DLPLCR4500EVM: Blue LEDs stopped working

Hi Jeff,

Thanks for contacting us in regards your concern on your EVM...
If I understand your approach correctly, you did put it in Manual mode and enabled the Blue LED only, isn't it? Can you confirm if this worked and what is the LED current reading?

Below are a couple of troubleshooting activities to understand the signature:
- Try an internal TPG pattern with a solid field color as red, then as green, and lastly as blue.
- Flash the system with the original firmware to confirm settings are back to default on the system, then confirm if blue LED comes back ON.
- Try scoping the blue LED input using a voltmeter to determine if we see anything abnormal.

Please check with us on any findings to continue exploring this event.

Thanks for the quick response!

Yes, that's correct. I put it in Manual mode with only the Blue LED enabled. That's when I get no light output.

The LED current is red=104, green=135, blue=130.

1. With the "color bars" internal test pattern and manual LED selection set to Red. I get red bars. With Green, I get Green bars. With Blue, I get no light output.
2. Re-flashed DLPR350PROM_v3.1.0.bin --- Same results.
3. Blue LED Input voltage --- Sorry, can you tell me specifically what test point or pins I should probe for voltage?

Thanks
Jeff

Hi Jeff,

No problem... I can explain.

Under TI Designs, you will find the schematic for such board. Here is a link as a reference: www.ti.com/.../tidr157a.pdf
By looking at it, it seems like TP64 would be the one you need to check voltage on. Since we know green LED is working, try comparing TP59 (Green Anode) to TP64 (Blue Anode).

Please let me know if any findings in here.

TP59 = 3.1 V
TP64 = 29 mV

Thanks,
Jeff

I think we have confirmed we have some sort of strange response from the hardware. We might need to decouple a little bit more.

Some extra questions below:
- Do you have an OScope handy to capture a waveform out of TP66 and TP67? We want to understand if the LED is getting enabled properly.
- In regards the actual blue cathode and anode, can you measure these two (TP64 to TP65), and TP65 to GND as well? This will tell us some more about the LED integrity. As comparison you can use the similar testpoints for a working LED.
- A little less technical, but valuable information for us: Can you comment in regards the storage conditions for this system (Estimated temperature and humidity)? You mentioned "...the projector did not move between last good operation and today...". Do you know if this was one year from now? Two weeks from now?

Hi -

1. Sorry, I don't have a scope available right now.
2a. TP64 - TP65 = 22 mV
2b. TP65 - GND = 0.9 mV
3. I've had this projector since April 2018. Its mostly been in my office ~70-80F, nothing unusually with the humidity. Last good operation was Monday of this week. No movement between Mon (Good) and Wed (Failure).

Thanks
Jeff

Is it warm near/close to the blue LED compared to the region near the working LEDs?

No, nothing remarkable, the temperature is pretty consistent across the parts. If there is a specific part that you'd like me to get the temperature from, please let me know, I have an IR thermometer.

Hi Jeff,

Thanks for your last inputs...
We are getting close to determining the root cause. As a follow up with your data, I did some analysis on my end to understand the suspected signature on your blue LED.
- On my end, any good system is highlighting a max of 2.3~2.5V at TP64, while your system is only outputting 29mV.
- Enable signal for Blue LED (TP66) should be highlighting an output similar to a square wave when probed using projection (Blue LED projection if set manual Blue only should be constant ~2.9V). It will be helpful to get this pin probed if you can get a hand to an OScope. This should answer to us if we perceive any problems with the LED driver on your system.
- Temperature will be good to capture on U47 and U46. These parts are located at the backside of the board when looking at the LCR4500EVM top down. I collected temp data after 10min continuous operation, and both are comparable on our good system.
- One last item would be a continuity test at the blue cable (From the LED input port to J33).

Please let me know if any inputs on any of these.

Hi Jeff,

Have you able to solve the problem with your blue LED? If so, I'll temporarily close this thread; but feel free to let us know if we can provide any further assistance here.

1.  Continuity - I was able to confirm the conductors from J33 to LED have good continuity.

2.  Temperature - I was not able to get the temperature at those spots because of the mounting configuration of the board.

3.  Sorry, don't have a scope to test TP66 waveform.

While doing the continuity test and re-checking voltages around TP64, the Blue LED turned on.  So, it seems that LEDs are ok.  However, after cycling the power, the Blue LEDs were off again.  So, its seems like some component on the board is bad.  Can I send it in to TI for repair?

Thanks

Jeff

Nope, not resolved.  Seems like a bad component on the board.  Can I send it in for repair?

Thanks
Jeff

Hi Jeff,

Can you provide the exact conditions at which you found the LED turning ON? We still cannot determine whether the problem is the flex , the driver, or the same LED (maybe intermittent).

Just so you know, there is a 90 days warranty policy. Since you have this projector since April 2018, we may be past the allowed timeframe.

Hi Jeff,

Did you have the chance to investigate the LED further? Any luck in here? Please feel free to contact us for any questions or concerns. Once the problem is found we can get the specific component replaced.