A rew things to try first. Will swap the circuits round so the one that won't work is on the pos5 side instead just to see if that does anything. I am also going to pick up another couple of 0r1 resistors, just to have a spare to swap out.
Failing these options I will be truly stumped and then it will be time for a trip to the post office!
Had a Eureka moment! with the 1r in par still nothing but with JUST the 1r I get a reading!
Admittedly the reading is wrong, I can only adjust between 33 to70 odd mA and it is fluctuating a lot but that is probably expected seeing the resistor is 1r now?
It just HAS to be a faulty resistor! Obviously it reads as a short on my meter so I can't say whats wrong with it unless it is 0r and not 01r?
Anyway I will be getting some tomorrow.
Do you think the adjustment range is because of the 1r or is that still part of the problem?
Had a Eureka moment! with the 1r in par still nothing but with JUST the 1r I get a reading!
Admittedly the reading is wrong, I can only adjust between 33 to70 odd mA and it is fluctuating a lot but that is probably expected seeing the resistor is 1r now?
It just HAS to be a faulty resistor! Obviously it reads as a short on my meter so I can't say whats wrong with it unless it is 0r and not 01r?
Anyway I will be getting some tomorrow.
Do you think the adjustment range is because of the 1r or is that still part of the problem?
Well I tried all the new resistors and still nothing! So I thought leave it for now! Let some fresh air blow past it for a while and get on with something else.
So I set about the temperature job again but this time I was determined to get the thing right.
Had a real bad night with pain, not a wink of sleep, but now have a perfectly stable temp reading. How do you get a stable reading with an old computer thermistor you ask? Cheated and used a DS18B20!
Anyway that is now sorted and after a good few hours messing with the old sensor I have come to the conclusion that I will never try to utilise one of them again. No wonder computers overheat sometimes.
Anyway since I got the temp working I now have no excuse not to go back to looking for the cause of the var current problem, but just can't think of a new way to go about finding the problem.
Yesterday I swapped the sense wires from one side of the OPA to the other, leaving the output wire where it was and got a reading on the var rail display. So that proves the OPA is ok.
Next I swapped the OPA output wires to match, so I have effectively changed the sides of the OPA completely and the readings are back on the +5 rail again ok. Now as expected nothing on the var rail reading.
Next I swapped the current sense resistor for a 1r and got some way off readings on the var rail, but readings never the less. So I got some more r1s and tried them ALL in but got nothing.
The only verdict I can reach is that ALL the r1s are faulty (would be very unlucky) or that the varying voltage side of the circuit is somehow effecting things.
Any thoughts or ideas on what I can try? Or is it time to call it a day and just be content with how ar I got?
Thanks for the offer mate but I really wouldn't know which bits to send.
From the investigation I have done so far it seems to be the actual resistor, or the supply to it that is at fault and that would basically mean sending the lot.
There must be a way of finding the fault logically? When I swapped things about I seem to have disproved everything at one time or another except the resistor itself. The only thing I didn't try is swapping the one that shunts the 5v onto the variable. I didn't want to end up with nothing working at all. But I will bite the bullet and try that.
If you have a logical way of determining the actual part(s) that is causing the problem I would gladly go through it, even if it means retrying some things.
Any thoughts mate? Have to be sure before I send you a parcel that it is the faulty bit.
I have just swapped the working 5v rail resistor for one of the others I got and it still works ok.
At 1A load (actually reads on DMM at 1.006) I get a reading on the LCd of 1023mA, thats very close and considering I just swapped the resistor and didn't even readjust the pot.
As for the pay, do you want sticky buns or cream when you call in mate? We will get double rations in!
I have just swapped the working 5v rail resistor for one of the others I got and it still works ok.
At 1A load (actually reads on DMM at 1.006) I get a reading on the LCd of 1023mA, thats very close and considering I just swapped the resistor and didn't even readjust the pot.
As for the pay, do you want sticky buns or cream when you call in mate? We will get double rations in!