I found the 5v supply to the hdmi port drops to zero after a minute or so, killing video and audio output. Attached is the relevant portion of the schematic. 5v comes in on the left from the SMPS and goes out on the right to the port. It is switched by the CEC_POWER line from the CPU. The CEC_POWER line is present even when the port goes down. I infer this because putting my finger on the gate of the mosfet brings the pic back after a couple of seconds.
At the moment I only have access to the Q1058, the three parallel resistors and the two caps, the rest are on the bottom side of the board. Something is pulling up the voltage on the gate. The circuit is mostly a mystery to me I know it's simple for some of you so any help is appreciated.
You have it right. Except something is charging up the Gate of Q1058 such that after a minute or so the Gate is high again and video cuts out. Grounding my finger on the gate brings the video back for another minute or so. I can do that all day long if I'd like. Same thing with a meter probe - the reading is high but falling fast, then video returns.
Before I answer that lets clarify something. I think you are saying that Q1057 is on the bottom of the board that you do not have access to. If that is correct then how do you know the CEC at the base of Q1057 is still high when you loose video?
Ok, I understand where you are coming from. But that does not confirm that you have a good CEC signal at Q1057 so you cannot rule that out as a possibility.
To first answer part of your question, whatever part is causing leakage is probably just enough voltage to cause the mosfet to go into shutoff and when you touch pin 3 with your meter or finger is causes just enough voltage loss to turn the mosfet back on again. That is not uncommon.
Here are 2 things you can try before you have to pull out that board.
If you have a resistor around 10K solder 1 leg to pin 3 of Q1058 and the other leg to DGND. This will essentially bypass 1057. See what happens.
The other thing would be, if you are real good at desoldering and soldering, swipe the mosfet from Q1063 or Q1067 or Q1061 or Q1074 and swap it into your Q1058 and see if anything changes on that circuit.
mastertech: Merry Christmas to you too. Not many holiday people around any more.
Dec 26, 2018 14:37:50 GMT -5
stridsvognen: Merry christmas everybody...
Dec 24, 2018 19:10:58 GMT -5
mastertech: Sounds nice. Would love to have many more pictures.
Oct 20, 2018 20:31:04 GMT -5
greg1292: Greetings from Denmark. Lots of ideas knowledge and bucket list. Gabor boards looking very nice indeed
Oct 20, 2018 16:38:34 GMT -5
kevin5418: Anyone has the Velodyne hgs12bg MPS board schematic ? thank U
Oct 6, 2018 0:58:34 GMT -5
mastertech: According to the SM ic711 must be installed with the firmware already in it. It can then later be upgraded. The correct ic is around 50 dollars. If you installed a blank ic it will not work.
Aug 19, 2018 20:01:39 GMT -5
ralph: Hello mastertech, sorry for the delay, if I replaced that IC, I was with short circuit, blocked the 3.3 volt regulator, put a new one but still do nothing, what could I do? Thanks for the reply
Aug 18, 2018 21:48:51 GMT -5
mastertech: Did you replace ic711?
Aug 12, 2018 18:55:42 GMT -5
mastertech: Just to clarify you replaced ic711 (STM32F101ZG), correct?
Aug 10, 2018 20:58:16 GMT -5
ralph: Hello, Mastertech, I'll send it to you
Aug 10, 2018 18:58:46 GMT -5