will be back later, going to watch my huskers play Iowa but i will check ocassionaly during the game
not sure where to go with this, Ill make sure q815 and Q816 is putting out the correct voltages
So DBT is now behaving ok - even when heatsink is electrically connected to chassis?
And the current problem is that relay now does not engage (what it did "just some posts ago" with the heatsink disconnected from the chassis)?
If so then start measuring DC on the boards outputs - perhaps the deviation is enough to trigger protecion.
And the current problem is that relay now does not engage (what it did "just some posts ago" with the heatsink disconnected from the chassis)?
If so then start measuring DC on the boards outputs - perhaps the deviation is enough to trigger protecion.
The transistor seems to be fully open and relay should be energized? What is the voltage across R883 and relay coil pins?
If I have got the correct ciruit diagram:
Nope.
Measure voltages:
across R883
across D674
rail voltage on the left leg of R883 (against ground).
Measure all these voltages, then we get some idea what is going on.
You can add the CE voltage of Q875 and voltage across R884 to the same result set - all these voltages should add up to the rail voltage (80V on the schematic?).
You can add the CE voltage of Q875 and voltage across R884 to the same result set - all these voltages should add up to the rail voltage (80V on the schematic?).
Are you sure your DMM is in working condition?
What are the voltages (against ground) on regulator transistors Q815 and 817?
Decided to check solder pads on thee reg board. Q815 had a bad solder joint on the collector. Resoldered and it works. I was measuring voltages on Q815 and it was wiggling which made me suspicious.
Especially when it is intermittent and in the power rail 🙂
These regulator transistors run hot and develop cracks between leads and solder that are frequently invisible.
So resoldering them should be a routine before starting to track further errors.