9A51. Given the unstable standby voltage however, the microprocessor is not able to boot up in order to be able to send that command.