Hi everyone, I have aquired another Duo to work on. Problem is tuner A works but tuner B doesn't. Has anyone had similar issues please? Thanks. Regards, Jules.
It could be caused due the lnb chip u808, or maybe a voltage delivery to it. Check at least the zero ohm resistors as the r841r211if they are not interrupted. Check if the main voltages as the 3v and 12v are present. When there is no issue to see, then you could consider to replace the lnb chip, however there is no guarantee that it will solve the issue, because the cpu is also involved with it.
Normally it shouldn't because both has his own circuits, as the tuner A has the U809 and B the U808. But be sure that it is a hardware problem and is not caused by any other cause.
As for the vdc measurement, when both has the same configuration, (best is to have them to a same channel), then it should give the same voltages circuits. As for compairing both by ohms measurements (between ground and the measurements spot) should both have a same value range. It does not have to be precisely, but close the same.
Hi JB, Solved this one, tuner B working now. No power to LNB chip found resisror missing (pic attached) Also have a problem with fan not starting without a push. Fan is OK, cos it does the same with another working fan. Can we solve or just find a different supply for it? One more thing whoever worked on this had swapped the 3 famous caps for 3 SMD ceramic ones but seem to be working OK. How odd. Anyway attached the pics for you. Thank again. Regards, Jules.
Thanks for sharing your repair solutions, as for the fan issue I'm thinking at the transistor Q702 or a bad inductor F702. See this picture for more about it.
No problem JB. Thanks for the pic. Maybe I could reduce tolerance of the resistor feeding the fan? What do you think about the SMD caps I found in this Duo?
Yeah as for the fan issue, I think it's a ohm value issue, the voltage to the fan is to low to startup the fan. Often caused due a outdated resistor or (internal) burned inductor (coil). About the ceramic caps instead of the use of electrolytic capacitors. Both can be used in some places, as also the use for this places, I've seen that same solution a while ago. Thus, in this case, both can be used, when it gives no issues, than I would leave it as it is. For more bout the choice to use one of them, I advice you to search with google to it, searching to using ceramic capacitor or electrolytic capacitor
Hi JB, just a quick update. In fan circuit I have replaced R7151 220 ohm resistor with a 100 ohm resistor. This seems to have cured the problem with the fan starting up when switching on and running soundly. Regards, Jules.
Yes, that is a good solution, and nice to hear that you have been able to solve it. Thank you for sharing it.