Mitsubishi Rear Projection makes funny shapes on Green and Blue

May 20, 2009

- What type of package are they in? Where would I be likely to find them on the PCB?


Green PCB:

http://lh3.ggpht.com/_5okkstBuUdc/ShOxcnwlEPI/AAAAAAAABQM/S0Tx01q2lcA/s800/Green.JPG


Brown PCB:

http://lh6.ggpht.com/_5okkstBuUdc/ShOxckagMdI/AAAAAAAABQI/5p5dhTLZII8/s800/Brown.JPG

May 20, 2009

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The Service manual indicates that the amp IC's are under this shield. Should I try to pop the lid off, or is desoldering from the underside the better choice? There is a shield underneath suspended from the pins of the box on top.

I looked at the underside and found that the Convergence IC's had been replaced, and had some sketchy solder joints. I am going to try and clean them up.

May 20, 2009

- I popped the cover off of the shield, I cooled the amps with an upside-down canned air, they had frost on them and were cold to the touch.

No change to the blue or green image.

I did a quick re-heat of the solder on all of the convergence IC pins, removing some of the excess, that didn't have any effect either.

May 21, 2009

- This is the circuit from the service manual, assuming I had an oscilloscope, what would I be looking for? (if there is a guide on scoping I could sure use it, I have used DSO scopes in the automotive field, so I would likely clip the ground to the shield, and then check to see if pin 7 and 8 on IC802 were making a similar signal, if not then I would see if they were receiving a similar signal on pins 2 and 13).

Is it standard to have one amp circuit fail in a package like the IC802/3? Because it would appear that is what happened to these two chips, as they are shared with RH and RV and those seem to be working fine.

I have checked the resistance from the CONV to the D/A, D/A to the AMP, and from the AMP to the Convergence IC for RH, BH and GH. The circuits appear to be fine.

May 22, 2009

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I took these connectors and swapped them, Red for Green and Red for Blue, there was no change in the picture!

I scoped pins 7, 8 on IC802 and pin 8 on IC803, Pin 8 (RH) on IC802 had a nice high waveform, whereas the other two pins had poor looking waveforms, not very high.

When I scoped the output of the circled wires above Red H+ had a waveform similar to the AMP pin, and Blue and Green + looked poor like their AMP pin's waveform.

Red H- had a tight waveform, as did Green H-, but Blue H- looked poor.

I am going to check the resistance of the yoke coils now, because there was no difference when swapping blue or green for red.

May 22, 2009

- To confirm, I swapped BH +/- for RV +/-, when I set the convergence in the menu the red moved up and down while the blue moved left to right.

When I chose to adjust the blue the red would move left to right.

Does this mean that there is a problem with the yoke? There is a PCB on the yoke with heavy wires coming from the High voltage section, Red, Blue Yellow and Brown, these travel to each yoke.

Yellow and brown appear to be in a series connection (vertical??) and Red/Blue have two wires apiece on the two yokes nearest the High-voltage PCB, with one blue and one red on the last yoke.

This is the schematic for that section:


It is starting to look like the convergance IC is working the deflection coils without help from the main deflection circuit, the IC451 (chip LA7845N), if it only has enough power to run the first yoke (the red one), then would it cause this kind of problem?

Could the fault be in the first yoke PCB that sends the deflection current in a parrallel circuit?

May 22, 2009

- Aaagh!!

I poked the first yoke PCB with a stick, and guess what? A spark, some ozone and all the colors!!

(I had just sprayed the two transistors on the power PCB with an upside-down can of air)

Unfortunately I reset the factory convergence settings in the service menu, and I don't have the original remote, so I will need to program my remote with an Audio button before I can get it properly aligned.

I guess it is time to swap back all the convergence wires and solder the RF shield back on the bottom.