Question about LG RD-JT91 Multimedia Projector
When the power cord is connected, all lamps flashing, and nothing happens. Try to wait for a hour but with no difference. Is there any way to reset the projector? It's a year old, and about 170 hours used.
In PSU, on the secondary side of switch supply there are electrolytic capacitors: for 13 V is 470uF/25V and for 5 (and subsequent 3V) is 1000 uF/16V. Those capacitors in some devices from this series use to break (why? I don't know: maybe cheep quality). Check voltage on rectifiers outputs with oscilloscope: if there are not constant voltage on one of them you should replace it with the new one (of course good quality). I've got the same failure subsequently on 5V supply (this reparation was done by LG service, but when I asked them they answered they replaced mother board - bull shit!) When the same "flashing" problem after guaranty occurred again, I had found soldering traces on the cap on 5V!And guess what - it was cap with a different brand than others.
This solution is maybe only for el-geckos, but no service wanted to repair my quite new, still worth something projector (not in Sweden any way). If you can’t do a job your self you still can ask some handy friend which know how to solder parts. Be careful! There is high, dangerous voltage on primary, so you must know what you are doing!
I'm sometime very irritated: that capacitor cost less in bulk than 2 cents each! But the ordinary people must buy a new projector because of lack of service!
There is PSU diagram:
Posted on Dec 11, 2007
I experienced the same flashing lights problem. Followed BruceRob's advice to fix the PSU board. To open the case, you unscrew all the screws marked with arrows on the case, plus a little hidden screw inside the lip of the connector flap cover! It is akward to unscrew this one. You have to remove the main PCB by undoing its 6 screws and carefully unclipping each of the cable connectors; the flexi-cable just pulls out. Now you have access to the PSU PCB. Undo 2 screws and the 2 hex pillars. Remove the PCB carefully - it might still have lurking high voltages on it! It disconnects from the the high voltage unit by unplugging the one cable.
Now you can check the caps that BruceRob referred to. In my case, the version seems a little different, i.e. the 5V section used a 220uF cap (the culprit in my case) and a 470uF cap instead of the two 1000uF ones. I replaced all four of the large electrolytic caps on the 13V and 5V sections for just in case.
Incidentally, if you measure the PSU outputs under no load conditions, it seems to work fine, but if you attach a load, it starts to oscillate. I used a 12V 120ohm bulb as test load on the 13V and 5V sections. After my fixes, the 13V section only delivered about 11.5V, but the 5V and 3.3V were fine. The 13V is intended mainly for the fans I think and they worked fine afterwards.
Before closing up, I blew out all the collected dust which gathered over the 2500 odd lamp hours of my unit. Buying replacement caps for all electrolytics on the PSU board cost me about R5 (ZAR).
Posted on Apr 17, 2008
Thanks for posting this great fix & the detailed descriptions!
I just managed to get my old RD-JT91 by replacing all 4 caps. Just a few cents investment - and a fully functional projector.
Thank you so much!!!
If anyone finds this helpful, here is the service manual - it contains some diagrams and part lists.
Posted on Jul 29, 2014
Amazing, one of my friends (with more skills into electronics and stuff) managed to make my projector come to life again with help of your great explanations, drawings and pictures. It was quite tricky but after a few hours we put all parts together - and it worked!
Again, thanks a lot for your help.
Posted on Oct 14, 2008
This site is fantastic.
Many thanks for the the detailled explanation of the problem.
By changing the capacitors my projector works properly again. The counter of lamp life time displays: 4089 h.
Posted on Jul 23, 2008
Where do you buy a power supply for this kind of projector?
Posted on Feb 25, 2007
Yes I had the same problem for a while ago. It was a defect power supply
Posted on Feb 23, 2007
Tips for a great answer:
on Apr 06, 2011 | Toshiba TDP-P9 DLP Projector
Probably overheated. Turn off the power and wait for the machine to cool. Then check that the filters are clean and that nothing is blocking air flow - and that fans are running. Turn it back on. If the same thing happens, they say to replace the lamp. I would check the number of hours on the lamp - it may be nearing end of life. Hopefully, it is a ventilation problem.
Feb 10, 2011 | Hitachi CP-X275 Multimedia Projector
Reset the lamp counter hours of operation for the projector TOSHIBA TLP-T720
1. Turn-off the device by pressing the "ON/STANDBY" and unplug the power cord
2. In the meantime, hold down buttons "ON/STANDBY", "MENU" and "INPUT and plug-in the power cord
3. The lamp operation counter will automatically turn to zero
4. Check if the lettering "0H" appears on the lamp operation counter in the status display
5. After the lamp operation counter has turned to zero, turn off the projector by pressing "ON/STANDBY" and unplug the device.
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