Power puzzle: 5V drops to 4.5V
Posted: Oct 26th, '17, 11:53
I have two Yocto's, and am having a problem with the 5V line on one of my IO boards that I just can't figure out.
My Main Board #1 and Main Board #2 are both functioning 100% when used with my IO Board #2.
But my IO Board #1 causes the sequencers to malfunction and frequently reset itself or lockup. It had worked fine for awhile, but I may have damaged something at some point while working on mods or fixing wiring etc.
Measuring the voltage of IO board #1, all measures correctly when disconnected from Main Board: 5V, 15V, -15V... And the 5V line still measures 5V when the power cable is connected to the Main Board. But it drops to 4.5V when the sequencer cable is connected to the main board. (Specifically, it drops to 4.5V when ground is connected to the sequencer circuit.)
This only happens with one of my IO boards. IO Board #2 holds steady at 5V and powers each Main Board with no sequencer problems..so logic dictates the problem is on IO Board #1, but I can't figure out what is causing it. I replaced the 2sa733's for Trig2 & Trig3, double-checked the resistors, redid the cabling, and even pulled the 6n138 out completely for now but the 5v still drops to 4.5v...The capacitors look fine..Could a diode be failing? What am I missing?
It seems that I have enough observations to be guided by logic to where the problem is, especially since the circuit on the IO Board is so simple, but I'm really stumped...Perhaps it is the 6n138, and that's why removing it didn't change the symptoms, and I need to replace it...I only have 6n139's on hand though..
Any help at all hugely appreciated!
My Main Board #1 and Main Board #2 are both functioning 100% when used with my IO Board #2.
But my IO Board #1 causes the sequencers to malfunction and frequently reset itself or lockup. It had worked fine for awhile, but I may have damaged something at some point while working on mods or fixing wiring etc.
Measuring the voltage of IO board #1, all measures correctly when disconnected from Main Board: 5V, 15V, -15V... And the 5V line still measures 5V when the power cable is connected to the Main Board. But it drops to 4.5V when the sequencer cable is connected to the main board. (Specifically, it drops to 4.5V when ground is connected to the sequencer circuit.)
This only happens with one of my IO boards. IO Board #2 holds steady at 5V and powers each Main Board with no sequencer problems..so logic dictates the problem is on IO Board #1, but I can't figure out what is causing it. I replaced the 2sa733's for Trig2 & Trig3, double-checked the resistors, redid the cabling, and even pulled the 6n138 out completely for now but the 5v still drops to 4.5v...The capacitors look fine..Could a diode be failing? What am I missing?
It seems that I have enough observations to be guided by logic to where the problem is, especially since the circuit on the IO Board is so simple, but I'm really stumped...Perhaps it is the 6n138, and that's why removing it didn't change the symptoms, and I need to replace it...I only have 6n139's on hand though..
Any help at all hugely appreciated!