as you say, its likely the clone quality at fault, cheap can have problems.dentex wrote:@Caladain: I would love to see how it ended.
I have one (clone, I suppose, as it misses just the "sainsmart" mark) of this relay boards and I noticed that relay 1 doesn't switch, although the led indicating its activity follows the switching logic; furthermore, the relay 4, after switching initially, after a few seconds loose power and switch autonomously.
I tested the board with all possible settings (5V JD-VCC/3V VCC/JD-VCC+VCC not jumpered; or 5V JD-VCC/5V VCC/JD-VCC+VCC not jumpered; and lastly 5V JD-VCC/5V VCC jumpered) but the problem remains: only channels 3 and 4 seems to work properly. The power supply I used for the JD-VCC is 5V and 1500mA. It's also possible that in my case the issue is related to the fact my board should be a chinese clone (respect: nothing personal).
In regards to the VCC/JD-VCC jumper, no one talked about it. I suppose you considered it always shorted.
I've never tried to use a Darlinghton array with it, I have a ULN2003A and I'll check now how it goes.
Voltage at the relay coils is around 4,8V for the 3 working ones. The unswitching one can be triggered applying manually 5V to its coils. With everything engaged (all 4 LEDs on), every octocoupler has ~1V on the source side and all have ~3.2V on the sensor side but the channel it's not switching.BMS Doug wrote: as you say, its likely the clone quality at fault, cheap can have problems.
Have you checked voltage at the relay coil while it is energised?
Thanks.BMS Doug wrote:A fairly simple board like this is perfect for first time repair efforts, I hope you have a good soldering iron (temperature controlled one) as it will make the job much easier.
Good luck with the repair.
I've always been amazed by how I cannot maintain track of replies on this board (or the mail system sucks, or all goes into the spam folder on my side)... But... REALLY thanks for the reply anyway, although I'm saying this with absolutely improper delay.BMS Doug wrote:
Diode D3 could be shorted out, that orit must be the resistor R6 or the transistor Q3 as they are the only remaining potential faults.
not the diode or you wouldn't be able to energise the relay by putting a voltage across it.
I would suggest checking the resistance between leg 3 of the opto-isolator and the base of the transistor Q3, if that is the same across all of the relays then the problem has to be Q3 (in my opinion).
... the end result is more or less the same, and you would likely be fine directly driving it from the raspi.