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Post by jeremy on Nov 21, 2017 14:04:11 GMT -5
So I have one of my more interesting repairs here I need some help with. I have a Panasonic PT-LW25HU that "works" for a couple of seconds, then shuts down. I'll better explain: Press power > Standby Indicator switches from blinking red to solid green > fans spin up, ballast ignites lamp, everything works for about 2 seconds > shuts down > Standby/on Indicator blinking red (Can repeat this over and over) So, User AND service manual both say if the Standby/ON indicator is blinking (no other indicators blinking) that the fans are cooling down the projector and the projector will not power on again until the standby/ON indicator is **SOLID RED** The issue is, it is NEVER solid red, not even after being plugged in, it just blinks red when I plug it in until I power it up, then it shuts off, and starts blinking red again. The warning and lamp indicator do nothing. I checked all the fans, they aren't the issue (used one from a diff PJ to test). Checked the voltages going to the fans, they are correct (right on the money even). So I am left with possible bad thermal sensors (which are 8 pin ICs surface mounted to the mainboard), or a PSU/possible ballast issue, and the indicators are just not indicating correctly... The service manual is full and detailed (reminiscent of a Sanyo SM), so with some help I am hoping I can get this barely used projector to work.  |
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Post by mastertech on Nov 21, 2017 19:35:31 GMT -5
Well I have looked over the manual and I agree that based on your description of the symptoms it points to an overheating problem even though it is probably not actually over heating. At least for now anyways. So you can start there. I see it looks like there are 2 temp sensors, lamp and room. Yeah, those temp ic's are really dumb. Hopefully you can test on them with the unit assembled with just the cover off. So here goes.
You will have to test right on the pins of both ic's. You will have to watch the DC voltage as you plug in the projector, turn it on and as it shuts down and is off. Unfortunately you will have to do this for each pin I give you to test. We need to see what is happening as it goes through shut down, if anything.
On ic8831, use pin 4 for gnd probe and test pins 1,2,3,6,7,8.
Same test on ic8811.
Let me know your voltage readings.
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Post by jeremy on Nov 21, 2017 23:24:49 GMT -5
One of the 8 pin ICs is on the top of the mainboard. I believe the other one is on the bottom. They are small, but I should be able to solder some wires to the pins and then I can clip my test leads to them and make it easier to check. I'll get back to you with my findings once I've done that Oh, FWIW... the lamp I pulled out of this projector when I got it was a genuine OSRAM, looks to be either brand new, or possibly the original lamp the projector came with, but the mercury chamber itself has a few cracks, and the lamp doesn't work at all. I have a new one in it so I can test it, but I just thought I'd tell you the condition of the old lamp, since that may help diagnose. |
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Post by jeremy on Nov 28, 2017 15:34:49 GMT -5
Ok sorry I'm so slow at testing this stuff out for ya MT  IC8831 readings - All voltages are positive (before and during/after): --BEFORE-- --AFTER-- Pin 1: 3.1v - 3.1v Pin 2: 3.1v - 3.1v Pin 3: 0v --- 0.57v Pin 4: GND - GND Pin 5: 0v --- 0v Pin 6: 0v --- 0v Pin 7: 3.2v - 3.2v Pin 8: 3.2v - 3.2v IC8811 readings - All positive voltages (before and during/after power on): --BEFORE-- --AFTER-- Pin 1: 3.2v - 3.2v Pin 2: 3.2v - 3.2v Pin 3: 0 ---- 1v - 0.57v (The before reading goes from zero to 1 volt every 2-3 seconds, stays stable during/after power on) Pin 4: GND - GND Pin 5: 0v --- 0v Pin 6: 3.3v - 3.3v Pin 7: 0v --- 0v Pin 8: 3.3v - 3.3v IC8811 is on the front remote control sensor board as well, took a while to locate that one. Also, IC4891 and the area within 1 centimeter of it looks like it has excess flux on it, while the rest of the board (both sides) has absolutely none. It looks like someone probed IC4891 a few times and may have replaced it as well, but I'm not 100% sure. Edit: This is from the SM regarding the IC4891 and fans: "An abnormality occurs on the fan control circuit; If one of the fans FN001, FN002, FN003, FN004, FN005 has an error, the FAN_ERR and P_FAIL signals become "L". If the FAN_ERR signal becomes "L", the lamp switch signal output from IC4891 becomes "H" to stop the operation of the lamp ballast circuit.." |
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Post by mastertech on Nov 28, 2017 17:58:03 GMT -5
You can check pin 1 of ic4891 for app 3.3v dc. Test during start up and shut down..
On your test of ic8811, pin 3 you say stays stable after pwr up. Stable at what? At 0.57v?
Both of those thermals look mostly ok but I wanted to see what pin 3 of both were doing. You may have to do another test on both of those just to verify. Set your DMM on diode scale and test between gnd and pin 3 of each ic and see if your DMM shows short at any time during startup and shut down.
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Post by jeremy on Nov 28, 2017 21:51:32 GMT -5
IC4891 has 3.298vdc+ on pin 1,
IC8311 Pin 3 shows 0mv before power, goes up to almost 400mv+ during power, slowly goes down when projector shuts down from error.
IC8811 Pin 3 shows 0mv before power, goes up to almost 200mv+ during power, slowly goes down when projector shuts down from error.
Checked it a few times to make sure it repeated, this is what happened during 4 checks.
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Post by mastertech on Nov 29, 2017 11:44:36 GMT -5
Try starting the projector with the lamp cover removed and see if it throws a different error.
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Post by jeremy on Nov 29, 2017 13:05:28 GMT -5
It doesn't throw a different error. In fact, it acts exactly the same, with the exception that the lamp doesn't light up. All other behavior is identical otherwise. Interesting...
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Post by mastertech on Nov 29, 2017 13:14:42 GMT -5
Oh, so the lamp does light with the cover on and does not when the cover is off?
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Post by jeremy on Nov 29, 2017 16:42:04 GMT -5
Correct |
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Post by mastertech on Nov 30, 2017 11:30:52 GMT -5
Well then that should eliminate IC4891 and circuit from problem since it is tied directly to the lamp cover switch circuit. And yes it is interesting an error was not triggered. Current problem is probably superseding any secondary problems.
Moving on, test dc voltage across caps C1871 and C1872.
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